NQF Level 4 · 1.1.3 Advantages and Disadvantages of Wind Power Generation 50 1.2 Economic and Environmental Beneﬁts of Hydrogen Fuel Cell Technology and E-Mobility 61 1.2.1 Hydrogen

SKILLS FORGREEN

JOBS

Renewable Energy Technologies

Introduction to Renewable Energy and Energy Effi ciencyNQF Level 4

Student Book

Editor

Skills for Green Jobs (S4GJ) Programme

Deutsche Gesellschaft für Internationale Zusammenarbeit (GIZ) GmbHRegistered offices: Bonn and Eschborn

GIZ Office PretoriaP.O. Box 13732, Hatfield 0028Hatfield Gardens, Block C, 1st Floor,333 Grosvenor StreetPretoria, South AfricaTel.: +27 (0) 12 423 5900E-mail: [email protected]

1st Edition

Responsible: Edda GrunwaldAuthors: S4GJ Team

Illustrations, Layout: WARENFORM

Photos: Dörthe Boxberg, Ralf Bäcker, version-foto

Pretoria, September 2017

Textbook provided free of charge by the Skills for Green Jobs ProgrammeFor classroom use only! Not for resale or redistribution without further permission!!

CONTENTS

List of Figures and Tables 3 Glossary 12 Preface 26 Foreword 27 Using this Student Book 28

Topic 11. Introduction to Renewable Energy Resources and Energy Effi ciency 29

1.1 Economic and Environmental Benefits of Wind Power Systems 301.1.1 Wind Power Applications: A Short History 311.1.2 Wind Energy Markets in South Africa and the World 411.1.3 Advantages and Disadvantages of Wind Power Generation 50

1.2 Economic and Environmental Benefits of Hydrogen Fuel Cell Technology and E-Mobility 61

1.2.1 Hydrogen and Fuel Cell Technologies 621.2.2 E-Mobility 75

Topic 22. Basic Scientifi c Principles and Concepts 85

2.1 Basic Principles of Wind Power Generation 862.1.1 What Causes Wind? 872.1.2 Wind Power Factors 942.1.3 Essential Wind Turbine Components and their Functions 1072.1.4 Wind Turbine Types 132

2.2 Basic Principles of Battery and Fuel Cell Technologies 1462.2.1 Electrochemical Processes in Batteries 1472.2.2 Electrochemical Processes in Fuel Cells 169

2.3 Basic Principles of E-Mobility 1882.3.1 Eco-Car Types Compared 1892.3.2 Essential E-Car Components and their Functions 203

Topic 33. Occupational Health and Safety 219

3.1 Hazards and Safe Work Practices Related to Wind Turbine Technologies 2203.1.1 Hazards Related to Wind Turbine Technologies 2213.1.2 Safe Work Practices Related to Wind Turbine Technologies 225

3.2 Hazards And Safe Work Practices Related To Fuel Cell Technologies 2313.2.1 Hazards Related To Fuel Cell Technologies 2323.2.2 Safe Work Practices Related To Fuel Cell Technologies 237

3.3 Hazards And Safe Work Practices Related To E-Mobility Technologies 2423.3.1 Hazards Related To E-Mobility Technologies 2433.3.2 Safe Work Practices Related To E-Mobility Technologies 247

Topic 44 Application of Wind Turbine and Fuel Cell Systems and Batteries 253

4.1 Connect Wind Turbine Components using Didactical Training Kits or Small-Scale Industrial Components 254

4.1.1 Experiments with Wind Turbine Training Sets 2554.1.2 Build your own wind turbine (DIY) 287

4.2 Connect Fuel Cell System Components using Didactical Training Kits 3014.2.1 Experiments with Fuel Cell Training Sets 302

4.3 Configuring Batteries for Renewable Energy Systems 3204.3.1 Experiments with Batteries 321

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LIST OF FIGURES AND TABLESFigures

Topic 1Theme 1.1.1 Figure 1: Simplified drawing (side and top view) of an early vertical-axis windmill 32Figure 2: A post mill 33Figure 3: A smock mill 34Figure 4: A technical drawing illustrating the mechanism for a self-regulating

windmill 35Figure 5: Windpumps at the Loeriesfontein Museum, South Africa 36Figure 6: A simplified schematic view into a wind turbine 37Figure 7: A 7 MW offshore wind turbine 38

Theme 1.1.2Figure 1: Global cumulative installed wind power capacity (2000 – 2015) 42Figure 2: Top 10 countries with the highest cumulative installed wind power

capacity (2015) 43Figure 3: Large-scale high resolution wind resource map 44Figure 4: Wind energy projects in South Africa 45

Theme 1.1.3 Figure 1: A possible transition to renewable/clean energy generation over time 51Figure 2: Comparison of life cycle greenhouse gas emissions for renewable and

conventional generation technologies 52Figure 3: Comparison of life cycle stages and GHG emissions for wind and coal power 53Figure 4: A typical EIA process for a wind power project (simplified) 56Figure 5: Main components of a 5 MW wind turbine and their overall share of

turbine costs 58

Theme 1.2.1Figure 1: Comparison of electrolysis and reverse electrolysis of water (schematic) 63Figure 2: Fuel cell applications in cutting-edge technologies (schematic) 64Figure 3: Fuel cell operation (schematic and simplified conceptional) 65Figure 4: Fuel cell in a lab converting chemical energy into electrical energy 65Figure 5: Hydrogen as alternative fuel powers fuel cell electric cars such as the

Toyota Mirai 66Figure 6: Overview of hydrogen production pathways (simplified) 67Figure 7: Overview of sustainable hydrogen production pathways (simplified) 68Figure 8: Illustration of non-sustainable and sustainable hydrogen production

techniques 68Figure 9: Hydrogen is an ‘energy vector’ or ‘energy carrier’ 69

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Theme 1.2.2 Figure 1: Component configurations in the three different EV-types 76Figure 2: uYilo’s DC fast charging facility 76Figure 3: Tesla’s Supercharger charging profile based on 90 kWh models 77Figure 4: A typical e-bike with rear hub configurations 78Figure 5: Ratios of electric motor assistance in a pedelec following EU regulations 79Figure 6: Different electric motor configurations of e-bikes 79Figure 7: PV shade canopies with integrated public seating and e-bike charging

docks 80Figure 8: Schematic drawing of the first ZEM inland passenger ship

FCS Alsterwasser 81

Topic 2Theme 2.1.1Figure 1: A rotor spinning fast in strong wind 88Figure 2: Directions of sea and land breezes along the coast 89Figure 3: Two different pressure gradient scenarios and their relative effect

on wind speed 89Figure 4: Sixteen principal bearings of wind direction 90

Theme 2.1.2 Figure 1: Mass of air fl owing through swept rotor area (schematic) 96Figure 2: Volume (V) of the wind ‘cylinder’ can be redefi ned as the swept rotor

area (A) multiplied by the length (s) of the wind ‘cylinder’. 96Figure 3: Relationship between wind speed and wind power 97Figure 4: Wind speeds and power increase with height 98Figure 5: The rotor’s swept area 98Figure 6: Power output increases as the swept rotor area increases 99Figure 7: Energy transformations relevant to a wind turbine 100Figure 8: Lift and drag 101Figure 9: The Betz limit 102Figure 10: Mechanical and electrical effi ciency 102Figure 11: Power coeffi cient (Cp) and Poutput vs wind speed 104Figure 12: Pinput and Poutput vs wind speed 104

Theme 2.1.3 Figure 1: HAWT subsystems (schematic) 108Figure 2: A single loop conductor placed in a magnetic fi eld (schematic) 109Figure 3: The conductor rotates in a magnetic fi eld into its horizontal position 110Figure 4: Flux lines - the pictorial representation of a magnetic fi eld 110Figure 5: Flemming’s right hand rule 111Figure 6: Rotating towards its vertical position the conductor is not inducing a

current (schematic) 111

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Figure 7: The conductor rotates into its horizontal position inducing a current in the loop (schematic) 112

Figure 8: The conducting loop is connected to two split rings and two carbon brushes which rest on the slip ring segments 112

Figure 9: Current fl ow under load resistance (schematic) 113Figure 10: Unidirectional DC current 113Figure 11: DC machines have many loops of wire wound together to form a coil 114Figure 12: Types of DC machines (simplifi ed) 114Figure 13: Schematic diagram of a separately excited DC machine 115Figure 14: Schematic diagrams of series-wound, shunt-wound and

compound-wound generators 115Figure 15: Schematic diagram of a permanent magnet DC generator 116Figure 16: Stator assembly for a twin axial fl ux permanent magnet (AFPM)

wind turbine 117Figure 17: Schematic diagram of a synchronous generator and its AC waveform 118Figure 18: Asynchronous generator diagram and squirrel-cage structure (simplifi ed) 119Figure 19: Pitch control (simplifi ed) 122Figure 20: Various blade angles due to pitch control ensuring maximum rated power 122Figure 21: Pitch control mechanism for a 1 kW wind turbine 123Figure 22: A typical confi guration for a category A1 installation

(schematic and simplifi ed) 124Figure 23: Switchgear and transformer layout in a typical wind farm confi guration

(schematic) 126Figure 24: Underground cable construction 126Figure 25: Wind farm power collection system (schematic layout) 127

Theme 2.1.4Figure 1: Position of principal wind turbine components in HAWTs and VAWTs 133Figure 2: Principal design comparison of Savonius and Darrieus rotors 134Figure 3: Comparison of Savonius and Darrieus rotor working principals (schematic) 134Figure 4: Proposed setups for combined Savonius-Darrieus rotors (schematic) 135Figure 5: Components of the IKS Windtrainer Junior set in their storage position 137Figure 6: IKS Windtrainer Junior set: some assembled components 137Figure 7: Components of the leXsolar-Wind training set in their storage position 138Figure 8: Two different anemometer types 138Figure 9: Two different wind machine types 142Figure 10: Setup for experiment 2 (schematic) 143

Theme 2.2.1Figure 1: The three basic components of a battery 148Figure 2: Simplifi ed structure of an atom 149Figure 3: Sodium cations (Na+) and chloride anions (Cl–) 150Figure 4: Table salt (NaCl) dissolves in water 151Figure 5: An enlarged image of Figure 4 c 152

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Figure 6: The Volta pile (schematic) 153Figure 7: Simplifi ed electrochemical processes in a voltaic pile / galvanic cell 154Figure 8: The zinc-carbon dry cell (schematic) 155Figure 9: Alkaline bottom cell (schematic) 156Figure 10 – 16: Lead-acid battery discharging via conduction between terminals 157Figure 11 157Figure 12 158Figure 13 158Figure 14 159Figure 15 159Figure 16 160Figure 17: Lead-acid battery charging by reversing the electrochemical process 160Figure 18: Lead-acid battery charging by reversing the electrochemical process 161Figure 19: Schematic setup for Experiment 2 164Figure 20: Schematic setup of Daniell cells in series creating a battery 167

Theme 2.2.2Figure 1: Two half-reactions occur at the anode and cathode assembly of

a fuel cell 170Figure 2: The basic components of a polymer electrolyte fuel cell

(PEFC schematic view) 171Figure 3: Catalyst reaction sites (Pt) at porous carbon electrodes 172Figure 4: A proton exchange membrane (PEM) 172Figure 5: Components and operation of a PEMFC (schematic) 173Figure 6: A PEMFC stack composed of a series of single cells separated by

bipolar plates 174Figure 7: Electrolysis: An electric current splits water to produce hydrogen

and oxygen 175Figure 8: Electrolysis: Gas quantity ratios and redox reaction 176Figure 9: IKS H2 Trainer Junior Set 177Figure 10: Setup for Experiment 1 178Figure 11: Setup of Experiment 1 (schematic) 181Figure 12: Setup for Experiment 2 183Figure 13: Setup of Experiment 2 (schematic) 184Figure 14: Two types of graphs illustrating simple linear regressions 185Figure 15: Regression lines / gas quantities vs current 186

Theme 2.3.1Figure 1: Greenhouse gas emissions of different sectors in the EU 190Figure 2: Greenhouse gas emissions from transport in the EU 191Figure 3: Global markets of electric vehicles (BEVs and PHEVs) 191Figure 4: FCEV operating principle simplifi ed (schematic) 192Figure 5: Different degrees of vehicle electrifi cation 193

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Figure 6: Simplifi ed HEV design concept (FWD schematic) 193Figure 7: Simplifi ed PHEV design concept (FWD schematic) 194Figure 8: Simplifi ed BEV design concept (FWD schematic) 195Figure 9: Simplifi ed FCEV design concept (FWD schematic) 196Figure 10: Shares of EV sales in European markets (2016) 197

Theme 2.3.2Figure 1: Power train, i.e. engine and drivetrain of a conventional ICE car (FWD) 204Figure 2: Powertrain of a modern BEV 204Figure 3: Three-phase AC synchronous pancake motor for a modern BEV 205Figure 4: In-wheel electric motor for a modern BEV 206Figure 5: Acceleration and magnetic braking simplifi ed 208Figure 6: Single-pedal speed control mechanism 209Figure 7: Estimations for battery cost reductions and performance improvements 210Figure 8: Growth projection for lithium batteries (Production capacities in GWh) 211Figure 9: Cutaway of an EV showing the fl oor position of the battery unit 211Figure 10: Two different charging cables (400 V left and 230 V right) 212Figure 11: Six different connector types (from left to right: US, EU, China and Japan) 213Figure 12: Standard VDE three-phase connector for charging BEVs 213Figure 13: FCEV components simplifi ed (schematic) 214Figure 14: Hydrogen fuelling control system for FCEVs (simplifi ed) 215

Topic 3Theme 3.1.1Figure 1: PPE required for working with renewable energy technologies 222

Theme 3.1.2Figure 1: Fuses and surge protection for a small-scale wind turbine

installation (off-grid) 226Figure 2: Lockout/tagout procedures 227

Theme 3.2.1Figure 1: Basic structure of a hydrogen safety system 233Figure 2: A fuel cell powered bus manufactured by Toyota (Japan) 234Figure 3: Hydrogen tanks on the Honda FCX Clarity platform 235

Theme 3.2.2Figure 1: The Hindenburg zeppelin disaster in 1937 239Figure 2: A modern hydrogen-powered aircraft 239Figure 3: A modern hydrogen-powered SUV 240

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Theme 3.3.1Figure 1: EV warning decals 244Figure 2: High ‘voltage’ components of a typical BEV (schematic) 245

Theme 3.3.2Figure 1: Lithium-ion battery pack of an EV 248

Topic 4Theme 4.1.1Figure 1: The IKS Windtrainer Junior set (left) and the leXsolar-Wind

training set (right) 256Figure 2: Each training kit uses different components 256Figure 3: Inserting the rotor blades (IKS Windtrainer Junior) 257Figure 4: Wind turbine and rotor blade sets (leXsolar) 258Figure 5: Schematic setup of Activity 1 using IKS Windtrainer Junior 258Figure 6: Schematic setup of Activity 1 using the leXsolar-Wind training set 259Figure 7: Carefully tighten the rotor blade locking bolts 259Figure 8: Hypothetical progression of the output curve in the leXsolar chart 261Figure 9: Hypothetical progression of the output curve in the IKS chart 261Figure 10: Different HAWT types 262Figure 11: The IKS Windtrainer Junior setup for Activity 2, 3 and 4 263Figure 12: Schematic setup of Activity 2, 3 and 4 using IKS Windtrainer Junior 264Figure 13: Schematic setup of Activity 2, 3 and 4 using the leXsolar-Wind training set 264Figure 14: Enter the measured values into the tables provided 265Figure 15: Hypothetical progression of curves in different charts 267Figure 16: Curved rotor blades (concave / convex) from IKS’s Windtrainer Junior set 268Figure 17: Air foil cross-section and aerodynamic forces 269Figure 18: Enter the measured values into the tables provided and answer

all questions 270Figure 19: Hypothetical curve progression (power vs wind speed) 271Figure 20: Angle of attack, angle of incidence or pitch angle 273Figure 21: Relationship between lift, drag and angle of attackc (pitch) 274Figure 22: Pitch control adjustments along the cord line of rotor blades 274Figure 23: Hypothetical progression of curves in different chart types 276Figure 24: Relationship between ‘voltage’ (V) and current (I) in a circuit 278Figure 25: Schematic setup of Activity 5 using the leXsolar Wind training set 280Figure 26: Hypothetical progression of I/V lines and output curves in different

chart types 282Figure 27: Schematic setup of Activity 6 using IKS Windtrainer Junior 284Figure 28: Detailed view for Activity 6 connections using IKS’s capacitator module 285Figure 29: Schematic setup of Activity 5 with the leXsolar Wind training set 285

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Theme 4.1.2Figure 1: DIY – building a HAWT and/or a VAWT (Savonius model) 287Figure 2: Some of the tools you will need for this activity 288Figure 3: The materials you need 289Figure 4: The two VAWT designs once assembled 289Figure 5: Pattern on the baseplate 290Figure 6: Improved stator coil design 291Figure 7: Clockwise connection of eight coils 292Figure 8: Rotor and stator option for VAWT Design #1 292Figure 9: Rotor and stator option for VAWT Design #2 293Figure 10: Circular pattern on cardboard for rotor disk 294Figure 11: Magnets need to be placed in an alternating polarity arrangement 295Figure 12: Circular pattern on cardboard for top and bottom cover of turbine blades 296Figure 13: Assembled VAWT Design #1 297Figure 14: Assembled VAWT Design #2 297Figure 15: Circuit diagram of a full-wave bridge rectifi er and smoothing capacitor 298Figure 16: Simple stator plate based on 3 coil design with a six diode rectifi er unit 299Figure 17: Connecting/soldering the coils to a rectifi er unit 299

Theme 4.2.1Figure 1: Electrolysis reaction: 2 H2O (l) 2 H2 (g) + O2 (g) 304Figure 2: Setup for Activity 1 305Figure 3: Setup for Activity 1 306Figure 4: Electrolyser I/V chart based on hypothetical results obtained from Table 3 308Figure 5: Setup for Activity 3 309Figure 6: Setup for Activity 3 310Figure 7: Combined I/V and P/I chart based on hypothetical results obtained

from Table 4 311Figure 8: RET Level 2 training set: 2, 3 or 4 PV cells connected in series 313Figure 9: The electrolyser powered by 2, 3 or 4 PV cells connected in series 313Figure 10: Hypothetical electrolyser and PV cell I-V characteristics 314Figure 11: Setup for Voc and Isc measurements of the turbine generator 316Figure 12: Turbine generator connected to power the electrolyser 317Figure 13: Hypothetical I-V electrolyser and PV cell I-V characteristics 318

Theme 4.3.1Figure 1: Required tools and components 321Figure 2: Pay attention to polarity when connecting batteries 322Figure 3: Four SLAs connected in series 323Figure 4: Four SLAs connected in series and parallel 323Figure 5: Draw your circuit diagram next to the illustration 324Figure 6: Draw your circuit diagram next to the illustration 325Figure 7: Draw your circuit diagram next to the illustration 326

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Figure 8: Draw your circuit diagram next to the illustration 327Figure 9: Overcurrent protection for four individual batteries connected in series 328Figure 10: Overcurrent protection for four individual batteries connected in series 329

Tables

Topic 1Theme 1.1.2Table 1: Wind energy projects in South Africa 46

Theme 1.1.3 Table 1: Potential impacts associated with wind power and wind farm

development 54Table 2: Cost structure of a typical medium-sized (2 MW) wind turbine 57

Theme 1.2.1Table 1: Number of existing public hydrogen refuelling stations and 2020 targets 70Table 2: Existing FCEV fleet and 2020 targets 70

Topic 2Theme 2.1.1Table 1: Beaufort wind speed scale in km/h 91

Theme 2.1.3 Table 1: Main control techniques used in wind turbines 120Table 2: Turbine design concepts based on generator confi guration and

pitch control 121

Theme 2.1.4Table 1: Criteria for wind turbine categorisation 133Table 2: Symbols for experimental setup by the leXsolar-Wind training set 139

Theme 2.2.1Table 1: Standard electrode reduction potentials (E° V) of selected metals 166

Theme 2.2.2Table 1: Standard electrode reduction potentials (E° V) of hydrogen and oxygen 170Table 2: Symbols used for devices in the experimental setups 179Table 3: Gas volumes 182Table 4: Gas volumes 185

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Theme 2.3.2Table 1: Examples of feedback signals sent from EV components to the

controller system 206

Topic 4Theme 4.1.2Table 1: Material required for Step 1 290Table 2: Material required for Step 2 291Table 3: Material required for Step 3 293Table 4: Material required for Step 4 294Table 5: Material required for Step 5 295Table 6: Material required for Step 6 296Table 7: Material required for Step 7 298Table 8: Troubleshooting 300

Theme 4.2.1Table 1: Hypothetical results (blue fonts) of Activity 1 305Table 2: Calculating energy effi ciency factor η using hypothetical results 305 Table 3: Hypothetical results (blue fonts) of Activity 2 307Table 4: Hypothetical results (blue fonts) of Activity 3 310Table 5: Hypothetical results (blue fonts) of Activity 4 314Table 6: Hypothetical results (blue fonts): measuring Voc and Isc

of the turbine generator 317Table 7: Hypothetical results (blue fonts): measuring wind speed (vwind),

Voc and Isc of the turbine at electrolyser current (I = 0 mA) 317

Theme 4.3.1Table 1: Document your measurements (V and I) in the table below: 324Table 2: Document your measurements (V and I) in the table below: 325Table 3: Document your measurements (V and I) in the table below: 326Table 4: Document your measurements (V and I) in the table below: 327

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GLOSSARY

Accumulator A rechargeable battery or cell (see also ‘secondary battery’).

Air foil The cross section profile of a rotor blade, designed to provide low drag and good lift. Also found on an airplane wing.

Alkaline battery The most common are AAA, AA, A, C and D dry cell batteries. The cathode is composed of a manganese dioxide mixture, while the anode is a zinc powder. It gets its name from the potassium hydroxide electrolyte, which is an alkaline substance.

Alternating Current (AC)

Charge can vary with time in several ways, resulting in different types of current. An electric charge flowing back and forth at a set frequency will, for example, result in a time-varying current called alternating current (AC). AC is a current that varies sinusoidally over time, for example 100 times per second at a frequency of 50 hertz. AC is provided by most power stations and is transmitted through the national grid to residential and commercial power users.

Ambient Factors found in the surrounding area or environment, e.g. ambient temperature.

Anemometer An instrument used to measure the velocity or speed of wind.

Angle of attack The angle between the line of the chord of an aerofoil and the relative airflow.The angle of relative air flow to a wind turbine’s blade.

Anion A negatively charged ion which has more electrons than protons. In a fuel cell anions, being positively charged, migrate toward the anode.

Anode One of the two electrodes in a battery or fuel cell, the anode is positively charged. It gives up electrons into the circuit and ions into the electrolyte.

Armature Usually synonymous with rotor plate, the moving part of an electric machine. In many generator and motor designs, the armature carries the magnets and rotates around the axis of the stator, i.e. the disk carrying the coils.

Asynchronous generator

The terms asynchronous and induction are often used interchangeably to describe these types of AC machines. Many wind turbines use so-called three phase asynchronous generators to generate alternating current. Most induction machines contain a rotational element, the rotor is dubbed a squirrel cage. The stationary part of the motor windings is called the armature or the stator. The asynchronous nature of induction machine operation comes from the slip, i.e. the difference between the rotational speed of the stator field and the somewhat slower speed of the rotor.

Axis The centre line of a rotating object‘s movement.

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Battery (cell) An electrochemical device used to store energy. The term is usually applied to a group of two or more electric cells connected together. A battery cell consists of a positive electrode, a negative electrode, and other necessary electrochemical and structural components. A battery cell is a self-contained energy conversion device whose function is to deliver electrical energy to an external circuit via an internal chemical process.

Battery An electrochemical device used to store electrical energy. The term is usually applied to a group of two or more electric cells connected electrically.

Battery capacity The electric output of a cell or battery on a service test delivered before the cell reaches a specified final electrical condition. It may be expressed in ampere-hours, watt-hours, or similar units. The capacity in watt-hours is equal to the capacity in ampere-hours multiplied by the battery ‘voltage’.

Battery charger A device capable of supplying electrical energy to a battery.

Battery charge rate The current expressed in amperes (A) or milliamps (mA) at which a battery is charged.

Battery module A grouping of interconnected battery cells in a single mechanical and electrical unit.

Battery pack/Traction battery

Interconnected battery modules that have been configured for a specific energy storage application.

Battery system Completely functional energy storage system consisting of the pack(s) and necessary ancillary subsystems for physical support, thermal management, and electronic control.

Beaufort scale A scale of wind forces which describes the wind by name and range of velocity, and classifies it from force 0 to 12. The initial wind force scale of Francis Beaufort (1805) did not reference wind speed numbers but related qualitative wind conditions to effects on the sails of a frigate of the Royal Navy, namely from ‘just sufficient to give steerage’ to ‘that which no canvas sails could withstand’.

Betz coefficient The maximum power coefficient (Cp) of a theoretically perfect wind turbine is equal to 16/27 (59.3%). This coefficient had been mathematically proven by the German physicist Albert Betz in 1919. In reality, this limit cannot be achieved due to drag, electrical losses, and mechanical inefficiencies (see capacity factor).

Bipolar plate A fuel-cell stack component. They are often designed to channel the flow of gases and heat to and from the cell.

Blades Flat long panels connected to the rotor hub providing the aerodynamic active surface. Blades converting linear wind power into a circular motion.

Braking system A device to slow a wind turbine’s shaft speed down to safe levels.

Brushes Conducting devices that transfer a current to or from a rotating object. They are usually made of carbon-graphite.

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Capacity factor (Cp) A power coefficient and a measure of a wind turbine’s overall efficiency. Cp values indicate the ratio of input power extracted from the wind relative to the output power over a given time period. The Cp thus represents the combined efficiency of the various turbine system components.

Capacity The capacity of a battery is a measure of the amount of energy that it can deliver in a single discharge. Battery capacity is normally listed as amp-hours, milliamp-hours or watt-hours.

Catalyst Any substance that increases the rate of a chemical reaction, but which is not used up by the reaction and can thus be used over and over again. Platinum and Palladium, for example, are used as a catalyst in many fuel cells.

Cathode One of the two electrodes in a battery or fuel cell. The cathode is negatively charged. Reduction occurs at the cathode, meaning electrons are captured rather than released (anode).It is an electrode that, in effect, oxidises the anode or absorbs the electrons. During discharge, the positive electrode of a voltaic cell is the cathode.

Cation A positive ion, e.g. a proton liberated from hydrogen is called a cation.

Cell Composed of positive and negative plates and an electrolyte, a cell is an electrochemical device which is capable of storing electrical energy. It is the basic ‘building block’ of a battery.

Charge (electric) There are two types of electric charges, positive and negative, commonly carried by protons and electrons respectively. Electric charge is the physical property of matter that causes a force when placed in an electromagnetic field.

Charge The conversion of electrical energy, provided in the form of a current, into chemical energy within the cell or battery.

Charging The process of supplying electrical energy for conversion, i.e. converting electrical energy to chemical energy.

Chemical hazards These are present when a worker is exposed to chemical substances be it solids, liquids or gases. Some of these substances can have dangerous health effects and could cause illnesses, skin irritation or breathing problems.

Circuit A closed conducting path through which electric charges can flow.

Combustion Also known as burning of fossil fuels in different types of machines that convert heat energy into mechanical energy. A complex sequence of exo-thermal chemical reactions between a fuel and oxidant (usually oxygen). The reaction is accompanied by the production of heat and/or light.

Commutator The rotating axis part of a DC generator.

Compressed hydrogen Hydrogen in the gaseous state kept under pressure greater than standard atmospheric pressure.

Constant-current charge

A charging process in which the current applied to the battery is maintained at a constant value.

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Cryogenic storage Under high pressure and very low temperatures gases can be stored in high-pressure cylinders in liquefied form. Cryogenic storage of hydrogen or other gases is a common technology, however hazards resulting from the very low storage temperatures, e.g. around -250º C for hydrogen, include severe cold-burns.

Cut-in / cut-out wind speed

The wind speed at which a wind turbine begins (cut-in) or ceases (cut-out) to generate power.

Cut-off voltage/final voltage

The prescribed lower-limit voltage at which battery discharge is considered complete. The cut-off or final voltage is usually chosen so that the maximum useful capacity of the battery is realised. The cut-off voltage varies with the type of battery used and what the battery is used for. When testing the capacity of a NiMH or NiCD battery a cut-off voltage of 1.0 V is normally used. 0.9V is normally used as the cut-off voltage of an alkaline cell. A device that is designed with a too high cut-off voltage may stop operating while the battery still has significant capacity remaining.

Cycle life For rechargeable batteries, cycle life refers to the total number of charge/discharge cycles the cell can sustain before its capacity is significantly reduced. End of life is usually considered to be reached when the cell or battery delivers only 80% of rated ampere-hour capacity. NiMH batteries typically have a cycle life of 500 cycles. NiCd batteries can have a cycle life of over 1 000 cycles. The cycle of a battery is greatly influenced by the type of depth of the cycle (deep or shallow) and the method of recharging. Improper charge cycle cut-off can greatly reduce the cycle life of a battery.

Cycle One sequence of charge and discharge.

Darrieus A vertical-axis wind turbine (VAWT) design using lift forces. Initially designed by F.M. Darrieus (1920 – 1930), a French wind turbine developer. A modern variant is the H-Darrieus rotor – its rotor blades are straight and sit on support arms.

DC/DC converter A power converter that produces an output ‘voltage’ greater than or less than the input ‘voltage’.

Deep cycle A cycle in which the discharge is continued until the battery reaches its cut-off voltage, usually 80% of discharge.

Density Mass per unit of volume.

Depth of discharge The amount of energy that has been removed from a battery (or battery pack), usually expressed as a percentage of the total capacity of the battery. For example, 50% depth of discharge (DOD) means that half of the energy in the battery has been used. 80% DOD means that eighty percent of the energy has been discharged, so the battery now holds only 20% of its full charge.

Diffusion The movement of molecules from a region of higher concentration to a region of lower concentration.

Diode A solid-state device that allows current to flow in a circuit in only one direction.

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Direct current (DC) There can be several different types of current as charge can vary with time in several ways. If the current does not change with time but remains constant, we call it a direct current (DC). Direct current is usually provided by batteries, photovoltaic cells and other DC generators.

Direct drive Referring to a rotor and generator configuration where the two components are connected directly so that one rotor revolution equates to one revolution of the generator.

Discharge The conversion of chemical energy from a battery or fuel cell into electric energy.

Drag An aerodynamic force that acts parallel and in opposition to the direction of travel for an object moving through a fluid.

Drain Withdrawal of current from a battery or fuel cell.

Dry cell A primary cell in which the electrolyte is absorbed in a porous medium or is otherwise restrained from flowing.

Efficiency The ratio of energy output to energy input.

Electrical hazards Workers in the wind power industry are exposed to a variety of potentially serious electrical hazards. Often, these include electrical shock and severe burns from arc flashes. Falls and also crushing injuries have been reported as a result of these injuries.

Electric machines Electric machines are electromechanical energy conversion devices. Motors convert electrical energy into mechanical energy while generators do exactly the opposite, converting mechanical power into electrical power.

Electrode A terminal that carries an electric current.An electrical conductor through which an electric current enters or leaves a conducting medium, whether it be an electrolytic solution, a solid, molten mass, a gas or a vacuum. For electrolytic solutions, many solids and molten masses, an electrode is an electrical conductor at the surface of which a change occurs from conduction by electrons to conduction by ions.

Electrolyser An electrochemical device which works like a fuel cell in reverse, i.e. the device can split water into its constituent molecules, hydrogen and oxygen, by passing an electric current through it.

Electrolysis The breakdown of a chemical through the application of an electric charge to it. This process is commonly used to break up water into hydrogen and oxygen.

Electrolyte A chemical compound which, when fused or dissolved in certain solvents - usually water - will conduct an electric current. All electrolytes in the fused state or in solution give rise to ions which conduct the electric current. In a fuel cell, the electrolyte allows ions to move from one electrode to the other, but is impermeable to electrons.

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Electromagnetic fields Electromagnetic fields, also known as EM fields, are present everywhere in our environment but are invisible to the human eye. EM fields are produced by electrically charged objects. EM fields affect the behaviour of charged objects in their vicinity. They can be considered as the combination of an electric field and a magnetic field. The electric field is produced by stationary electric charges and the magnetic field by moving electric charges.

Electromotive force (EMF)

The potential difference generated by either an electrochemical cell or a changing magnetic field. Commonly denoted by the acronym emf or EMF.

Energy monitor A display that indicates the charge/discharge status of the high ‘voltage’ battery.

Explosion limit (LEL/UEL)

Some gas mixtures, e.g. air and hydrogen, will readily ignite and explode within a certain range of concentration. For example, air/hydrogen mixtures containing as little as 4% hydrogen, which is the lower explosion limit (LEL), up to as much as 75%, the upper explosion limit (UEL), will readily ignite and explode. If a flammable mixture of hydrogen and air is allowed to form, the likelihood of an explosion occurring is very high, because the energy necessary to initiate a hydrogen/air mixture is very small.

Falling hazard Workers who erect and maintain wind turbines work at heights and are thus exposed to falls with potentially dangerous consequences (serious injuries or death).

Flemming‘s right hand rule

This rule says that if you stretch thumb, index finger and middle finger of your right hand perpendicular to each other, then the thumb indicates the direction of motion of the conductor field, the middle finger indicates the direction of flow of the current through the conductor and the index finger indicates the direction of the magnetic field.

Float charging Method of recharging in which a secondary cell is continuously connected to a constant-voltage supply that maintains the cell in fully charged condition. The method is typically applied to lead acid batteries.

Fossil fuel Any hydrocarbon fuel produced from organic matter (long dead).

Frequency Cycles per second, measured in Hertz. For example, the number of times an AC circuit reaches both minimum and maximum values in one second.

Fuel cell An electrochemical device which converts chemical energy to electrical energy without combustion. Unlike a battery, a fuel cell will continuously produce electricity as long as fuel is supplied and the catalyst remains active.

Fuel cell electric vehicles (FCEV)

Fuel cell electric vehicles use fuel cells to generate electric power for propulsion.

Galvanic cell A combination of electrodes, separated by an electrolyte, capable of producing electrical energy by electrochemical action.

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Gassing The evolution of gas from one or both of the electrodes in a cell. Gassing is commonly the result of self-discharge or the electrolysis of water in the electrolyte during charging.

Gearbox Usually a mechanical device containing a gearing system for the purpose of transferring forces between machines or mechanisms, often with changes of torque and speed. In wind turbines, gearboxes connect the low-speed shaft to the high-speed shaft, aiming to increase rotational speed to the speed required by the generator.

Generator An electric machine that converts mechanical (rotational) energy into electrical energy.

High voltage Nominal ‘voltage’ levels equal or greater than 44 kV up to and including 132 kV.

Horizontal-axis wind turbine (HAWT)

The most common type of commercial utility scale wind turbine design, where the rotor axis and the shaft is parallel to the ground and the blades are perpendicular to the ground.

Hydride A negatively-charged hydrogen ion. Metal hydrides, e.g. in nickel metal hydride (NiMH) batteries, are metals which have been bonded to hydrogen ions to form a new compound. Most hydrides behave as reducing agents in chemical reactions. Metal hydrides are used in certain fuel cells and as hydrogen storage compounds.

Hydride ion The smallest possible anion. It is made up of two electrons and a proton.

Hydrocarbon An organic compound that consists only of hydrogen and carbon atoms.

Hydrogen economy A scenario where a country uses hydrogen as the primary energy carrier in place of fossil fuels. Hydrogen would be used to provide electrical power, heat homes and power vehicles. Ideally this hydrogen would be generated from renewable energy, resulting in zero emissions.

Hydrogen fuel cell A sub-type of proton exchange membrane fuel cell in which only hydrogen and oxygen are used as fuels. The only byproducts are water, heat, and electricity. These fuel cells are the main focus for use in FCEVs.

Hydrogen The smallest of all elements, consisting of a single proton and a single electron. Hydrogen is used as fuel in most fuel cells and it is the most abundant element in the universe.

ICE Internal Combustion Engine

Induction Electromagnetic induction or just induction is a process where a conductor is placed in a changing magnetic field or moves through a stationary magnetic field, causing a potential difference across the conductor. This process of electromagnetic induction, in turn, causes an electrical current or in other words, induces a current.

Induction machine An AC type of generator or motor (see asynchronous).

Internal resistance The resistance to the flow of an electric current within the cell or battery.

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Inverter A device that converts direct current (DC) to alternating current (AC).

Ion An atom that becomes positively or negatively charged through the loss or gain of electrons.

Lead-acid battery (rechargeable)

This is the chemistry used in a typical car battery, the electrodes are usually made of lead dioxide and metallic lead, while the electrolyte is a sulfuric acid solution.

Lift An aerodynamic force that acts at right angles to the airstream flowing over an air foil.

Liquid hydrogen Elemental hydrogen in the liquid state. This can only be achieved at very low temperatures: -287° C. Please note, that this is only 20° above absolute zero!

Lithium-ion battery (rechargeable)

Lithium chemistry is often used in high-performance devices, such as cell phones, digital cameras and even electric cars. A variety of substances are used in lithium batteries, but a common combination is to use lithium cobalt oxide for the cathode and carbon for the anode.

Lockout/tagout To prevent the DC and AC circuits from inadvertently re-energising during wind turbine installation or scheduled maintenance work, documented lockout/tagout procedures should be followed both on the DC and AC side of the system.

Low voltage In South Africa low voltage is considered as nominal potential up to and including 1 kV.

Magnet A device that attracts ferromagnetic materials.

Magnetic field Also called magnetic flux. Historically described in terms of its effect on electric charges. An electrically charged particle moving in a magnetic field will experience a force known as the Lorentz force pushing it in a direction perpendicular to the magnetic field and the direction of its motion.

Medium-voltage grid Part of the public distribution grid with a typical nominal potential, i.e. in South Africa a nominal potential greater than 1 kV and less than 44kV.

Megawatt (MW) 1 000 kilowatts (kW) or 1 million watts (W). The standard measure of electric power generating capacity.

Megawatt hour(MWh)

The amount of energy used if work is done at an average rate of 1 million watts for 1 hour.

Megawatt peak (MWp) Unit of measurement for the nominal output, e.g. the peak or maximum output of a wind turbine.

Membrane A membrane separates the two electrodes of a fuel cell. It acts as the electrolyte, allowing passage of ions between the electrodes.

Membrane electrode assembly (MEA)

Membrane electrode assembly, a structured component in a PEMFC consisting of a membrane with an electrode on each side.

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Memory effect A phenomenon in which a cell, operated in successive cycles to less than full depth of discharge, temporarily loses the remainder of its capacity at normal voltage levels (usually applies only to NiCd cells). Note, memory effect can be induced in NiCd cells even if the level of discharge is not the same during each cycle. Memory effect is reversible.

Motor/Generator An electromechanical device that can operate in two modes without changing rotational direction. As a motor, it consumes electricity to produce mechanical power. As a generator, it consumes mechanical power to produce electricity.

Nacelle The nacelle sits on top of the tower and contains the gearbox, shafts, and generator etc. of a wind turbine.

Negative terminal The terminal of a battery from which electrons flow in the external circuit when the cell discharges.

Neodymium-(Iron-Boron) magnet

The composition of a very powerful permanent magnet. The materials, so-called rare-earth elements, are mined, processed, and sintered into shape and used in various types of AC and DC machines.

Ohm’s Law The formula that describes the amount of current flowing through a circuit. In a given electrical circuit, the amount of current in amperes (I) is equal to the pressure in volts (V) divided by the resistance, in ohms (R). Ohm‘s Law can be shown by three different formulas:

• To find Current I = V/R• To find Voltage V = I x R• To find Resistance R = V/I

Open circuit The condition of a battery which is neither on charge nor on discharge (i.e. disconnected from a circuit).

Open-circuit voltage The difference in potential between the terminals of a cell when the circuit is open (i.e. a no-load condition).

Output Energy or power provided per time unit.

Oxidation A chemical reaction that results in the release of electrons by an electrode’s active material.

Oxygen The eighth chemical element with 8 protons and 8 electrons. One of the primary fuels in all fuel cells. Combines with two hydrogen atoms to create water.

Palladium (Pd) A rare metal often used as a catalyst in fuel cells. Its atomic number is 46.

Parallel connection The arrangement of cells in a battery made by connecting all positive terminals together and all negative terminals together. The ‘voltage’ of the group remains the same as the ‘voltage’ of the individual cell. The capacity is increased in proportion to the number of cells.

Permanent magnet A material that retains its magnetic properties without an external magnetic field.

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Pitch The angle between the edge of the blade and the plane of the blade’s rotation. Blades are turned or pitched in or out of the wind to control rotor speed.

Platinum (Pt) A rare metal often used as a catalyst in fuel cells. Its atomic number is 78. Over 80% of the world’s platinum is mined in South Africa.Platinum is a commonly used catalyst material for PEMFC technologies.

Polarity Refers to the charges residing at the terminals of a battery.

Polymer A compound made by linking small subunits (called monomers) together in a repeating pattern.

Polymer electrolyte membrane (PEM)

Also referred to as proton exchange membrane. A solid polymer membrane used as an electrolyte in certain fuel cells.

Polymer electrolyte membrane fuel cell (PEMFC)

A type of acid-based fuel cell that uses the transport of protons from the anode to the cathode through a solid polymer electrolyte membrane. These fuel cells run at temperatures less than 100° C.

Portable fuel cell Any type of fuel cell that can be carried by hand. These are often used for emergency power applications and in high tech applications (space/aeronautic etc.).

Power flow display An animated graphic indicating the direction of the flow of energy.

Pressure gradient force The primary force influencing the formation of wind from local to global scales.

Primary cell A cell designed to produce electric current through an electrochemical reaction that is not efficiently reversible. The cell, when discharged, cannot be efficiently recharged by an electric current. Alkaline, lithium and zinc air are common types of primary cells.

Rated capacity The number of ampere-hours a cell can deliver under specific conditions (rate of discharge, end voltage, temperature); usually the manufacturer’s rating.

Rechargeable Capable of being recharged; refers to secondary cells or batteries.

Redox Short for reduction-oxidation reaction. A chemical reaction in which atoms undergo a change in the oxidation number, thus usually gaining or losing electrons.

Reduction A chemical process that results in the acceptance of electrons by an electrode’s active material.

Reformate The output of a fuel reformer. Such a gas stream often contains hydrogen, carbon monoxide and carbon dioxide. Reformate gas can be fed to a fuel cell, generally after some degree of clean-up.

Reformer A device that extracts hydrogen from hydrocarbons. Part of indirect fuel cell systems in which the fuel is processed prior to injection into the fuel cell stack.

Rotor hub The centre of a rotor which holds the blades and is attached to the gearbox or generator shaft.

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Safety checklists Checklists determine compliance with industry specific standards and to ensure consistency. Many companies use checklists as documentary evidence that they have a system in place to identify and control hazards and risks.

Savonius A drag powered vertical-axis wind turbine (VAWT) initially designed by Mr. Savonius in the 1920s and 30s.

Seal The structural part of a galvanic cell that restricts the escape of solvent or electrolyte from the cell and limits the ingress of air into the cell (the air may dry out the electrolyte or interfere with the chemical reactions).

Self discharge Discharge that takes place while the battery is in an open-circuit condition.

Separator The permeable membrane that allows the passage of ions, but prevents electrical contact between the anode and the cathode. Separators can be made from a variety of non-conducting materials. Separators do not chemically react with the anode, cathode or electrolyte.

Separator plate Plates used to physically separate individual fuel cells in a stack.

Series connection The arrangement of cells in a battery configured by connecting the positive terminal of each successive cell to the negative terminal of the next adjacent cell so that their ‘voltages’ are cumulative. See “parallel connection”.

Service life (years or cycles)

A general term that describes the length of time a battery can remain in service. Service life can be specified in terms of either time or duty cycles.

Service plug A high ‘voltage’ electrical disconnect device that is used when performing repairs on the high ‘voltage’ vehicle circuits.

Shaft The rotating part in the centre of a nacelle that transfers rotational motion to a gearbox or a generator.

Shallow cycling Charge and discharge cycles which do not allow the battery to approach its cut-off ‘voltage’. Shallow cycling of NiCd cells leads to ‘memory effect’, whereby the batteries end up temporarily holding less charge. Shallow cycling is not detrimental to NiMH cells and it is beneficial for most lead-acid batteries.

Shelf life For a dry cell, the period of time (measured from date of manufacture), at a storage temperature of 21°C after which the cell retains a specified percentage (usually 90%) of its original energy content.

Short-circuit A condition that occurs when a short electrical path is unintentionally created. Batteries can supply hundreds of amps if short-circuited, potentially melting the terminals and creating sparks.

Short-circuit current That current delivered when a cell is short-circuited (i.e., the positive and negative terminals are directly connected with a low-resistance conductor).

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Single cell The smallest and most basic form of a battery or fuel cell consisting of an anode, cathode and electrolyte. While batteries are used commercially as single cells, single fuel cells are only useful for testing and development purposes, e.g. predicting how a stack will perform etc.

Stack (fuel cells) Individual fuel cells connected to create a larger unit consisting of multiple stacked fuel cells.A fuel cell stack is an arrangement of individual fuel cells, usually in series, to provide a useful output current.

Stall Is similar to pitch control, but instead of pitching the blades out of alignment with the wind, the blades are turned so that they impede further rotor movement.

Starting-lighting-ignition (SLI) battery

A battery designed to start internal combustion engines and to power the electrical systems in automobiles when the engine is not running. SLI batteries can be used in emergency lighting situations.

Stationary battery/fuel cell

A fuel cell unit that is not movable, often used for electric power generation for larger applications such as hospitals.

Stator The stationary part of an electric machine related to the collection of stationary parts in its magnetic circuits. The stator and rotor interact to generate power in a generator or to turn the driveshaft in a motor.

Steam reforming A process of producing hydrogen from hydrocarbons at high temperatures (700° - 1100° C) and in the presence of a metal-based catalyst such as nickel.

Storage battery An assembly of identical cells in which the electrochemical action is reversible so that the battery may be recharged by passing a current through the cells in the opposite direction to that of discharge. While many non-storage batteries have a reversible process, only those that are economically rechargeable are classified as storage batteries.

Storage cell An electrolytic cell for the generation of electric energy in which the cell after being discharged may be restored to a charged condition by an electric current flowing in a direction opposite the flow of current when the cell discharges. Synonym: secondary cell, also see ‘storage battery’.

Substation A facility usually owned by the national or municipal utility stepping potential difference up or down to suit the electric parameters of long-distance transmission lines.

Swept area Also synonymous with rotor diameter. The area swept by the turbine rotor.

Switch gear The combination of disconnect switches, fuses or circuit breakers used to control, protect and isolate electrical equipment. Switchgear is used both to de-energise equipment to allow work to be done and to clear faults downstream.

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Synchronous machine An electric machine with a special rotor construction that rotates at the same speed, thus synchronising with the stator field. There are basically two types of synchronous machines, i.e. self-excited ones using principles similar to those of induction motors, and directly excited ones.

Terminals The parts of a battery to which the external electric circuit is connected.

Tower The base structure that supports and elevates a wind turbine rotor and nacelle.

Transformer Initially an electric device with multiple individual coils of wire wound on a laminate core. Nowadays, electronic elements are used to transfer power from one circuit to another using magnetic induction, usually to step the potential difference up or down.

Trickle charging A method of recharging in which a secondary cell is either continuously or intermittently connected to a constant-current supply that maintains the cell in fully charged condition.

Turbine A rotary engine that extracts energy from the flow of a fluid such as air (wind), steam or water.

Upwind Synonymous with windward, i.e. the same direction from which the wind is blowing.

Vent A normally sealed mechanism that allows for the controlled escape of gases from within a cell.

Vertical-axis wind turbine (VAWT)

A wind turbine whose rotor spins around a vertical axis.

Wind farm Also known as a wind power plant. A group of wind turbines often owned and maintained by one company/utility.

Wind The movement of air masses, i.e. air in motion.

Wind vane Wind vane m easures wind direction and communicates with the yaw drive to orient the turbine into the wind.

Working at height Working at height occurs frequently throughout all phases of construction and operation of wind turbines and is especially relevant when it comes to maintenance. The main focus when managing working at height should be the prevention of a fall.

Yaw drive To rotate the nacelle and the rotor around a vertical axis on a turbine tower, a yaw drive is used. This mechanism ensures that the nacelle and the rotor are constantly facing into the wind.

Zinc-carbon battery The zinc-carbon chemistry is common in many inexpensive AAA, AA, C and D dry cell batteries. The anode is composed of zinc, the cathode of manganese dioxide, and the electrolyte is ammonium chloride or zinc chloride.

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PREFACE

On behalf of the German Ministry of Economic Cooperation and Development (BMZ), the Skills forGreen Jobs (S4GJ) programme, together with the South African Departments of Higher Education and Training (DHET) and Science and Technology (DST), jointly developed and implemented a number of activities which aim to:

1. Support qualifi ed TVET lecturers in their continuous professional development through train-ing in Renewable Energy and Energy Effi ciency Technologies.

2. Develop and support the implementation of a new optional vocational subject on Renewable Energy Technologies for NC(V) students.

3. Develop appropriate training material, such as student textbooks and lecture guides, for the new subject.

Subsequently, we are very happy that the student book for NC(V) level 4 Renewable Energy Technologies is now available. Th e new subject and student book is for students of the technical NC(V) programmes who want to learn more about renewable energy technology, its potentials and limitations. Th e student book introduces students to the relevant technical concepts, illustrates examples from real world applica-tions, and others exercises and practical work/experiments.

Yours in renewable energy…

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FOREWORD BY THE DIRECTOR-GENERAL OF THE DEPARTMENT OF HIGHER EDUCATION AND TRAINING

Th e Department of Higher Education and Training is pleased to introduce the subject Renewable Energy Technologies in the National Certifi cate (Vocational) NC(V) Electrical Infrastructure Construction programme. Th is new subject is the latest addition to the vocational specialisation options off ered in Technical and Vocational Education and Training (TVET) colleges and has been developed for students who want to learn more about renewable energy generation and the technologies related therewith.

Outlined in Accord 4 of South Africa’s new growth path, government commits to the procurement of renewable energy, with the aim to expand and diversify the nation’s energy generation capacity, whilst lowering greenhouse gas emissions, in order to meet the challenges posed by climate change. To fully re-alize these commitments the economy needs informed and trained people in this fi eld, which continues to be a signifi cant driver for future employment. Th e Industrial Development Corporation (IDC) and the South African Development Bank (SADB) estimated in 2011 that the total employment potential in the energy generation and energy and resource effi ciency categories would be 130 000 and 68000 new jobs respectively.

Under the auspices of the German Ministry of Economic Cooperation and Development (BMZ) and supported by the Department of Higher Education and Training (DHET) and the Department of Science and Technology (DST), the Skills for Green Jobs (S4GJ) programme drove the process of developing this new subject, the training material, student textbook and lecturer guide and trained TVET College lecturers on the subject matter content on new didactical training equipment as part of their continuous professional development so that they can teach the subject in a practical and progressive manner.

Th us, in January 2015 the subject Renewable Energy Technologies was successfully implemented on NC(V) Level 2 in six TVET colleges, namely Boland, Ingwe, Northlink, Port Elizabeth, Umfolozi and West Coast TVET Colleges.

Th e development and implementation of this new subject is the result of cordial collaboration and suc-cessful cooperation between Germany and South Africa and I wish the colleges, the lecturers and mostly our students a good start with Renewable Energy Technologies in 2015 and beyond.

Mr GF QondeDirector-General: Higher Education and Training

Foreword written by the Director-General for the RET Level 2 student book in 2015.

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USING THIS STUDENT BOOK Th is textbook is comprised of 4 topics for NC(V) level 4.

Th e structure of each topic includes various units, for example Unit 1 of Topic 1, International and National Climate Change Policies, and each unit is made up of several themes. In essence, the themes form the core of the student book. Th ey contain keywords, the desired outcomes, technical terms and defi nitions, illustrative examples, as well as questions, exercises and experiments through which the students can independently check their knowledge and understanding. Lastly, each theme ends with a bibliography section which will enable students to supplement the described subject matter.

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Introduction to Renewable Energy Resources

and Energy Effi ciency

Topic Overview

South Africa’s domestic economy largely depends on fossil fuels, particularly for electrical energy generation, manufacturing and transport. Subsequently, the country is one of the largest greenhouse gas (GHG) emitters on the continent and in the world. South Africa, however, is also an example of how quickly energy transition can happen. While the construction of two new coal-fi red power sta-tions, Kusile in Mpumalanga and Medupi in Limpopo, is seriously behind schedule and over-budget by almost double the original price, South Africa’s renewable energy programme (REI4P) in 2016 has over 50 fully operational renewable energy plants and nearly 100 additional plants in development. Wind turbines play an important role in South Africa’s clean energy transition. Thus, in this topic we will introduce you to the socio-economic and environmental benefi ts of wind turbine technologies. South Africa also has a large potential to play a leading role in e-mobility in Africa. Currently, e-mobil-ity is still an insignifi cant niche market, albeit most manufacturers have at least one model on offer. Japan already has more charging stations for e-cars than gasoline stations according to a recent study by Nissan (May 2016), and Norway aims to ban the sale of fossil fuel-based cars by 2025. These are indications that e-mobility is defi nitely coming. These developments will be defi ned by renewable energy generation into smart grids, charging networks, local standardisation, battery and fuel cell technology, electric drive train components and smart connectivity. We will thus also introduce you to the socio-economic and environmental benefi ts of hydrogen fuel cell technology and e-mobility.

Topic 1 covers the following units:Unit 1.1 Economic and Environmental Benefi ts of Wind Power SystemsUnit 1.2 Economic and Environmental Benefi ts of Hydrogen Fuel Cell Technology and E-Mobility

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UNIT 1.1 ECONOMIC AND ENVIRONMENTAL BENEFITS OF WIND POWER SYSTEMS

Introduction

This unit briefly explains the history and rationale behind wind power generation, allowing you to not only interpret resource maps based on South Africa’s Wind Atlas, but also enabling you to debate the economic and environmental benefits of wind power generation.

Unit Outcomes

At the end of this unit, you should be able to:(i) Explain how wind energy has been used for centuries to pump water and grind corn.(ii) Explain when and where the industrial breakthrough for wind power started.(iii) Provide an overview of the world wind energy market and industry.(iv) Interpret resource maps from South Africa’s Wind Atlas.(v) Explain where exactly in South Africa the potential for wind power generation can be regarded

as significant.(vi) Explain why wind power generation has a realistic potential to reduce CO2 emissions in South

Africa.(vii) List and compare the advantages and disadvantages of wind power generation.(viii) Explain why wind farm developments, like all other infrastructure developments, require envi-

ronmental impact assessments.(ix) Explain a simplified cost structure for a wind farm.

Themes in this Unit

Unit 1.1 covers the following three themes:Theme 1.1.1 Wind Power Applications: A Short History of its DevelopmentTheme 1.1.2 Wind Energy Markets in South Africa and the WorldTheme 1.1.3 Advantages and Disadvantages of Wind Power Generation

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THEME 1.1.1

WIND POWER APPLICATIONS: A SHORT HISTORY

Introduction

Since antiquity, man has used wind energy. It is thus not a new idea. For centuries, windmills and wa-termills were the only source of motive power for a number of mechanical applications, some of which are even still used today. Humans have been using wind energy in their daily work for some 4000 years. Sails, for example, revolutionised seafaring and muscle power for rowing became almost obsolete. At around 700 A.D., farmers in present-day Iran, Afghanistan and China started using wind-powered devices consisting of rotor blades or fl apping sails on a vertical axis. Th ese early windmills were mostly used to grind grain. Th us, we still speak of ‘windmills’ today, even when we are talking about machines that do not actually grind, such as sawmills and even wind turbines for generation of electrical energy.

Keywords

Th e fi rst wind-powered devicesTh e fi rst horizontal-axis windmillsAdvanced horizontal-axis windmills Multi-blade windmillsModern wind turbines

Theme Outcomes

At the end of this theme, you should be able to:(i) Explain how wind energy has been used for centuries to pump water and grind corn.(ii) Explain when and where the industrial breakthrough for wind power started.

Defi nition of Terms

The First Wind-Powered DevicesTh e earliest known use of wind power is of course the sail boat, and this technology had an important impact on later developments of sail-type windmills. Ancient sailors understood lift and used it every day, even though they did not have the physics to explain how or why it worked. Apart from sailing, the history of wind-powered devices shows a general evolution from the use of relatively small devices driven by aerodynamic drag forces (blades on a vertical axis) to larger material-intensive drag devices with sails or blades on a horizontal axis.

Th e fi rst windmills were developed to ease the tasks of grain grinding and water pumping and the earli-est-known design is the vertical axis system developed in Persia and Afghanistan around 500-900 A.D. Th e fi rst known documented design is a Persian windmill, one with vertical blades made of bundles of reeds or wood which were attached to the central vertical shaft by horizontal struts (Figure 1). Th ese type of windmills are called panemone devices.

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FIGURE 1: SIMPLIFIED DRAWING (SIDE AND TOP VIEW) OF AN EARLY VERTICAL-AXIS WINDMILL

Image source: GIZ/S4GJGrain grinding was the fi rst documented windmill application and was very straightforward. Th e grind-ing stone was affi xed to the same vertical shaft . Th e mill machinery was commonly enclosed in a build-ing, which also featured a wall or shield to block the incoming wind from slowing the side of the drag-type rotor that advanced toward the wind. Vertical-axis windmills were also used at around the same time in China. Here, the primary applications were also apparently grain grinding and water pumping.

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The First Horizontal-Axis WindmillsTh e fi rst windmills to appear in Western Europe were of the horizontal-axis confi guration. Th e reason for the sudden evolution from the vertical-axis panemone design is unknown, but the fact that improved water wheels also had a horizontal-axis confi guration may provide part of the answer. Another reason may have been the higher structural effi ciency of drag-type horizontal machines over drag-type vertical machines, which can lose up to half of their rotor collection area due to shielding requirements. Th e fi rst illustrations (1270 A.D.) of horizontal-axis mills show a four-bladed device mounted on a central post (Figure 2) which was already fairly technologically advanced compared to the panemone type mills. Th ese early horizontal-axis mills used wooden cog-and-ring gears to translate the motion of the hori-zontal shaft to vertical movement to turn a grindstone. Th is gear was apparently adapted for use on post mills from the horizontal-axis water wheel already developed by Roman engineers.

FIGURE 2: A POST MILL

Image source: Shutterstock A post mill mounted on a single vertical post around which the whole mill can be turned manually to bring the sails into the wind.

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Advanced Horizontal-Axis Windmills Around 1400, the Dutch started to refi ne their mill design, particularly with a multi-story fi xed tower. By pushing a large lever at the back of the mill, early horizontal-axis mills had to be oriented into the wind manually. Later inventions, such as smock mills (Figure 3) featured a revolving upper section, a so-called rotatable cap which featured the sails, the wind shaft and the brake wheel, plus the fantail and the mech-anism to rotate the cap into the wind.

FIGURE 3: A SMOCK MILL

Image source: S4GJ/GIZA smock mill, which diff ers from post mills in that the main body does not rotate, with only the cap that rotates to face the wind.

Cap

Dust floor

Bin floor

Stone floor

Reefing stage

Meal floor

Fantailwormdrive

Shutter control chain

Tenteringgear

Sweep

Spider

CanisterStriking rod

WindshaftBreak wheel

WallowerSack hoist

Stock

Grain hoppers

Upright shaft

Stones

Great spur wheel

Stone nutShutters

Drive toengine houseadded in 1908

Sack hoistchain

Meopharm Green, Kent 1820

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Th e process of perfecting the windmills by making step-by-step incremental improvements in effi ciency took another 500 years. During the second half of the eighteenth century, several complex but eff ective techniques were developed that made it possible for a traditional windmill to be left mostly unattend-ed, at least when it came to changes in wind speed and direction. Figure 4 illustrates the mechanism that automatically adapted the positioning of the windmill into the wind. It consisted of a fantail and sophisticated gear work all made out of wood. By around 1900, the total amount of wind-powered mills in Europe was estimated to be around 200 000, compared to some 500 000 waterwheels. Windmills were built in the countryside and in cities and applications were diverse, ranging from the common water well, irrigation or drainage pumping to grain-grinding, saw-milling of timber, and the processing of other commodities such as paints and dyes.

FIGURE 4: A TECHNICAL DRAWING ILLUSTRATING THE MECHANISM FOR A SELF-REGULATING WINDMILL

Image source: WikimediaA technical drawing from 1820, illustrating the mechanism for a self-regulating windmill, based on sophis-ticated mechanical gear work that automatically adapted the positioning of the mills rotor into the wind.

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Multi-Blade WindmillsFor centuries, an important application of windmills at subsistence level has been mechanical water pumping. Th ese systems were perfected in the United States during the 19th century and are direct-drive devices that transfer kinetic (wind) energy via gears, rods and a piston in a cylinder to pump water. Th ese mills had tails to orient them into the wind but the most important refi nement of the multi-fan-type windmill was the development of steel blades and improved gearboxes. In South Africa, these types of windmills are known as windpumps, given that their primary use was the pumping of water on farms.

FIGURE 5: WINDPUMPS AT THE LOERIESFONTEIN MUSEUM, SOUTH AFRICA

Image source: https://upload.wikimedia.org/wikipedia/commons/f/fd/WindmillMuseumLoeriesfontein01.jpg

Modern Wind TurbinesTh e development of modern wind turbines that generate electrical energy began with technical innova-tions in the fi eld of aerodynamics, mechanical/electrical engineering, control technology and electronics. Since 1980, wind turbines have become larger and more effi cient at rates otherwise only seen in computer technology.

Today, large-scale wind turbines (Figure 6) have the following primary components:(i) A rotor, which consists of two or more propeller-like blades that are tied to a rotating shaft . Th e

force of the wind turns the blades, which transfer the kinetic energy into a rotating shaft , which in turn spins a generator to produce electric charges.

(ii) A nacelle, which is the enclosed body of the turbine. In a large wind turbine the nacelle houses the drive train, gearbox and generator, or a gearless direct-drive generator.

(iii) A tower, which supports the rotor and nacelle. Th e tower elevates the turbine in order to increase exposure to higher velocities of wind.

(iv) A mainframe, which is a structure that contains the slip ring. It connects the nacelle and its wiring to the tower in such a way that the rotor can spin freely and face into the wind.

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FIGURE 6: A SIMPLIFIED SCHEMATIC VIEW INTO A WIND TURBINE

Rotor blade

Gear boxNacelle

Generator

Power cables

Tower

Wind

Overhead powerlines

Transformer

Image source: GIZ/S4GJ

But let us look back in history. In 1920 and 1926, Albert Betz, a German physicist and a pioneer of wind turbine technology, determined the maximum wind turbine performance, now called the ‘Betz limit’, and the optimal geometry of rotor blades. In 1950, a German professor named Ulrich Hütter detailed the theoretical basics for modern turbines with rotors of two or three blades. Hütter’s theory for blade-element momentum, developed from his aeronautical background, is said to be current even today. He applied modern aerodynamics and modern fi bre optics technology to the construction of rotor blades on the wind turbines in his experimental system.

Even earlier in the late 19th century, Poul la Cour, a Danish scientist did some experimental work on aerodynamics and practical implementation of wind power plants. He was the fi rst in Denmark to install a generator into a windmill using the mill to produce electrical energy. At the same time he educated many electricians and made it possible for farmers and craft smen to establish small power plants in the countryside. In the 1980s, Danish scientists developed small turbines with a nominal output of 20 kW to 100 kW. Th anks to state subsidies, these turbines were set up on farms and on the Danish coast to pro-vide electric power. At the same time (1980s) in other countries, research focused on large systems, two examples being NASA’s research in the US or the German GroWiAn project. Unfortunately, these plans turned out to be too ambitious and the research at the facilities was discontinued.

However, higher cost of conventional electrical energy generation and severe environmental impacts of fossil fuels on the one hand and excellent wind resources in northern Europe on the other hand crea-ted a small but stable market for single, co-owned wind turbines and small clusters of machines. Aft er 1990, more market activity shift ed to Europe and Asia. Driven by high utility power purchase rates, the installation of 50 kW, then 100 kW, then 200 kW, then 500 kW and now 5+megawatt wind turbines by commercial consortiums and private landowners in the Netherlands, Denmark and Germany has been particularly impressive. Today large wind turbine manufacturers such as Nordex, Siemens and Enercon in Germany, Ming Yang, Goldwind and United Power from China, Gamesa in Spain, General Electric in the United States, the Sulzon Group from India and, the largest of all, Vestas in Denmark are the industry leaders. By the end of 2015, global wind power generating capacity totalled over 430 000 mega-watts (430 GW). Key attributes of this current period are: scale increase (Figure 7), commercialisation, competitiveness, grid integration, energy independence, environmental benefi ts (climate change) and turbine standardisation. Th ese type of turbines usually use 3-blade upwind, horizontal-axis rotors on a monopole tower, and direct-drive systems connected to a synchronous AC permanent magnet generator. Because the generator’s speed determines both its potential and frequency, an inverter rectifi es the ‘wild AC’ to DC and then converts it back to AC before connecting to the grid.

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FIGURE 7: A 7 MW OFFSHORE WIND TURBINE

Image source: GIZ/S4GJ Current 7 MW off shore wind turbines have a rotor diameter of 154 m. Th e length of each blade is rough-ly the same as the wingspan of an Airbus A380.

A 380

79.80 meters

154 meters

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Exercises

1. List the earliest known uses of wind power. Where and when exactly were these devices developed?

………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

2. Explain the design of panemone-type windmills and explain how they function.

………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

3. What type of windmills were developed aft er the panemone types? Explain their technologi-cally advanced setup compared to the panemone type of windmill!

………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

4. Try drawing the mechanical mechanism early horizontal-axis mills used, i.e. wooden cog-and-ring gears, to translate the motion of the horizontal shaft to vertical movement to turn a grindstone.

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5. Explain the process of perfecting horizontal-axis windmills, focussing on the mechanism for self-regulating windmills, i.e. positioning of the rotor into the wind!

………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

6. In South Africa, multi-blade windmills are known as windpumps. Explain how these mills moved themselves into the wind!

………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

Further Information on the Resource CD

Historical development of windmills, Springer, PDF

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THEME 1.1.2

WIND ENERGY MARKETS IN SOUTH AFRICA AND THE WORLD

Introduction

In this theme, we provide you with an overview of the world’s wind energy market and present wind resource maps from South Africa’s Wind Atlas. Furthermore, we will explain where exactly in South Africa the potential for wind power generation can be regarded as signifi cant.

Keywords

Global wind power generation in 2015Wind Atlas South Africa (WASA)Wind power projectsRenewable Energy Independent Power Producer Procurement (REI4P) Programme

Theme Outcomes

At the end of this theme, you should be able to:(i) Provide an overview of the world wind energy market and industry.(ii) Interpret resource maps from South Africa’s Wind Atlas.(iii) Explain where exactly in South Africa the potential for wind power generation can be regarded

as signifi cant.


Global Wind Power Generation in 2015In 2015, the wind power industry set new records across the world. Wind power is leading the transfor-mation of global power systems. Wind power can now be considered mainstream, supplying competitive, reliable and clean energy for economic growth and cutting emissions in established economies. At the same time, the technology is creating new jobs in manufacturing and maintenance and is enhancing energy security. Th ese developments are long overdue and very necessary to achieve the climate ob-jectives agreed internationally in Paris (2015) and in Marrakech (2016). Th e Paris Agreement requires decarbonised power generation by 2050 (if not before), to keep the temperature increase below 2°C above pre-industrial levels.

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FIGURE 1: GLOBAL CUMULATIVE INSTALLED WIND POWER CAPACITY (2000 – 2015)

450,000 400,000 350,000 300,000250,000200,000150,000100,000

50,000

MW

2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015

17,400 23,900 31,100 39,431 47,620 59,091 73,95793,924

120,690159,016

197,946

282,842

318,463

369,705

432,883

238,089

Image Source: Th e Global Wind Energy Council (GWEC 2015).

Globally, at the end of 2015, almost 433 GW of wind power was installed in total (Figure 1). Particular-ly the Chinese industry continues to amaze, having installed no less than 30.8 GW of new capacity in 2015. China thus surpassed the EU in total installations, ending 2015 with 145 GW in total (Figure 2). Both Europe and the US markets performed respectably as well. Th e European off shore sector set a new record, installing over 3 GW in 2015. At the same time, new markets are emerging across Africa, Asia and Latin America.

At the end of 2015, the number of countries with more than 1 GW installed capacity was 26, including 17 countries in Europe, 4 in Asia-Pacifi c (China, India, Japan & Australia), 3 in North America (Canada, Mexico and U.S.), 1 country in Latin America (Brazil) and 1 country in Africa (South Africa). By the end of 2015 eight countries had more than 10 GW installed capacity, including China (over 145 GW), the U.S. (over 74 GW), Germany (almost 45 GW), India (over 25 GW), Spain (over 23 GW), UK (over 13 GW), Canada (over 11 GW), and France (over 10 GW). China already crossed the 100 GW mark in 2014, adding another milestone to its already exceptional history of renewable energy development.

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FIGURE 2: TOP 10 COUNTRIES WITH THE HIGHEST CUMULATIVE INSTALLED WIND POWER CAPACITY (2015)

PR China

Rest of the world

USA

Germany

Brazil

Italy

France

Canada

United Kingdom

Spain

India

Country MW % Share

PR China 145,362 33.6

USA 74,471 17.2

Germany 44,947 10.4

India 25,088 5.8

Spain 23,025 5.3

United Kingdom 13,603 3.1

Canada 11,205 2.6

France 10,358 2.4

Italy 8,958 2.1

Brazil 8,715 2.0

Rest of the world 67,151 15.5

Total TOP 10 365,731 84.5

World Total 432, 883 100

Data/Image Source: Th e Global Wind Energy Council (GWEC 2015).

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Wind Atlas South Africa (WASA)WASA (2009 to 2014) is an initiative of the Department of Energy where the South African National En-ergy Research Institute (SANERI) coordinates and contracts contributions from the implementing part-ners, such as the Council for Scientifi c and Industrial Research (CSIR) and the University of Cape Town (UCT). Th e Wind Atlas shows the generalised, climatological (30 year) annual mean wind speed (m/s) at 100 m above ground level for the Northern Cape, Western Cape and Eastern Cape. Th e wind resource map depicts the local wind resources that a wind turbine would encounter at a particular location. Th e WASA Large Scale High Resolution (250m) Wind Resource Map (Figure 3) confi rms that South Africa has excellent wind resources.

Th e latest technology has been used to map the wind resources in the Eastern, Western and parts of Northern Cape provinces of South Africa. Th e results confi rm a very high potential with a number of locations with an annual average wind speed of more than 8 m/s (orange/red) and between 6 and 8 m/s (green/yellow). Th e average wind resource potential reported for South Africa is thus high. Th e WASA map shown in Figure 3 reveals the presence of high wind speeds along the coasts of the KwaZulu-Natal, Eastern Cape, Western Cape, and Northern Cape provinces. Th e Atlas is consistent in showing that the Eastern, Western and Northern Cape provinces are the most favourable locations for wind energy proj-ects. South Africa is endowed with good wind resources and it is important to mention that it also boasts policies and programmes that support the development of a utility-scale renewable energy sector.

FIGURE 3: LARGE-SCALE HIGH RESOLUTION WIND RESOURCE MAP

Data/Image Source: WASA project (2014)

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Wind Power ProjectsTh e WASA initiative came at a critical time in the development of the wind industry in South Africa. Th e extremely robust affi rmation it provided of the excellent wind resource in the country and its wide geo-graphical distribution served to enhance developer interest and urgency and to reassure policy makers that wind is a reliable energy source. Th ese aspects have been instrumental in the rapid growth and the success of South Africa’s wind industry. Wind turbines are thus largely located along the coastal regions of the Eastern, Northern and Western Cape provinces based on the strong wind resources along these shores and further inland. Th e following graphics (Figure 4 and Table 1) detail South Africa’s wind ener-gy projects, and where they are located. Th e Eastern Cape has the highest number of wind projects (16), the Western Cape follows with 10 and the Northern Cape with 8. With numerous utility-scale wind farm projects in South Africa, the wind-energy landscape in the country is continuing to expand.

FIGURE 4: WIND ENERGY PROJECTS IN SOUTH AFRICA

Image Source: Data from REI4P project database, http://energy.org.za/ (November 2016). See also Table 1.

16 10

18 19

8

365 14

6

9

28 3117 32

23

Bloemfontein

Pretoria

Cape Town

South Africa

12

20 21

25 7

24 26 21 3 11

33 27 22 1513 34 35

29 30

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TABLE 1: WIND ENERGY PROJECTS IN SOUTH AFRICA

Nr. Name Capacity (MW) Programme Nearest Town Status

1Amakhala Emoyeni (Phase 1)

134.4 REI4P Window 2 Bedford Fully operational

2 Chaba 20.6 REI4P Window 2 Komga Fully operational3 Cookhouse Wind Farm 135 REI4P Window 1 Cookhouse Fully operational

4 Copperton Windfarm 102 REI4P Window 4 CoppertonApprovals, planning and financing

5 Darling Wind Farm 5.2 Other Yzerfontein Fully operational

6Dassiesklip Wind Energy Facility

26.2 REI4P Window 1 Caledon Fully operational

7 Dorper Wind Farm 97 REI4P Window 1Molteno/Sterkstoom

Fully operational

8 Eskom Sere Wind Farm 100 Other Koekenaap Fully operational

9Excelsior Wind Energy Facility

32 REI4P Window 4 SwellendamApprovals, planning and financing

10 Garob Wind Farm 136 REI4P Window 4 CoppertonApprovals, planning and financing

11 Golden Valley 120 REI4P Window 4 CookhouseApprovals, planning and financing

12 Gouda Wind Facility 135.2 REI4P Window 2 Gouda Fully operational13 Grassridge 59.8 REI4P Window 2 Port Elizabeth Fully operational14 Hopefield Wind Farm 65.4 REI4P Window 1 Hopefield Fully operational15 Jeffreys Bay Wind Farm 138 REI4P Window 1 Jeffreys Bay Fully operational

16 Kangnas Wind Farm 137 REI4P Window 4 SpringbokApprovals, planning and financing

17 Karusa Wind Farm 140 REI4P Window 4 SutherlandApprovals, planning and financing

18 Khobab Wind Farm 138 REI4P Window 3 Loeriesfontein Under construction

19Kouga Wind Farm - Oyster Bay

80 REI4P Window 1 St Francis Bay Fully operational

20Loeriesfontein 2 Wind Farm

138 REI4P Window 3 Loeriesfontein Under construction

21Longyuan Mulilo De Aar 2 North Wind Energy Facility

139 REI4P Window 3 De Aar Under construction

22Longyuan Mulilo De Aar Maanhaarberg Wind Energy Facility

96 REI4P Window 3 De Aar Under construction

24MetroWind Van Stadens Wind Farm

27 REI4P Window 1 Port Elizabeth Fully operational

25 Noblesfontein 72.8 REI4P Window 1 Noblesfontein Fully operational26 Nojoli Wind Farm 87 REI4P Window 3 Cookhouse Under construction

27Noupoort Mainstream Wind

79 REI4P Window 3 Noupoort Fully operational

28 Nxuba Wind Farm 140 REI4P Window 4 CookhouseApprovals, planning and financing

29 Oyster Bay Wind Farm 140 REI4P Window 4 Oyster BayApprovals, planning and financing

30Perdekraal East Wind Farm

108 REI4P Window 4 MatjiesfonteinApprovals, planning and financing

31 Red Cap - Gibson Bay 111 REI4P Window 3 St Francis Bay Under construction

32 Roggeveld 140 REI4P Window 4 SutherlandApprovals, planning and financing

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33The Soetwater Wind Farm

139 REI4P Window 4 LaingsburgApprovals, planning and financing

34Tsitsikamma Communi-ty Wind Farm

94.8 REI4P Window 2 Tsitsikamma Fully operational

35 Waainek 23.4 REI4P Window 2 Grahamstown Fully operational

36Wesley-Ciskei Wind Farm

33 REI4P Window 4 PeddieApprovals, planning and financing

37 West Coast 1 90.8 REI4P Window 2 Vredenburg Fully operationalTotal 3460.6

Source: REI4P project database, http://energy.org.za/ (November 2016)

Renewable Energy Independent Power Producer Procurement Programme (REI4P)Most of these projects form part of the Renewable Energy Independent Power Producer Procurement Programme (REI4P), which aims to procure 17.8 GW of renewable energy capacity by 2030. Th e REI4P is proving to be extremely successful in assisting to meet South Africa’s energy demand, which has had a number of concerns over recent years due to demand exceeding supply capabilities. Apart from miti-gating slowed economic development growth due to unpredictable provision of power, the programme also encourages foreign investment, as well as a number of socio-economic benefi ts due to job creation and skills development. Th e programme will continue to provide benefi ts over the upcoming bidding periods, as well as permanent benefi ts through the development of local factories, as well as job creation and skills development.

Funding is provided through a variety of foreign private equity, local private equity and large commer-cial and development banks. Some of the funding is composed of local private equity funds for black economic empowerment purposes to represent surrounding communities. Approved projects of the programme thus far represent over R192 billion of which 28% is attributed to foreign investment. So far four rounds of bidding have been completed, with the fi ft h round of bidding to be held in 2017. Projects covered by the REI4P are amongst others, onshore wind, photovoltaic, concentrated solar power, bio-mass, landfi ll gas, small hydropower and biogas. In just four years, the REI4P alone has already delivered over 5 GW throughout 79 diff erent projects, which accounts for over a quarter of the 2030 renewable energy target.

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Exercises

1. Using the GWEC data from 2015, list and rank the eight countries that had more than 10 GW of wind power installed according to their installed capacity!

………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

2. What kind of information does the large-scale high resolution resource map in the Wind Atlas South Africa (WASA) demonstrate?

………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

3. According to the WASA resource map, where are the most favourable locations for wind ener-gy projects? Be as specifi c as possible!

………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

4. Verify/compare your answer in question 3 with the facts given in Figure 4 and Table 1, i.e. locations and capacity of South Africa’s wind energy projects!

………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

5. Th e Renewable Energy Independent Power Producer Procurement Programme (REI4P) aims to procure almost 18 GW of renewable energy capacity by 2030. Is there already any indica-tion that this target will be met?

………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

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(i) Global Wind Report: Annual Market Update, Th e Global Wind Energy Council (GWEC), April 2016, Brussels.

(ii) Wind Atlas for South Africa (WASA), Council for Scientifi c and Industrial Research (CSIR), April 2014.

(iii) Wind Atlas for South Africa Phase 1, SANERI, 2015(iv) Wind Energy Localisation Study, Department of Trade and Industry (DTI), 2015.(v) REI4PP focus on wind, DoE/IPP Offi ce, Quarter 1, 2015/16.

Your own notes

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THEME 1.1.3

ADVANTAGES AND DISADVANTAGES OF WIND POWER GENERATION

Introduction

Th ere is suffi cient evidence available that wind power is viable, reliable and ready to go. ESKOM needs to buy coal for their coal-fi red power plants to generate electrical energy. No or very little input costs are required for wind or photovoltaic technologies, as they are powered by the Sun. Most renewable ener-gy technologies are thus already cheaper than coal and nuclear power. A unit of electrical energy from Eskom’s new coal plants costs around R1.00/kWh, while wind power generation in round three of the REI4P off ered average prices of 74 cents per kWh. Market price aside, coal and nuclear power have huge hidden costs that are not included in the price we pay for electrical energy. Th ese are for instance the costs of water and water pollution, human health impacts and climate change. Th ese costs are massive, both in monetary terms and in terms of social and health costs. Th ey are unfortunately usually not taken into account when the price per unit of electrical energy from Eskom’s coal power plants is calculated. Th us, in this theme we present you with the advantages and disadvantages of wind power generation.

Keywords

Mitigation scenarioReduction in CO2 emissionsLife cycle assessment of wind power systemsAdvantages and disadvantages of wind power systemsEnvironmental impact assessmentsImpact mitigationEIA process and methodologySimplifi ed cost structure for a wind farm

Theme Outcomes

At the end of this theme, you should be able to:(i) Explain why wind power generation has a real potential to reduce CO2 emissions in

South Africa.(ii) List and compare the advantages and disadvantages of wind power generation.(iii) Explain why wind farm developments, similar to all other infrastructure developments,

require environmental impact assessments.(iv) Explain a simplifi ed cost structure for a wind farm.


Mitigation ScenarioAs already indicated in the student book Renewable Energy Technogolies NQF Level 2, countries can respond to climate change by reducing greenhouse gas (GHG) emissions. Th e capacity to mitigate cli-mate change depends on, inter alia, country specifi c socio-economic circumstances, political will and the availability of information and technology. Reduction of GHG emissions can potentially be accom-plished through (i) reduction of energy use (energy effi ciency), and/or (ii) by using more renewable/clean energy technologies such as photovoltaic or wind power plants.

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Let us thus recall some facts: (i) Demand for energy services is increasing.(ii) Current energy systems are still dominated by fossil fuels (coal, gas etc.).(iii) GHG emissions resulting from the provision of fossil fuel sources contribute signifi cantly

to the increase in atmospheric GHG concentrations.

On the other hand:(i) Th e technical potential of renewable/clean energy technologies to supply energy services

exceeds current global demands.(ii) Renewable energy technology growth, particularly wind power, has increased rapidly in

recent years. (iii) Wind power generation costs are already competitive.

South Africa has perfect conditions for an integration of renewable technologies into the national grid. Wind energy, for example, can be used as a low-cost bulk energy provider. Th e very low seasonality of wind supply reduces fl uctuation risks. A mix of renewable resources spread over a wide geographical area will ensure an almost suffi cient supply of electrical energy. South Africa can decrease its reliance on coal and nuclear over time; investing increasingly in renewable technologies is a gradual transition. During peak times natural gas, for example, can bolster supply and can also be used to meet sudden peaks in energy demand.

FIGURE 1: A POSSIBLE TRANSITION TO RENEWABLE/CLEAN ENERGY GENERATION OVER TIME

Total energy output

Renewable energy output

As coal power outputdrops, energy outputfrom other sourcesincreasesNo new coal

plants are builtover time, old coal plants are shut down as renewableenergy increases

Time

Elec

tric

ity

dem

and

Image source: S4GJ/ GIZ

Coal power output

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Reduction in CO2 EmissionsConsidering such a mitigation scenario, i.e. the transition to renewable energy generation over time, the ques-tion arises whether wind power generation has a realistic potential to reduce CO2 emissions in South Africa, ideally even over their entire life cycle. Clean energy is increasingly becoming part of national dialogues - lenders, utilities and lawmakers need the most comprehensive and accurate information on GHG emissions from renewable and conventional generation technologies to inform policy, planning and investment decisions. A very comprehensive study is available from the U.S. in form of a Life Cycle Assessment (LCA) Harmoni-sation project. Th e National Renewable Energy Laboratory (NREL) off ers more precise estimates of life cycle GHG emissions for renewable and conventional generation, clarifying inconsistent and confl icting estimates in the published literature, aiming to reduce uncertainty. Analysts at the NREL developed and applied a systematic approach to review the LCA literature, identify primary sources of variability and, where possible, reduce variability in GHG emissions estimates through a procedure called “harmonisation.” NREL considered more than 2,100 published LCA studies on utility-scale electricity generation from renewable and convention-al generation technologies.

FIGURE 2: COMPARISON OF LIFE CYCLE GREENHOUSE GAS EMISSIONS FOR RENEWABLE AND CONVENTIONAL GENERATION TECHNOLOGIES

Data source: NREL LCA Harmonization Project

Please note that each resource category, i.e. PV, CSP, wind, nuclear, gas and coal displays the number of reviewed published data, the harmonised data and the number of unique references used in the study, e.g. for wind 126/126/47. Th e distributional information was calculated based on the harmonised data and compared with the as-published data using the following range: minimum, 25th percentile value, 50th percentile value, 75th percentile value, and maximum. Th e interquartile range (between 25th and 75th percentile) is highlighted except for natural gas (grey/white or blue/turquoise). Th ese results of the NREL study show that the total life cycle GHG emissions from renewables and nuclear energy are much lower and generally less variable than those from fossil fuels. For example, from cradle to grave, coal-fi red generation releases about 20 times more GHGs per kilowatt-hour than renew-able technologies based on median estimates for each technology. Lifecycle GHG emissions of renewable technologies are thus, in general, considerably lower than those of fossil fuel options.

Non-RenewableRenewable

Life

cyc

le g

reen

hous

e ga

s em

issi

ons

(g C

O2e/

kWh)

340

680

1,020

1,360

1,700

0PV (46/46/17)

CSP (42/42/13)

Wind (126/126/47) Nuclear (130/130/34)

Natural gas (62/na/38)

Coal (164/164/51)

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Life Cycle Assessment of Wind Power SystemsAs indicated, life cycle assessments (LCA) of energy systems can help determine environmental burdens from “cradle to grave” and facilitate comparisons of energy technologies. Comparing life cycle stages and proportions of GHG emissions from each stage for wind power and coal shows that for coal-fi red power plants, fuel combustion during operation emits the vast majority of GHGs. For wind power plants, the majority of GHG emissions are upstream of operation.

FIGURE 3: COMPARISON OF LIFE CYCLE STAGES AND GHG EMISSIONS FOR WIND AND COAL POWER

Image source: NREL LCA Harmonization Project

Advantages and Disadvantages of Wind Power SystemsAs indicated in the life cycle assessment section, GHG emissions of wind power systems are considerably lower than those of fossil fuel options. Th ere are however many advantages and disadvantages of wind turbines. We will now present most of these so that you can determine whether controversy surrounding this clean and renewable energy technology is justifi ed.

Advantages(i) Wind is a renewable resource. Unlike fossil fuel reserves such as coal, oil and gas, wind energy

off ers sustainable power supply. Wind power can reduce a country’s dependency on fossil fuel and increases the energy mix and thus also energy security.

(ii) Th e majority of GHG emissions are upstream of operation.(iii) Wind energy reduces the need to burn fossil fuel. Th is can help to conserve these resources,

allowing them to support future generations.(iv) Unlike some other energy sources, wind energy is free. (v) Wind turbines have a relatively small environmental footprint. Th eir tower is high above the

ground but the impact on the land area at the base is minimal. (vi) Wind turbines are not limited to industrial-scale installations but can also be installed on a

domestic scale and can be coupled with other clean energy technologies.(vii) Wind turbines can bring power to remote locations.(viii) Wind turbines are relatively low maintenance and have fairly low running costs.(ix) In many countries where the wind energy industry has boomed, jobs have been created, i.e. for

the manufacture of turbines, installation and maintenance and also in wind energy consulting, where specialist consultants will determine whether or not a wind turbine installation will pro-vide a return on investment.

Operational ProcessesLife Cycle Upstream Processes

WIND

COAL

< 1% < 1% > 98%

Downstream Processes

• Raw materials extraction

• Module manufacture

• Parts manufacture

• Wind/turbine/farm construction

• Power generation

• Plant operation and maintenance

• Wind turbine/farm decommissioning

• Raw materials extraction

• Construction materials manufacture

• Power plant construction

• Coal mining

• Coal preparation

• Coal transport

• Coal combustion

• Power plant operation and maintenance

• Power plant decommis-sioning

• Waste disposal

• Coal mine land rehabil-itation

~ 86% ~ 5% ~ 9% ~10 g CO2 eq/kWh

~1000 g CO2 eq/kWh

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Disadvantages(i) Albeit wind is abundant and inexhaustible, wind power can have a drawback similar to photo-

voltaic systems because wind is not always a constant energy source (wind is not always blow-ing). Th is is why wind turbines are built along the coast, on top of hills or out at sea (constant wind resources).

(ii) Th e installation of large-scale wind turbines is considered expensive. First, a site survey needs to be carried out which involves measuring wind speeds over a signifi cant period of time. If deemed adequate, the wind turbine will need to be manufactured, transported and erected on top of a pre-built foundation and connected to the national grid. For off shore wind farms costs become even greater.

(iii) Wind turbines pose a threat to wildlife, primarily birds and bats and are contributing to high mortality rates.

(iv) Noise pollution, i.e. audible eff ects generated by the turbine’s rotors can be severe. Th is is why new wind farms are usually planned away from dwellings and face strong public objection.

(v) Visual pollution, i.e. a technical structure in the landscape/nature. While this tends to come down to personal opinion, public acceptance of wind farms can be controversial.

Environmental Impact AssessmentsWind farm developments, similar to all other infrastructure developments, require environmental impact assessments (EIA). Th e construction and operation of wind turbines may possibly lead to unfa-vourable environmental impacts on biodiversity, land-use and communities, for example in the form of noise and visual impacts. In addition to species disturbance and mortality, the issues of habitat loss and fragmentation need to be considered for all aff ected living organisms inclusive of plants, invertebrates and vertebrates including birds and bats. Potential impacts from wind energy installations must there-fore be assessed and mitigated when necessary.Th e National Environmental Management Act (NEMA, Act 107 of 1998) defi nes environmental impact assessment as the procedure which ensures that impacts of projects are identifi ed and assessed before au-thorisation is considered. Th e main objective is to avoid or minimise negative eff ects from the beginning of a project rather than trying to mitigate them later.

TABLE 1: POTENTIAL IMPACTS ASSOCIATED WITH WIND POWER AND WIND FARM DEVELOPMENT

Impact Description Relevant Legislation Reference (Part B)

Visual impact NEMA B2

Noise impact NEMA, NEMBA, Health Act B2, B3

Land use NEMA, NEMBA, NEMICMA, NEMPAA, NWA, NHRA

B2, B3, B5, B6, B9, B11

Impacts on biodiversity NEMA, NEMBA, NEMPAA, NFA B2, B3, B6, B21

Electromagnetic interference NEMA, NEMBA, CAA B2, B3, B20

Air safety CAA B20

Impacts on cultural heritage NEMA, NHRA B2, B11

Habitat fragmentation SALA B19

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Impact MitigationAssuming a new wind power project triggers the need for an Environmental Impact Assessment (EIA) under the EIA regulations, project-specifi c measures need to be designed to mitigate negative impacts and enhance positive impacts. An independent environmental assessment practitioner needs to be contracted by the project applicant (usually a fi rm) to prepare the EIA to applicable standards. Common mitigation measures associated with wind power installations include:

(i) Minimising the project’s footprint by utilising existing roads and disturbed areas as much as prac-ticable.

(ii) Implementing adequate dust control-, visual disturbance-, erosion control- and noise reduction measures.

(iii) Site selection outside of all relevant invertebrates, birds and bats and other animals' migratory routes/corridors and nesting/breeding areas.

(iv) Locating developments away from sensitive habitats for species, especially those that are threatened or have restricted ranges, and are collision-prone or vulnerable to disturbance, displacement and/or habitat loss.

(v) Developing and implementing a site-specifi c spill management plan.(vi) Conducting pre-disturbance environmental and social surveys to assess the presence of sensitive

resources, receptors, habitats and species.(vii) Burying electrical transmission infrastructure.(viii) Confi guring turbines to avoid attraction as landscape features, thus discouraging nesting raptors

or other species prone to colliding with turbines.(ix) Minimising lighting development in order to minimise light pollution, disturbance to visible com-

munities, and attraction of invertebrates, birds, bats and other animals.(x) Installing raptor-proof poles or similar measures on appropriate infrastructure to deter nesting,

hunting and migrating species.(xi) Continuous monitoring of relevant species including invertebrates, birds and bats and other ani-

mals during pre- and post-project development.

EIA Process and Methodology As already indicated, an EIA is a legislative tool used to ensure that potential impacts that may occur due to the proposed development are avoided or mitigated (minimised). In South Africa this includes social, economic and bio-physical aspects and the EIA must assess these equitably. Th e EIA procedures are based on the principles of Integrated Environmental Management (IEM) which, in short, comprise pro-active planning, informed decision making, a transparent and participatory approach to development, a broad understanding of the environment, and accountability for decisions and the information on which they are based. An EIA process is thus complex and is controlled through regulations published under the Govern-ment Notice No. R. 385, R. 386 and R. 387 and associated guidelines promulgated in terms of Chapter 5 of the National Environmental Management Act (Act No. 107 of 1998). As an example, a full/fi nal EIA report submitted for authority (DEA) review is available on the resource CD.

Th e EIA process (Figure 4) can be divided into 4 distinct components:(i) Application and initial notifi cation

• Submit an EIA application to the Department of Environmental Aff airs (DEA).• DEA acknowledgement of the EIA application (within 14 days).• Notify the public of the proposed development through inter alia, newspaper adverts, notifi ca-

tion letters, bids and notice boards.(ii) Scoping phase

• Investigate and gather information on the proposed study area in order to establish an under-standing of the area.

• Establish how the proposed project will potentially impact the surrounding environment.• Identify Interested and Aff ected Parties (I&APs) and relevant authorities by conducting a Public

Participation Process (PPP).• Identify potential environmental impacts through investigation and PPP.• Describe and investigate the alternatives that may be considered.

(iii) Impact assessment phase• Detailed specialist assessment of all issues and proposed alternatives identifi ed in the scoping phase.• Identify mitigation measures and recommendations to reduce the signifi cance of potential impacts.• Compile an Environmental Management Plan (EMP) which will prescribe environmental specifi -

cations to be adhered to during the construction and operational phases of the project.

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• As with the scoping phase, the PPP is an integral and important part of the impact assessment phase.(iv) Environmental Authorisation (EA)

• Environmental Authorisation (EA) issued to the applicant (project developer) once DEA has made a decision regarding the proposed project.

• Decision may be positive or negative based on information received in the scoping and impact assessment phases.

FIGURE 4: A TYPICAL EIA PROCESS FOR A WIND POWER PROJECT (SIMPLIFIED)


Public Participation Process (PPP)

PPP

• Notice boards

• Landowners

• Ward Councillor

• Municipality

• Other authorities

• Newspaper adverts

• Gazette

PPP30 day comments period

PPP30 day comments period

Environmental Authorities

Authority to acknowledge receipt within 14 days

Authority to reply in 30 days

• Accept report

• Reject report

• Require amendments

Authority to decide within 60 days to

• Accept report

• Refer for reviews

• Request amendments

• Reject report

Task

• Submit application to authorities including declaration of interest, application fee and consent of landowner(s)

• Conduct public participation process

• Notify relevant authorities and landowners

• Prepare Draft Scoping Report and Plan of Study for EIA

• Solicit comments on Draft Scoping Report

• Prepare Final Scoping Report and submit to authorities

• Prepare Draft Environmental Impact Report (EIR), draft EMP and Environmental Impact Statements (EIS)

• Solicit comments on the Draft EIR / EMP

• Prepare Final Environmental Impact Report. Submit to authorities

PPPAdvise I&APs of decision

Within 45 days of accep-tance authority must grant

authorisation or refuseDecision

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Simplifi ed Cost Structure for a Wind Turbine/FarmOver 90% of the total cost of energy for a wind turbine is related to “upfront” costs such as the cost of the turbine, foundation, electrical equipment, grid-connection etc. Compared to conventional fossil fuel technologies, the cost structure of a wind turbine or wind farm is thus very diff erent, as 40-70% of costs for conventional technologies are related to fuel and observation and measurement (O&M). As an exam-ple, a wind power project illustration is available on the resource CD. Table 2 indicates the price structure of a typical 2 MW wind turbine and Table 3 indicates the main components of a wind turbine and their share of the overall turbine cost.

TABLE 2: COST STRUCTURE OF A TYPICAL MEDIUM-SIZED (2 MW) WIND TURBINE

Share of total costs (%)

Turbine (ex works) 75.6

Grid connection 8.9

Foundation 6.5

Land rent 3.9

Electric installation 1.5

Consultancy 1.2

Financial costs 1.2

Road construction 0.9

Control systems 0.3

Total 100

Data: Calculated based on selected data for European wind turbine installations (EWEA, 2007)

Your own notes

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FIGURE 5: MAIN COMPONENTS OF A 5 MW WIND TURBINE AND THEIR OVERALL SHARE OF TURBINE COSTS

Nr Components Share of total costs (%)1 Tower 26.32 Rotor blades 22.23 Gearbox 13.04 Power converter 5.05 Transformer 3.66 Generator 3.57 Main frame 2.88 Pitch system 2.69 Main shaft 1.910 Rotor hub 1.411 Brake system 1.312 Nacelle housing 1.313 Yaw system 1.214 Rotor bearings 1.2

Total 86

Image source: GIZ/S4GJ Data: Figures are based on a Repower turbine with 45.3 metre length blades and a 100 metre tower (EWEA, 2007). Main compo-nents of a large-size wind turbine (5 MW) and their share of the overall turbine cost.

Due to fi erce competition in the wind industry in South Africa, prices for new wind farm projects have dropped dramatically. In round three of the REI4P, wind energy averaged 74 cents a kilowatt-hour (kWh), i.e. 26% cheaper than the predicted cost of new coal at ESKOM’s power stations. South Africa can thus produce electrical energy on par or even below the cost of fossil fuels.

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Exercises

1. South Africa has the perfect conditions to decrease its reliance on coal and nuclear over time by integrating renewable technologies into the national grid. Illustrate a possible and gradual transition scenario in a diagram, using time, energy demand and power output as categories for the vertical and horizontal axis.

2. Compare the life cycle GHG emissions from renewables and conventional energy generation, i.e. ‘from cradle to grave’.

………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

3. Compare the life cycle stages (upstream, operational and downstream) in terms of GHG emissions for wind and coal power.

………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

4. List the advantages and disadvantages of wind power systems in the table below.

Advantages Disadvantages

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5. Compare the cost of life cycle stages (upstream, operational and downstream) between wind and coal power!

………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

6. Explain the main objective of EIAs.

………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………


(i) Wind and Solar PV Resource Aggregation Study for South Africa, CSIR, 2016(ii) IPCC Special Report: Renewable Energy Sources and Climate Change Mitigation, 2011.(iii) State of Renewable Energy in South Africa, Department of Energy, 2015.(iv) National Renewable Energy Laboratory (NREL) LCA Harmonization Project, U.S. Depart-

ment of Energy, 2011.(v) Wind LCA Harmonization, National Renewable Energy Laboratory (NREL), U.S. Depart-

ment of Energy, 2013.(vi) EIA for the proposed Caledon Wind Farm, Western Cape Province, DEA Reference Num-

ber: 12/12/20/1701.(vii) EIA Guideline for Renewable Energy Projects. Department of Environmental Aff airs

(DEA), 2015.(viii) Cost Analysis of Wind Power, IRENA 2012.(ix) Th e Economics of Wind Energy, European Wind Energy Association (EWEA), 2007.(x) Eva Creek Wind Project, GVEA, 2013.

UNIT 1.2

ECONOMIC AND ENVIRONMENTAL BENEFITS OF HYDROGEN FUEL CELL TECHNOLOGY AND E-MOBILITY

Introduction

Oil is still the main resource that fuels the world’s transport economy in the form of petroleum fuels. Similarly, South Africa‘s transport system depends on petroleum fuels, petrol and diesel for almost all of its energy needs in the transport sector and beyond. South Africa relies on imports of crude oil and refined fuels to meet its liquid fuel needs. Over 60% of products refined locally are produced from the imported crude oil and about 36% of the demand is met by coal-to-liquid (CTL) synthetic fuels as well as gas-to-liquid (GTL) synthetic fuels plus a very small amount of domestic crude oil. Given that these fossil fuels are finite and the largest source of greenhouse gas emissions, clean alternative fuels are required in the future. Hydrogen is such a fuel and can provide a range of energy services while emitting only water. Focussing more on the transport sector, a growing global mobility and thus energy demand faces limited availability of fossil resources. To achieve the internationally agreed climate targets, a drastic reduction in transport-related CO2 emissions is needed. Fuel cell and battery powered electric vehicles have the potential to do exactly this, also offering substantial potential for economic growth. There are clear in-dications that e-mobility is definitely up-and-coming and that is why we are now introducing you to the socio-economic and environmental benefits of hydrogen fuel cell technology and e-mobility.

Unit Outcomes

At the end of this unit, you should be able to:(i) Provide an overview of the hydrogen economy and clarify the function of hydrogen and its use

in fuel cells.(ii) Explain why South Africa possesses competitive advantages and challenges with regard to hy-

drogen and fuel cell technology.(iii) Explain the advantages of combining renewable energy technologies, such as PV and wind tur-

bines, with hydrogen and fuel cell technology.(iv) List and describe the existing and potential applications of fuel cells. (v) Compile an overview of advantages and disadvantages of hydrogen and fuel cell technology.(vi) Compile an overview of advantages and disadvantages of e-mobility.

Themes in this Unit

Unit 1.2 covers two themes:Theme 1.2.1 Hydrogen and Fuel Cell TechnologiesTheme 1.2.1 E-Mobility

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THEME 1.2.1

HYDROGEN AND FUEL CELL TECHNOLOGIES

Introduction

Using hydrogen as fuel is not a new idea. Jules Vernes, a French novelist in the 19th century, best known for his adventure stories, including Journey to the Center of the Earth (1864), Twenty ousand Leagues Under the Sea (1870), and Around the World in Eighty Days (1873) already professed back then: “I believe that water will one day be employed as fuel, that hydrogen and oxygen which constitute it, used singly or together, will furnish an inexhaustible source of heat and light, of an intensity of which coal is not capa-ble…. Water will be the coal of the future!” Although hydrogen markets are still in their infancy, several initiatives are working towards clean, economical and safe hydrogen production and distribution for use in fuel cell electric vehicles (FCEVs). Interest in hydrogen is subsequently driven by a number of diff erent factors which we will investigate in this theme.

Keywords

Fuel cell and batteriesElectrolysis and reversing electrolysisExisting and potential applications of fuel cells Hydrogen as an alternative fuelTh e hydrogen economySouth Africa’s competitive advantagesCombining renewable energy technologiesAdvantages and disadvantages of fuel cell technology

Theme Outcomes

At the end of this theme, you should be able to:(i) Provide an overview of the hydrogen economy and clarify the function of hydrogen and its use

in fuel cells.(ii) Explain why South Africa possesses competitive advantages and challenges with regard to hy-

drogen and fuel cell technology.(iii) Explain the advantages of combining renewable energy technologies, such as PV and wind tur-

bines, with hydrogen and fuel cell technology.(iv) List and describe the existing and potential applications of fuel cells. (v) Compile an overview of advantages and disadvantages of hydrogen and fuel cell technology.


Fuel Cells and Batteries: A Little History and a Little ChemistryBatteries and fuel cells are based on fairly similar electrochemical processes and the historical back-ground of their discovery and development is thus related and kind of contemporaneous (early 1800s). Let us start with Alessandro Volta, an Italian scientist and a pioneer of electrical energy. He invented the “voltaic pile”, the fi rst electrical battery, in 1799. With this invention Volta proved that electrical energy could be generated chemically and he subsequently rejected the ideas of Luigi Galvani, another Italian scientist, on ‘animal electric fl uid’ (1791). Th e voltaic pile consisted of stacked pairs of alternating copper and zinc discs (electrodes) separated by cloth or cardboard soaked in brine, i.e. a solution of salt (usually sodium chloride), which acted as electrolyte to increase conductivity. Until the advent of the dynamo/generator in the 1870s, science and industry in the 19th century used batteries related to Volta’s inven-tion.

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Electrolysis and Reversing ElectrolysisTh e voltaic pile enabled a rapid series of discoveries, including the electrical decomposition (electroly-sis) of water into two components, hydrogen (H2) and oxygen (O2), in 1800 by two British researchers, William Nicholson and Anthony Carlisle. In 1883, William Grove, a British judge and scientist, reasoned that it should be possible to reverse the electrolysis process and generate electricity from the reaction of oxygen with hydrogen. Th e idea of reversing electrolysis led to the development of a device that was termed by Grove as the ‘gas battery’. Th e term ‘fuel cell’ was coined later in 1889 by two researchers, Ludwig Mond and Charles Langerand.

FIGURE 1: COMPARISON OF ELECTROLYSIS AND REVERSE ELECTROLYSIS OF WATER (SCHEMATIC)


Electrical energyWater

Hydrogen

Oxygen

Electrochemicalreaction

Water

Electrochemicalreaction

Oxygen

HydrogenElectrical energy

Your own notes

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Existing and Potential Applications of Fuel Cells In 1959 a British engineer, Francis Th omas Bacon wrote the next major chapter in the fuel cell story. He implemented a number of modifi cations to the original design, for example replacing platinum elec-trodes with less expensive nickel gauze, substituted the sulphuric acid electrolyte with alkali potassium hydroxide, and thus developed in essence the fi rst alkaline fuel cell (AFC). Th ese types of fuel cells were improved in the 1960s and used in NASA’s Gemini and Apollo Space Programmes. NASA’s interest pushed further development, as did the energy crisis in 1973. Since then, fuel cell research has continued unabated and fuel cell devices are now used successfully in a wide variety of NASA applications and produce electricity for spacesuits, airplanes, uninhabited air vehicles and reusable launch vehicles. Today many more sectors, both military and civil, are using fuel cell applications in cutting-edge technologies.

FIGURE 2: FUEL CELL APPLICATIONS IN CUTTING-EDGE TECHNOLOGIES (SCHEMATIC)


Hydrogen as an Alternative FuelA fuel cell is an electrochemical device that combines hydrogen (fuel) with oxygen. As a result, it produ-ces an electrical current, heat and water. Th e electrochemical reaction occurs as long as fuel (hydrogen, methanol etc.) is available. Because of the absence of combustion, there are no harmful emissions, and the only by-product is pure water. Unlike batteries, a fuel cell operates for as long as its fuel (hydrogen) is available. Batteries on the other hand, function as storage devices and supply electrical energy by trans-forming potential energy stored in chemical substances (reactants). When these reactants are consumed, the battery is no longer able to transform chemical energy into electrical energy.

Bus

Emission-free andnoiseless operation (PEM FC)

Delivery trucks

Emission-free andnoiseless operation (PEM FC)

Passenger car

Emission-free and energy-efficient operation (PEM FC)

Submarine

Air-independentpropulsion (PEM FC)

Space shuttle

Air-independentpower supply (PEM FC)

Storage systemfor regenerative energies

Siemens Electrolyzer(PEM FC)

H2/O2H2/air

Applications

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FIGURE 3: FUEL CELL OPERATION (SCHEMATIC AND SIMPLIFIED CONCEPTIONAL)


FIGURE 4: FUEL CELL IN A LAB CONVERTING CHEMICAL ENERGY INTO ELECTRICAL ENERGY

Image source: Shutterstock

Heat

Hydrogen Oxygen

Heat

Energy

H20

H

H

H

Oxygen

0

H

00

00

0

00

0

0H

0H H

WaterElectricpower

Hydrogen

H2

HH H

HH

H

HHH H

H

Excesshydrogen(for reuse)

Cata

lyst

Cata

lyst

Anod

e Cathode

Elec

trol

yte

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Hydrogen is thus considered an alternative fuel for various high-tech applications, but also due to its ability to directly power fuel cells in zero-emission electric vehicles, its potential for domestic produc-tion, and the fuel cell’s potential for high effi ciency. In fact, a fuel cell coupled with an electric motor is two to three times more effi cient than an internal combustion engine running on gasoline. Hydrogen needs to be produced, and sometimes it also needs to be transported and/or stored. Hydrogen for most of the fuel cell systems can be extracted from many hydrogen-bearing substances by fuel reforming and other procedures. Nevertheless, preparing the infrastructure required to extract, store and distribute hydrogen is a challenge but also an opportunity for economic development.

FIGURE 5: HYDROGEN AS ALTERNATIVE FUEL POWERS FUEL CELL ELECTRIC CARS SUCH AS THE TOYOTA MIRAI


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Hydrogen Production ProcessesHydrogen is the most abundant element in nature and chemically bound hydrogen can be found every-where on Earth: in water, fossil fuels and all living things. Yet, hydrogen rarely exists as free molecules (H2) in nature. Instead, for technical use hydrogen has to be extracted from resources such as water or hydrocarbons and its production is energy intensive. Th ere are many pathways (Figure 6) for commer-cial hydrogen production available and the energy and raw materials required for these processes can be obtained from various sources, such as fossil fuels, nuclear energy and renewable energy sources.

FIGURE 6: OVERVIEW OF HYDROGEN PRODUCTION PATHWAYS (SIMPLIFIED)

Crude oil

Energy Resource Processes Product

Reformer

Reformer

Coal Reformer

Reformer

Natural gas Reformer

Reformer

Nuclear

Nuclear Electric power plant

ElectrolyserHydrogen

Solar Generator

Hydro Generator

Wind Generator

Wave Generator

Geothermal Electric power plant

Wood

Organic waste

Biomass

Image source: S4GJ/GIZ

Currently the dominant technology for hydrogen production is steam reforming. Steam reforming refers to processes that change fossil fuel-based liquid hydrocarbons, mainly natural gas but also gasoline or methanol, to a gas-phase and fuel-rich steam. Given that these materials are all fossil fuel based and given that steam reforming releases carbon dioxide (CO2) as a by-product to the atmosphere, reforming cannot be considered as a sustainable hydrogen production process. However, more sustainable hydrogen production pathways are known, such as:

(i) Electrolysis, i.e. splitting water into hydrogen and oxygen using electricity from one of the many renewable sources. One advantage of electrolysis is that it is capable of producing high purity hydrogen (>99.999%). However, capital costs for an electrolysis facility can be a huge factor, and effi cient electrolysers require around 50 kWh of electrical energy to produce 1 kg of hydrogen. Even when considering its higher effi ciency as fuel in fuel cells, the high refi nery costs make hydrogen production costly compared to gasoline, which is non-renewable and causes additional impact costs.

(ii) Biomass conversion via either thermochemical or biochemical conversion to intermediate prod-ucts that can then be separated or reformed to hydrogen.

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(iii) ermolysis, using solar-generated heat for high temperature chemical cycle hydrogen produc-tion.

(iv) Photolysis, using photons in biological or electrochemical systems to produce hydrogen directly.

Th e order of the technologies mentioned above also represents the technological maturity of these pathways, and thus roughly the chronological order in which we might expect to see them commercially available. Figure 7 provides an overview of the various sustainable hydrogen production options while Figure 8 illustrates non-sustainable and sustainable hydrogen production techniques.

FIGURE 7: OVERVIEW OF SUSTAINABLE HYDROGEN PRODUCTION PATHWAYS (SIMPLIFIED)

Heat

ConversionElectricity

ElectrolysisThermolysis Photolysis

Mechanical energy

Biomass

Renewable energy

Hydrogen


FIGURE 8: ILLUSTRATION OF NON-SUSTAINABLE AND SUSTAINABLE HYDROGEN PRODUCTION TECHNIQUES


Reformation Electrolysis

H2Water

Wind

Reformer Elec-trolysis

Grid Wind farm

CO2

MethaneCH4

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Hydrogen as an Energy VectorFrom the above, we can already see that hydrogen is not an energy source but an 'energy vector' or ‘energy carrier’. Similar to fossil fuels, hydrogen can be used to carry chemical energy from one place to another or to store it. Interest in hydrogen is subsequently driven by a number of diff erent factors, including:

(i) Reduction of CO2 emissions, thus helping to mitigate climate change (ii) Reduction of energy imports (iii) Diversifi cation of energy supplies, reducing dependence on fossil fuels (iv) Improvement of local air quality (v) High effi ciencies in conjunction with new fuel cell technologies

Th ese attributes arise because hydrogen has the potential to be produced from energy sources which are carbon-free, local and renewable. Hydrogen can provide a range of energy services while emitting only water. Given these characteristics, hydrogen fuel, together with fuel cell energy converters may off er a unique opportunity to create a clean and effi cient energy system based on sustainable primary energy sources. Th e investment required to develop these new energy systems means that there is the additional prospect of developing new industries.

FIGURE 9: HYDROGEN IS AN ‘ENERGY VECTOR’ OR ‘ENERGY CARRIER’


The Hydrogen EconomyTh e term ‘hydrogen economy’ refers to the infrastructure supporting the energy requirements of a coun-try, based on the use of hydrogen rather than fossil fuels. Th e concept of using hydrogen as an energy system is not new. Hydrogen has previously been used both industrially and domestically, e.g. as town gas (50% hydrogen) in the UK until the 1950’s. Interest in hydrogen as a vehicle fuel heightened in the 1970’s with the oil crisis and with technological advances in the 1980’s.

Th e hydrogen economy is a network of primary energy sources linked to multiple end uses through hydrogen as ‘energy carrier’. Th e current key limitation in implementing a hydrogen economy is not so much production, but storage. Some attention has been given to the role of hydrogen to provide grid en-ergy storage for renewable energy sources, like wind power. Th e primary diffi culty with using hydrogen for grid energy storage is that converting power to hydrogen and back is not cheap under current market conditions. Compared to oil and other fossil fuel hydrocarbons, hydrogen is quite expensive to store or transport with current technology. Th e reason for this is that albeit hydrogen gas has good energy density per weight, it has poor energy density per volume compared to hydrocarbons. Hydrogen thus requires larger tanks for storage. Increasing hydrogen gas pressure would improve the energy density per volume, but compressing a gas will require energy to power the compressor.

Primary energytransmission

Potential marketapplications

Primary energysource

Hydrogengeneration

Hydrogeninfrastructure

End use

Hydrogen bus

H2

Water Oxygen

Hydrogen

Electrolyser Hydrogenstorage

Hydrogenrefuelling

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All things considered, there is real potential for a worldwide transportation economy based on hydrogen as the future fuel source, where the hydrogen is produced by renewable energy technologies, e.g. through wind power driven electrolysis. At the moment most countries are far from realising this potential, as they have no dedicated hydrogen production from renewables and have not developed easy ways to store and transport hydrogen. However, reducing CO2 emissions and improving security of energy supply are the two main drivers for hydrogen. As soon as the most signifi cant barriers to the commercialisation of hydrogen and fuel cells are resolved, and the current costs for generation, transporting and storing of hydrogen are reduced, the hydrogen economy will become a reality that you may well even still see in your lifetime.

TABLE 1: NUMBER OF EXISTING PUBLIC HYDROGEN REFUELLING STATIONS AND 2020 TARGETS

Country or region Existing refuelling stations (2015) Planned stations (2020)

Europe >100 >400

Japan >100 >200

Korea >50 >200

United States >50 >100

Sources: IEA (2015), Technology Roadmap Hydrogen and Fuel Cells

TABLE 2: EXISTING FCEV FLEET AND 2020 TARGETS

Country or region FCEVs on the road (before 2015)

Planned FCEVs on the road (2020)

Europe 192 ~350 000

Japan 102 100 000

Korea 100 50 000

United States 146 ~20 000

Sources: IEA (2015), Technology Roadmap Hydrogen and Fuel Cells

South Africa’s Competitive AdvantagesSouth Africa could participate in the fuel cell industry as a major platinum group metal (PGM) produc-er. PGMs are the key catalytic materials used in most fuel cells and with over 75% of the world’s known PGM reserves found in South Africa, the country could position itself as a fuel cell deployment hub, with opportunities for manufacturing, systems integration, and ancillary services. Branded as Hydrogen South Africa (HySA) in 2008, the strategy stimulates and guides innovation along the value chain of hydrogen and fuel cell technologies in South Africa. Th e HySA strategy addresses elements of fuel cell innovation that are likely to provide valuable opportunities for global industry participation. Howev-er, creating the knowledge, skills and infrastructure to seize this opportunity will depend not only on continued funding and direct research, but also on investigating commercialisation opportunities and creating a viable local industry by encouraging local deployment in key applications.In 2016 government started creating incentives for mines to benefi t from platinum fuel cell investments, i.e. research and development (R&D) spend in accordance with the Treasury’s R&D tax incentive. Impala Platinum (Implats) for example launched an initiative including fuel cell powered forklift s and a hydro-gen refuelling station at its platinum and base metals refi nery in Springs, some 35 km east of Johannes-burg. Implats plans to further install an 8 MW fuel cell power plant that uses natural gas as a fuel source as well as a 1.2 MW fuel cell power plant that uses hydrogen, with the ultimate aim of taking the entire site off -grid and using only fuel cell technologies to power the refi nery complex in Springs.

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Advantages and Disadvantages of Hydrogen and Fuel Cell Technology

Th e following advantages are known:

(i) E ciency: Fuel cells combine many of the advantages of both internal combustion engines (ICE) and batteries. Th anks to the direct conversion of chemical energy into electrical energy, fuel cells are 2‐3 times more effi cient than ICEs for vehicle propulsion. Interestingly, fuel cell ef-fi ciency does not drop for small systems because it does not depend on size. Unlike combustion engines and gas turbines that suff er from scale eff ects for example, small fuel cell devices are as effi cient as larger ones.

(ii) Reduced emissions: Fuel cells are clean energy technologies with near‐zero GHG emissions if compressed hydrogen is used as fuel and if the hydrogen is produced by water electrolysis pow-ered by renewable technologies.

(iii) Reliability, low maintenance and quietness: Fuel cells can help provide stability and continuity to the electric grid since they can maintain a continuous base power parallel to or independent of the grid. Fuel cells provide high quality power without any risk of power outage. Th ey have more predictable performance over wider operating temperature ranges than lead acid batteries. Fuel cells can be recharged everywhere within a few minutes by refuelling, while batteries have to be plugged in for time‐consuming recharge (and they have to be replaced eventually). Th ey operate at constant peak performance from fuel replenishment to depletion. Th erefore operation time is well‐known and directly proportional to the amount of fuel available/supplied. Fuel cells systems have practically no rotating or even moving parts. Certain types of fuel cells (PEMFC, SOFC) are all solid state, thus close to mechanically ideal. Th is means less noise and potential-ly reduced maintenance work. Fuel cells are relatively silent systems making them suitable for residential areas. Th e only parts that are liable to cause moderate noise are the pieces of ancillary equipment.

(iv) Sustainability: Fuel cells can be powered by hydrogen, the most abundant element on Earth which can be produced from a variety of sources, including various renewable energy technolo-gies. Th is is a key asset from the perspective of GHG reduction. Fuel cells are most probably es-sential in achieving carbon reduction goals and can contribute to the world’s end of dependence on hydrocarbons. Due to their low environmental footprint, fuel cells are a realistic option in several fi elds concerned with the international climate change debate, i.e. automotive, residential and industrial.

(v) Compactness: Fuel cells off er higher energy density and higher storage capacity compared to batteries, and thus good compactness, which is an interesting feature especially for portable applications.

(vi) Modularity and exibility: Fuel cells allow independent scaling between power, determined by the fuel cell size and capacity, and determined by the fuel reservoir. Fuel cell size can be adapted by simply changing the number of elementary cells and the active area. Scaling up can there-fore very easily be realised, from the watt range for small appliances to the megawatt range of a medium-sized power utility.

Th e following disadvantages are known:

Th ere are a number of issues limiting widespread adoption of fuel cell technologies, but by far the most important one is the lack of hydrogen infrastructure. Th e latter has long been considered as the big-gest obstacle for introduction of fuel cell electric vehicles. However, this challenge resembles the classic chicken‐and‐egg problem, i.e. there are no FCEVs because there are no hydrogen fuelling stations, but there are no hydrogen fuelling stations because there is too little demand for hydrogen as fuel for FCEVs. Establishing the necessary infrastructure for hydrogen production, transport and distribution would require signifi cant capital investment. Nonetheless, no absolute impediment exists and some countries made very reasonable progress in respect to hydrogen infrastructure developments. Th e early adopters, i.e. U.S., Japan, and Europe are thus in a unique position to capitalise on this opportunity, given that hundreds of hydrogen refuelling stations already exist in these countries. However, overcoming chal-lenges for a hydrogen technology roadmap, mainly related to investments for infrastructure, hinges upon close collaboration among many stakeholders, such as relevant industries, utilities and power grid providers, car manufacturers, and local, regional and national authorities.

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Exercises

1. Describe electrolysis and reversing electrolysis! Mention similarities and diff erences!

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2. List the main fuel cell applications!

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……………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………4. Draw a schematic diagram and briefl y explain how a fuel cell operates!

5. Draw a diagram that gives an overview of the various hydrogen production pathways!

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6. Explain why hydrogen is considered an ‘energy vector’ or ‘energy carrier’!

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7. List the advantages and disadvantages of hydrogen and fuel cell technology.

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(i) Video: 4K - Dolphin Class Hydrogen Fuel Cell Submarine at German Naval Yard Kiel(ii) Accelerating the fuel cell Industry in South Africa, Jones &Botha, 2014(iii) Fuel Cell Electric Vehicles: Th e Road Ahead, Fuel Cell Today, 2013 (iv) IEA (2015), Technology Roadmap Hydrogen and Fuel Cells(v) Hydrogen Production Roadmap, Technology Pathways to the Future, Freedom CAR &

Fuel Partnership, 2009(vi) HYDROGEN and fuel cell technologies in South Africa, Department of Science and Tech-

nology’s (DST), 2010(vii) OVERVIEW OF PETROL AND DIESEL MARKET, IN SOUTH AFRICA BETWEEN

2002 AND 2013, Department of Energy, 2015(viii) Technology Roadmap, Hydrogen and Fuel Cells, International Energy Agency (IEA), 2015

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THEME 1.2.2

E-MOBILITY

Introduction

Smart electric vehicles, battery-electric powered or plug-in hybrids guarantee freedom of mobility for future generations. Th us, in China for example, the government off ers various incentives for the deploy-ment of alternative-energy vehicles and has set a target of 5 million alternative energy vehicles by 2020. France, Germany, Norway, the Netherlands and the United States also have electric mobility targets. Germany for example has set itself the goal of becoming the lead market and provider for electric mo-bility by 2020 as part of its long-term zero-emission mobility vision. One million electric vehicles on the road by 2020, this is the bold aim of Germany’s National E-Mobility Development Plan. E-mobility is defi nitely also coming to South Africa and that is why we are now introducing it to you in this theme.

Keywords

Electro-mobilityElectric vehicles uYilo E-Mobility Technology Innovation Programme (EMTIP)Charging infrastructure requirements for e-mobility Range of BEVsYour fi rst EV could be an e-bike!Advantages and disadvantages of e-mobility

Theme Outcomes

At the end of this theme, you should be able to:(i) Defi ne e-mobility terms.(ii) Explain the infrastructure requirements for e-mobility.(iii) Compile an overview of the advantages and disadvantages of e-mobility.


Electro-MobilityE-mobility represents the concept of using various technologies to enable the electric propulsion of vehi-cles, including e-bikes/pedelecs, passenger cars, buses, trucks, forklift s, trains, ships and even planes and shuttles. Focussing on passenger cars, buses and trucks, powertrain technologies include battery-pow-ered electric vehicles (BEV) and plug-in hybrids (PHEV), as well as fuel cell electric vehicles (FCEV) that convert hydrogen into electricity. E-mobility eff orts are motivated by the need to address fuel effi ciency and emission requirements, as well as market demands for lower operational costs.

Electric Vehicles Th e range of electric cars is a continuum, from plug-in hybrid vehicles with internal combustion engines up to full electric cars. In this textbook, electric vehicles refer mainly to three diff erent car confi gurations and e-bikes. Th e three electric car confi gurations we refer to are:

(i) Battery powered electric vehicle (BEV), also sometimes referred to as Full Electric Vehicle (FEV), charged by plugging it into a fi xed power supply, with no auxiliary on-board power.

(ii) Hydrogen-powered fuel cell electric vehicles (FCEV).(iii) Plug-in hybrid vehicles (PHEV), which use a battery bank as the primary source of energy and

charge their batteries via a fi xed electric power supply. But these cars also have an internal com-bustion engine as a range extender or backup on board to recharge their batteries and/or drive the wheels directly.

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FIGURE 1: COMPONENT CONFIGURATIONS IN THE THREE DIFFERENT EV-TYPES


uYilo E-Mobility Technology Innovation Programme (EMTIP)Th e EMTIP, hosted at the Nelson Mandela Metropolitan University (NMMU) seeks to ready South Afri-ca for the introduction of e-mobility by creating new business opportunities and generating the know-how to support electric vehicles. Th e programme was initiated by the Technology Innovation Agency (TIA) as a fi ve year national multi-stakeholder innovation programme. Th e focus is towards e-mobility defi ned by renewable energy generation into smart grids, charging networks, local standardisation, bat-tery technology, electric drive train components and smart connectivity. Th e name uYilo is derived from isiXhosa and means ‘to create’.

FIGURE 2: UYILO’S DC FAST CHARGING FACILITY

Image Source: D. Boxberg/ GIZ

Fuel cell electric vehicle(FCEV)

Transmission

E-motor

Powerelectronics

Power batteryFC stackBOP

Tank

Battery electric vehicle(BEV)

Plug-in hybrid electric vehicle (PHEV)

Transmission

E-motor

Powerelectronics

Energy battery

Plug-in-charger

ICE powertrain

Transmission

E-motor

Powerelectronics

Energy battery

Plug-in-charger

Tank

ICE

Gene-rator

Transmission Electric powertrain Battery FC powertrain

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Charging Infrastructure Requirements for E-MobilityTh e desired switch from conventional internal combustion engine-based mobility to e-mobility poses several challenges. Long charging times, the limited range of EVs and the availability of suffi cient recharg-ing infrastructures are some concerns. It takes less than 10 minutes to fi ll up a tank and pay for gasoline at the average fuel pump. EV drivers face longer charging times and there are diff erent aspects of charging which need to be considered, such as:

(i) On-board charger: Th e actual charging device for Level 1 and Level 2 charging (see Figure 3) comes factory-installed. It converts AC power from the wall to DC power that charges the battery in the vehicle. Th e charging speed may vary, but the most common on-board chargers are 6.6 kW on battery electric vehicles (BEVs) and 3.3 kW on plug-in hybrid electric vehicles (PHEVs). DC Fast Charging (see below) uses its own off -board charger.

(ii) EVSE: Stands for 'electric vehicle service equipment'. It is the intermediary between a power source and the vehicle’s charging port, and is typically mounted on a wall or up on a pedestal. Its role is to simply relay the AC power to the vehicle safely.

(iii) Level 1 Charging: Th e slowest form of charging. Uses a plug to connect to the on-board charger and a standard household (120 V) outlet. Th is setup provides up to 8 km range per hour. While this does not sound at all impressive, it can work for those who travel less than 60 km a day and have all night to charge.

(iv) Level 2 Charging: Uses an EVSE to provide power at 220 V or 240 V and up to 30 ampere. Drivers can add around 30 km of range in an hour of charging at home or at a public charging station.

(v) DC Fast Charging: Some refer to this charging as Level 3 charging and the best known examples are Tesla’s Supercharger network (see below), Nissan’s CHAdeMO model, while other manufactur-ers use the SAE Combo model. All of the above fast chargers deliver about 80% battery charge in 40 to 60 minutes.

FIGURE 3: TESLA’S SUPERCHARGER CHARGING PROFILE BASED ON 90 KWH MODELS


Range anxiety is the fear that a vehicle has insuffi cient range to reach its destination. Particularly with reference to battery electric vehicles (BEVs), this concern is considered to be one of the major barriers to large-scale adoption of BEVs. A large public network with powerful and strategically located charging points could address these issues and assist in facilitating mass adoption of EVs. Four of the world’s major automakers have joined forces in a bid to develop Europe’s most powerful network of electric car

80%

100%

75 minutes40 minutes

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charging points to be installed from 2017 onwards. BMW, Mercedes Benz/Daimler, Ford and the VW Group have signed a Memorandum of Understanding to jointly build 400 charging sites in Europe by 2020. Th is means that electric car drivers can plug into thousands of 350 kW individual charging points to replenish the batteries in their cars in signifi cantly shorter times. Th is initiative will almost triple the current 120 kW supercharger network owned by Tesla. Tesla’s network can fully charge its cars in 75 minutes (Figure 3) and consists of 744 sites containing 4703 individual charging points across Europe. Th e overall aim of the new European network is to make long-range travel in a battery electric car feasi-ble; a bid European car manufacturers hope will rapidly facilitate mass adoption of EVs.

RangeTh e range of a BEV depends on the number and type of batteries used. Th e weight and type of vehicle and the performance demands of the driver also have an impact just as they do on the range of tradition-al combustion engine vehicles. Range may also signifi cantly be reduced in cold weather. Th e following list of BEVs indicates the average range for some electric cars sold worldwide:

(i) Tesla Model S with 90 kWh battery and dual motors has a range of 470 km. Th is model has been built since 2014.

(ii) BMW’s new i3, available in 2017 with a 33 kWh battery has a range of 180 km.(iii) Th e bestseller Nissan Leaf model year 2016 with 30 kWh battery has a range of 170 km.(iv) Th e Renault Zoe was the bestselling electric car in Europe in 2015. Renault announced recently

that it has increased the size of the battery to 40 kWh, giving the small sedan around 300 km of range in the European driving cycle.

FIGURE 4: A TYPICAL E-BIKE WITH REAR HUB CONFIGURATIONS


Your First EV could be an E-Bike!Albeit not very common in South Africa yet, pedelecs or e-bikes are quickly conquering markets in China and Europe. Over a million e-bikes are sold in Europe annually and even more in China. Th ere is growing evidence that e-bikes are replacing urban car trips, as people tend to drive around 50% further than with a normal bicycle, use them in hilly or even mountainous areas, use them in older age or use them when they do not want to arrive tired and sweaty in the offi ce. With the big advantage that no other infrastructure is required, the rapidly rising market share guarantees a high impact on mobility behaviour.

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FIGURE 5: RATIOS OF ELECTRIC MOTOR ASSISTANCE IN A PEDELEC FOLLOWING EU REGULATIONS


How do pedelecs work? Pedelecs are electric bicycles that must be pedalled. Pedal assist works automat-ically when you start pedalling. Th e electric motor assistance will come on only when you pedal. It will make pedalling really easy and you will feel like cycling with constant tail wind. Th e battery-powered motor will automatically turn off when you stop pedalling or press the brake. Pedelecs were developed due to regulation of some countries in Europe. Th is function is based on a control mechanism, i.e. an electronic circuitry, including an advanced pedal torque sensor (motion sensing) which measures the amount of human power and an advanced computer chip that handles the pedalling data and ultimately sends the calculated data to the electric motor. Th e amount of assistance ranges from no assistance at all to a great deal of assistance. At a certain speed limit, the motor assistance usually cuts out. In the European Union this limit is usually set at 25 km/h.

FIGURE 6: DIFFERENT ELECTRIC MOTOR CONFIGURATIONS OF E-BIKES

Image source: S4GJ/GIZFront hub motors provide propulsion by spinning the front wheel and create the sensation that the bike is ‘pulled’ forward. Rear hub confi gurations spin the back tire which feels more natural for conventional bike riders. Mid-drive arrangements power the bike’s drive train instead of a hub and create a more natu-ral riding sensation than hub motors.

Front hub Rear hub Mid-drive

Overall power

Human power

25 km/h

Speed

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FIGURE 7: PV SHADE CANOPIES WITH INTEGRATED PUBLIC SEATING AND E-BIKE CHARGING DOCKS


To conclude, electric powered vehicles (EVs) are those that use an electric motor and which rely on plug-in power, whether or not they have an auxiliary internal combustion engine for range extension or for keeping the battery charged up.

Advantages and Disadvantages of E-Mobility (BEVs and FCEVs)Electrifi cation of privately owned cars and particularly commercial vehicle fl eets provides a major op-portunity for decarbonising transport. E-mobility is thus more and more seen as one of the promising policies to pursue. Th e European Union subsequently promoted EVs as part of its clean and energy-effi cient strategy and many member states have a wide range of strategies and incentives which promote e-mobility. All automotive manufacturers already have a number of models on off er and are continuously launching new BEV and FCEV models. Impediments for rapid mass adoption of EVs are relatively high purchase costs and residual values, battery life and cost, road safety aspects, acceptance and usability of new technologies, the range and speed of vehicles and the availability of recharging infrastructures.

Future Zero-Emission (ZEM) VehiclesZEM-ShipsTh e vision of a ship sailing without pollutant emissions has become a reality in Hamburg, Germany. In August 2008, the FCS Alsterwasser was the fi rst inland passenger ship in the world to set off under fuel cell propulsion and with hydrogen as its source of energy. Th e terminology FCS stands for Fuel Cell Ships.

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FIGURE 8: SCHEMATIC DRAWING OF THE FIRST ZEM INLAND PASSENGER SHIP FCS ALSTERWASSER


A zero-emission ferry for Scandlines’ “Vogelfl uglinie”, linking Puttgarden, Germany with Rødby, Denmark has been designed. Th e propulsion is based on liquid hydrogen converted by fuel cells for the electric propulsion. Th e hydrogen could be obtained near the ports using excess electricity from wind turbines. Excess on-board electricity is stored in batteries for peak demand. Total energy needs are re-duced by optimised hull lines, propeller shape, ship weight and procedures in port. Other ferry concepts have been developed in Norway (Wärtsilä’s ship design) and a similar design for a container feeder ship has been presented.Constructed by the Japanese conglomerate Mitsubishi, the cargo ship “Emerald Ace” which is already sailing the high seas, incorporates PV panels along with lithium-ion batteries which help to power the ship at all times, even while moored. Th ough not totally a zero-emission ship when at sea, the car carrier ship holds the unique distinction of being a vessel that does not emit any noxious gases while berthed. Further, several navies design and use submarines which feature diesel propulsion and an additional air-independent propulsion (AIP) system using compressed hydrogen fuel cells. Th e submarines can operate at high speed on diesel power or switch to the AIP system for silent slow cruising, staying sub-merged for up to three weeks without surfacing and with little exhaust heat. Th e system is also said to be vibration-free, extremely quiet and virtually undetectable.

ZEM-AircraftsOn September 30, 2016, the hydrogen-powered experimental aircraft HY4 made its fi rst offi cial fl ight, taking off and landing at Stuttgart Airport, Germany. Developed primarily by Germany’s DLR Institute of Engineering Th ermodynamics, the twin-fuselage plane is the fi rst four-seater aircraft in the world powered solely by a hydrogen fuel cell. Its power train consists of a hydrogen storage system, a low-tem-perature hydrogen fuel cell that converts hydrogen directly into electrical energy, and a lithium battery that covers peak power loads during take-off and ascent. If the hydrogen the HY4 uses is generated via electrolysis using renewable energy technologies, the aircraft can theoretically operate while generating zero emissions. However, due to the specifi c energy density of hydrogen used in the HY4, larger passen-ger aircraft will continue to fl y using conventional propulsion for the foreseeable future.

Propulsion motor100 kW Hybrid system

Energy management & battery

2 fuel cell systemsProton motor, each

50 kW

Hydrogen storagetanks

350 bar

Bow thruster20 kWel

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Exercises

1. Explain the e-mobility concept and list the vehicles falling under this concept!

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2. Prepare a schematic drawing outlining the component confi gurations of three diff erent EV-types, i.e. BEV, FCEV and PHEV.

3. Which university is hosting the uYilo programme?

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4. Which factors could impede on rapid mass adoption of EVs?

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5. Explain the three charging options for EVs and outline their diff erences!

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6. Prepare a schematic drawing indicating the three diff erent electric motor confi gurations of e-bikes!

7. Explain electric motor assistance in pedelecs!

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(i) Video: 2017 Chevrolet Bolt EV Animation(ii) Video: BMW i3 Electric Car (iii) Video: TOYOTA Fuel cell - How does it work(iv) AnimationElectromobility in Germany: Vision 2020 and Beyond, gtai 2016.(v) TOWARDS E-MOBILITY: THE CHALLENGES AHEAD, Fédération Internationale de

l’Automobile (FIA), 2011.(vi) Zero-Emission Ferry Concept for Scandlines, 2013(vii) Fuel Cell Systems for Zero Emission Ships: Experience from Regular Line Operation, 2010

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TOPIC

Basic Scientifi c Principles and Concepts

Topic Overview

We now introduce you to the basic underlying principles of wind power, batteries and fuel cell tech-nologies. The latter two technologies are both based on electrochemical principles, while the fi rst technology is based on kinetic and electrical energy and the laws of electromagnetism. All three tech-nologies have energy conversion in common and we will clarify the basic principles of electrochemical and wind power in the following units. Lastly, we will introduce you to the concept of e-mobility, as well as give you an eco-car market overview and presentation of a typical e-car drive chain, including key components and their functionality.

Topic 2 covers the following units:Unit 2.1 Basic Principles of Wind Power Generation Unit 2.2 Basic Principles of Battery and Fuel Cell Technologies Unit 2.3 Basic Principles of E-Mobility

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UNIT 2.1

BASIC PRINCIPLES OF WIND POWER GENERATION

Introduction

Traditionally, wind power was used for milling grain and pumping water, but today wind turbines are most commonly used to convert kinetic energy into electric energy. Wind energy is becoming an increasingly impor-tant part of the global power supply mix. A major advantage of wind is that it is a clean and renewable form of energy. Wind power generation does not cause direct carbon emissions or air pollutants and does not consume water. Wind turbines also have relatively low operational and maintenance costs after initial construction. Wind energy however also faces challenges and this unit briefly explains the basic principles of wind power generation.

Unit Outcomes

At the end of this unit, you should be able to:(i) Explain what causes wind.(ii) Explain wind as a type of kinetic energy and ultimately as a form of solar energy. (iii) Describe the principle of energy conversion.(iv) Describe the enormous potential wind energy holds.(v) Illustrate by means of a sketch the inside of a larger wind turbine and explain the components’

different functions.(vi) Describe the purpose and principle function of a DC generator.(vii) Explain why wind turbines are usually set up on a pole or tower.(viii) Differentiate between the different wind turbine technologies and designs.(ix) Explain the most important arrangements required to connect wind turbines to the grid, includ-

ing transformers, medium and high voltage switchgears and high- and low tension power lines.(x) Identify training kit components or small-scale industrial components.(xi) Measure wind speed in the environment.(xii) Measure wind speed using a wind machine.

Themes in this Unit

Unit 2.1 covers the following four themes:Theme 2.1.1 What Causes Wind?Theme 2.1.2 Wind Power FactorsTheme 2.1.3 Essential Wind Turbine Components and their FunctionsTheme 2.1.4 Wind Turbine Types

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THEME 2.1.1

WHAT CAUSES WIND?

Introduction

Wind is an ever-present phenomenon. We experience wind every day as a pleasant air scent, as a light breeze or even as a storm. We usually do not really think about what wind is or what causes wind. In this theme we will thus try to explain what exactly wind is.

Keywords

What is wind? What causes wind?Pressure gradient force Wind directionWind speed

Theme Outcomes

At the end of this theme you should be able to:(i) Explain what wind is and what causes wind.(ii) Perform an experiment and observe how changes in air temperature can cause convection cur-

rents.


What is Wind?Wind is air in motion! Air is a mixture of several gases, mainly nitrogen (78%) and oxygen (21%). It is thus a matter and has mass and weight. We usually perceive air as invisible and odourless, and to us air oft en may not seem like anything at all. In fact we look right through it all the time – it is only during a storm that air really makes its presence known. Winds are not only able to move sailing boats and wind turbine rotors; strong winds are also able to lift roofs off buildings, blow down power lines and uproot trees. Th us wind, being air in motion, can be considered as a force due to the fact that it is able to alter the motion of objects (see student book Renewable Energy Technologies (RET) NQF Level 2 for force, mass and acceleration, F = m x a). You might also recall that we cannot see forces, but we can see or feel their eff ects. Wind is a very good example for this statement.

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FIGURE 1: A ROTOR SPINNING FAST IN STRONG WIND

Image source: S4GJ/GIZ Wind is air in motion and can be a force! An image of late evening light creating a shadow of the rotor blades and the wind vane in the swept rotor area of a small 1kW wind turbine located at Port Elizabeth TVET college.

What Causes Wind? Wind is caused by solar radiation that is absorbed diff erentially by the Earth’s surfaces and is converted through convective processes due to temperature and air pressure diff erences. We dealt with temperature diff erences and convection currents in student book RET Level 3, but the explanation above, by making reference to a number of diff erent factors is probably diffi cult to understand. Let us thus try to explain the processes that result in wind step by step.

During the day the Sun’s rays (radiation) heat up the Earth’s surfaces. Land and sea surfaces heat up diff erently. For example, radiation heats the air above the land faster than the air above the sea. Now the following can happen:

1. Warm air, being less dense and thus lighter than cold air rises upwards. As the air rises, it creates low atmospheric (air) pressure.

2. Air masses on surfaces with cooler temperatures sink down. Th e sinking creates higher atmo-spheric pressure.

3. When warm air rises (low air pressure), cooler air will move in (high air pressure) to replace the rising warm air.

4. Th us wind, being air in motion, oft en moves from areas where it is colder to areas where it is warmer.

5. Th e greater the diff erence between the high and low air pressure zones or the shorter the dis-tance between the high and low pressure zones, the faster wind will blow.

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FIGURE 2: DIRECTIONS OF SEA AND LAND BREEZES ALONG THE COAST

Image source: S4GJ/GIZ Th e image shows directions of sea and land breezes along the coast caused by convection currents. A sea breeze describes a wind that blows from the ocean inland towards land. At night, the roles will usually reverse and wind will blow from the land to the ocean creating a land breeze.

Let us conclude: Air masses of diff erent temperature have diff erent pressure. Cold air has a higher pressure than ascending hot air. Th e zone in which warm air rises is called the low pressure zone. When air is warmed by radiation it rises, leaving behind less air, so there are fewer air molecules and therefore less pressure. Low pressure zones are oft en cloudy, and it might rain or snow. In high pressure zones air masses sink downwards – this increases the air pressure. Air moves from high to low pressure areas. Th is movement of warm air masses moving upward and being replaced by cooler air masses is called convec-tion. Th e heat (energy) transfer during convection is called convectional current.

Pressure Gradient Force We explained that wind is air in motion, i.e. wind originates from diff erences in air pressure within our atmosphere. Wind is thus a result of the steepness or gradient of atmospheric air pressure found between high and low pressure zones. When expressed scientifi cally, pressure change over a unit distance is called pressure gradient force and the greater this force, the faster the winds will blow (Figure 3). Th e pressure gradient force is the primary force infl uencing the formation of wind from local to global scales.

FIGURE 3: TWO DIFFERENT PRESSURE GRADIENT SCENARIOS AND THEIR RELATIVE EFFECT ON WIND SPEED

Day Night

Warm airrises

Cool airsinks

Cool air repla-ces warm air

Cooler sea

Warmer land

Sea breezes caused by convection currents

Cooler land

Warmer sea

Cool airsinks

Cool air replaces warm air

Warm airrises

Image source: S4GJ/GIZ. Air pressure and pressure gradient is stated in millibar (mb), i.e. one thousandth of a bar, the unit of atmospheric pressure equivalent to 100 pascals.

1020 mb 1010 mb 1020 mb 980 mb10 mb change 40 mb change

Pressure gradient0.1 mb/kilometer

Pressure gradient0.4 mb/kilometer

Wind speed will be 2 times greater

Wind direction

100 kilometers

Wind direction

100 kilometers

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Wind DirectionWind has direction and speed. Wind direction is expressed as the direction from which the wind is blowing (Figure 4). For example, easterly winds blow from East to West, while westerly winds blow from West to East.

FIGURE 4: SIXTEEN PRINCIPAL BEARINGS OF WIND DIRECTION


Wind SpeedWinds have diff erent levels of speed, and common terms such as breeze and gale describe how fast they blow. Wind speed (v in km/h) is the rate at which air fl ows past a point above the Earth’s surface. Wind velocity can vary throughout the day and year based on geography, topography and season. As a result, certain locations are better suited for wind turbine placement than others. In general, wind speeds are higher near the coast, off shore and inland at hilltops, since there are fewer objects and structures to slow the wind down. Commonly, wind speeds are described using a scale called the Beaufort scale, which divides wind speeds into 12 diff erent categories.

N

NENW

W E

SESW

S

360°0°

45°315°

90°270°

225° 135°

180°

NNE

ENE

ESE

SSESSW

WSW

WNW

NNW

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TABLE 1: BEAUFORT WIND SPEED SCALE IN KM/H

Code Speed (km/h) Description Effects on the environment

0 < 1 Calm Smoke rises vertically

1 1 - 5 Light air Smoke drifts slowly

2 6 - 11 Light breeze Leaves rustle, wind can be felt, wind vanes move

3 12 - 19 Gentle breeze Leaves and twigs on trees move

4 20 - 29 Moderate breeze Small tree branches move, dust is picked up from the ground surface

5 30 - 38 Fresh breeze Small trees move

6 39 - 51 Strong breeze Large branches move, telephone and power overhead wires whistle

7 51 - 61 Near gale Trees move, difficult to walk in the wind

8 62 - 74 Gale Twigs break off from trees

9 75 - 86 Strong gale Branches break off from trees, shingles blown off roofs

10 87 - 101 Whole gale Trees can become uprooted, structural damage to buildings

11 102 - 120 Storm Widespread damage to buildings and trees

12 > 120 Hurricane Severe damage to buildings and trees

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Exercises

1. Visualising convection currents in the atmosphere (air). Do the following experiment: Use a small tank/aquarium fi lled with water placed over a bowl of hot water and a bowl of ice.

Carefully place red food dye into the left side of the tank and blue food dye into the right side of the tank. Observe and describe how changes in fl uid temperature cause a convection current indicated by the red and blue food dye.

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each of the three pictures below and decide which one correctly describes air in motion.

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3. During summer a sea breeze can appear along the coast. Th is is due to diff erent surface tempera-tures, a phenomenon illustrated in the image below. Explain the term 'sea breeze' and using each of the four pictures, describe what exactly caused the breeze during the day.

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(i) Forces Acting to Create Wind, Fundamentals of Physical Geography, 2006.

Sun ray

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THEME 2.1.2

WIND POWER FACTORS

Introduction

Wind is air in motion due to temperature and air pressure gradients that are caused by solar irradiation, i.e. heat energy absorbed by the Earth’s surfaces. Wind can thus be considered as solar power in kinetic form. In this theme we are interested in identifying the key factors for the conversion of wind’s kinetic energy into useful work, i.e. wind speed and swept rotor area.

Keywords

Wind powerCrucial factors for wind powerPower coeffi cientAerodynamic effi ciency Mechanical and electrical effi ciencyCalculations

Theme Outcomes

At the end of this theme you should be able to:(i) Explain wind as a type of kinetic energy and ultimately as a form of solar energy.(ii) Explain the key factors aff ecting the amount of energy a turbine rotor can harness. (iii) Describe the principle of energy conversion.(iv) Describe the enormous potential wind energy holds.(v) Explain why wind turbines are usually set up on a pole or tower.


Wind PowerWind possesses energy by virtue of its motion. Any device capable of slowing down the mass of moving air can extract part of the energy and convert kinetic energy into useful work. Th e mechanism used to convert air motion, i.e. kinetic energy of wind into useful work is referred to as wind energy converters, such as wind turbines which capture and convert air fl ow into a rotational movement.

Let us look at kinetic energy of wind in more detail. Using physical variables, wind power (Pwind), or power input of wind (Pinput) can be described using the following parameters in formula (1):

(1) Pwind = 12 x ρ x A x (v3)

(one-half, times the air density (ρ), times the swept rotor area (A), times the cube of the wind speed (v)).

Albeit the three physical variables describing wind power (Pwind) in formula (1) are not new to us, i.e. air density (ρ), area (A) and speed (v), we shall have a detailed look at how one arrives at formula (1). Before we do this, we should consider that we have discussed power (P) and energy (E) in engineering terms in student book RET Level 2 and indicated that both terms are oft en used in everyday language but in a diff erent context and with completely diff erent meanings. In engineering, energy (E) is defi ned as the capacity to do work (W). Th e concept of power (P) is a measure of how rapidly work (W) is done. Th rough the concept of work (W), i.e. work (W) as the transfer of energy (E) from one object to another, we can measure the energy (E) transferred during interactions between systems or objects. Work (W) always requires motion of a system or parts of it. In this context we also need to remember the concept of energy conservation, i.e. energy (E) is never created nor destroyed, but merely transformed (fi rst law of thermodynamics). In practical terms, this just means that if energy (E) is transferred from one object to another, e.g. converting air fl ow (kinetic energy) into a rotational movement (mechanical energy), some

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energy (E) will be transformed into thermal energy (heat), e.g. friction between the moving parts (bear-ings and shaft s etc.).Considering the above, we shall now have a detailed and step-by-step look to better understand how one arrives at formula (1) Pwind = 1

2 x ρ x A x (v3) :

Step 1:

Simply put, we can defi ne work (W) as the transfer of energy (E) from one object to another, power (P) as the rate of doing work (W), and energy as power (P) multiplied by time (t). Th ese defi nitions give us the following mathematical equations:

(2) P = Wt (power is equal to work divided by time)

(3) E= P x t (energy is equal to power times time)

Step 2:

We have defi ned energy (E) as the ability to do work and work (W) as a specifi c form of energy transfer. You can see there is an intimate relationship between work and energy, and albeit diff erent, work (W) and energy (E) are treated as the same. It thus follows that power (P) can also be defi ned as energy trans-ferred per unit time (t).

(4) P= Et (power is equal to energy transferred divided by time)

Step 3:

Wind as air molecules in motion has kinetic energy. Given that wind is nothing more than the mass of moving air molecules, we can assume that the amount of kinetic energy depends on two variables, mass (m) and velocity (v) of moving air molecules. Th us, the following equation is used to represent kinetic energy (Ek):

(5) Ek = 12 x m x v2 (kinetic energy is equal to one-half, times mass, times velocity squared)

Step 4:

By using formula (4) and (5), and substituting energy (Ek) in formula (4) with formula (5), i.e. one-half, times mass, times velocity squared ( 1

2 x m x v2), it follows that wind power can be described as:

(6) P = Et = 1

2 x mt x (v2) (wind power is equal to one-half, times mass fl ow rate ( m

t ), times velocity squared)

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FIGURE 1: MASS OF AIR FLOWING THROUGH SWEPT ROTOR AREA (SCHEMATIC)

Image source: S4GJ/GIZTh e volume (V) of air fl owing through the circular swept rotor area (A) along the length (s), i.e. the wind ‘cylinder’ indicated in orange colour, defi nes the mass (m) of air passing through. Th us, mass (m) can be obtained from the product of air density (ρ) and air volume (V).

Step 5:

Th e mass of air (m) which fl ows through a surface (A) swept by a rotor can be obtained from the product of air density (ρ) and air volume (V).

m = ρ x V

Step 6:

Redefi ning volume (V) as area (A) times length (s) will permit us to replace the volume (V) by:

m = ρ x A x s

FIGURE 2: VOLUME (V ) OF THE WIND ‘CYLINDER’ CAN BE REDEFINED AS THE SWEPT ROTOR AREA (A) MULTIPLIED BY THE LENGTH (S ) OF THE WIND ‘CYLINDER’.


S

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Wind passes along this length (s) per unit time (t)

Area, A

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Step 7:

Considering that length over time is velocity ( st = v), we can now substitute the term mass fl ow rate ( m

t ) in formula (6) with the product of air density (ρ), swept rotor area (A) and wind speed (v):

mt = ρ x A x v

Step 8:

By inserting the term (ρ x A x v) for mass fl ow into formula (6), i.e. P = Et = 1

2 x mt x (v2), we derive at our

formula (1) for wind power:

(1) Pwind = 12 x ρ x A x v x (v2) = 1

2 x ρ x A x (v3)

Th us, wind power is equal to one-half, times the air density (ρ), times the swept rotor area (A), times the cube of the wind speed (v). Wind power (P) is given in watt, i.e. joules/second, density (ρ) in kg/m3, swept area (A) in square metres (m2), and the velocity (v) in metres per second (m/s).

Crucial Factors for Wind PowerTh e three factors in formula (6) Pwind = 1

2 x ρ x A x (v3), clearly indicate that wind velocity (v) is the most crucial factor, and power output of a wind turbine rotor is thus proportional to the cube (third power) of the wind speed. In other words, if velocity of wind doubles, power increases by a factor of eight (23 = 2 x 2 x 2 = 8) (Figure 3). Th us, small changes in wind speed have a large impact on the amount of power available.

FIGURE 3: RELATIONSHIP BETWEEN WIND SPEED AND WIND POWER

Image source: S4GJ/GIZ.If wind speed doubles, power increases by a factor of eight (23 = 2 x 2 x 2 = 8).

Considering that wind speed increases with height, increases to the turbine tower height can result in enormous power increases generated by wind turbines (Figure 4).

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FIGURE 4: WIND SPEEDS AND POWER INCREASE WITH HEIGHT

Image source: S4GJ/GIZWind speeds increase with height (metre), and so does power (kWh in %).

Th e swept rotor area (A) of the turbine is the second most crucial factor for power output. Th e larger the swept rotor area i.e. the size of the area through which the rotor spins, the more power the turbine can capture. Th e swept rotor area can be calculated from the length of the turbine blades using the equation for the area of a circle, i.e. A=π x r2 , where the radius is equal to the blade length (Figure 5). Th us, a small increase in blade length, i.e. equal to the radius of a circle, and considering its squared power (r2), results in a large increase in power. In other words, since the swept rotor area increases with the square of the radius, a turbine with blades twice as large will receive 22 = 2 x 2 = four times as much kinetic energy. Th e rotor area is subsequently the second most important determinant for a wind turbine.

FIGURE 5: THE ROTOR’S SWEPT AREA

Image source: S4GJ/GIZTh e rotor’s swept area can be calculated using the formula for a circle where the radius (r) is equal to the blade length.

Swept area of blades Rotor

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Increase in wind power %0 41 75 100 124

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FIGURE 6: POWER OUTPUT INCREASES AS THE SWEPT ROTOR AREA INCREASES

Image source: S4GJ/GIZA typical turbine with a 600 kW electrical generator will typically have a rotor diameter of between 40 - 44 m. If you double the rotor diameter to 80 m, your swept rotor area is four times larger (22 = 2 x 2 = 4, i.e. two squared). Th is means that you also get four times as much power output from the rotor, i.e. around 2400 kWh.

Air density (ρ) is the fi nal determining factor for wind power. Air density varies with elevation and temperature. At normal atmospheric pressure and at 15°C, air weighs some 1,225 kilogrammes per cubic metre (kg/cm3), but the density decreases slightly with increasing humidity. Air is less dense at higher elevations than at sea level, and warm air is less dense than cold air. All else being equal, turbines will produce more power at lower elevations and in locations with cooler average temperatures. However, these diff erences in air density are usually considered as marginal compared to the cube power (23) of wind speed and the squared power (22) of the swept rotor area.

Power Coeffi cient (Cp)A common misconception is that all of the kinetic energy from the wind can be converted into mechani-cal and subsequently electrical energy. Th is is impossible - should the entire kinetic energy be converted, there would be no wind left , i.e. wind would be completely absorbed. Many factors make this impossible (aerodynamic, mechanical and electrical effi ciencies). A power coeffi cient (Cp) has thus been introduced as a measure of overall wind turbine effi ciency. You might recall the symbol η , the small Greek letter eta, which is used to represent effi ciency.

Th e Cp is the ratio of actual electric power produced by a wind turbine divided by the total wind power fl owing into the swept rotor area at specifi c wind speed. When defi ned in this way, the Cp represents the combined effi ciency of the various turbine system components, including the turbine blades, the shaft bearings and gear train, generator and power electronics, and can be included in formula (6) so that we arrive at:

(7) P = Cp x 12 x ρ x A x (v3)

Th us, power is equal to the turbine-specifi c power coeffi cient, one-half times the air density (ρ), times the rotor area (A), times the cube of the wind speed (v). Power (P) is given in watt, i.e. joules/second, the Cp always has a value smaller than 1 (usually between 0.3 - 0.4), density (ρ) in kg/m3, swept area (A) in square metres (m2), and the velocity (v) in metres per second (m/s).

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Th e Cp for a particular turbine is measured or calculated by the manufacturer and usually provided at various wind speeds. If you know the Cp at a given wind speed for a specifi c turbine you can use it to es-timate the electrical power output. Please note that the power coeffi cient should only be used to compare the performance of wind turbines. Th e Cp has no relationship to the effi ciencies of other electrical power technologies, such as PV, gas-turbines etc. Th e energy conversion process, i.e. the kinetic energy from the wind converted to mechanical and sub-sequently electrical energy, can be described by three major conversion steps: aerodynamic, mechanical and electrical conversion. During each step, some energy is transformed into heat energy and in every-day language we say some energy is ‘lost’ in the process. Th is is not entirely correct, because if energy is transformed from one form into another the total energy involved in this process is conserved. Th us, the total energy involved in the interaction does not become less or more, we only cannot directly use most of the thermal energy (heat) that is radiated into the environment during transformation processes for the purpose intended.

FIGURE 7: ENERGY TRANSFORMATIONS RELEVANT TO A WIND TURBINE


Aerodynamic Effi ciency Th e fi rst and largest ‘losses’ are due to aerodynamic processes. Th e effi ciency with which the rotor blades convert the available kinetic wind energy into rotating shaft motion (mechanical energy) is referred to as aerodynamic effi ciency. To understand this better we need to understand some basic aerodynamic prin-ciples fi rst. Th e two primary aerodynamic forces at work at rotor blades are li , which acts perpendicular to the direction of wind fl ow, and drag, which acts parallel to the direction of wind fl ow.

Kineticenergy

WIND

Mechanicalenergy

TURBINE

Electricalenergy

GENERATOR

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FIGURE 8: LIFT AND DRAG

Image source: S4GJ/GIZLift and drag, the two primary aerodynamic forces at work at rotor blades. Turbine blades are shaped similar to airplane wings, i.e. they have an air foil type of design.

In an air foil, one surface of the blade is somewhat rounded, while the other is relatively fl at. A simplifi ed explanation of lift is when wind travels over the upper curved surface of the blade, it has to move faster to reach the end of the blade in time to meet the wind travelling under the lower fl at surface of the blade. Th e faster air moves, the lower the static pressure is. Lower pressure pulls on the surface, high pressure pushes. As a result, the upper part of the airfoil is pulled and the lower is pushed. Collectively this creates the lift . Under the lower fl at surface of the blade, the wind moves slower and creates an area of higher pressure that pushes on the blade, creating a slowing down eff ect. Drag is the retarding force acting on the blade while moving through the air. Th is phenomenon is called Bernoulli’s principle (see the three videos provided on the resource CD).

Th e limited aerodynamic effi ciency of a wind turbine is caused by the braking of the wind from its upstream speed v1 to its downstream speed v2, while allowing a continuation of the fl ow regime (v2 < v1). Th e additional losses in aerodynamic effi ciency are caused by the viscous and pressure drag on the rotor blades, and the swirl imparted to the air fl ow by the rotor. Th is allows a theoretical maximum of around 59% of the wind’s kinetic energy to be captured. Th ese fi ndings were published in 1919, by the German physicist Albert Betz, and this is thus called Betz’s limit (Figure 9). In practice only 40-50% of aerody-namic effi ciency is achieved by current rotor designs.

Wind flow

Wind flow Lift

Drag

Lift

Drag

Drag

Lift

Lift

Drag

Airfoilmotion

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FIGURE 9: THE BETZ LIMIT

Image source: S4GJ/GIZTh e Betz limit calculates the maximum theoretical effi ciency of a horizontal rotor by withdrawing energy from the wind by passing with v1 from A1 to A2. At a certain distance (A2) behind the rotor, the wind fl ows with a reduced velocity (v2). In other words, Betz’ limit shows that as air fl ows with a speed of v1 from a certain area A1 through a horizontal rotor, it slows from losing energy to extraction from the rotor, and spreads out to a wider area (A2) with a reduced velocity (v2). As a result, rotor geometry limits aerodynamic effi ciency (η) to a maximum of 59.3%.

Mechanical and Electrical Effi ciencyOverall turbine effi ciency is reduced due to mechanical transmission, i.e. various rotating gears and shaft s, and due to electrical and electronical system performance, including generator and power elec-tronics ‘losses’, for example due to conversion of much less-than-perfect electric frequencies into precise 50 Hz power needed for the grid.

FIGURE 10: MECHANICAL AND ELECTRICAL EFFICIENCY


Wind in

Aerodynamicalefficiency

Mechanicalefficiency

Electricalefficiency

Power out

Wind out Shaft support bearings

GearboxGenerator and powerelectronics

High speed shaftLow speed shaft

A1 v1 A2 v2

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Step 2: We can now show that Cp is the product of all three subsystem effi ciency types:

Step 3: We can then use the following values for each of the three effi ciency types, assuming that all three sub-systems operate at near maximum effi ciency, and near the best operating design point of all components:

ηa = aerodynamic effi ciency = 0.397 (39.7%)ηm = mechanical effi ciency = 0.96 (96%)ηe = electrical effi ciency = 0.94 (94%)

It follows that Cp = ηa x ηm x ηe = 0.397 x 0.96 x 0.94 = 0.358 (35.8%)

Step 4: Using formula (1) Pwind = 1

2 x ρ x A x (v3), with wind speed at 12 m/s, an assumed standard air density (ρ) at sea level of 1.225 kg/m3, and a blade diameter of 101 m, we can calculate the power input into the turbine:

(6) Pinput =12 x ρ x A x (v3) = 0.5 x 1.225 kg/m3 x 8015.07 m2 x 1728 m/s = 8483 kW.

Step 5: With a Cp given at 35.8% and Pinput at 8483 kW, we can easily calculate the actual output power produced by the imaginary turbine:

Poutput = Cp x Pinput = 0.358 x 8483 kW = 3037 kW

Th e maximum calculated power of the imaginary turbine is 3037 kW.

Step 6: Look at the diagram in Figure 11. It is a diagram for a specifi c wind turbine showing the Cp and power output (kW) vs wind speed (m/s). Remember, turbines vary and each specifi c model will have its own data, this is just one example. Firstly, note that the Cp value (yellow line in chart) varies signifi cantly with wind speed. Further, please note that a power coeffi cient of 35.8% is about the Cp value in the diagram below at a wind speed of 12 m/s (indicated by a red star). For this particular turbine, maximum effi ciency occurs around the wind speed range of 8 to 10 m/s. Other turbines may attain maximum effi ciency at other speeds. Th e blue line shows the electric power produced as a function of wind speed. When the turbine reaches maximum power, which in this case is 3037 kW, it levels off (indicated by red arrow). Th is is because the turbine blades are turned or feathered to keep them from spinning too fast or breaking from too much force. Th e turbine control system will keep the rotor spinning at or near a constant value. Th ough it is not shown in the diagram, at some point the rotor is stopped for safety, and power rapidly goes to zero.

Calculation Example

Considering all of the above, the next seven steps illustrate how to calculate the maximum power of an imaginary turbine and interpret Cp and power output diagrams.

Step 1: We fi rst need to designate the symbols for aerodynamic, mechanical, and electrical effi ciencies (η):ηa = aerodynamic effi ciency ηm = mechanical effi ciency ηe = electrical effi ciency

(8) Cp = ηa x ηm x ηe

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FIGURE 11: POWER COEFFICIENT (CP) AND POUTPUT vs WIND SPEED

Image source: S4GJ/GIZ Cp (orange line) and electric power, Poutput (blue line). Th e top fl at part of the blue line is what is usually called rated power, or maximum power. Rated power in this case starts at about 12 m/s. Once the turbine reaches maximum power, the power coeffi cient starts to fall off rapidly. Th is is because Poutput remains constant while the Pinput increases rapidly with higher wind speed. Remember the Pinput is a function of the wind speed cubed. Poutput stays constant while Pinput increases very quickly, thus the Cp values have to get smaller.

Step 7: Look at the diagram below (Figure 12). Th e wind power into the turbine blades is shown by the orange line. Pinput increases with the cube of the wind velocity. Poutput is shown by the green line which levels off at 3037 kilowatts (see Step 5).

FIGURE 12: PINPUT AND POUTPUT vs WIND SPEED

Image source: S4GJ/GIZPinput is a function of the wind speed cubed and thus increases rapidly with increasing wind speeds. In order to maintain system functioning Poutput is kept constant once maximum (or rated) power is reached.

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Pinput Poutput

Pinput =12 x ρ x A x (v3)

Pout = Cp x Pinput

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Exercises

1. Draw a Sankey diagram to illustrate the energy transformation processes in a wind turbine where:(i) 100 units of energy are available in the incoming air (wind) as kinetic energy.(ii) 40 units are converted into rotational/mechanical energy by the rotor.(iii) 35 units are transferred by the shaft , some units are absorbed by the brake and gears as

thermal energy.(iv) 33 units are converted from mechanical energy into electrical energy by the generator.(v) 30 units is the net output, as 3 units are ‘lost’ in further conversion and distribution processes.

2. Wind turbine power calculationOne of the world’s largest turbines has a rotor diameter of 126 metres. As a fi rst step, calculate the rotor sweep area using the formula for a circle, i.e. A=π x r2. Th is turbine is an off shore wind turbine. We thus know that it is situated at sea-level and can put air density (ρ) at 1.23 kg/m3. For a wind speed at 14 m/s the generator is rated at 5 MW. Use formula (1), insert the known values and calculate Pinput. State Pinput clearly and answer the following question: Why is Pinput so much larger than the rated power of the turbine generator (5 MW)?

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3. Size matters in wind turbines. Th e longer the rotor blades, and therefore the greater the diameter of the rotor, the more kinetic energy a turbine rotor can capture from the wind and the greater the electricity-generating capacity. Generally speaking, doubling the rotor diameter can result in a four-fold increase in energy output. Please explain why this is the case!

……………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………4. Some people claim that in some cases, e.g. in lower wind speed areas, a smaller- diameter rotor

can end up producing more energy than a larger rotor. What is your opinion? Please explain your view!

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5. Tower height is a major factor for input power (Pinput). Please explain why this is the case! Please also estimate the Pinput % increase by doubling elevation (tower height).

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(i) Aerodynamics of rotor blades, M. Ragheb, pdf 2013.(ii) WE Handbook- 2- Aerodynamics and Loads, pdf, www.gurit.com/fi les/documents/2aero-

dynamicspdf.(iii) Wind Turbines Th eory - Th e Betz Equation and Optimal Rotor Tip Speed Ratio, Ragheb &

Ragheb, pdf, 2011.(iv) Bernoulli’s Principle, video(v) Wind turbine air foil forces, video(vi) Wind turbine design, video

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THEME 2.1.3

ESSENTIAL WIND TURBINE COMPONENTS AND THEIR FUNCTIONS

Introduction

Th e most common type of commercial wind turbines are horizontal axis wind turbines (HAWT). Th e rotor axis of a HAWT lies horizontal, parallel to the air fl ow, with the blades sweeping a circular plane usually situated upwind in front of the tower. In this theme we will focus on the most essential com-ponents of a HAWT. We will later also introduce you to diff erent turbine designs and their relevant components.

Keywords

Tower Yaw drive NacelleLow-speed shaft Brakes GearboxGenerator High-speed shaft Control systems AnemometerWind vaneRotorBladesPitch systemDC machinesWorking principle of a single loop DC generatorDC machine typesSeparately-excited DC machinesSelf-excited DC generatorsPermanent magnet DC generatorAC machine types: synchronous generatorAC machine types: induction/asynchronous generatorWind turbine control systemsConnecting small-scale renewable embedded generation (SSREG) to the gridConnecting large-scale wind power plants to the gridTransformer, switchgear and power lines

Theme Outcomes

At the end of this theme, you should be able to:(i) Illustrate by means of a sketch the inside of a larger wind turbine and explain the components’

diff erent functions.(ii) Describe the purpose and principle function of a DC generator.(iii) Explain the most important arrangements required to connect wind turbines to the grid includ-

ing transformer, medium and high voltage switchgear and high and low tension power lines.

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HAWT SubsystemsHorizontal axis wind turbines (HAWT) consist of three principal components: the nacelle, rotor, and tower (Figure 1). Th e nacelle compartment is connected to the rotor hub by a shaft and contains the brakes, gears, generator and controlling mechanisms. Th e rotor, usually consisting of three wing-shaped blades connected to a central hub, converts the kinetic energy of the wind into rotational energy. Th e tower, including the supporting foundation, contains the yaw drive, and provides access to the nacelle and the height necessary to access the targeted wind resources.

FIGURE 1: HAWT SUBSYSTEMS (SCHEMATIC)

Image source: S4GJ/GIZ Key components: Tower (1), Yaw drive (2), Nacelle (3), Low-speed shaft (4), Brakes (5), Gearbox (6), Generator (7), High-speed shaft (8), Control systems (9), Anemometer (10), Wind vane (11), Rotor (12), Blades (13), Pitch system (14).

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(1) Tower, made from tubular steel, concrete or steel lattice, supports the nacelle and rotor. Taller tow-ers enable turbines to capture more kinetic energy because wind speed increases with height.

(2) Yaw drive orients the nacelle and rotor into the wind (upwind concept).(3) Nacelle sits on top of the tower and contains the breaks, gears, generator and controlling mecha-

nisms. Some nacelles are large enough for a helicopter to land on.(4) Low-speed sha , turns at about 30-100 rpm.(5) Brakes (mechanical, electrical, or hydraulic) can stop drive shaft s in emergency situations.(6) Gearbox, connects the low-speed shaft to the high-speed shaft and increases the rotational speeds

up to about 1000 - 2000 rpm, as this is the rotational speed required by most generators. As indicat-ed in Th eme 1.1.3, the gearbox is usually the third most costly component of a HAWT. Th us, some modern turbines use direct-drive generators that operate at lower rotational speed and thus do not require gearboxes.

(7) Generator, converts mechanical (rotational) energy into electrical energy, i.e. a rotating magnetic fi eld induces current. Please note that two main generator types are employed, i.e. asynchronous (induction) type generators and synchronous (permanent magnet) type generators. Th e latter have the potential to work without gearboxes, but bear higher cost.

(8) High-speed sha , drives the generator.(9) Control systems (electronics), for drivetrain and wind (cut in/out) speed and blade regulation

(pitch/stall).

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3DC MachinesElectric machines are electromechanical energy conversion devices. Motors convert electrical energy into mechanical energy while generators do exactly the opposite, i.e. converting mechanical power into electrical power. It is the latter which are relevant to a wind turbine. However, the working principles of motors and generators have much in common, whether it is a DC (direct current) or AC (alternating current) machine. In our context we will focus on DC machines. In most cases, regardless of type, DC machines consist of a stator (stationary fi eld) and a rotor (the rotating fi eld or armature). DC machines operate through the interaction of magnetic fl ux and electric current, based on the fundamental prin-ciple of Faraday’s law of electromagnetic induction. According to this law, when a conductor moves in a magnetic fi eld it cuts through magnetic lines of force, inducing an electromagnetic force (emf) in the conductor. Th e magnitude of this induced emf depends on the rate of change of fl ux (magnetic line force). Th e emf will cause a current to fl ow if the conductor circuit is closed. Hence, the two most essential fea-tures of a generator are a magnetic fi eld and conductors which move inside that magnetic fi eld.

Working Principle of a Single Loop DC GeneratorLet us start with the most basic type of DC generator, a single loop (armature) generator. As indicated in Figure 2, a single loop of a rectangular conductor is placed between two opposite magnetic poles (N-pole/red and S-pole/blue). Th e corners of the rectangular conductor loop are A, B, C and D.

FIGURE 2: A SINGLE LOOP CONDUCTOR PLACED IN A MAGNETIC FIELD (SCHEMATIC)

Image source: S4GJ/GIZ Due to mechanical input energy, e.g. wind power, the conductor rotates inside a magnetic fi eld around its axis a and b. When the loop rotates from its vertical position to its horizontal position, its two sides, i.e. AB and CD of the loop always cut through the fl ux lines of the magnetic fi eld (Figure 3). As a result, an emf is induced in both sides (AB and CD) of the loop.

A

B D

C

a

b

N S

(10) Anemometer measures wind speed and transmits wind speed data to the control system.(11) Wind vane reacts to and measures wind direction and communicates with the yaw drive to orient

the turbine into the wind.(12) Rotor, blades and hub together form the rotor.(13) Blades create lift due to their air foil cross-section and rotate the rotor. Most large commercial

turbines have either two or three blades.(14) Pitch system turns the blades in or out of the wind.

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FIGURE 3: THE CONDUCTOR ROTATES IN A MAGNETIC FIELD INTO ITS HORIZONTAL POSITION

Image source: S4GJ/GIZTh e conductor rotates within a magnetic fi eld into its horizontal position, thus inducing a current in the loop.

FIGURE 4: FLUX LINES - THE PICTORIAL REPRESENTATION OF A MAGNETIC FIELD


B

D

b

N SC

A

aDirection of rotation

Direction of induced currentDirection of flux

S N S N

Lines of magnetic flux

Unlike poles - 'attract'

Like poles - 'repel'

N SS N

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As the loop ABCD is closed, there will be a current circulating through the loop. Th e direction of the cur-rent can be determined by Flemming’s right hand rule (Figure 5). Th is rule says that if you stretch thumb, index fi nger and middle fi nger of your right hand perpendicular to each other, then the thumb indicates the direction of motion of the conductor, the index fi nger indicates the direction of the magnetic fi eld, i.e. N-pole to S-pole, and the middle fi nger indicates the direction of fl ow of current through the conductor. If we apply this right hand rule to our example, we can see that at the horizontal position of the loop (Figure 3), current will fl ow from point A to B and on the other side of the loop current will fl ow from point C to D.

FIGURE 5: FLEMMING’S RIGHT HAND RULE


If the loop rotates further, it will return to its vertical position, but now the upper side of the loop will be CD and the lower side will be AB (Figure 6), just opposite the vertical position shown in Figure 2. In this position the tangential motion of the sides of the loop is parallel to the fl ux lines of the fi eld. Hence, there will be no fl ux cutting and consequently no current induced in the loop.

FIGURE 6: ROTATING TOWARDS ITS VERTICAL POSITION THE CONDUCTOR IS NOT INDUCING A CURRENT (SCHEMATIC)


If the loop rotates further, it returns to its horizontal position but now the AB side of the loop is in front of the N-pole and the CD side stays in front of the S-pole. In this position the tangential motion of the loop

Motion

Magneticfield

Current

D

C A

Bb

N S

aDirection of rotation

Direction of flux

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FIGURE 8: THE CONDUCTING LOOP IS CONNECTED TO TWO SPLIT RINGS AND TWO CARBON BRUSHES WHICH REST ON THE SLIP RING SEGMENTS


sides is perpendicular to the fl ux lines, hence the rate of fl ux cutting is at its maximum and according to Flemming’s right hand rule, current fl ows from B to A and on the other side from D to C (Figure 7).

FIGURE 7: THE CONDUCTOR ROTATES INTO ITS HORIZONTAL POSITION INDUCING A CURRENT IN THE LOOP (SCHEMATIC)


If the loop continues to rotate around its axis, every time the side AB is in front of the S-pole, a current fl ows from A to B and when it comes in front of the N-pole, the current fl ows from B to A. Similarly, every time the side CD is in front of the S-pole, a current fl ows from C to D and when it comes in front of the N-pole the current fl ows from D to C.We now connect the loop with a split ring as shown in Figure 8. Split rings are made out of a conduct-ing cylinder cut into two halves or two segments which are insulated from each other. Th e external load terminals are connected with two carbon brushes which rest on the slip ring segments.

Brush andterminal

Segment of split ring

I I

I

ISN

Resistor/Load

C

a

b

N SB

D

Direction of rotation

Direction of induced currentDirection of flux

A

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In Figure 9 (left -hand side) it can be seen that in the fi rst half of the revolution, current always fl ows along ABLMCD, i.e. brush 1 is in contact with segment a of the split ring. In the next half revolution (right-hand side of Figure 9) the direction of the induced current in the coil is reversed, but at the same time the position of the segments a and b are also reversed which results in brush 1 coming in contact with segment b. Hence, the current in the load resistance again fl ows from L to M via a resistor.

FIGURE 9: CURRENT FLOW UNDER LOAD RESISTANCE (SCHEMATIC)


Th e position of the brushes of this DC generator is arranged in such a way that the change-over of the segments a and b from one brush to the other takes place when the plane of the rotating coil is parallel to the fl ux lines of the fi eld. Hence, there will be no fl ux cutting and consequently no current induced in the loop - in this position the induced emf in the coil is zero. Th e unidirectional (but not continuous) wave-form of the DC current through the load circuit is shown in Figure 10. Th is is the basic working principle of a DC generator, explained in a single loop generator model. It would be very helpful for you to also have a look at the video clips provided on the resource CD. Several of the clips show a 3D-animation of the fl ux lines and current fl ow in a single loop conductor. Some other video clips show the complete construction and functioning of more sophisticated DC generators, i.e. brushed and brushless types with permanent magnets. Th e latter are the preferred choice of DC machines.

FIGURE 10: UNIDIRECTIONAL DC CURRENT


A D

B C

a b

+ _

1 2

D A

C B

b a

+ _

1 2

LL MM

0 90° 180° 270° 360°Cycle ( )

emf

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Stator magnets

Windings

Brushes

Armature

Commutator

Terminals

DC Machine TypesInstead of a single individual loop of wire as shown in the previous working principle, DC machines have many loops wound together to form a coil of wire (Figure 11), so that much more emf and therefore current can be generated for the same amount of magnetic fl ux. All generators consist of two main parts, the stator and the rotor. Th e stator is the stationary part of the machine and the rotor is the part of the machine that rotates.

FIGURE 11: DC MACHINES HAVE MANY LOOPS OF WIRE WOUND TOGETHER TO FORM A COIL


Based on the type of production of magnetic fl ux DC machines can be classifi ed as follows:

FIGURE 12: TYPES OF DC MACHINES (SIMPLIFIED)


DC machines

Separately-excited Self-excited Permanent magnet

Shunt-excited Series-excited Compound-excited

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Separately-excited DC MachinesWith these types of machines, the armature current does not fl ow through the fi eld windings, as the fi eld magnets are energised by an external DC source.

FIGURE 13: SCHEMATIC DIAGRAM OF A SEPARATELY EXCITED DC MACHINE


Self-excited DC GeneratorsTh e fi eld magnets of these type of machines are energised by the current supplied by the generator itself. Th eir fi eld coils are internally connected with the armature and due to residual magnetism some fl ux is always present in the poles. When the armature rotates, some emf is produced and thus some current induced. Th is relatively small current fl ows through the fi eld coil and increases magnetic fl ux, causing a further increase of current. Th is kind of cumulative phenomenon continues until the excitation reaches the rated value of the generator. According to the position of the fi eld coils, self-excited DC generators can be sub-classifi ed as series-wound, shunt-wound and compound-wound generators.

FIGURE 14: SCHEMATIC DIAGRAMS OF SERIES-WOUND, SHUNT-WOUND AND COMPOUND-WOUND GENERATORS


Field

Armature

Armaturesupply

Field supply

Load

Field

Armature

DC supply

Armature

DC supply Field FieldField

Armature

DC supply

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Permanent Magnet DC GeneratorPermanent magnet DC (PMDC) generators can be considered as separately-excited DC machines with a constant magnetic fl ux. PMDC machines use high strength magnets usually made from rare earth materials, such as neodymium iron/boron (NdFeB) or samarium cobalt (SmCo). Th ese type of perma-nent magnets provide a constant magnetic fi eld and eliminate the need for fi eld windings, thus leading to a simpler, more rugged construction. Due to their very similar design, nearly all PMDC machines can either be used as a generator or motor. In fact, the same PMDC machine may be driven electrically as a motor to move a mechanical load, or it may be driven mechanically as a simple generator to generate output power. When used as generators, PMDC machines can respond to changes in wind speed very quickly due to their strong and constant magnetic fi eld. Th ey are thus a good choice for small-scale wind turbine systems which operate at low rotational speeds, as their cut-in point is fairly low.

FIGURE 15: SCHEMATIC DIAGRAM OF A PERMANENT MAGNET DC GENERATOR


Field magnetField magnet

ArmatureDC armaturesupply

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FIGURE 16: STATOR ASSEMBLY FOR A TWIN AXIAL FLUX PERMANENT MAGNET (AFPM) WIND TURBINE

Image source: D. Boxberg Assembly of the centre set, i.e. 2 stator plates with coils back to back for a ‘four stator plate’ design which is oft en used for 1kW AFPM machines. A front stator plate with coils can also be seen in the image. A similar stator plate for the back and the non-metallic rotor are not visible in the image. Th e latter holds the permanent magnets (neodymium boron) and appears to be pressed into a heavy duty wood board or into a retainer ring. A ‘four stator plate’ design is based on four stator coil sets and two magnet rotors sandwiched between them. In the set shown in the image, each coil appears to be individually recti-fi ed (AC to DC) and is wound with very small wire (approx. 0.5 mm/32 gauge) around a laminated steel core. Given that all AC coils are rectifi ed in the generator itself, DC can be sent down the monopole steel tower. Please consult the ‘Kestrel e300i Installation and Maintenance Manual’ for additional information on the resource CD.

AC Machine Types: Synchronous GeneratorSynchronous generators are diff erent from DC machines in that they are usually used to generate three-phase grid connected AC. Th eir simplicity and increased effi ciency relates mainly to a direct drive system, i.e. the rotor is more or less mounted directly onto the generator’s main pulley shaft . However, similar to DC machines, the operation of synchronous generators is also based on Faraday’s law of elec-tromagnetic induction. Basically, the synchronous generator’s main components consist of:

1. Stator, carrying the three separate (3-phase) armature windings (A, B and C in Figure 17) which are displaced from each other by 120°.

2. Rotor, producing a magnetic fi eld either via permanent magnets or via wound fi eld coils con-nected to an external DC power source.

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FIGURE 17: SCHEMATIC DIAGRAM OF A SYNCHRONOUS GENERATOR AND ITS AC WAVEFORM

Image source: S4GJ/GIZTh e fi gure shows the basic construction of a synchronous generator. Th e rotor winding is connected to a DC power supply required for producing an electromagnetic fi eld around the coil. When the rotor poles turn, the magnetic fi eld also rotates at the same angular velocity. While rotating, magnetic fl ux cuts through the individual stator coils one by one and by Faraday’s law, an emf and therefore a current is induced in each stator coil. Th e magnitude of the current induced in the stator winding is a function of the magnetic fi eld intensity, which is determined by the fi eld current, the rotating speed, and the number of turns in the three stator windings. As the synchronous machine has three stator coils, the 3-phase waveform corresponds to the geometry of the coils (A, B and C).

AC Machine Types: Induction/Asynchronous GeneratorInduction generators are based on common squirrel-cage machine types (Figure 18) and are considered as cheap and reliable. Th ey are readily available in a wide range of sizes up to multi-megawatt capaci-ties, making them ideal for use in commercial wind power applications. Unlike synchronous generators which have to be ‘synchronised’ with the electric grid, induction generators can be directly connected to the utility grid and driven by the turbine’s rotor blades at variable wind speeds. For economy and reliability, many wind power turbines use induction generators connected to mechanical gearboxes to increase rotation speed, and thus performance and effi ciency. Induction machines are also known as asynchronous machines, i.e. if they rotate below synchronous speed they can be used as a motor, and above synchronous speed they can be used as a generator producing AC. Because an induction generator synchronises directly with the main utility grid and produces the same frequency and potential, no recti-fi ers or inverters are required. However, induction generators require reactive power to their windings for self-excitation. Magnetic fi eld excitation is performed diff erently via a so-called squirrel-cage struc-ture, conducting bars embedded within the rotor body and connected together by shorting rings (Figure 18). Th ree-phase induction machines have a fi xed stator and a rotational rotor similar to synchronous generators.

2-polerotor Excitation

current

C

A

B

If

Three stator windings 120° apart

+V

+V 3-phase supply

Stator coil outputs

120° 120° 120°

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FIGURE 18: ASYNCHRONOUS GENERATOR DIAGRAM AND SQUIRREL-CAGE STRUCTURE (SIMPLIFIED)


Wind Turbine Control SystemsAs wind turbines increase in size and power, control systems play a major role to operate these machines in a safe manner and also to improve effi ciency and quality of power conversion. Th e main objectives of wind turbine control systems are:

1. Optimising wind power capture, i.e. operating the turbine to its extract power maximum con-sidering safe restrictions like rated power, rated speed, cut-out wind speed etc.

2. Minimising mechanical stress and protecting the systems from transient loads.3. Power quality, i.e. conditioning generated power according to grid interconnection standards.

3-phase stator

C

A

B

Conducting bars formingthe squirrel cage

End rings

Rotor shaft

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TABLE 1: MAIN CONTROL TECHNIQUES USED IN WIND TURBINES

Pitch control Yaw control Stall control Generator torque control

Electronic controller monitors power output and wind speed. At certain high wind speeds the power output will be too high, at which point the blades can alter their pitch so that they become unaligned with the wind, slowing the blades’ rotation speed down. Pitch control requires the blades’ mounting angle to be adjustable.

In a HAWT, a yaw drive is used to keep the rotor facing into the wind (upwind). Initially, wind-mills used ropes or chains in order to rotate the nacelle by means of human or animal power. The fantail or vane was another historical innova-tion. In the event of change in wind direction, the fantail could rotate the cap of a windmill through a gearbox (a gear-rim-to-pinion system). This rotation positioned the rotor into the wind. Modern yaw drives, even though electronically controlled and equipped with large electric motors and planetary gearboxes, have great similarities to the old windmill concept.

Stall control works by increasing the angle of attack. As the wind speed increases, drag forces on the blade increase and lift forces decrease, resulting in reduced rotation speed. Fully stalled turbine blades have the flat side of the blade facing directly into the wind, elimi-nating the force of lift. This is similar to pitch control, but instead of pitching the blades out of alignment with the wind, it pitches the blades to produce stall.

As the aerodynamic torque control changes, rotor speed changes which subsequently changes output power frequen-cy. A frequency converter is connected between the genera-tor and the network to maintain constant generator frequency.

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TABLE 2: TURBINE DESIGN CONCEPTS BASED ON GENERATOR CONFIGURATION AND PITCH CONTROL

Fixed speed wind turbine

A squirrel-cage induction generator (SCIG) is directly connected to the grid via a trans-former. This configuration requires reactive external power and uses capacitors. Smoother grid connection is achieved by incorporating a soft starter.

Variable speed wind turbine concept with variable rotor resistance

Wound rotor induction generator (WRIG) and pitch control is where the rotor winding of the generator is connected in series with an optically controlled external resistance. This optical coupling eliminates the need of slip-rings. By varying the rotor resistance, the slip and thus the power output in the system are controlled. Reactive power compensation and a soft starter are re-quired.

Variable speed wind turbine concept with partial-scale power converter (DFIG)

This configuration is similar to the previous one, but with a stator that is directly connected to the grid, while the rotor is connected through a partial-scale frequency converter. The latter ensures reactive power compensation and smooth grid connection. Variable speed range is +/- 30% around synchronous speed.

Variable speed concept with full-scale power converter

This concept has full control of the synchro-nous speed range (0 to 100%), but given that all generated power passes through the converter, power losses due to the electron-ics are higher compared to the previous type. Various generator machines, i.e. permanent magnet excited types or squirrel-cage induction generators can be used. Typically however, a direct-driven, multipole synchronous generator without gearbox is used.

Image source: Adapted from Hansen et.al. 2004

SCIGGear

Softstarter

Capacitor bank

Type A

Grid

WRIGGear

Softstarter

Capacitor bank

Type B

Grid

DFIGGear

Type C

Grid

Partial scalefrequency converter

PMSG/WRSG/WRIG

Gear

Type D

Grid

Full scalefrequency converter

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FIGURE 19: PITCH CONTROL (SIMPLIFIED)

Image source: S4GJ/GIZPitch control requires the blades’ mounting angle to be adjustable so that the blades can be turned out of alignment with the wind in above-threshold wind speeds. Electronic controllers and hydraulics are used to adjust the pitch of each blade and thus the lift force, so that the rotor continues to generate power at nominal capacity even at high wind speeds.

FIGURE 20: VARIOUS BLADE ANGLES DUE TO PITCH CONTROL ENSURING MAXIMUM RATED POWER

Image source: S4GJ/GIZOutput power (orange and blue line) builds up due to increasing wind speeds, while pitch control alters the angle of attack. At 11 m/s turbine rotation is reduced towards maximum rated power (blue line).

Positive blade angle (10 degrees) for initial position and low start up wind speed

Zero degree blade angle for running condition

Negative blade angle for overspeed (cut-off) condition

10°

<3 m/s <11 m/s >11 m/s

-20°0°

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FIGURE 21: PITCH CONTROL MECHANISM FOR A 1 KW WIND TURBINE

Image source: D. Boxberg Th is type of pitch control system consists of a patented design including three nosecone pillars and centre bosses. When the turbine reaches its rated rpm, the centrifugal force generated by the blades and blade mounts begin to compress the springs. Consequently, as the blades move outward they are rotated, altering the angle of attack. Turbine rotation is also reduced towards maximum rated power and rpm.

Connecting Small-Scale Renewable Embedded Generation (SSREG) to the GridIn our context, the following renewable technologies with a rated power capacity of less than 1 MVA are referred to as small-scale renewable embedded generation (SSREG): rooft op or ground-mounted PV, wind turbines, biomass/gas, landfi ll gas, and small-hydro. NERSA, the National Energy Regulator dif-ferentiates in its Renewable Energy Grid Code three SSREG sub-categories using low voltage connection options, i.e. a nominal voltage ≤ 1 kV:

1. Category A1, includes SSRE generators with a rated power in the range of 0 to 13.8 kVA.2. Category A2, includes SSRE generators with a rated power in the range greater than 13.8 kVA

but less than 100 kVA.3. Category A3, includes SSRE generators with a rated power in the range of 100 kVA but less than

1 MVA.

We will however refer only to category A1 systems, i.e. SSRE generation with less than 13.8 kWp. We also need to consider that in most areas of South Africa, embedded photovoltaic (PV) generation is currently in higher demand than any other SSRE technology. However, many technical aspects pertaining to grid connection of PV generators also apply to wind turbines. Please note that we are not discussing the important aspect of regulatory rules for a modifi ed net-me-tering scheme (or net-billing scheme), given that these are not yet available/agreed on. Power purchase agreements based on diff erent tariff s for exporting and importing energy from small-scale embedded

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generation currently only exist for the Cape Town metro, the Nelson Mandela Bay Municipality and the eTh ekwini municipality. We will thus only focus on the general technical aspects of grid interconnection of SSEG as far as these are available/agreed on, considering that technical standard development, follow-ing SABS regulations, is still in progress.

For small-scale generators of up to a 100 kWp, i.e. sub-categories A1 and A2, the requirements for com-pliance are covered in NRS 097 Grid Interconnection of Embedded Generation, Part 2: Small-scale embed-ded generation series of documents (NRS 097-2). So far only two of the four-part NRS series of quality of supply standards have been developed. Th ese include NRS 097-2-1: Section 1 – Utility Interface. Th e other part of this series that has been developed is the NRS 097–2-2: Section 2 – Embedded Generator Require-ments. Th e other parts of this series to be developed in the future are the: NRS 097-2-3: Section 3– Utility Framework; and NRS 097-2-4: Section 4 – Procedures for Implementation or Application.

For quality of supply, small-scale embedded generators are also required to comply with standards set in the:

1. Grid Connection Code for Renewable Energy Plants Connected to the Electricity Transmission or the Distribution System in South Africa.

2. NRS 048-2: Electricity Supply - Quality of supply Part 2: Voltage Characteristics, Compatibility Levels, Limits and Assessment Method.

3. NRS 048-4: Electricity Supply - Quality of Supply Part 4: Application Guidelines for Utilities.

Th e above-mentioned municipalities/metros require certifi cation of the embedded generator, i.e. that any installation that is connected to their municipal grids must be certifi ed by an electrical engineer as conforming to requirements outlined in SANS 10142 ‘Wiring of Premises, Low Voltage Installations’. All inverters used in the installation must be compliant with NRS-097-2-1. Th e electrical installation must be done by a qualifi ed electrician (wireman’s licence required!), i.e. SANS 10142 needs to be followed and a Certifi cate of Compliance (CoC) must be issued in order to safely transmit power to all loads and to comply with the utility’s grid-connection requirements. Lastly, to insure the installation against any potential and related risks (in case the house burns down…), the short-term insurance industry probably also requires certifi cation of the embedded generator and the electrical compliance certifi cate.

FIGURE 22: A TYPICAL CONFIGURATION FOR A CATEGORY A1 INSTALLATION (SCHEMATIC AND SIMPLIFIED)

Image source: Please note that AC and DC switch gear and earthing are not indicated!

As already mentioned in student book RET Level 2, earthing of small-scale renewable embedded systems need particular attention (see Tables B.2 to B.5 for earthing and wiring guidelines in the NRS 097). Each installation shall thus have a consumer’s earth terminal (see 3.18 of SANS 10142) at or near the point where the supply cables enter the building or structure. All conductive parts (see 3.29.4 and 6.12.3 in SANS 10142) shall be connected to the consumer’s main earthing terminal. Th e latter shall be earthed by connecting it to the supply earth terminal (see 3.78 in SANS 10142) or the protective conductor (see

Windgenerator

Windcontroller

Batterybank Inverter

Utility grid

Mainloads

AC Service entrance

Backed-uploads

DC DC AC AC

AC

ACACsubpanel

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3.15.8 in SANS 10142) and the earth electrode. Th e eff ectiveness of the supply protective conductor shall be determined in accordance with 8.7.5 in SANS 10142 (see also 6.11.1 in SANS 10142-1:2009). A suitable earth electrode must be installed where no earth electrode exists. When installed, the electrode shall be bonded to the consumer’s earth terminal and to the earthing point of the embedded generator with a conductor of at least half the cross-section of the phase conductor, but with not less than 6 mm2 copper or equivalent conductors.

Connecting Large-Scale Wind Power Plants to the GridNational or municipal grid networks are complex systems and the rather vague term ‘power quality’ is oft en used to describe the interaction between power generators/plants, substations, switchgears and consumers. Considering that electrical energy cannot be stored as such, there should ideally always be a balance between power supply and demand. Th is is however hardly achieved and if renewable supply resources are connected to the grid, the matter can get even more complicated because all relevant re-newable supply resources generate power when the source is available (eg. for wind power, suffi cient wind speeds are needed). Th is characteristic is of little importance when the amount of wind power is modest compared to the installed fossil fuel-based power plants, but if wind power grid penetration is compar-atively large, as is the case in Denmark, Germany and Spain, certain technical challenges need to be addressed. Th ese include electrical grid parameters, such as short-circuit power levels, voltage variations and fl icker, harmonics, frequency, reactive power, protection, network stability, and switching operations and soft starting. Th ese parameters can be limiting factors for the amount of wind power which can be connected to the grid.

Transformer, Switchgear and Power LinesTh e main components for grid connection of wind turbines are transformers and substations. Because of potential high losses in low voltage lines, each turbine usually has its own transformer stepping the low voltage level of the turbine generator (<1kV) up to the medium voltage line (<35 kV). Power supply systems can, for example, be divided into three categories:

1. Low voltage system with nominal voltage < 1kV2. Medium voltage system with nominal voltage above 1kV up to 35kV3. High voltage system with nominal voltage above 35kV

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FIGURE 23: SWITCHGEAR AND TRANSFORMER LAYOUT IN A TYPICAL WIND FARM CONFIGURATION (SCHEMATIC)

Image source: S4GJ/GIZWhen the output power lines of the turbine generator come down the turbine tower, their voltage is usually less than the required medium voltage (<35 kV) for the wind farm’s collection system. Th us, a step-up transformer at the base of the tower increases the voltage to meet the <35 kV requirement. Next, and particularly for large wind farms, a separate substation for transformation from the medium voltage system to the high voltage system is required, i.e. stepping up of medium voltage from 132 to 400 kV which resembles the operating range typical for ESKOM’s overhead power lines. At the point of common coupling between the single turbines of a wind farm and the grid, a circuit breaker for the disconnection of the whole wind farm and individual turbines must exist. Oft en this circuit breaker is located at the medium voltage system inside a substation. Modern wind farm designs employ gas-insulated medi-um-voltage switchgears for this and various other applications. Depending on the operator’s require-ments, these type of switchgears ensure that diff erent medium-voltage confi gurations allow individual wind turbines to be safely connected to the wind farm’s own power grid. Th is ensures a safe connection of the sustainably generated power to the high-voltage transmission grid.

FIGURE 24: UNDERGROUND CABLE CONSTRUCTION

Image source: S4GJ/GIZModern wind farms oft en use medium voltage underground collection systems, i.e. 35 kV cables that are rugged and suitable for the mechanical requirements associated with direct buried applications. Th ese cables have to withstand changes in ground conditions, such as dry soil that causes cables to run hot, or wet soils where moisture can aff ect the life of the cable. Overhead transmission lines must withstand windy environments and other environmental concerns expected at wind farm locations. Overhead transmission lines form the fi nal connection to the grid.

SCIG

Gear Softstarter

Capacitor bank

Tower cable

Point ofcommoncoupling

Step-up transformer

Switch gear or breaker

Grid connection

Other windturbine units

Conductor

Conductorshield

Insulation

Insulationshield

Metallic shield

Jacket

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FIGURE 25: WIND FARM POWER COLLECTION SYSTEM (SCHEMATIC LAYOUT)


Prevailing wind

direction

Underground power collection systembetween turbines

Above-ground medium-volta-ge power collection system

Substation transformer

Interconnectionswitching equipment

High-voltageinterconnectionline to grid

Medium-voltagepower collectionsystem

Inter-turbine spacing optimised for energy produc-tion and minimising turbulence

Existing high-voltagetransmission line

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Exercises

1. Th e illustration below provides a simplifi ed layout of a typical wind turbine drivetrain. Identify each component and explain its function!

……………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………… ………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

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2. Try to interpret the drawings and the diagram below and describe the working principle of a DC generator (single loop). You may use numbers for the fi ve loop positions. Also indicate missing features and units in the drawing and the diagram.

……………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………… ………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

3. What are the principal diff erences between a DC motor and a DC generator?

……………………………………………………………………………………… ………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

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4. Draw a hierarchical diagram indicating the diff erent types of DC machines!

5. Explain why PMDC generators can be considered as separately-excited DC machines!

……………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………… ………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

6. Briefl y describe the diff erences between the two principal types of AC machines, i.e. synchro-nous and asynchronous generators!

……………………………………………………………………………………… ………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

7. Explain the four main control techniques used in wind turbines!

……………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

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8. Explain how various blade angles due to pitch control ensure maximum rated power of a wind generator!

……………………………………………………………………………………… ………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………


(i) Why large wind turbines need blade pitch control, video.(ii) Power electronics as effi cient interface in dispersed power generation system, Hansen et.al.,

PDF, 2004(iii) Kestrel e300i installation and maintenance manual, PDF,(iv) Small-Scale Renewable Embedded Generation: Regulatory Framework for Distributors

(Draft ), NERSA, 2014(v) Small-Scale Renewable Embedded Generation: Regulatory Rules (Consultation Paper),

NERSA, 2015(vi) Grid Connection Code for Renewable Energy Power Plants connected to the Electricity

Transmission System or Distribution System in South Africa, NERSA, 2014(vii) SANS 10142-1:2009, THE WIRING OF PREMISES, PART 1: LOW-VOLTAGE INSTALLA-

TIONS, SABS, 2012(viii) NRS 097-2-1, GRID INTERCONNECTION OF EMBEDDED GENERATION, Part 2:

Small-scale embedded generation, Section 1: Utility interface, NRS/ESKOM/SABS, 2010.(ix) Wind Turbine Grid Connection and Interaction, Deutsches Windenergie-Institut GmbH

Germany · Tech-wise A/S Denmark · DM Energy United Kingdom, European Communi-ties, 2001

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THEME 2.1.4

WIND TURBINE TYPESIntroduction

Wind turbines can be categorised according to a number of criteria. One obvious criterion is the position of the rotor axis, horizontal or vertical. Historical wind mills can already be diff erentiated using rotor axis position as a measure. With modern wind turbines we distinguish between a horizontal-axis wind turbine (HAWT) and a vertical-axis turbine (VAWT). Each of these two types can be further divided using various sub-criteria which we will deal with in more detail in this theme.

Keywords

Wind turbine categorisationHorizontal-axis wind turbine (HAWT)Vertical-axis wind turbine (VAWT)Savonius and Darrieus rotorsTraining kit components Measuring wind speeds

Theme Outcomes

At the end of this theme you should be able to:(i) Diff erentiate between the diff erent wind turbine technologies and designs.(ii) Identify the training kit components of the wind turbine training set.(iii) Measure wind speed in the environment.(iv) Measure wind speed using a wind machine.


Wind Turbine CategorisationSome possible criteria are indicated in Table 1 to help illustrate how to distinguish between diff erent wind turbine types. Th e fi rst criterion in Table 1, the position of the rotor axis, is a very obvious one as we can distinguish between horizontal-axis wind turbines (HAWT) and vertical-axis turbines (VAWT).

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TABLE 1: CRITERIA FOR WIND TURBINE CATEGORISATION

Criteria Rotor axis Rotor orientation

Wind power control Drivetrain Tower

structureGenerator

technology

Options HAWT

VAWT

Upwind

Downwind

Pitch

Stall

Direct

Gear box

Tubular

Lattice

Asynchronous

Synchronous

Horizontal-Axis Wind Turbines (HAWT)Th e rotor axis in a HAWT is parallel to the wind stream and the ground (left in Figure 1). Today almost all large commercial grid-connected wind turbines are built with a propeller-type rotor on a horizontal axis, i.e. a horizontal main shaft . Most HAWTs built today have three blades. Th e rotor blades convert the linear motion of the wind into rotational energy that can be used to drive a generator. Th e conversion of linear motion into rotational motion is based on the Bernoulli principle, i.e. wind passes over both surfaces of the air foil shaped blade but passes more rapidly over the longer (upper) side of the air foil, thus creating a lower-pressure area above the air foil. Th e pressure diff erential between top and bottom surfaces results in a lift force.In an aircraft wing, the lift force causes the air foil shaped wings to rise, lift ing the aircraft off the ground. Since the blades of a wind turbine are constrained to move in a plane with the hub as its centre, the lift force causes the blades to rotate around the hub of the rotor. In addition to the lift force, a drag force perpendicular to the lift force impedes rotor rotation. A prime objective in HAWT rotor blade design is to ensure that the blades have a relatively high lift -to-drag ratio. Th is ratio can be varied along the length of the blades to optimise the energy output at various wind speeds.

FIGURE 1: POSITION OF PRINCIPAL WIND TURBINE COMPONENTS IN HAWTS AND VAWTS


Vertical-Axis Wind Turbines (VAWT)Th e axis of rotation in a VAWT is perpendicular to the wind stream and the ground. Th e VAWT working principal is similar to the one of the classical Persian wind mills used, i.e. the wind stream is at a right angle (perpendicular) to their rotational axis (shaft s). Modern VAWTs can be further divided into two major categories: the lift -force-driven Darrieus type turbines and the drag-force-driven Savonius type turbines.

Rotor

Gear box

Generator

Roto

r dia

met

er (D

)

Hub

hei

ght

Tower

Rotor diameter (D)

Hub

hei

ght

Roto

r hei

ght (

H)

GeneratorGear box

Tower

Rotor

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FIGURE 2: PRINCIPAL DESIGN COMPARISON OF SAVONIUS AND DARRIEUS ROTORS


FIGURE 3: COMPARISON OF SAVONIUS AND DARRIEUS ROTOR WORKING PRINCIPALS (SCHEMATIC)

Image source: S4GJ/GIZDesign comparison of Darrieus type rotor using cup shapes to generate drag forces (left ) and lift force driven Savonius rotor with air foil blades (right).

Since drag-based designs rotate with the wind, they cannot move faster than the wind, whereas lift -based designs can move faster than the wind. Th e drag design is very rugged and therefore suitable for diffi cult situations - however the effi ciency of wind power conversion in drag devices is approximately only half of the more effi cient lift design found in Darrieus turbines. Th e Darrieus turbines are unable to self-start; a mechanism is needed to start them before they can generate power. Currently, the trend all around the world is to combine the two mechanisms on the same axis to utilise the Savonius’ drag ability which then provides suffi cient torque to start a Darrieus wind turbine. In other words, these turbines are combined in an eff ort to minimise the limitations of each of them.

Savonius type

Darrieus type

Direction of rotation

Wind

e D

Lift force

Lift force

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FIGURE 4: PROPOSED SETUPS FOR COMBINED SAVONIUS-DARRIEUS ROTORS (SCHEMATIC)

Image source: S4GJ/GIZProposed setups for hybrid Savonius-Darrieus rotors. On the left : Savonius rotor either on the top or bottom of the H-type Darrieus rotor. On the right: Savonius rotor in the middle of the H-type Darrieus rotor.

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Experiments

For training to be truly eff ective, it is necessary to practically apply your knowledge in hands-on experi-ments and real-world installations. Given that these are oft en diffi cult to realise in some TVET colleges, we can off er you some resources and equipment for practical work. Components required for practical activities range from low-cost components that can be used to build and experiment with simple HAWT and VAWT models, to commercial training kits and vocational training versions to simulate real wind turbine systems. We will introduce you to all of the above in Topic 4 and in more detail, but we suggest that you already start with some practical activities which are based on commercial training kits, such as the IKS Windtrainer Junior set or the leXsolar-Wind training set (one of the two options are available at your college for RET Level 4). Both types of training sets include modular experiments designed to demonstrate important aspects of wind turbine systems covered in this textbook, albeit on a miniature scale.

Training Kit Components Before you start with the fi rst practical activities, we recommend that you familiarise yourself with the training kit and identify all components of the wind turbine training set. One of the two options are available at your college, either the IKS Windtrainer Junior set or the leXsolar-Wind training set. Please consult the student manual of your respective training set for more information and descriptions of the components, as these diff er in respect to their names, forms and functions, and subsequently to their operating instructions. We will now briefl y describe the components of each training set and show you some images illustrating them. Please note that all components, particularly the wind machines and the rotor parts, need to be handled with care! Please also note that the rotor must not be touched during rotation/movement due to the risk of injury!

IKS Windtrainer Junior SetTh e IKS Windtrainer Junior set comes in a white suitcase with a shaped foam inlet for all components except for the base board, which you will fi nd in the lid together with the instruction manual and the CD. Th e base board houses the load, resistor and storage boxes, the two multi-meters, the 12 V wind machine with its power supply and the small wind power generator. Th e latter resembles a tiny HAWT for mounting 2, 3, and 4 blades. You will fi nd a total of eight blades included, 4x straight and 4x convex. You will also fi nd eight 2 mm connector cables, a screwdriver and an anemometer. Your IKS Windtrainer Junior set does not provide you with a Savonius rotor, this optional extension was not included.

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FIGURE 5: COMPONENTS OF THE IKS WINDTRAINER JUNIOR SET IN THEIR STORAGE POSITION

FIGURE 6: IKS WINDTRAINER JUNIOR SET: SOME ASSEMBLED COMPONENTS

Image source: S4GJ/GIZPlease consult the IKS instruction manual for component assembly of each experiment.

leXsolar-Wind Training SetTh e leXsolar-Wind training set comes in an aluminium suitcase with three shaped foam inlets housing all components. A custom-designed breadboard is the construction base for up to three components which can be plugged in a series and parallel connection. A 12 V wind machine is powered by a compact and intuitively usable DC power module (output 0-12 V adjustable in 0.5 V steps) to control the wind conditions in the experiments. Th e rotor set entails eight blades and there is a hub for four blades with a pitch angle of 25° and hubs for three blades with pitch angles of 20°, 25°, 30°, 50° and 90°. Th e little blue wind turbine, resembling a miniature HAWT model, needs to be connected into the turbine module plate, which has an angle scale printed on top of it. In addition to the miniature HAWT model, the leX-


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solar-Wind training set also off ers a Savonius rotor which is already connected to a module plate. Two digital multimeter and various loads, e.g. a motor module, a light bulb, an LED-module, and a buzz-er module are provided. Further, two resistor modules, one with two potentiometers (a 0-100 Ω-poten-tiometer and a 0-1kΩ-potentiometer) and a conventional 33 Ω resistor module are available, as well as a capacitor module (220 mF and 2.5 V). A diode is supplied to allow current to pass in one direction only and an anemometer to measure wind speed. Lastly, an optical tachometer as a ‘round per minute (rpm) counter’ and four 4 mm connector cables complete the training set.

FIGURE 7: COMPONENTS OF THE LEXSOLAR-WIND TRAINING SET IN THEIR STORAGE POSITION

Image source: S4GJ/GIZ Please consult the leXsolar instruction manual for component assembly of each experiment.

FIGURE 8: TWO DIFFERENT ANEMOMETER TYPES

Image source: S4GJ/GIZ Th e anemometer in the IKS Windtrainer Junior set (left ) has a Savorius type of rotor, while the anemome-ter in the leXsolar-Wind set (right) uses a horizontal-axis rotor to measure wind speed.

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TABLE 2: SYMBOLS FOR EXPERIMENTAL SETUP BY THE LEXSOLAR-WIND TRAINING SET

Modules Symbols

Construction base

Wind machine (12V)

Wind turbine module (HAWT model)

Savonius rotor (VAWT model)

DC power module, 0-12 V adjustable in 0.5 V steps

V

Multimeter V A

Motor module

Light bulb module

LED module

Buzzer module

Potentiometer module

Resistor module

Capacitor module

Diode module

Anemometer

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EXPERIMENT 1: MEASURING WIND SPEED IN THE ENVIRONMENT

Th is experiment is designed to generate a fi rst idea of the dimension, the temporal and local diff er-ences of wind speed.

Assignment 1: Familiarise yourself with the anemometer. Please consider that you may have either the IKS Windtrainer Junior set or the leXsolar-Wind training set available at your college, so you will have only one of the two diff erent anemometer types (Figure 8). Please consult the student manual of your respective training set for more information and a description of the anemometer, as these two handheld gauges diff er in respect to their form and function, and subsequently to their operat-ing instructions.

Assignment 2: Use the available anemometer and measure the wind speed at 6 to 8 diff erent locations on your campus at diff erent times. Document your measurements in the table below similarly to the given examples:

No Location on campus Date/Time Wind speed (m/s)

1 GATE 8:00/9:00/10:00/12:00/14:00 6, 3, 3, 4, 1

2 OUTSIDE WORKSHOP 8:30/9:30/10:30/12:30/14:30 6.5, 3.2, 3.4, 4.5, 2

Assignment 3: Answer the following three questions below!

3.1 Specify the overall highest and lowest wind speed indicated in your table, and calculate the ratio of these two values!Example: vmax = 6.5 m/s, vmin = 1 m/s, vmax / vmin = 6.5

vmax = …. m/s, vmin = …. m/s, vmax / vmin = ….




……………………………………………………………………………………… ……………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

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3.2 Compare the measured wind speed per location, i.e. wind speed measured at the same location but at diff erent times!Example: Location: GATE, vmax = 6 m/s, vmin = 1 m/s, vmax / vmin = 6

Location: ………………………….., vmax = …. m/s, vmin = …. m/s, vmax / vmin = ….




……………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

3.3 Recall the three factors in formula (6), i.e. Pwind = 12 x ρ x A x (v3) and consider that wind

velocity (v) is the most crucial factor in the formula. Th us, power output of a wind turbine rotor is proportional to the cube (third power) of the wind speed. In other words, if velocity of wind doubles, power increases by a factor of eight (23 = 2 x 2 x 2 = 8). Use four of your vmax / vmin values (ratios) and calculate the cube (third power) of the wind speeds to under-stand better how velocity infl uences power output of a wind turbine.Examples: vmax / vmin values = 2, 3, 4, etc.

vmax / vmin = 23 = 2 x 2 x 2 = 8

vmax / vmin = 33 = 2 x 2 x 2 = 27

vmax / vmin = 43 = 2 x 2 x 2 = 64

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EXPERIMENT 2: MEASURING WIND SPEED USING A WIND MACHINE

Th is experiment is designed to determine the performance values of the respective wind machines, i.e. which kind of wind speeds correspond to certain ratings of the DC regulator, either by 1 V steps or along given scale division at the control knob (potentiometer settings). Th ese measurements will characterise the respective wind machine and the resulting diagram can be used in all subsequent experiments as reference values.

Assignment 1: Familiarise yourself with the anemometer and the wind machine. Please consider that you may have either the IKS Windtrainer Junior set or the leXsolar-Wind training set available at your college, i.e. only one of the two diff erent wind machine types (Figure 9). Please consult the student manual of your respective training set for more information and a description of the anemometer and the wind machine, as these diff er in respect to their form and function, and subsequently in their operating instructions.

FIGURE 9: TWO DIFFERENT WIND MACHINE TYPES


Th e wind machine in the IKS Windtrainer Junior set (left ) is a hairdryer type of machine, while the leXsolar-Wind set (right) uses a ventilator type of machine to generate appropriate wind speeds.

Assignment 2: Use the following setup and the available anemometer to measure wind speed either at 12 diff erent 1 V steps (leXsolar-Wind set) or along the given scale division (1-10) at the control knob at the IKS Windtrainer Junior wind machine. Document your measurements in the table and use the data to create a graph in the given diagram.

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FIGURE 10: SETUP FOR EXPERIMENT 2 (SCHEMATIC)

Image source: S4GJ/GIZ Please consult the student manual of your respective training set for more information on the setup, e.g. distance between wind machine and anemometer.

Use the table below to document your measurements and use the diagram to draw a graph line linking the power settings with the corresponding wind speed.

Divisions 1 2 3 4 5 6 7 8 9 10 11 12

Wind speed (m/s)


12

11

10

9

8

7

6

5

4

3

2

1

01 2 3 4 5 6 7 8 9 10 11 12

Potentiometer settings/ Divisions on power module

Wind speed(m/s)

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Exercises

1. Which criteria can be used to diff erentiate between diff erent wind turbine designs?

………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

2. Indicate the position of the main wind turbine components in both horizontal-axis wind tur-bines (HAWT) and vertical-axis turbines (VAWT) in a drawing!

3. Compare the design of Darrieus and Savonius types of VAWT rotors and explain what kind of forces each rotor type uses!

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4. A Savonius drag type rotor can be combined with a Darrieus type of rotor. Please explain why this makes sense!

………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………


(i) Technical introduction on Darrieus wind turbine, <http://energia.salgopc.hu/?wpfb _dl=222>.

(ii) Vertical Axis Wind Turbines, M. Ragheb, 2015.(iii) Rural electrifi cation and small wind turbines, Position Paper 2012.(iv) Water pumping solutions, Kestrel, 2016.(v) e300i, Installation and Maintenance Manual, Kestrel, 2016.

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t 2.2

UNIT 2.2

BASIC PRINCIPLES OF BATTERY AND FUEL CELL TECHNOLOGIES

Introduction

This unit briefly explains the basic principles of battery and fuel cell technologies. These technologies are based on combined chemical and electrical processes, i.e. separation and transportation of charged particles. One of the most important applications of electrochemistry appears in context with energy storage and conversion of energy. You already know that energy stored in an ‘energy vector’ or ‘energy carrier’ can be converted into another form of energy. Such energy carriers comprise substances, systems or devices that carry these conversions out and include batteries and hydrogen (fuel cells), but also capacitors, pressurised/liquefied gas, water stored in a dam, and fossil fuels. Battery and fuel cell technologies play a significant role in all portable electronic applications and almost all modern transport systems (e–mobility). It is therefore important to understand their functional principles better.

Unit OutcomesAt the end of this unit, you should be able to:

(i) Describe the basic electrochemical processes that take place in batteries.(ii) Explain general battery design, components and construction.(iii) Differentiate between various lead-acid battery types and explain their functional differences.(iv) Explain the chemistry of lead-acid batteries.(v) Describe the electrochemical process where hydrogen and oxygen interact within a fuel cell to

generate electricity.(vi) Explain the two electrochemical reactions occurring at the anode and cathode of a fuel cell.(vii) Explain why fuel cells are also referred to as electrochemical energy converters.(viii) Sketch and explain a proton exchange membrane (PEM) fuel cell.(ix) Discuss the principles of water electrolysis for hydrogen generation and why the association with

renewable energy systems is advantageous.(x) Explain why energy generation through fuel cells can be regarded as a climate–friendly technology.(xi) Identify the training kit components for hydrogen and fuel cell experiments.(xii) Measure the volume ratio of the gases produced.(xiii) Measure the quantities of gas produced per unit time depending on current.

Themes in this UnitUnit 2.2 covers the following four themes:

Theme 2.2.1 Electrochemical Processes in BatteriesTheme 2.2.2 Electrochemical Processes in Fuel Cells

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THEME 2.2.1

ELECTROCHEMICAL PROCESSES IN BATTERIES

Introduction

Th is theme will briefl y introduce you to the basic electrochemical reactions and principles responsible for generating an electric current. We will introduce you to the main types of batteries and explain their basic principles of operation.

Keywords

BatteryBattery componentsElectrodeAnodeCathodeElectrolyteAtomIonCationsAnionsChemical reactionRedox reactionsTwo half (reactions) make one (redox reaction)Voltaic pile: the ancestor of modern electrical batteries Electrochemical processes in the voltaic pile/galvanic cellPrimary cellsZinc dry cellsAlkaline dry cellsOther dry cell typesSecondary cellsLead-acid storage cells Other lead-acid battery typesBatteries: general principle of operationBattery vs fuel cell

Theme Outcomes

At the end of this theme you should be able to:(i) Describe the basic electrochemical processes that take place in batteries.(ii) Explain general battery design, components and construction.(iii) Diff erentiate between various lead-acid battery types and explain their functional diff erences.(iv) Explain the chemistry of lead-acid batteries.


Th e processes by which batteries provide an electric current diff er slightly from battery to battery. Th e basic electrochemical reactions however appear to be rather similar, but before we can explain and ex-pose you to the chemistry in battery operation, we need to introduce you to some new technical terms. Electrochemistry has an extensive vocabulary and a signifi cant amount of jargon. We will discuss some basic technical terms concerned with composition, structure and properties of batteries, as well as the changes they undergo during chemical reactions.

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BatteryTh e word ‘battery’ was used to describe any series of similar objects grouped together to perform a function (a battery of something, e.g. a battery of pain killers or an artillery battery). In 1749, Benjamin Franklin, one of the so-called ‘founding fathers’ of the United States and a renowned polymath, used the term to describe a series of capacitors he had linked together for his physics experiments. Later, the term would be used for electrochemical cells linked together for the purpose of providing electric power (see also ‘voltaic pile’).

Battery ComponentsIn batteries chemical reactions can create an electric current in a circuit. All batteries are made up of three basic components: two electrodes and a substance called electrolyte (see Figure 1). Th is arrange-ment, i.e. two electrodes separated by an electrolyte, is the basic setup required for a battery to conduct an electrical current through a circuit.

FIGURE 1: THE THREE BASIC COMPONENTS OF A BATTERY


ElectrodeElectrodes are terminals through which an electric current can enter or leave a battery. Two types of ter-minals can be diff erentiated: a negative terminal (anode) and a positive terminal (cathode).

Anode Th e anode is the negative terminal from which electrons fl ow if a battery is connected to a circuit. In a battery, the chemical reaction between the anode and electrolyte causes a buildup of electrons (negative charge) in the anode. Th e negative electric charge moves to the cathode, but cannot pass through the electrolyte.

CathodeTh e positive terminal into which electrons fl ow if the battery is connected to a circuit. In batteries, the chemical reaction in or around the cathode uses the electrons provided via the anode. Th e only way for the electric charge to get to the cathode is through an external circuit, e.g. via a wire and/or a load.

Electrode

Electrode

Cathode (+)

Anode (-)

Electrolyte

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ElectrolyteAn electrolyte1 is a substance, oft en a liquid solution, a gel or a paste that is capable of transporting elec-trically charged particles. Th e electrolyte also inhibits the fl ow of electrons between the anode and cath-ode so that the charge fl ows more easily through the external circuit rather than through the electrolyte.

AtomAll matter is made up of fundamental building blocks known as atoms. Each atom consists of protons, neutrons and electrons (see Figure 2). Protons and neutrons form the nucleus or the centre of an atom. Electrons are constantly spinning in shells or orbitals surrounding the nucleus of an atom. Electrons and protons carry a charge. Th e charge of an electron is negative, while a proton carries a positive charge of the same magnitude as the electron. Electric charge, either negative or positive, is the most basic quantity in an electric circuit.

FIGURE 2: SIMPLIFIED STRUCTURE OF AN ATOM


1 Th e term ‘electrolytes’ is also used for minerals in your body fl uids. Maintaining the right balance of electrolytes helps your body’s blood chemistry, muscle action and other processes. Sodium (Na), calcium (Ca), potassium (K), chlorine (Cl), phosphate (Ph) and magnesium (Mg) are all electrolytes. You get them from the foods you eat and the fl uids you drink.

q-q-

q+q+

q+

q-

Protons

Neutrons

Electrons

q- q-

q+q+

q+

q-

PROTONS

ELECTRONS

NEUTRONS

Each atom consists of electrons, protons and neutrons. The charge of an electron is negative and a proton carries a positive charge of the same magnitude as the electron.

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Ion In an atom, the number of protons usually does not change. Th e number of electrons however, might change in an atom. Fewer or extra electrons can create an electrically charged atom called an ‘ion’. Two types of ions can be diff erentiated: a cation (positive ion) and an anion (negative ion). Th e term ‘ion’ was introduced by the English scientist Michael Faraday. It stems from the Greek word ‘ion’ meaning ‘go or move’, so called because ions move towards the electrode of opposite charge.

Cations A cation is an ion, an electrically charged particle that has fewer electrons and thus carries a positive charge. Table salt, i.e. sodium chloride (NaCl), for example, dissolves in water to form sodium cations (Na+) and chloride anions (Cl-). Th e sodium cation, denoted as Na+ carries a single positive charge: the sodium cation (Na+) lost or donated one of its electrons to the chloride anion (Cl-). Another example is the zinc cation, denoted as Zn2+. Th is cation carries a twofold positive charge, i.e. the neutral zinc atom (Zn) lost or donated two of its electrons in a chemical reaction.

AnionsAnions have extra electrons that create a negative charge. Th e chloride anion (Cl-) or the hydroxide anion (OH-) both carry a single positive charge as each of them have gained one additional electron. Another example for an anion is the sulphate anion SO4

2- which carries a twofold negative charge. Th e sulphate anion is a salt of the sulfuric acid H2SO4. Th is acid is highly soluble in water and dissociates into two ions as indicated in the following equation: H2SO4 2H+ + SO4

2-, i.e. the sulphate anion SO42- has gained

two additional electrons in a chemical reaction. Th e following symbols are used to diff erentiate between diff erent types of reactions: Th e arrow symbol pointing to the right (→) is used to denote a net forward reaction and usually reads as ‘yields’. Th e double arrow symbol () is used to denote a reaction in both directions.

FIGURE 3: SODIUM CATIONS (Na+) AND CHLORIDE ANIONS (Cl-)

Image source: GIZ/S4GJ Th e salt sodium chloride (NaCl) is comprised of two atoms: sodium (Na) and chloride (Cl). Th e salt forms ions in water by sodium losing/donating one electron and chloride gaining this electron. Th e sodium cation (Na+) carries a single positive charge and the chloride anion (Cl-) carries a single negative charge.

Sodium Chlorine

Cl

Cl-Na+

Na

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Chemical ReactionA chemical reaction is a process in which one or more substances, the reactants, are converted to one or more diff erent substances, the products. Equations are the symbolic representation of a chemical reaction in the form of symbols for reactants and products. In equations, each individual reactant and product is separated from others by a plus sign (+). Th e reactant entities are placed on the left -hand side and the product entities on the right-hand side of the equation. A simple example is the equation for the reaction of table salt with water - sodium chloride (NaCl) dissolving in water (H2O) can be denoted as:

H2O (l) + NaCl (s) → Na+ (aq) + Cl-

(aq) + H2O (l)

Th e physical state of chemicals is also very commonly stated in parentheses aft er the chemical symbol, especially for ionic reactions. When stating physical state, (s) denotes a solid, (l) denotes a liquid, (g) de-notes a gas and (aq) denotes an aqueous solution.Table salt (NaCl) is soluble in water. NaCl dissolves into separate Na+ and Cl- ions. A hydration shell is formed around these ions and we can thus say the salt is dissolved. Th is equation could be read as: water plus sodium chloride yields sodium and chloride ions both covered by hydration shells (water molecules).

FIGURE 4: TABLE SALT (NaCl) DISSOLVES IN WATER

Image source: GIZ/S4GJ Sodium and chloride ions separate and hydration shells (water molecules) are formed around the ions due to electrostatic interactions (charge–based attractions).

a) b) c)

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FIGURE 5: AN ENLARGED IMAGE OF FIGURE 4 C

Image source: GIZ/S4GJ Water molecules form hydration shells around sodium cations (Na+) and chloride anions (Cl-). Th is is the contemporary atomic understanding of a salt (NaCl) dissolved in water.

Redox ReactionsChemical reactions that involve charge transfer, i.e. electron transfer similar to the previous example where sodium transfers an electron to chloride and both atoms turn into ions, are termed oxidation/reduction reactions. Oxidation/reduction reactions, or redox reactions in short, involve a transfer of neg-ative charge (electrons) from one atom to another. In terms of electrochemistry, the following defi nition applies: Loss of electrons is called oxidation, and gain of electrons is called reduction. Ways to remember oxidation/reduction as chemical reactions include two mnemonic aids. Th e fi rst one is: OIL RIG, mean-ing oxidation is loss and reduction is gain. Th e second mnemonic aid is: LEO says GER, meaning losing electrons = oxidation and gaining electrons = reduction.

Two Half (Reactions) make One (Redox Reaction)Oxidation and reduction reactions cannot be carried out separately. Th ey always appear together in a chemical reaction. Subsequently, a redox reaction includes a reducing agent and an oxidising agent. Both form a redox couple which can be described as:

1st half reaction at the anode: reducing agent → oxidising agent + electrons (e–)2nd half reaction at the cathode: oxidising agent + electrons (e–) → reducing agent

Each one of the two reactions is called a half-reaction and together they form a redox couple. In other words, oxidising agents gain electrons and are thus reduced. Reducing agents lose electrons and are thus oxidised. Th e reaction where sodium chloride (NaCl) dissolves in water (H2O), denoted as

H2O (l) + NaCl (s) → Na+ (aq) + Cl- (aq) + H2O (l)

can be regarded as a simple redox couple if we consider that sodium and chloride carry no charge as table salt (NaCl). Th is situation changes when table salt (NaCl) dissolves in water. When table salt dissolves, sodium (Na) loses/donates one electron to chloride (Cl) and subsequently carries a charge of plus one (Na+) while chloride (Cl) gains one electron from sodium (Na) and subsequently carries a charge of mi-nus one (Cl-). Th erefore, one could say that sodium (Na) was oxidised (loss of electrons) by the oxidising agent chloride (Cl). Th is is called the fi rst half-reaction and Cl was reduced (gain of electrons) by the re-ducing agent Na. Similar types of redox reactions take place in batteries.

Cl-

02-

H+

H+

0 2-H +

H +

02-H +

H +

02-

H+

H+

02-H+

H+

02 - H

+H

+

02-H+

H+

0 2-H +

H +

02-H+H+

02- H+

H+

02-H+

H+

02-H+

H+

Na+

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Voltaic Pile: The Ancestor of Modern Electrical Batteries In Th eme 1.2.1 we introduced you to the voltaic pile, the fi rst electrical battery invented by A. Volta in 1799 (see Figure 6). Th is early battery consisted of stacked pairs of alternating copper (Cu) and zinc (Zn) discs which served as electrodes separated by cloth or cardboard soaked in brine, a solution of table salt (sodium chloride, NaCl) or diluted sulphuric acid (H2SO4). Th is solution acts as an electrolyte to increase conductivity. Th e pile produced an electric current and can be considered the fi rst electrochemical cell.

FIGURE 6: THE VOLTA PILE (SCHEMATIC)

Image source: GIZ/S4GJTh e Volta pile consists of stacked pairs of alternating copper (orange) and zinc (grey) discs (electrodes) separated by an electrolyte (blue).

Electrochemical Processes in the Voltaic Pile/Galvanic Cell (simplifi ed) Th e contemporary, atomic understanding of a voltaic cell element with zinc and copper electrodes sepa-rated by an electrolyte is the following: When the cell provides an electrical current through an external circuit, the metallic zinc (Zn) at the surface of the zinc electrode (anode, negative terminal) dissolves in the form of electrically charged ions (Zn2++, Zn-cation) and two negatively charged electrons (2e–) that enter into the electrolyte. Th is type of chemical reaction is called oxidation and takes place at the nega-tive terminal, the anode. Remember, oxidation is a chemical reaction where electrons are released. Th is process is called the 1st half reaction of the redox couple and can be expressed by the following equation:

Zn → Zn2+ (aq) + 2e–

While the zinc cations (Zn2+) enter the electrolyte (H2SO4 , diluted sulphuric acid), two positively charged hydrogen ions (H+) from the electrolyte (H2SO4 2H+ + SO4

2-) combine with the two electrons (2e–) at the copper (Cu) electrode (cathode, positive terminal) and form an uncharged hydrogen molecule (H2), a gas. Th is reaction is called reduction and takes place at the positive terminal, the cathode. Reductions are chemical reactions where electrons are gained. Th e hydrogen molecules formed on the surface of the copper by reduction ultimately bubble away as hydrogen gas (H2). Th is process is called the 2nd half reaction of the redox couple and can be expressed by the following equation:2

2H+(aq) + 2e– H2 (g)

2

Remember: (s), (aq), (l) and (g) in chemical equations refer to (s) = solid, (aq) = aqueous solution (dis-solved in water), (l) = liquid, and (g) = gas.

2 Or more accurately: 2H3O+(aq) + 2e– H2 (g) + 2H2O (l)

Zn

Cu

Cu

Zn

-

+

+

-

-

+

Electrolyte

one voltaic cell

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FIGURE 7: SIMPLIFIED ELECTROCHEMICAL PROCESSES IN A VOLTAIC PILE / GALVANIC CELL

Image source: GIZ/S4GJVoltaic cells, also called galvanic cells, are simple electrochemical devices (batteries) that generate an electric current by using two diff erent metals that diff er in their tendency to lose electrons. For example, zinc (Zn) tends to lose electrons more easily than copper (Cu), so by placing zinc and copper metal in an electrolyte (H2SO4, diluted sulphuric acid), a charge fl ows through a wire from the zinc electrode (anode) to the copper electrode (cathode).

Primary CellsIn primary cells electrochemical reactions are irreversible (not reversible). During discharging the chem-ical components are permanently changed and an electric current is released until the original battery compounds are completely exhausted. Th us, these type of cells can be used only once (throwaway cells).

Zinc Dry Cells Th e most well-known primary battery has long been the common dry cell (zinc-carbon cell) which is still widely used to power common electric and electronic devices (fl ashlight battery). Modern dry cells are based on a battery unit invented by Georges Leclanché in 1866. Despite its name, the zinc-carbon dry cell is not really dry. Th e electrolyte is a wet paste or non-fl owing jelly containing zinc chloride (ZnCl2), am-monium chloride (NH4Cl), manganese dioxide (MnO2), starch, graphite and water. Th e anode is a zinc container covered with an insulating fabric and the cathode is the carbon rod at the centre of the cell (see Figure 8). A fully charged (unused) dry cell delivers around 1.5 V.

Zn 2e-

-0,76V

Zn Zn2++2e-

H2SO4 2H++SO42-

Cu +

0 V

2H++2e- H2

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FIGURE 8: THE ZINC-CARBON DRY CELL (SCHEMATIC)


Th e following redox reactions take place at the electrodes of the zinc-carbon cell:

Th e 1st half reaction at the anode (negative terminal):Zn → Zn2+ + 2e– (0.74 V)

Th e 2nd half reaction at the cathode (positive terminal):2MnO2 + 2NH4

+ + 2e– → Mn2O3 + 2NH3 + H2O (0.76 V)

Th e chemistry of this cell is more complicated than it would appear from these equations, and there are many side reactions which we do not need to consider for our purposes here. Th ese types of cells have a limited shelf life due to self-discharge. In some of the older types of zinc dry cells an attack by the acidic ammonium ion (NH4

+) would release hydrogen gas, causing the battery to swell and rupture, oft en ruin-ing a fl ashlight or other electric devices.

Alkaline Dry CellsA more modern dry cell version introduced in 1949, is the alkaline dry cell. Th e alkaline dry cell is more expensive than a zinc-carbon cell, but it is also more effi cient. Zinc is again used as reducing agent at the anode and manganese dioxide acts as the oxidising agent at the cathode. Th e electrolyte however is 40% potassium hydroxide (KOH) saturated with zinc oxide (ZnO) which permits the cell to deliver higher currents and avoids the corrosive eff ects of the acidic ammonium on the zinc. Th e cathode is a paste of manganese dioxide (MnO2), graphite and water. A plastic sleeve separates the inner steel case from the outer steel jacket. Nominal cell voltage is again 1.5 V.

+

-

Fabric bag

Protectiveplastictube

Zinc caseCarbon rod

Powered carbon and manganese

dioxide

Jelly containingammonium

chloride

Powdered

156

Th e following redox reactions take place at the electrodes of the alkaline dry cell:

Th e 1st half reaction at the anode (negative terminal):Zn + 2OH- → Zn2

+ + H2O + 2e– (1.25 V)

Th e 2nd half reaction at the cathode (positive terminal):2MnO2 + H2O + 2e– → Mn2O3 + 2OH- (0.15 V)

FIGURE 9: ALKALINE BUTTON CELL (SCHEMATIC)

Image source: GIZ/S4GJApart from the diff erent type of casing the chemistry of the alkaline button cell is the same as that of the standard alkaline dry cell.

Other Dry Cell TypesTh ere are many more types of primary cells available which use diff erent components as reducing agent at the anode and as the oxidising agent at the cathode:

(i) Lithium dry cells use Li as reducing agent at the anode, MnO2 as the oxidising agent at the cathode and KOH as electrolyte. Th is is only one of a whole family of lithium-based batteries. Others are: Li/SO2 , Li/SOCl2 , Li/CuO, Li-poly(vinyl pyridine)/I2 solid electrolyte. Lithium batteries will most probably replace most other types of batteries with a whole new range of high-power, low-mass cells. In the next years we could see substantial development in this area. Nominal cell voltage is around 3.0 V.

(ii) Mercury batteries use a zinc-mercury amalgam as reducing agent at the anode while the cathode is a paste of mercury oxide (HgO), graphite and water. Th e mercury cell, developed in 1942, is usually produced as a button dry cell devised for use in small appliances such as watches. Th ese cells deliver only around 1.3 V, but they have the advantage of maintaining a fairly constant voltage during their lifetime. Th eir high toxicity (mercury) however is a huge environmental burden.

(iii) Silver oxide button batteries use Zn, Ag2O and KOH, and are similar to the mercury and alkaline manganese cells. Th ey have a very high storage capacity but are expensive because of the use of silver oxide.

Anode cap

Cell case

Anode(Zn plus KOH electrolyte)

Gasket

Separator

Cathode (MnO2 plus conductor)

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Secondary CellsPrimary cells as exemplifi ed above cannot be recharged effi ciently. Th us, the amount of power they can deliver is limited to the chemical energy obtainable from the reactants that were placed in the cell at the time of its manufacture. Conversely, electrochemical reactions in secondary cells are reversible and the original chemical compounds can be reconstituted or reactivated by the application of an electrical potential between the cell electrodes. Consequently, secondary cells can be discharged and recharged many times.

Lead-Acid Storage CellsTh e most well-known rechargeable storage cell is the lead-acid cell, which was invented by Gaston Planté in 1859 and is still the most widely used device of its type. Th e anode consists of a lead grid fi lled with porous lead (Pb). Th e cathode is a lead grid fi lled with lead dioxide (PbO2). Th e electrolyte is a liquid (pure H2O) containing 38% (by mass) sulfuric acid (H2SO4).

FIGURE 10 – 16: LEAD-ACID BATTERY DISCHARGING VIA CONDUCTION BETWEEN TERMINALS

Image source: GIZ/S4GJTh e conducting terminals are made of porous lead (Pb) and lead dioxide (PbO2).

FIGURE 11

Image source: GIZ/S4GJTh e electrolyte, i.e. sulfuric acid (H2SO4) contains aqueous cations (H+, hydrogen protons) and anions (SO4

2-, sulphate anions). Th ese ions react with the electrode materials (Pb and PbO2).

Negativeelectrode:

Porous lead

Positiveelectrode:Lead-dioxide

Pb PbO2

H2OH2SO4

Electrolyte: Sulfuric acid, diluted in pure water

Pb PbO2

H2O

SO4-2

H+

H+

H+

H+

SO4-2

158

FIGURE 12

Image source: GIZ/S4GJTh e aqueous sulphate anions (SO4

2-) react with the anode material (Pb = reducing agent) and as a result, lead as the reducing agent loses two electrons and is thus oxidised. Th e ionised lead becomes a cation (Pb2+) and forms an ionic bond with the sulphate anion (SO4

2-). Th e two electrons, carrying a negative charge, are released into the lead anode. Th is is the 1st half reaction of the redox couple and can be de-scribed with the following equation:

Pb (s) + SO42- (aq) → PbSO4 (s) + 2e– (in conductor)

FIGURE 13

Image source: GIZ/S4GJTh e aqueous cations (H+, hydrogen protons) and anions (SO4

2-, sulphate anions) also react with the cathode material (PbO2). As a result, the lead cation (Pb4+ = oxidising agent) gains two electrons and is reduced to Pb2+. Th is cation forms an ionic bond with the sulphate anion (SO4

2-) similar to the process at the anode. Th e positively charged hydrogen ions (H+) combine with the oxide ions (O2−) at the cathode and form water molecules (H2O). Th is is the 2nd half reaction of the redox couple and can be described with the following equation:

PbO2 (s) + SO4

2- (aq) + 4H+ (aq) + 2e– (in conductor) → PbSO4 (s) + 2H2O (l)

SO4-2 SO4

-2

H2OH+

H+H+

H+

Pb0

Pb0

Pb0

Pb0

Pb0

Pb0

Pb0

Sulfuric acid electrolyteLeadelectrode

-

-

H2O

Sulfuric acid electrolyte Lead-dioxide

electrodePb+4

Pb+4

O-2

O-2

O-2

O-2

O-2

Pb+4

O-2

H+

H+

H+

H+

-

-SO4-2

SO4-2

H2O

Sulfuric acid electrolyte Lead-dioxide

electrodePb+4

Pb+4

O-2

O-2

O-2

Pb+4

O-2

SO4-2

SO4-2

H2O

H2O

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FIGURE 14

Image source: GIZ/S4GJBoth half reactions cause the electrodes to become coated with lead sulphate, a poor conductor, and at the same time reduce the concentration of the acid electrolyte.

FIGURE 15

Image source: GIZ/S4GJIn a commercial lead-acid battery one cell consists of multiple pairs of Pb and PbO2 plates. Th e potential diff erence per cell is usually around 2.1 V and thus adds up to around 12.6 V when connected in series with 6 cells (specifi c battery types may vary). Connection of an electrical load allows a charge to fl ow from the negative to the positive terminal. Th is reduces the potential diff erence at the terminals. Th e chemical reactions however proceed and generate a continuous charge fl ow until the cell is completely discharged, i.e. lead sulphate (PbSO4) buildup at the terminals and electrolyte dilution.

Pb PbO2

Pb0

Pb0

Pb0

Pb0

Pb0

Pb0

Pb0

-

-

H2O

H2O

H2O

Pb+4

Pb+4

O-2

O-2

O-2

O-2

O-2

Pb+4

O-2

H+

H+

H+

H+

H+

H+

H+

H+

SO4-2

SO4-2

SO4-2

SO4-2

SO4-2 -

-

Pb PbO2

H2O

SO4-2

H+

H+

H+

H+

SO4-2

PbSO4

ca. 2.1V

ca. 1.7V

ca. 0.4V

V

R

160

FIGURE 16

Image source: GIZ/S4GJConclusion discharging: Chemical energy is converted into electrical energy through the reaction of electrodes with an electrolyte. Diff erent electrode materials (Pb and PbO2) cause a redox potential and subsequently an electric current. Sulphuric acid is decomposed by the fl ow of charge and active material (Pb and PbO2) is transformed to lead sulphate (PbSO4). As the cell is discharged, the terminals become coated with lead sulphate and reduce the concentration of the acid electrolyte. Th e state of charge can be estimated by measuring the density of the electrolyte. As sulfuric acid is about twice as dense as water, as the cell is discharged, the density of the electrolyte decreases.

FIGURE 17: LEAD-ACID BATTERY CHARGING BY REVERSING THE ELECTROCHEMICAL PROCESS

Image source: GIZ/S4GJConnection of an electric power source forces charge fl ow from the positive to the negative terminal. Th e chemical reactions are driven into reverse direction, i.e. electrical energy is converted into chemical (stored) energy.

Pb PbO2

H2O

SO4-2

H+

H+

PbSO4

ca. 1.9V

ca. 1.6V

ca. 0.3V

V

R

Pb PbO2

H2O

SO4-2

H+

H+H+

H+

SO4-2

PbSO4

ca. 2.1V

ca. 1.7V

ca. 0.4V

V

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FIGURE 18: LEAD-ACID BATTERY CHARGING BY REVERSING THEELECTROCHEMICAL PROCESS

Image source: GIZ/S4GJConclusion charging: Th e lead sulphate at the terminals is transferred into active electrode materials (Pb and PbO2), i.e. the electrodes are reactivated and the concentration of the acid electrolyte becomes stron-ger. A secondary battery cell is thus capable of being recharged as its electrode reactions can proceed in either direction. During charging, electrical work is done on the cell to provide the energy needed to force the reaction in the non-spontaneous direction.

Please note: Th e technology of lead-acid storage batteries has undergone remarkably little change since the late 19th century. Th eir main drawback as power sources for electric vehicles is the weight of the lead. Th e maximum energy density is about 35 Ah/kg lead and actual values may be only half as much. Th ere are also a few other problems:

(i) Th e sulphuric acid electrolyte becomes quite viscous when ambient temperature is low, thus in-hibiting the fl ow of ions between the plates and reducing the current that can be delivered. Th is eff ect is well-known to anyone who has had diffi culty starting a car in cold weather.

(ii) Lead-acid batteries tend to slowly self-discharge. A car left idle for several weeks might be unable to start if the battery is not brand new.

(iii) Over time, lead sulphate (PbSO4) cannot be converted to lead dioxide (PbO2) at the cathode. Th is is usually due to lack of complete discharge which gradually changes PbSO4 into an inert form, subsequently limiting battery capacity. Also, ‘fast’ charging can cause rapid hydrogen gas (H2) in the electrolyte and along the lead surfaces, tearing PbO2 off the positive plate. Eventually, enough solid material accumulates at the bottom of the electrolyte to short-circuit the battery, leading to its permanent demise.

Other Lead-Acid Battery TypesTh ere are many more types of primary cells available which use diff erent components as reducing agents at the anode and as the oxidising agents at the cathode. Examples include:

(i) Car batteries (SLI – starter, lighting and ignition): Designed to provide a short burst of high cur-rent to crank the engine. Th is type of battery cannot handle deep discharge applications and the typical lifetime is around 1000 cycles at 20% of discharge.

(ii) Deep discharge batteries: Th ese types are usually sealed and valve regulated. Th ey have thicker electrodes, usually a calcium alloy that maintains a low leakage current and more space below the electrodes for accumulation of debris preventing plates from easily shorting.

(iii) Golf cart or forklift batteries: Th ese are similar to type 2 batteries but bigger and very rugged. Th ey use antimony alloy for their large electrodes and can last many years (> 10).

Pb PbO2

H2O

SO4-2

H+

H+H+

H+

SO4-2

!

162

Batteries: General Principle of OperationTh e chemical reactions which take place in batteries are called redox reactions, i.e. oxidations and re-ductions. When both battery electrodes are connected to form a circuit, a reaction takes place between the negative terminal (anode) and the electrolyte. As a result, this reaction causes an electric current (electrons) to run through the circuit and back into the cathode where another reaction takes place. Both chemical reactions, i.e. at the cathode and anode, consume or chemically change the material of both terminals. When the material in the cathode or anode is fully consumed or changed by the reaction, the battery is no longer able to produce an electric current. At that point, your battery is ‘dead’.

Battery vs Fuel CellBatteries and fuel cells are based on fairly similar electrochemical processes but there are some diff er-ences. In ordinary batteries (storage cells), the chemical components, i.e. electrodes and electrolytes, are contained within the battery itself (self-contained). Th ey react and convert chemical energy into electri-cal energy. During this process electrodes and electrolytes are consumed. An example is the simplifi ed lead-acid battery reaction:

Pb + PbO2 + H2SO4 2PbSO4 + 2H2O

Pb (porous lead) and PbO2 (lead dioxide) are the electrodes and H2SO4 (sulfuric acid) is the electrolyte. As the battery is discharged the electrodes ‘disintegrate’ and become coated with lead sulphate (PbSO4) and the acid electrolyte (H2SO4) becomes weaker and weaker.In a fuel cell, fuel and oxidant, e.g. H2 and air, need to be supplied from an external source. Th e electro-chemical energy conversion, i.e. chemical energy into electrical energy appears without consumption of its electrodes or electrolytes (see Th eme 2.2.3 for more detailed information).

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ExercisesInvestigate electrochemical processes of galvanic cellsExperiment 1

(i) Clarify the purpose of the experiment and its expected outcomes.Th e purpose of the experiment is to investigate electrochemical processes of voltaic cells. As a fi rst step in understanding the operation of galvanic cells, redox (oxidation-reduction) reactions need to be considered. A classic example is provided by the resulting chemical reaction when a strip of zinc metal is placed into an aqueous solution of cupric sulphate, CuSO4. Th e expected observation is that some changes on the zinc and the cupric solution can be observed!

(ii) Ask a question, formulate an assumption or construct a hypothesis (If ... then ...).What kind of electrochemical processes might happen when a strip of zinc metal is placed into a cupric sulphate solution? Th e hypothesis is: If a redox reaction takes place, then electrons are being transferred from the zinc to the cupric ion and the system behaves like a shorted battery according to the following chemical equation:

Zn (s) + CuSO4 (aq) → Cu (s) + ZnSO4 (aq)

(iii) Decide what kind of material is needed to set up the experiment.Material list:1. Zink metal strips2. 10 grams (one tablespoon) of dry cupric sulphate (blueish colour) for the aqueous solution 3. 75 ml of distilled water4. 100 ml glass beaker5. One plastic table spoon

(iv) Following safety instructions:1. Wear your PPE, particularly safety glasses, overall or coat and nitrile/latex gloves at all

times while doing experiments with chemical substances.2. Make sure to wash your hands aft er completing the experiments.3. Waste disposal and clean-up: all solutions should be poured into a waste collection con-

tainer provided by the lecturer. Do not put any solid metal in the trash. A collection con-tainer for the metal strips will provided by the lecturer.

(v) Develop an activity worksheet indicating the following:1. Name(s) and Surname2. Date and Time3. Activity Title: Experiment 1 – Electrochemical Cells4. Procedure (modus operandi)

a. Prepare an aqueous solution of copper sulphate with 75 ml of distilled water and one tablespoon (about 10 grams) of the dry chemical (CuSO4). Use the beaker and the plastic spoon!

b. Put a piece of zinc metal in the cupric sulphate solution of the beaker.c. Store your setup in a safe place and try to observe what happens to the zink strip and the

colour of the aqueous solution of cupric sulphate aft er around 3 hours and aft er around 24 hours (next day). Record you observations in the activity worksheet.

(vi) Analyse your results and draw a conclusion related to your hypothesis (see ii).Th e results confi rm the hypothesis. Over time, one can observe the disappearance of the blueish colour of the cupric solution, i.e. the Cu2+ ion and note further the appearance of a dark coppery plating on the zinc metal. Th e zinc metal also appears to be dissolving. Here one can observe that zinc is being oxidised while the cupric ion is being reduced. Th us, electrons are being transferred from the zinc metal to the cupric ion and the system behaves like a shorted battery. Th is is described by the following chemical equations:

Oxidation: Zn → Zn2+ + 2e–

Reduction: Cu2+ + 2e– → Cu

Overall reaction: Zn + Cu2+ → Cu + Zn2+ or Zn (s) + CuSO4 (aq) → Cu (s) + ZnSO4 (aq)

164

Experiment 2(i) Clarify the purpose of the experiment and its expected outcomes.

Th e purpose of the experiment is to further investigate electrochemical processes of gal-vanic cells. Following up on the chemical reaction in Experiment 1, the results can be used to construct a so-called Daniell cell by separating the redox reaction observed in Exper-iment 1 into two half-reactions, i.e. one half-reaction associated with oxidation and the other one with reduction.

Oxidation: Zn → Zn2+ + 2e–

Reduction: Cu2+ + 2e– → Cu

We must thus arrange the two half-reactions in such a way that they occur in separate compartments of the cell. Th is must be done in a way so that the charge is forced to travel through an external device in order for the cell reaction to progress forward.

(ii) Ask a question, formulate an assumption or construct a hypothesis (If ... then ...).Is it possible to physically separate the redox-reaction of Experiment 1 into two half-reactions? Th e hypothesis is: It is possible to arrange the two half-reactions in a way that they occur in separate compartments. In the present example, we can do this by using two diff erent beakers for each two half-reactions and by connecting the two compartments with an external device (salt bridge) so that the charge is forced to travel through the device.

FIGURE 19: SCHEMATIC SETUP FOR EXPERIMENT 2


Vq q

Salt bridge2 Na+ SO4

2-

2 e-

SO42-Cu2+

Cu SO42-

2 e-

Zn2+

Zn

Zinc (anode)

Copper (cathode)

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(iii) Decide what kind of material is needed to set up the experiment.Material list:1. Zink metal strips functioning as an anode 2. Copper metal strips functioning as a cathode 3. 10 grams (one tablespoon) of dry copper sulphate (CuSO4, blueish colour) for the aqueous

solution in beaker A4. 10 grams (one tablespoon) of dry zinc sulphate (ZnSO4 , white colour) for the aqueous solu-

tion in beaker B5. 10 grams (one tablespoon) of sodium sulphate, also known as sulphate of soda (Na2SO4 ,

white colour) for the aqueous solution in beaker C 6. 225 ml of distilled water7. Th ree 100ml glass beakers8. Th ree plastic tablespoons, one for the copper sulphate, one for the zinc sulphate and one for

the sodium sulphate9. One plastic or glass U-tube10. One plastic syringe (60 ml)11. Cotton wool12. Two cables (red and black) with crocodile clamps13. One multimeter

(iv) Develop an activity worksheet indicating the following:1. Name(s) and Surname2. Date and Time3. Activity Title: Experiment 2 – Electrochemical Cells4. Procedure (modus operandi)

a. Use a white board marker and mark one beaker with a large A and the other beakers with a large B and a large C.

b. Prepare solution A: an aqueous solution of copper sulphate with 75 ml of distilled water and one tablespoon (about 10 grams) of the dry chemical (CuSO4). Use beaker A!

c. Prepare solution B: an aqueous solution of zinc sulphate with 75 ml of distilled water and one tablespoon (about 10 grams) of the dry chemical (ZnSO4). Use beaker B!

d. We will use beaker A and beaker B as the two half cells.e. Prepare solution C: an aqueous solution of sodium sulphate with 75 ml of distilled water

and one tablespoon (about 10 grams) of the dry chemical (Na2SO4). Use beaker C!f. Prepare the salt bridge: We will use a U-tube as a salt-bridge to link beaker A and B. Use

solution C (Na2SO4) to fi ll the U-tube and create a salt bridge. Th e syringe is useful for fi lling the tube. Th e cotton balls are needed to plug each end of the salt bridge. 1. Insert one cotton plug into one end of the U-tube. 2. Fill the syringe with solution C and use the syringe to fi ll the U-tube.3. Make sure that no gaps or big bubbles appear in the tube, as this would seriously

impede current fl ow. 4. Close the other end of the U-tube with a cotton plug, leaving some cotton protruding

from each end of the tube. g. Place the salt bridge in such a way that it connects beaker A with beaker B.h. Make sure that both ends of the U-tube are immersed in solution A and solution B

(see Figure 19).i. Insert a copper strip into beaker A and a zinc strip into beaker B.j. Set the multimeter to a low DC setting (< 1 V).k. Connect the two cables to the multimeter and the two metal strips (see Figure 19).l. Record your observation/measurement in the activity worksheet. Record any changes in

the voltmeter reading. Note the maximum reading. Note any changes at the copper and the zinc electrode.

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(iv) Analyse your results and draw a conclusion related to your hypothesis (see ii).Th e results confi rm the hypothesis. Th e setup is an example of an electrochemical cell and produces a current which can be measured in volt (usually between 0.7 and 1.1 V). Each beaker acts as a half-cell and the salt bridge serves as a barrier between the two diff erent electrolytes while allowing the fl ow of charges. When the cell is set up, electrons fl ow from the zinc electrode through the wire/cable to the copper cathode. As a result, zinc dissolves in the anode solution to form Zn2+ ions. Th e Cu2+ ions in the cathode half-cell pick these electrons up and convert the cupric ion to pure Cu atoms on the cathode.Like any battery, the Daniell cell does not last forever – it only lasts as long as there are Cu2+ ions available and the zinc electrode is not consumed. In reality, the production of current diminishes as the concentration of the electrolyte at the zinc electrode increases, while the electrolyte at the copper electrode decreases. In fact, the positive ions produced by the zinc electrode need SO4

2- ions to balance the charges. Th e exact opposite occurs in the copper solution, which becomes depleted of positive ions.In other words, charge transfer from the zinc electrode to the copper ions takes place along a circuit. Th e potential diff erence refl ects the greater electrochemical activity of zinc over copper. Th e current fl ow depends on the size and rate of the reaction:

Zn (s) + CuSO4 (aq) → Cu (s) + ZnSO4 (aq)

TABLE 1: STANDARD ELECTRODE REDUCTION POTENTIALS (E° V) OF SELECTED METALS

Half-reaction Li+ + e– Li Mn2+ + 2e– Mn Zn2+ + 2e– Zn

(E° V) −3,04 −1,18 −0,76

Half-reaction Pb2+ + e– Pb Cu2+ + 2e– Cu Ag+ + e– Ag

(E° V) −0,13 +0,34 +0,8

It is important to remember that these are not absolute values, but potentials that have been mea-sured relative to the potential of hydrogen if the standard hydrogen electrode is taken to be zero. In the examples we used earlier, the zinc’s electrode reduction potential is −0,76 and copper’s is +0,34. So, if an element or compound has a negative standard electrode reduction potential, it means it forms ions easily. Th e more negative the value, the easier it is for that element to form ions, i.e. to be oxidised and be a reducing agent. If an element or compound has a positive standard elec-trode potential, it means it does not form ions as easily.

Please note: To increase the potential diff erence you may want to consider setting up a battery of galvanic cells as indicated in Figure 20.

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FIGURE 20: SCHEMATIC SETUP OF DANIELL CELLS IN SERIES CREATING A BATTERY



(i) Th e Chemical Process Inside A Bosch Battery. Video by Bosch.(ii) Electrochemistry, Chemical reactions at an electrode, galvanic and electrolytic cells

A Chem1 Reference Text, Stephen K. Lower @ Simon Fraser University, PDF.

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THEME 2.2.2

ELECTROCHEMICAL PROCESSES IN FUEL CELLS

Introduction

is theme will brie y introduce you to the basic electrochemical reactions relevant to fuel cells and explain their basic principles of operation.

Keywords

Fuel cell vs batteryRedox reactionProton exchange membrane fuel cell (PEMFC)PEFC componentsElectrodesAnodeCathodeElectrolyteCatalystPEMFC components and operationElectrolysis of water for hydrogen generationElectrolysis: a redox reactionTraining kit componentsRegression line

Theme Outcomes

At the end of this theme you should be able to:(i) Describe the electrochemical process where hydrogen and oxygen interact within a fuel cell

to generate electricity.(ii) Explain the two electrochemical reactions occurring at the anode and cathode of a fuel cell.(iii) Explain why fuel cells are also referred to as electrochemical energy converters.(iv) Sketch and explain a proton exchange membrane (PEM) fuel cell.(v) Discuss the principles of water electrolysis for hydrogen generation and why the association

with renewable energy systems is advantageous.(vi) Explain why energy generation through fuel cells can be regarded as a climate-friendly

technology.(vii) Identify the training kit components for hydrogen and fuel cell experiments.(viii) Measure the volume ratio of the gases produced.(ix) Measure the quantities of gas produced per unit time depending on current.


Fuel Cell vs Battery e processes by which fuel cells provide an electric current di er slightly from battery processes, as explained in eme 2.2.1. Fuel cells need to be supplied with fuel and oxidants from an external source. Batteries on the other hand contain their chemical components, i.e. electrodes and electrolytes. Fuel-cell operation is based on reversing electrolysis, generating an electrical current as long as external fuel, such as hydrogen, methanol etc. and oxidants such as air, are available. Various types of fuel cells exist, in-cluding proton exchange membrane fuel cells (PEMFCs), direct methanol fuel cells (DMFCs), alkaline fuel cells (AFCs), molten-carbonate fuel cells (MCFCs) and solid-oxide fuel cells (SOFCs). Among the di erent types of fuel cells, polymer electrolyte fuel cells (PEFCs), which include PEMFC, receive the

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most attention because of their higher electrical e ciency, power density and durability. Similar to bat-teries, fuel cell technologies involve an extensive vocabulary and a signi cant amount of jargon. Some basic technical terms concerned with composition, structure and properties of fuel cells (focussing on PEMFC), are provided below.

Redox ReactionA fuel cell is a device that converts the chemical energy from a fuel and oxidants, e.g. hydrogen and oxygen, into electrical energy through a redox reaction. is process involves two half-reactions which are catalysed at separate electrodes (see Table 1).

TABLE 1: STANDARD ELECTRODE REDUCTION POTENTIALS (E° V) OF HYDROGEN AND OXYGEN

Anode Cathode

Half-reaction 2H+ + 2e– H2 (g) O2 (g) + 4H+ + 4e– 2H2O

(E° V) +/- 0 +1,23

FIGURE 1: TWO HALF-REACTIONS OCCUR AT THE ANODE AND CATHODE ASSEMBLY OF A FUEL CELL


PEFC ComponentsSimilar to batteries, PEM fuel cells are made up of two electrodes, i.e. the anode and the cathode, and an electrolyte. In addition, each fuel cell has sealings and ow plates (see Figure 1) through which the fuel is passed to reach the electrodes. is arrangement of two electrodes separated by an electrolyte is the basic setup required for a fuel cell to conduct an electrical current through a circuit. In a PEFC, anode, electro-lyte (membrane) and cathode are put together in a sandwich structure. To achieve higher output voltages and higher power, single cells are o en combined into a large fuel cell stack.

V

4e-

Electrical energy

O2

Atmosphericoxygen

2H2OWater

Anode Cathode

Membrane

2H2Hydrogen

O2+ 4H+ + 4e- 2H2O2H2 4H+ + 4e-

4H+

2O2-

+-

+

+-

-

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FIGURE 2: THE BASIC COMPONENTS OF A POLYMER ELECTROLYTE FUEL CELL (PEFC SCHEMATIC VIEW)


ElectrodeIn fuel cells two types of electrode terminals can be di erentiated: a negative terminal (anode) and a positive terminal (cathode). Both are usually made of porous carbon containing platinum (Pt) or platinum alloy as a catalyst.

Anode e anode, the negative terminal, is also called the fuel electrode due to the fact that fuel, for example hydrogen, is supplied here. e half-reaction occurring at the anode (see redox reaction) requires a catalyst.

Cathode e chemical reaction occurring at the cathode uses the electrons, the hydrogen ions and the oxygen to form water. is half-reaction also requires a catalyst.

Electrolyte In a PEFC, the electrolyte is a polymer membrane (see polymer membrane). is membrane is capable of transporting electrically charged particles, i.e. conducting hydrogen ions from the anode to the cathode. e electrolyte also inhibits the ow of electrons between the anode and cathode.

CatalystA catalyst is a substance that participates in a chemical reaction without being consumed or changed. Catalysts modify and increase the rate of the chemical reaction. In other words, catalysts lower the activation energy required for a reaction without altering the reaction equilibrium. In a fuel cell, catalysts such as platinum (Pt) or platinum alloy are used in the electrodes to lower the activation energy required for the redox reaction (see Figure 3).

Flow plate Sealing Electrode

Electrolyte

Electrode Sealing Flow plate

CathodeAnodeH2 O2

+-

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FIGURE 3: CATALYST REACTION SITES (Pt) AT POROUS CARBON ELECTRODES

Image source: GIZ/S4GJIn this schematic drawing the H2 and O2 fuel pathways are shown on the right-hand side of the illus-tration. e le -hand side shows the reaction side of the catalytic oxygen reduction, and subsequent forming of water molecules on the surface of platinum (Pt) sites in more detail. ese catalytic sites are located as multi-layered Pt membranes on the porous carbon electrode structures. us, at the cathode the catalyst lowers the activation energy required for the redox reaction which causes electrons, hydrogen ions and oxygen to react and to produce water. At the anode the catalyst lowers the activation energy re-quired for the redox reaction, which causes decomposition of hydrogen into protons and electrons.

Polymer membranePolymer membranes separate the two electrodes of a fuel cell, thus acting as the electrolyte by allowing passage of ions between the electrodes while inhibiting electron conduction. Na on membranes for example are synthetic polymers used in PEMFCs, permitting hydrogen ion transport while preventing electron conduction. Such membranes are very thin, only a few micrometres. e cation exchange mem-brane is positioned between a backing lm and a coversheet (see Figure 4).

FIGURE 4: A PROTON EXCHANGE MEMBRANE (PEM)


H2O

O2

H+

Pt reaction sites at the cathode

Carbon10nm

Pt reaction sitesV

H+

Hydrogen Oxygen

H2O2

H2O

Water

Anode Electrolyte Cathode

Backing film

Membrane

Coversheet

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Proton Exchange Membrane Fuel Cell (PEMFC) ComponentsPEMFCs are a type of proton exchange fuel cells that take their name from the special polymer membrane used as the electrolyte. Typical cell components include the ion exchange membrane, an electrically conductive porous backing layer, an electro-catalyst at the interface between the backing layer and the membrane, and ow plates that deliver the fuel and oxidant to the reactive sites via ow channels. e most common material for this membrane is Na on, a per uorinated sulphonic acid polymer. e membrane is compressed between the two porous carbon electrodes coated with a minimum amount of platinum catalyst. Platinum is essential for the reaction to take place, due to the low operating temperature of this type of fuel cell. e assembly of the membrane and the electrodes is called membrane electrode assembly (Figure 5). A PEMFC stack is composed of a series of single cells separated by bipolar plates with integrated gas ow channels (Figure 6).

Proton Exchange Membrane Fuel Cell (PEMFC) Operation e fuel gas (usually hydrogen) and the oxidant (air or pure oxygen) are supplied to the membrane electrode assembly (MEA). Here fuel and oxidant pass through a series of plates, which di use them in the most uniform way to the two membrane sides. A PEMFC transforms the chemical energy liberated during the electrochemical reaction of hydrogen and oxygen into electrical and thermal energy. e exothermic redox reaction is shown in Figure 5.

A stream of hydrogen is delivered to the anode side of the MEA. At the anode side it is catalytically split into protons and electrons, conducting the oxidation reaction. ese protons permeate through the poly-mer electrolyte membrane to the cathode side. e electrons travel along an external load circuit to the cathode side of the MEA, thus creating the current output of the FC. In the meantime, a ow of oxygen is delivered to the cathode side of the MEA. ere, oxygen molecules are reduced and, subsequently, react with the protons permeating through the membrane to form water molecules and also liberating heat.

FIGURE 5: COMPONENTS AND OPERATION OF A PEMFC (SCHEMATIC)


VHydrogen

Oxygen

e -

e -

e -

e -

e -

e -

e -

e - --O -

O -2H2

H2O

Heat

Cathode/ Flowplate

Anode/ Flowplate

Gas diffusion layer with catalyst


Membrane

2H2 4H++4e- O2+4e- 2O2-

O2

HHHH

++++

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FIGURE 6: A PEMFC STACK COMPOSED OF A SERIES OF SINGLE CELLS SEPARATED BY BIPOLAR PLATES


End plate


Membrane

Bipolar-plate with flow field

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Electrolysis of Water for Hydrogen GenerationCompared to most other hydrogen production processes (see eme 1.2.1), electrolysis o ers a more sustainable hydrogen production pathway. One advantage of electrolysis is that it is capable of producing high purity hydrogen (>99.999%). However, re nery costs for electrolysis are huge, mainly due to the high amount of electric power needed to produce pure hydrogen. Nonetheless, if the required power is supplied via renewable technologies (see experiments further on: Operation of the electrolyser with PV cells and wind turbine as a hybrid system), negative environmental impact costs, compared to fossil fuel combustion, could drastically be reduced (see also eme 1.2.1: Hydrogen as an energy vector). Electrolysers are electrochemical devices which work like a fuel cell in reverse and can split water into its constituent molecules, hydrogen (H2) and oxygen (O2), by passing an electric current through water (Figure 7).

FIGURE 7: ELECTROLYSIS: AN ELECTRIC CURRENT SPLITS WATER TO PRODUCE HYDROGEN AND OXYGEN


H2O2

e-

e-

H

e- H+

O e-

OH-

H2O

+-

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Electrolysis: A Redox ReactionIn pure water, a reduction reaction takes place at the cathode. Electrons combine with hydrogen cations to form hydrogen gas.

Reduction at cathode: 4H+ (aq) + 4e− → 2H2 (g)

Oxidation occurs at the anode, generating oxygen gas and releasing electrons to the anode to complete the circuit.

Oxidation at anode: 2H2O (l) → O2 (g) + 4H+(aq) + 4e−

Combining either half reaction pair yields the following overall decomposition of water into oxygen and hydrogen:

Overall reaction: 2H2O (l) → 2H2 (g) + O2 (g)

e number of hydrogen molecules produced is thus twice the number of oxygen molecules produced. Assuming ideal e ciency, the produced hydrogen gas therefore has twice the volume of the produced oxygen gas (Figure 8). e number of electrons pushed through the water is twice the number of generat-ed hydrogen molecules and four times the number of generated oxygen molecules.

FIGURE 8: ELECTROLYSIS: GAS QUANTITY RATIOS AND REDOX REACTION

Image source: GIZ/S4GJ When a DC voltage is applied, water molecules at the anode are oxidised to oxygen. At the cathode, protons (H+ ions) are reduced to hydrogen gas by incorporating the electrons released from the oxygen at the anode.

Cathode(graphite)

Hydrogen gas H2 (g)2 volumes of gas

Oxygen gas O2( g)1 volume of gas

Anode(graphite)

Anode(graphite)

At the cathode:

At the anode:

Overall: 2O2- (aq) + 4H+ (aq) 2H2 (g) + O2 (g)

4e- + 4H+(aq) 2H2(g)

2O2- (aq)

- 4e- O2(aq)

+ -

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Electrolyte (water)

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ExperimentsFor training to be truly e ective, it is necessary to practically apply your knowledge in hands-on experi-ments and real-world installations. Given that these are o en di cult to execute in most TVET colleges, we can o er you some resources and equipment for practical work. Components required for practical activities include fuel cell training kits to simulate real fuel cell operations. We will introduce you to all of the above in Topic 4 in more detail, but we suggest that you already start with some practical activities which are based on the IKS H2 Trainer Junior Set available at your college for RET Level 4. is training set includes modular experiments designed to demonstrate, albeit on a miniature scale, important as-pects of fuel cell operation covered in this textbook.

Training Kit ComponentsBefore you start with the rst practical activities, we recommend that you familiarise yourself with the training kit and identify all of its components. Please also consult the student manual in the training set for more information and descriptions of the components, as well as the operating instructions. We will brie y describe the components and show you some images illustrating them. Please note that all compo-nents, particularly the fuel cell and the electrolyser, need to be handled with care!

FIGURE 9: IKS H TRAINER JUNIOR SET

Image source: Doerthe Boxberg

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FIGURE 10: SETUP FOR EXPERIMENT 1


e fuel cell training set comes in a red suitcase with a shaped foam inlet for all components except for the base board, which you will nd in the lid together with the instruction manual and the CD. e base board houses the electrolyser, gas storage and fuel cell, experimentation modules and multimeters. e power supply and other accessories come separately. Table 2 lists the components supplied and its sym-bols used in the experiment descriptions.

Safety and Commissioning Read the notes on safety before starting with the experiments. Prepare the individual devices for the ex-periments, particularly the electrolyser, the fuel cell and the gas storage set. Use only distilled water for operation. Ensure that all connections have the correct polarity. Remove all tting caps from the sleeves and store them in the correct baseplate compartment. Be careful with the Plexiglas housing of each de-vice as they are sensitive to impact stress.

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TABLE 2: SYMBOLS USED FOR DEVICES IN THE EXPERIMENTAL SETUPS

Timer

Electrolyser

Power supply / Power regulator

Gas storage

Fuel cell

2 multimeters with 2 mm connectors

Measuring box with variable resistor

PV modules and light source

Wind machine (12V) and HAWT

O2 H2

+ -

O2H2

O2 H2

+ -

V A

O2 H2

+ -

O2H2

O2 H2

+ -

V A

O2 H2

+ -

O2H2

O2 H2

+ -

V A

O2 H2

+ -

O2H2

O2 H2

+ -

V A

O2 H2

+ -

O2H2

O2 H2

+ -

V A

O2 H2

+ -

O2H2

O2 H2

+ -

V A

O2 H2

+ -

O2H2

O2 H2

+ -

V A

O2 H2

+ -

O2H2

O2 H2

+ -

V A

O2 H2

+ -

O2H2

O2 H2

+ -

V A

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In this theme we will start with the rst two experiments only and will continue with the other experi-ments in eme 4. However, with the set of equipment supplied, the following experiments are possible:

(i) Measurement of the volume ratio of the generated gases(ii) Measurement of the generated volumes of the gases per unit of time depending on the current(iii) Determination of the power e ciency and the Faraday e ciency of the electrolyser(iv) Determination of the U/I-characteristic of the electrolyser(v) Determination of the power e ciency and the Faraday e ciency of the fuel cell(vi) Determination of the U/I-characteristic of the fuel cell

Experiments in combination with the Solartrainer Junior:(i) Operation of the electrolyser with PV cells

Experiments in combination with the Windtrainer Junior:(i) Operation of the electrolyser with a wind turbine

Experiments in combination with the Solartrainer Junior and the Windtrainer Junior:(i) Operation of the electrolyser with PV cells and wind turbine as a hybrid system(ii) Building up of a stand-alone operation net

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Exercises

Experiment 1: Measure the volume ratio of the gases produced

is experiment is designed to generate a rst idea about electrolysis and hydrogen production by using an electrolyser. Electrolysis of water is a redox reaction yielding the following overall decom-position of water into oxygen and hydrogen:

Overall reaction: 2 H2O (l) → 2H2 (g) + O2 (g)

As you can see in the above equation, the number of hydrogen molecules produced is twice the number of oxygen molecules. Assuming ideal e ciency, we can expect that the produced hydrogen gas has twice the volume of the produced oxygen gas (Figure 8). In this experiment, we attempt to examine the ratio of the produced gases and attempt to verify the above-mentioned equation as a scienti c statement. If required, please consult the student manual of your training set for more information, e.g. description of the devices and their operating instructions.

FIGURE 11: SETUP OF EXPERIMENT 1 (SCHEMATIC)


Assignment:

For this experiment you need the power supply / power regulator, the electrolyser and the gas storage units. Further, you will need two cables and two of the transparent silicon tubes. Set the experiment up as indicated in Figure 11. Ensure that all connections have the correct polarity.Use distilled water and the syringe to ll the gas storage unit up to the 0 ml mark. Ensure that the correct sleeves of gas storage unit are closed with the red tting caps (see Figure 10). is prevents the gases from steaming out of the storage unit. Set the power regulator to maximum and wait until 20 ml of hydrogen gas has been produced. Determine the gas volume of oxygen. Document your measurements in Table 3.

O2 O2H2H2

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TABLE 3: GAS VOLUMES

Gas volumes in ml

Hydrogen

Oxygen

Determine the volume of gases produced:

Volume H2 : Volume O2 = ………… : …………

Explain your ndings, making reference to the redox reaction:

…………………………………………………………………………………………………………..………

…………………………………………………………………………………………………………..………

…………………………………………………………………………………………………………..………

…………………………………………………………………………………………………………..………

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…………………………………………………………………………………………………………..………

…………………………………………………………………………………………………………..………

…………………………………………………………………………………………………………..………

…………………………………………………………………………………………………………..………

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Experiment 2: Measure the quantities of gas produced per unit time depending on current

is experiment is designed to generate further ideas about electrolysis and hydrogen production by using an electrolyser. As we have seen from the theory and in Experiment 1, electrolysis of water results in quantitative relationships of gas volumes. e ratio of produced volumes of H2 and O2 are approximately 2 : 1, and correspond with the equation of the redox reaction.

FIGURE 12: SETUP FOR EXPERIMENT 2


We could observe further relationships between other factors if we consider, for example, the quantity of electrical charge that passes through the electrolyte per unit time. is relationship is described by Faraday’s rst law of electrolysis. It states, that the gas volumes produced due to ow of charge through water are directly proportional to the quantity of the electrical current passed through it.

is can be expressed as m ∝ Q, whereas m = mass (or volume) of gases produced and Q = charge (quantity of current).

In this experiment we thus attempt to examine this relationship between quantity of charge and gas volumes, aiming to verify Faraday’s rst law.

If required, please consult the student manual of your training set for more information, e.g. description of the devices and their operating instructions.

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FIGURE 13: SETUP OF EXPERIMENT 2 (SCHEMATIC)


Assignment:

For this experiment you will need the power supply / power regulator, the timer, one multimeter, the electrolyser and the gas storage units. Furthermore, you need three cables and two of the trans-parent silicon tubes. Set the experiment up as indicated in Figure 12 and 13. Ensure that all connec-tions have the correct polarity.Use distilled water and the syringe to ll the gas storage unit up to the 0 ml mark. Ensure that the correct sleeves of gas storage unit are closed with the red tting caps (see Figure 10). is prevents the gases from steaming out of the storage unit. Set the power regulator to 0 mA and the multimeter to 2000 mA. Consult Table 4, rst column, and conduct your measurements with the six di erent current settings. In other words, set the six current values in six 100 mA steps from 0 – 500 mA and document your volume measurements per advised time interval in Table 4 below.

Calculate the values for the volume di erences (ΔV in ml) and the volume di erences per time (ΔV in ml/min) for each type of gas.

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TABLE 4: GAS VOLUMES

Hydrogen Oxygen

Current (I) mA

Time (t) in min

Volume H2

in ml∆V

in ml∆V/t

in ml/minVolume O2

in ml∆V

in ml∆V/t

in ml/min

Start End Start End

0 0 0 0 0 0 0 0 0 0

100 6 0 0

200 5

300 3

400 2

500 2

Register your calculations, i.e. volume di erences per time (ΔV in ml/min) against the six current values (0 – 500 mA) in Figure 15. Indicate the oxygen values as red dots and the hydrogen colours as blue dots in the diagram. Now nd the best- tting straight line through the points for each gas type (see Figure 14 as an example). ese two lines are so-called linear regression lines. Use red and blue for each line in Figure 15 and discuss your results. If almost all of your calculated values are on or very close to the respective regression line, one can assume that the proposed gas volumes are proportional to the current and Faraday’s rst law (m ∝ Q) is veri ed. If this is not the case, check your calculations again and/or repeat the experiment.

FIGURE 14: TWO TYPES OF GRAPHS ILLUSTRATING SIMPLE LINEAR REGRESSIONS

Image source: GIZ/S4GJ A simple linear regression uses one independent variable, and it describes the relationship between the independent variable and dependent variable as a straight line.

Independent variable

Graph A

Dep

ende

nt v

aria

ble

Independent variable

Graph B

Dep

ende

nt v

aria

ble

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FIGURE 15: REGRESSION LINES / GAS QUANTITIES VS CURRENT

∆V in

ml/

min

5 Oxygen

Hydrogen

4

3

2

1

0 100 200 300 400 500 600

Current (mA)

…………………………………………………………………………………………………………..………

…………………………………………………………………………………………………………..………

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(i) Video: TOYOTA Fuel cell - How does it work (mp4).(ii) Video: How does a fuel cell work, Naked Science Scrapbook (mp4).(iii) Video: How It’s Made Hydrogen Fuel Cells (mp4).(iv) Video: Hydrogen Fuel Cells, Ballard explains PEM fuel cells (mp4).(v) Video: PEM Fuel Cell- How it works (mp4).(vi) Comparison of Fuel Cell Technologies, US department of energy, 2016 (pdf).

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Uni

t 2.3

UNIT 2.3

BASIC PRINCIPLES OF E-MOBILITY

Introduction

Various factors such as the energy-related anthropogenic greenhouse effect and other negative environ-mental effects, including diesel-particle and nitrogen-oxide emissions have led to the fact that mobility and transportation in its current form can no longer be considered as sustainable. Globally, the aim is thus to develop and test sustainable mobility concepts, and to minimise most negative and unwanted transport impacts. For this purpose a variety of different approaches have been developed, ranging from biofuels as fuel substitute or petrol additive to electro and hydrogen powertrains as new mobility concepts. This unit introduces you to the basic principles of some alternative mobility solutions.

Unit OutcomesAt the end of this unit, you should be able to:

(i) Explain why alternative fuels are important for modern mobility concepts.(ii) List the various fuel options relevant for the automotive sector.(iii) Compare different eco-car types.(iv) Provide an eco-car market overview. (v) Explain why fuel cells provide interesting opportunities for e-mobility concepts.(vi) Provide a detailed sketch of the powertrain of a typical e-car, including key components

and their functionality.

Themes in this UnitUnit 2.3 covers the following two themes:

Theme 2.3.1 Eco-Car Types ComparedTheme 2.3.2 Essential E-Car Components and their Functions

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THEME 2.3.1

ECO-CAR TYPES COMPARED

Introduction

Climate action and the modernisation of the economy are two sides of the same coin. Subsequently, it is important to incentivise investments in innovations, as this could result in more sustainable mobility options and job-creating growth. However, our notion of mobility usually hinges on modernising individual and personalised automotive transport. Innovation however does not stop here: in the short-term more and more transport services will be shared and soon a growing number of them might even be automated. Driverless cars are also in the not too distant future. Th us, in this theme we will introduce you to the main types of alternative passenger cars, as well as other transport options.

Keywords

Sustainable mobility conceptsAlternative fuel optionsDiff erent eco-car typesHybrid electric vehicles (HEVs)Plug-in hybrid electric vehicles (PHEVs)Battery electric vehicles (BEV)Fuel cell electric vehicles (FCEV)EV market overviewGlobal marketsEU marketsChinese marketsJapanese marketsUS markets

Theme Outcomes

At the end of this theme you should be able to:(i) Explain why alternative fuels are important for modern mobility concepts.(ii) List the various fuel options relevant for the automotive sector.(iii) Explain why fuel cells provide interesting opportunities for e-mobility concepts.(iv) Compare diff erent eco-car types.(v) Provide an eco-car market overview.(vi) Provide a detailed sketch of the powertrain of a typical EV, including key components.


Sustainable Mobility ConceptsIn recent years, the automotive sector in developed countries has gained renewed momentum with the growth in the demand for passenger cars, especially in emerging countries. Making conventional trans-port sustainable is however far from being achieved. Th e transport sector continues to be one of the largest emitters of CO2 (Figures 1 and 2) and a considerable source of air pollution, severely impacting on human health, especially in urban areas. Th is needs to be considered as a cost that burdens public spending, ranging from health- all the way to cleaning services. Overall, 13% of an average European household’s budget is spent on mobility, which is very ineffi cient. In the EU, a passenger car is parked on average 92% of the time and, when the car is used, fewer than two of its fi ve seats are occupied. Furthermore, even though a car sold in 2014 was 25% more effi cient in terms of CO2 emissions than one sold in 2000, growth in travelled distance and car ownership, due to a lack of

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alternative solutions, and the increased average weight of vehicles, have excessively off set effi ciency gains. Finally, the 2015 car emission scandal in Germany and France (VW, Audi, Renault etc.) highlighted the need to reduce carbon emissions and air pollutants altogether, since CO2 is only part of the problem.

FIGURE 1: GREENHOUSE GAS EMISSIONS OF DIFFERENT SECTORS IN THE EU

Image source: S4GJ/GIZ (Data by EEA, GHG data viewer 2015)Greenhouse gas emissions of diff erent sectors in the EU (% change between 1990 and 2014)

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Transport

Residential and Commercial

Waste and Others

Energy Industries

Agriculture

Industry

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FIGURE 2: GREENHOUSE GAS EMISSIONS FROM TRANSPORT IN THE EU

Image source: S4GJ/GIZ (Data by EEA, GHG data viewer 2015) Greenhouse gas emissions from transport in the EU (2014, in %)

Th e transport sector is therefore both a curse and a blessing for most economies and societies - on the one hand, transport and logistics provides its economic lifeblood, on the other hand it hampers the very economic gains it helps to increase by being less sustainable than desired. Renewable fuel options and modern mobility concepts are thus important for the transformation of transport and the low-carbon transition. A more competitive global mobility market is emerging, and new players, including China who is the new largest passenger e-car market (mainly BEV and PHEV light-duty types) in the world, are putting pressure on established car manufacturers in Europe and the US (Figure 3).

FIGURE 3: GLOBAL MARKETS OF ELECTRIC VEHICLES (BEVS AND PHEVS)

Image source: S4GJ/GIZ (Data by Argonne National Laboratory, and OECD/IEA, 2016) – Cumulative registrations as of December 2016 by country/region

China

Europe

United States

Japan

Norway

The Netherlands

France

United Kingdom

Germany

645,708

637,552

570,182

147,488

135,276

113,636

108,065

91,627

74,754

100,000 200,000 300,000 400,000 500,000 600,000

72%

12%

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1 1 1 1

OtherDomestic aviation

Domestic navigation

International aviation

International navigation

Road transportation

Railways

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Alternative Fuel OptionsVehicles that operate primarily on fossil-based hydrocarbon fuels such as petrol or diesel historically dominated passenger car and truck sales. In the last two decades however, sales of cars that operate on alternative fuels like ethanol, natural gas and electric power have been growing. Millions of fl exible fuel vehicles, e.g. vehicles that can run on a mixture of about 85% ethanol and 15% petrol have been sold primarily in North and South America in the past decade. At the same time, a number of European and Japanese automobile manufacturers developed bi-fuel models that can run equally well on both autogas and petrol. Autogas is the common name for liquefi ed petroleum gas (LPG) when it is used as a fuel in internal combustion engines in vehicles as well as in stationary applications, such as generators. It is a mixture of propane and butane. Lastly, new models of electric vehicles (EV), including fuel cell electric vehicles (FCEV), battery electric vehicles (BEV) and plug-in hybrid electric vehicles types have also entered the market in increasing numbers.Relative to fossil-based hydrocarbon fuels, many of these fuels, depending on how they are produced, reduce overall emissions of CO2 into the atmosphere. In fact, operating a vehicle exclusively on electric power or hydrogen produces no harmful GHG emissions if these types of fuel are generated from renewable resources, including PV or wind turbine plants. Interest in hydrogen as an alternative fuel for transportation applications developed as a result of increasing social awareness of environmental degradation. Th e possibilities of reducing environmental challenges by selecting more environmentally-friendly energy systems, e.g. fuel cell systems, have a high potential for green energy conversion. Th e effi ciency of applying hydrogen-powered fuel cell technologies, for example as in FCEVs (Figure 4),depends on the characteristics of the many production steps and chains involved, which include manufacturing, distribution and the conversion of the chemical energy of hydrogen into mechanical work in a vehicle (Figure 4). Adequate evaluation of environmental impact and energy consumption throughout the overall hydrogen production and utilisation life cycle, in comparison with that of mineral fuels, is critical for making proper strategic decisions about its competitiveness in the future.Investing in transitional technologies such as hybrid cars or fully electrical solutions, be it FCEVs or BEVs, is a feasible and available option. In addition, the transition towards a low-carbon mobility system requires a sizeable amount of private and public investment to improve access to alternative fuel infrastructure capacities.

FIGURE 4: FCEV OPERATING PRINCIPLE SIMPLIFIED (SCHEMATIC)


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H2O

H2

H2

H

Hydrogen refueling

STEP 4 POWER suppliedto motor

Current

Powergeneration

Oxygen Hydrgen

Fuel cell stack Battery

High-pressurehydrogen tank

Motor

Air (Oxygen)

STEP 1 Air (oxygen) taken in

STEP 5Motor is activatedand vehicle moves

Current

STEP 2 Oxygen and hydrogensupplied to fuel cell stack

STEP 3POWER and watergenerated through chemical reaction

STEP 6Water emittedoutside vehicle

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Different Eco-Car TypesTh e electrifi cation of vehicles is a not too distant reality and a critical juncture between modernisation and sustainability. E-cars however are diff erent in terms of engine components, range, energy effi cien-cy and costs. One could, for example, diff erentiate between diff erent degrees of vehicle electrifi cation with diff erent impacts on CO2 emissions. Consequently there are indeed diff erent solutions available (Figure 5).

FIGURE 5: DIFFERENT DEGREES OF VEHICLE ELECTRIFICATION

Image source: S4GJ/GIZ (Data by Industrial Innovation for Competitiveness, JRC) Estimate of percentage of electrifi cation for each category. ICE = Internal combustion engine, HEV = Hybrid electric vehicle, PHEV = Plug-in hybrid electric vehicle, FCEV = Fuel cell electric vehicle, and BEV = Battery electric vehicle

Hybrid Electric Vehicles (HEVs)Hybrid cars can either be partly fossil fuel (or biofuel) powered or partly electric or hydrogen-powered. Most combine an internal combustion engine with an electric engine, though other variations do exist. Th e internal combustion engine is oft en either a petrol or diesel engine.

FIGURE 6: SIMPLIFIED HEV DESIGN CONCEPT (FWD SCHEMATIC)

Image source: S4GJ/GIZ Th is HEV with four-wheel drive (4WD) uses both a conventional internal combustion engine and an electric motor. Th e latter functions as an alternator, drive unit and starter motor. Both propulsion sys-tems transfer their power via a clutch to the transmission system.

ICE

HEV

PHEV

FCEV

BEV

200 40 60 80 100

Electric motor Transmission High-voltage batteryCombustionengine

Airconditioningcompressor

Power electronics High-voltage lines

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Usually, HEVs start off using the electric motor, then the mineral fuel engine cuts in as load or speed rises. Th e two motors are controlled by an internal computer which ensures the best economy for the driving conditions. Oft en the energy for the electric engine is provided by the car’s own braking system to recharge the battery. Th is is called regenerative braking, a process which converts some kinetic ener-gy into electric energy for the battery pack. Th e Honda Civic Hybrid and Toyota Camry Hybrid are both examples of HEVs, as are the older versions of Toyota’s Prius, one of the highest-volume and most suc-cessful electrifi ed cars sold until now.

Plug-In Hybrid Electric Vehicles (PHEVs)PHEVs are similar to conventional hybrids in that they have both an electric motor and an internal combustion engine, except that PHEV batteries are larger and can be charged by plugging them into an outlet. So why opt for a PHEV instead of a conventional hybrid? Well, unlike conventional HEVs, PHEVs can substitute electric power from the grid with mineral fuels. Th eir range is however limited before the combustion engine kicks in, usually between 50 – 100 km on a full charge (full electric km of range). Th ough this does not sound like a great distance, many people living in metros drive less than this dis-tance each day. Almost all car manufacturers nowadays off er PHEVs: Audi (A3 E-tron), BMW (330e, X5 xdrve40e and the sleek futuristic supercar i8), Chevy (Bolt), Chrysler (Pacifi ca), Ford (C-max energy), Hyundai (Ioniq and Sonata), Kia (Niro), Mercedes (C350, S550 and GLE550e), Mitsubishi (Outlander), Porsche (918 Spyder, Cayene S and Panamera S), Toyota (Prius Prime), and Volvo (XC90 T8).

FIGURE 7: SIMPLIFIED PHEV DESIGN CONCEPT (FWD SCHEMATIC)

Image source: S4GJ/GIZ Th is type of PHEV design is unusual in that it uses a twin drive, i.e. two electric motors. One of the electric motors is used exclusively as an alternator or starter and the other electric motor is used as an electric motor and alternator. Th e two electric motors and the combustion engine are connected to each other via clutches. Th e high-voltage battery in the PHEV can also be charged via an external outlet or charge station.

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Battery charger

High-voltage battery

Combustionengine


Power electronics 2

Charging contactHigh-voltage lines

Gearbox

Power electronics 1

Electric motor 1

Electric motor 2

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Battery Electric Vehicles (BEVs)Battery electric vehicles run exclusively on electric power via on-board batteries that are charged by plugging them into an outlet or charging station. Smaller and medium cars such as the BMW i3, Chevy Spark EV, Mercedes B Electric, Nissan LEAF, Fiat 500e, Ford Focus Electric, Kia Soul EV, Mitsubishi iMiEV, Smart Electric Drive, and VW e-Golf fall into this category, though there are many other BEVs on the market. Th ese type of vehicles have no combustion engines, but have longer electric driving ranges compared to PHEVs. Th ough there are emissions associated with charging BEVs, they never produce tailpipe emissions and are thus ideal for inner-city and city-to-city commuting. Th e BEVs currently on the market reach around 100 to 200 km per full charge, though the new generation models, such as the Tesla Model S, can travel over 350 km on a single charge. As battery technology continues to improve, BEV ranges will extend even further, off ering an even larger number of drivers the option of driving exclusively on electric power.

FIGURE 8: SIMPLIFIED BEV DESIGN CONCEPT (FWD SCHEMATIC)

Image source: S4GJ/GIZ A BEV is a purely electric-powered vehicle without a combustion engine. Th is type of BEV design uses a front-wheel drive (FWD), while other designs, such as the Tesla models, are based on rear-wheel propulsion. Please note that all electric cars are also available in 4WD, for example Tesla’s model X. Th e large battery can either be positioned as indicated in the drawing or can be located along the fl oor section. Th e battery can only be charged using regenerative braking or an external power source. Th e electric motor powers the drive chain directly via a transmission and diff erential. Th e driver operates the vehicle exactly the same way as a vehicle with an automatic transmission.

Battery charger


High-voltageheating system

Airconditionercompressor

Power electronics

Charging contactHigh-voltage linesElectric motorwith gearbox

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Fuel Cell Electric Vehicles (FCEVs)FCEVs use an electric-only motor similar to a BEV. However, instead of recharging a battery via an outlet or a charging station, FCEVs store and use hydrogen gas as fuel (Figure 4). Th e fuel cell stacks in FCEVs provide electric power to the electric motor, which powers the vehicle just like a BEV. And like BEVs, there is no emission forming from FCEV tailpipes - the only by-product is water (Figure 5). Refi lling with hydrogen can take as little as 5 minutes at a fi lling station. But similar to charging PHEVs or BEVs from non-renewable resources, producing hydrogen also generates emissions. However, producing hydrogen from renewable sources via electrolyses can produce an alternative and nearly emission-free fuel. Moreover, hydrogen fuelling infrastructure, similar to public electric vehicle charging stations, needs to be developed. With increased public policies aimed at getting more of these vehicles on the road, FCEVs can become a large part of future transportation systems. Th e Hyundai Tucson, its ix 35 and Toyota Mirai are both examples of passenger car FCEVs. Other examples include fuel cell powered busses (Toyota/Hino, Tata, Citaro/Daimler/Ballard Power, Th or Industries, Irisbus etc.), trains (Alstrom/Coradia iLint) and marine vessels such as the Zemships (see Topic 1) and submarines (HDW Type 212 and 214).

FIGURE 9: SIMPLIFIED FCEV DESIGN CONCEPT (FWD SCHEMATIC)

Image source: S4GJ/GIZ Th e FCEV is fuelled with hydrogen and obtains the electrical energy for the electric motor from a fuel cell module stack. Th ere is no combustion engine. Th e high-voltage battery can also be charged externally via a special battery charger.

EV Market Overview

Global MarketsCurrently, passenger EVs are available in over 40 markets with over 100 model specifi cations. Th ese include all global BEV and PHEV passenger car sales, light trucks in the USA/Canada and light commercial vehicles in Europe. Th e number of plug-in electric cars on the world’s roads surpassed the 2 million vehicles landmark at the end of 2016. As indicated in Figure 3, China has overtaken the EU and US in market size. In terms of electric car adaptation, Norway is the world leader and has shown how fast a national car market can shift to EVs. One in three new cars sold in Norway are now EVs, a proportion that is rising every month, spurred on by big tax breaks for new EVs and a major nation-wide investment in charging infrastructure. Norway and the Netherlands, which is also an EV market leader, both aim to

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High-voltageheating system


Power electronics

High-voltage linesElectric motor

Fuelcell

Hydrogen fuel tank

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phase out all new fossil-fuel car registrations by 2025. Th e world’s bestselling EVs in the fi rst half of 2016, according to sales statistics from EV-Volumes.Com, were the Nissan Leaf, followed by the expensive Tesla Model S. But the third and fourth spots were taken by models from the Chinese fi rm Build Your Dreams (BYD), with the Tang SUV and the Qin model. Chevrolet’s Volt took fi ft h place.

EU MarketsTh e plug-in share in Norway is off the charts (Figure 10). No other country comes close to the 24% share which Norway has achieved during 2016. Nearly one quarter of 2016 car and light commercial vehicle (LCV) sales were EVs, including a BEV share of 13% and a PHEV share of 11%. Th e Netherlands retains its 2nd rank in Europe. Among the big 5 EV markets in Europe, France clearly leads, followed by the U.K., Germany and Italy. In nearly all European markets, PHEVs grew faster than pure BEVs.

FIGURE 10: SHARES OF EV SALES IN EUROPEAN MARKETS (2016)

Image source: S4GJ/GIZ (Data by EV-Volumes.Com)

Chinese MarketsChina has not only become the biggest automotive market in the world, but also the biggest EV market in the world. In 2016, the country’s fl eet of EVs stood at around 650 000 units. You probably have not heard much about EV types sold in China - we will thus introduce you to three of China’s largest all-electric vehicle (BEV) manufacturers.

Volume Change vs2015

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Iceland

Sweden

Switzerland

Belgium

Austria

France

UK

Finland

Portugal

Germany

Luxembourg

Denmark

Ireland

Spain

Italy

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Total Europe

BEVs PHEVs

- 5 % + 163 %

+ 5 % - 52 %

- 7 % + 323 %

- 1 % + 85 %

- 12 % + 6 %

+ 45 % + 228 %

+ 122 % + 20 %

+ 26 % + 28 %

+ 4 % + 54 %

- 4 % + 191 %

+ 12 % + 109 %

+ 13 % + 21 %

+ 273 % + 309 %

- 72 % + 28 %

- 17 % + 205 %

+ 39 % + 98 %

+ 14 % + 77 %

+ 64 % - 1 %

+ 8 % + 20 %

0 % 1 % 2 % 3 % 4 % 5 %

Norway has 24 % combined share, 13 % for EV, 11 % fpr PHEV

BEV PHEV

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Plug-in hybrids still dominate the Chinese EV market with Build Your Dreams’ (BYD’s) Tang and Qin models still holding the two top sales spots with over 20 000 new deliveries each in 2016. But China’s EV market diff ers in its variety of EV models on off er. Over 60 EV models are available and 13 of these models have sold over 10 000 units in 2016. In comparison, only 5 EV models sold more than 10 000 units in the US in 2016, including Tesla’s Model S, Tesla’s Model X, Chevy’s Volt, Ford’s Fusion Energi, and the Nissan LEAF. While BYD’s plug-in hybrids dominate, some BEVs have made progress in 2016. BYD’s e6 for example is a compact cross-over with an updated powertrain, including a 82 kWh battery pack which might reach a range of over 350 km.Aft er BYD, Geely is probably the second most well-known Chinese carmaker outside of China, especially since its acquisition of Volvo. 2016 was the fi rst full year of production for its Emgrand EV, which is based on its LPG-powered sedan version. Th e BEV is equipped with a 45 kWh battery pack suffi cient for a 250 km range. Geely managed to deliver 12 000 units of this BEV in 2016. Th e company has been working with Volvo to develop a new EV platform architecture which might form the base for a successful BEV production programme.Beijing Automotive Group, also known as BAIC Group, is a state-owned automaker with joint-ventures of global car brands like Mercedes and Hyundai. Its EU260 model arrived in 2016 and held the top spot for BEVs with over 18 000 deliveries.

Overall, one can expect Chinese EV manufacturers to step up their production ranges in the next few years, as the national government is preparing to let foreign manufacturers build EVs in China without having to share technology with a local joint-venture. Th is move is likely to increase competition and consequently the quality of EVs available in the Chinese car market. Given the extremely high levels of air pollution in the inner cities, BEVs are a priority for China’s transition to electric propulsion.

Japanese MarketsTh e Japanese EV market consists almost entirely out of Japanese car manufacturers. Over the past few years, the Nissan LEAF for example has dominated the market. Although the fi rst generation Toyota Prius PHEV had respectable sales, together with the release of the Toyota Prius Prime, the second generation PHEV version of the Prius might be just as successful. One could thus expect that Nissan will produce a second generation LEAF model, with for example a 40 kWh-plus version.

US MarketsIn 2016, 30 diff erent EV models were on off er and with far over half a million EVs, the US is the third largest EV market. Five diff erent models sold at least 10 000 units, including Tesla’s Model S, Tesla’s Model X, Chevy’s Volt, Ford’s Fusion Energi, and the Nissan LEAF. More than half of all EV sales took place in California, driven by the state’s zero-emission vehicle (ZEV) mandate, which requires a certain percentage of car manufacturers’ sales to be ZEVs. California’s goal is to put 1.5 million ZEVs on the roads by 2025. Th is is a very ambitious target and it is anyone’s guess if other federal states will follow the Californian example (probably not).

Your own notes

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Exercises

1. Briefl y explain the relevance of alternative fuels for modern mobility concepts.

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2. Which alternative fuel options do you know?

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3. Briefl y explain why fuel cell technologies are relevant for e-mobility concepts.

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4. Use the following component symbols and place them (draw) in the correct positions in the vehicle drawings so that you can illustrate three diff erent EV types.

Components Symbols Components Symbols

Power electronics Battery charger

High-voltage lines

Charging contact


Fuel cell stack

Gearbox Electric motor

Combustion engine

Fuel tank

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Fuel Cell Electric Vehicle (FCEV)

Battery Electric Vehicle (BEV)

Plug-In Hybrid Electric Vehicle (PHEV)T

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(i) Video: 2017 Chevrolet Bolt EV Animation (mp4)(ii) Video: BMW i3 Electric Car Animation (mp4)(iii) Electric vehicles in Europe: gearing up for a new phase? McKinsey & Company (2016)(iv) Electro-mobility in Germany: Vision 2020 and Beyond, www.gtai.com (2015)(v) Towards Low-Emission Mobility, Driving the Modernisation of the EU Economy, EPSC

Strategic Notes, Issue 17, 20 July 2016(vi) Global EV outlook 2016, Beyond one million electric cars, OECD/IEA, 2016

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THEME 2.3.2

ESSENTIAL E-CAR COMPONENTS AND THEIR FUNCTIONS

Introduction

At fi rst glance electric vehicles (EVs) look quite similar to vehicles powered by internal combustion en-gines (ICE). Th e chassis or body of many electric vehicles on the road today come from vehicles that once contained an ICE. In most electric vehicles, even the interior has remained unchanged and almost all electric vehicles contain the same accessories as their internal combustion cousins. However, an EV can operate far more effi ciently and environmentally friendly than an ICE car, while off ering more immedi-ate torque (rotational force) and smooth power delivery compared to ICEs. Th e electric powertrain and its electronic control system, as well as the rechargeable battery supplies and its management and unique system components such as regenerative braking, makes the EV’s design unique and fundamentally dif-ferent to ICE cars. Th ere are however also major disadvantages in EV technology, for example the relative weight of batteries compared to an equivalent tank of fuel. In this last theme of Topic 2 we will introduce you to the essential components of an EV powertrain and their functions.

Keywords

EV powertrainControl systemsRegenerative brakingSingle-pedal speed controlBatteriesCharging infrastructureFCEV componentsExternal circulating humidifi er (previous system)Fuel cell boost converter High-pressure hydrogen storage tanksHydrogen refuelling

Theme Outcomes

At the end of this theme, you should be able to explain the functionality of an EV’s key components.


EV Powertrain of BEVsTh e powertrain of a motor vehicle includes by defi nition both the engine or motor and the drivetrain. Th e latter is the group of components that deliver power to the driving wheels (clutch, transmission, diff , shaft s etc.).

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FIGURE 1: POWER TRAIN, I.E. ENGINE AND DRIVETRAIN OF A CONVENTIONAL ICE CAR (FWD)

Image source: S4GJ/GIZ (adapted aft er Wikimedia, https://upload.wikimedia.org/wikipedia/commons/5/5d/Transverse_engine_layout.png)

An EV’s drive system performs the same functions as that of a vehicle powered by an internal combustion engine (Figure 1), i.e. transmitting mechanical energy to the traction wheels. However, the components used in an EV powertrain are very diff erent to a standard ICE vehicle (Figure 2).

FIGURE 2: POWERTRAIN OF A MODERN BEV

Image source: https://upload.wikimedia.org/wikipedia/commons/f/f3/Tesla_Motors_Model_S_base.JPG Tesla’s model S chassis, showing the rear powertrain in front and the battery unit located in the fl oor section between the front and the rear axles.

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DriveshaftBalancer

U-joint

Engine

U-joint U-joint

U-joint

Transmission

Fywheel / Clutch

Differential

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Modern BEVs use three-phase AC synchronous motors, composed of a magnet rotor and coil stator (see also Th eme 2.1.3 and Figure 3 below). Passing a current through the motor turns the stator into an electrical magnet and generates magnetic force. Th rough this magnetic force, the rotor turns and produces dynamic power. Th e stronger the magnetic force, the higher the torque (rotational force). Similar to wind turbine generators, as indicated in Th eme 2.1.3, the two main methods of raising magnetic force are (i) using a powerful permanent magnet, and (ii) applying a powerful current. Th ese facts also apply to electric motors in BEVs, given that a large amount of power is required to move an object as heavy as a car. Th erefore, high output lithium-ion batteries are generally used for EVs and their electric engines (Figure 3) use powerful permanent magnets to enhance magnetic force.

FIGURE 3: THREE-PHASE AC SYNCHRONOUS PANCAKE MOTOR FOR A MODERN BEV

Image source: http://wonderfulengineering.com/download-electrical-motor-images-free-here/

Currently, there are several diff erent drive system designs in use, including EVs with single large electric motors coupled to the rear wheels through a diff erential housing. Other designs utilise two smaller electric motors to power each wheel separately through independent driveshaft s. Th e most effi cient design to date utilises powertrains which are attached directly to the wheel. Th ese are referred to as in-wheel motors. By eliminating drive shaft s and diff erentials, mechanical losses between the motor and wheels are minimised. While standard ICE vehicles require transmission units to provide the vehicle with a certain torque (rotational force) at certain speeds by changing the gear input/output ratio, modern BEVs do not need sophisticated transmission technologies. In EVs the change in gear ratio is governed by the speed (RPM) at which the vehicle’s electric engine is turning. Transmission units add complexity and weight to a car and also reduce its effi ciency due to friction/mechanical losses. It is thus an advantage that EVs do not require major transmission systems, driveshaft components, and in some designs, not even axles or diff erentials. Further, the powertrain of newer EVs integrates the electric motor, inverter, reducer and power delivery module (PDM) into a smaller and lighter package. Th is integration reduces the number of moving parts, such as the driveshaft , as well as some high-voltage components, while also optimising the torque output of the motor and the reduction gear ratio.

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FIGURE 4: IN-WHEEL ELECTRIC MOTOR FOR A MODERN BEV

Image source: https://upload.wikimedia.org/wikipedia/commons/2/27/Honda_FCX_rear_in-wheel_motor_Honda_Collection_Hall.jpg

Control SystemsTh e most complex and important system in an EV is the control system. Th e control system is re-sponsible for governing the operation of the electric vehicle. Th e control system receives inputs from the operator, feedback signals from the motor module and other systems within the EV. Th e control system must receive and process data from other systems in milliseconds. Th is requires the control system to contain a microprocessor, just like a computer. Th ough no two control systems are identical, most of the feedback signals are similar. Table 1 lists common components of a control system and the feedback signals that are sent to the microprocessor.

TABLE 1: EXAMPLES OF FEEDBACK SIGNALS SENT FROM EV COMPONENTS TO THE CONTROLLER SYSTEM

Components Feedback signal

Electric motor

Winding temperature

Rotor speed (RPM)

Current (and direction of current)

Potential difference

Traction battery

Potential difference

Output current

Temperature

Accelerator pedal Potential difference as a function of pedal position

Shift selectorFWD/REV

Range selection

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Th e control system must continuously monitor the various feedback signals. For instance, if the tempera-ture of the windings in the motor gets too hot, the magnetic properties of that motor can be permanently altered or the windings may melt. By feeding a signal back to the microprocessor, the control system can limit the output of the motor if it senses a temperature rise. Th e same limiting or shutdown of any system can take place if an undesirable condition is or has occurred. Other feedback signals send information to the microprocessor to control the speed of the vehicle. Th e accelerator pedal functions in much the same way as in conventional vehicles: as the pedal is depressed, an increasing signal (potential diff erence) is sent to the microprocessor, which instructs the motor controller to increase the amount of current in the motor windings, causing the motor to spin faster. As the signal from the accelerator pedal is decreased, the motor spins slower.

Early controller versions used a simple variable resistor type of controller governing the acceleration and speed of the EV. Full current and power was drawn from the battery at all time. At lower speeds when little power was needed, high resistance was used to reduce the current to the motor. Th is resulted in a large percentage of the battery’s energy being wasted as heat dissipated by the resistor. Modern controllers adjust speed and acceleration through an electronic process called pulse width modulation (PWM). Switching devices such as very fast, high-current rated transistors rapidly interrupt, turning the fl ow of current to the motor on or off as needed. High power is achieved when the intervals (time between pulses) are very short. By increasing the time between pulses, the current is limited.

In these advanced control systems, it is possible to limit the amount of current that fl ows to the motor, based on a switch selection. Th is allows the operator to adjust to a driving style that fi ts a particular situation. For instance, if a driver needs a certain range (in km) from a single charge, the range selection can be set so that the microprocessor will limit the amount of output current from the motor controllers to a preset limit. If the preset limit is, for example, set at 100 A, the microprocessor will not allow any current above this limit to fl ow to the motors. In this mode, acceleration ability is sacrifi ced for range. If the driver is in an area where the vehicle must climb steep grades, the range selector can be set so that the maximum current capability of the motor controller and motor can be used. Th e range selection feature adds to the effi ciency of the motor controller. Th e ultimate goal of a control system is to maximise the energy stored within the traction battery and to prevent unsafe conditions from occurring within the electric vehicle.

Regenerative BrakingEvery time a vehicle’s brakes are applied and the vehicle slows down, the kinetic energy that propelled it forward is transformed and dissipates as heat, thus becoming useless for vehicle propulsion. Th is amount of energy, which could have been utilised to do work, is essentially no longer available for the application. Let us explain the matter in a more concrete way: In a traditional braking system, brake pads produce friction in the brake’s drum or disk to slow or stop the driveshaft and ultimately the vehicle. Th us, with the application of friction, kinetic energy is converted into heat energy. With regenerative brakes in EVs on the other hand, the system that drives the vehicle can also do the majority of the braking. How does this work?

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FIGURE 5: ACCELERATION AND MAGNETIC BRAKING SIMPLIFIED

Image source: S4GJ/GIZ – Stator = orange, Rotor = blue. Th e top drawing in Figure 5 illustrates acceleration in an electric motor. Th e stator’s rotating magnetic fi eld leads the rotor’s magnetic poles. Consequently, the magnetic forces act in the same direction as the shaft ’s rotation. Subsequently, the car moves or accelerates forward at a constant pace. Th e bottom drawing indicates magnetic braking. Th e stator’s rotating magnetic fi eld lags the rotor’s magnetic poles. Consequently, the magnetic forces act in the opposite direction to the shaft ’s rotation. Subsequently, the car slows down.

We outlined the working principles of motors and generators in Th eme 2.1.3, indicating that motors and generators are electromechanical energy conversion devices that have a lot in common. Consequently, a motor can be converted into a generator and vice versa. Let us quickly recall: In a motor, a current pass-es through the coil or is induced in the rotating coils, generating torque. In a generator, the mechanical turning of a coil in a magnetic fi eld produces an electromotive force (emf) in the coil. Th us, the rotation of the coil continually changes (sinusoidal) the magnetic fl ux through the coil, thereby generating a po-tential diff erence. Electric motors when operated as generators convert mechanical energy into electrical energy. Th is prin-ciple is used in regenerative braking. However, the term regenerative braking does not really explain why an EV slows down when the acceleration pedal is fully lift ed/off the fl oor (single-pedal speed control). With conventional brakes, it is friction that slows down the car. With the EV, it is magnetic force that slows down the vehicle. How does this work? Th e armature of the motor is slowed down by the force of inducing current (emf) in the windings as it passes over the opposing poles of the magnets in the stator (Figure 5). In other words, when electric power to the motor is cut, the stator’s rotating magnetic fi elds continue in the same direction as the rotor rotation, but the motor’s electronic controller directs the stator’s magnetic poles to lag behind the rotor’s opposite poles.Th e magnetic forces now pull against the direction of shaft rotation (magnetic braking).

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Power flowsinto motor

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Single-Pedal Speed ControlSingle-pedal speed control uses magnetic braking and the brake pedals only control the friction brakes, which most EVs also have as a kind of backup system in situations where regenerative braking simply cannot supply enough stopping power. Th e vehicle’s electronics must therefore decide which braking system is appropriate at which time. It is even possible for the driver to select certain presets to determine how the vehicle reacts in diff erent situations. For instance, in some vehicles a driver can select whether regenerative braking should begin immediately when the driver’s foot comes off the accelerator pedal and whether the braking system will take the car all the way to a stop or will let the car coast slightly. Oft en regenerative braking is implemented in conjunction with anti-lock braking systems (ABS), so the regenerative braking controller is similar to an ABS controller which monitors the rotational speed of the wheels and the diff erence in that speed from one wheel to another. Th e brake controller thus not only monitors the speed of the wheels, but can calculate how much torque is available to generate electric power that is fed back into the batteries. Designing a single pedal to control an EVs’ speed, i.e. either up or down or constant, is consequently mainly based on soft ware. Writing that soft ware requires some real talent. Determining the path, fre-quency and strength of electric power into and out of the motor, which in turn controls the magnetic fi elds in the motor making it go faster or slower is fully electronically controlled.Th is is the direction modern automotive engineering is taking.

FIGURE 6: SINGLE-PEDAL SPEED CONTROL MECHANISM


Coasting

Pedal travel To fl oorLift off

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BatteriesBattery prices have fallen dramatically already and in 5-10 years, they are likely to be made suffi ciently small and cost-eff ective for EVs to become aff ordable for the average consumer (Figure 7 and 8). Lithium-ion batteries are crucial for EVs and for storage solutions. It is estimated that global production capacity will increase dramatically between 2016 and 2020. Production will take place in so-called mega- or gigafactories with annual production capacities between 1 and 54 GWh. In 2016, Tesla’s fi rst gigafactory was the centre of attention for its growing momentum behind green energy, electric cars and battery production. However, as exciting as this project is, it is actually just one of multiple large-scale factories being built, most of them in China. All lithium-ion plants in China currently have a capacity of 16.4GWh, but by 2020 they will combine to a total of around 108 GWh.

FIGURE 7: ESTIMATIONS FOR BATTERY COST REDUCTIONS AND PERFORMANCE IMPROVEMENTS

Image source: S4GJ/GIZ aft er Goldman Sachs (2016)

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Battery rangekm

2015 2020

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+50%

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FIGURE 8: GROWTH PROJECTION FOR LITHIUM BATTERIES (PRODUCTION CAPACITIES IN GWH)

Image source: S4GJ/GIZ (Data by Benchmark Mineral Intelligence 2016)

FIGURE 9: CUTAWAY OF AN EV SHOWING THE FLOOR POSITION OF THE BATTERY UNIT

Image source: https://upload.wikimedia.org/wikipedia/commons/f/fe/Nissan_Leaf_cutaway_at_FutureFest_2016_01.jpg

62%

22%

USA(38 GWH)

13%3%S.KOREA

(23 GWH)

CHINA(108 GWH)

POLAND (5 GWH)

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Charging InfrastructureA high-voltage vehicle can consume between 3.3 kW and 10 kW of electrical power while the high-volt-age battery is being charged. Normal household sockets have one phase and supply a maximum current of 16 A at 230 V (AC).

P (single-phase) = U x I = 230 V x 15 A* [1 VA ~ 1 W] = 3450 W = 3.45 kW (absolute)

* In a residential setting the standard DB has a rated main circuit breaker (main switch) of 60 A. Light circuits normally have 10 A, geyser and plug circuits 15 – 20 A and the stove circuit 35 A. Th e diff erent ratings are designed to prevent overload and associated risks. Due to electrical losses during charging (power dissipation), the value must be corrected to 3.4 kW of the absolute value.

If the BEV can be charged using a three-phase socket, for example via a charging station or an industrial outlet, electrical power increases. As a result, the charging process is shorter. In a symmetrical three-phase four-wire system, the three-phase conductors have the same voltage as the system neutral. Th e voltage between line conductors is √3 times the phase conductor to neutral (potential diff erence). Th us, when calculating power (VA) in a three-phase installation, a factor of 1.73 is introduced (√3 = 1.73, 230V x √3 = 400 V).

P (three-phase) = 400 V x 15 A x 1.73 = 10380 W = 10.38 kW

FIGURE 10: TWO DIFFERENT CHARGING CABLES (400 V LEFT AND 230 V RIGHT)


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FIGURE 11: SIX DIFFERENT CONNECTOR TYPES (FROM LEFT TO RIGHT: US, EU, CHINA AND JAPAN)

Image source: S4GJ/GIZ - Across the world a large number of diff erent connector types are used for a wide range of EVs.

FIGURE 12: STANDARD VDE THREE-PHASE CONNECTOR FOR CHARGING BEVS

Image source: S4GJ/GIZ - VDE = Association for Electrical, Electronic & Information TechnologiesDuring the charging process, the vehicle body is grounded for electrical safety via the electrical connection (protective conductor). Th e safety contact of the charging connector activates the charger in the vehicle. Th e vehicle cannot be driven when the cable is connected. Th e connector contacts are scoop-proof with deep sockets to prevent connector cocking angle. In addition, a pilot line is used. Th is type of connector and charging socket on the vehicle allow a charging process to be performed safely in any weather conditions.

Phase L3

Pilot line NeutralGround

Phase L1

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FCEV Components

FIGURE 13: FCEV COMPONENTS SIMPLIFIED (SCHEMATIC)


Fuel Cell Boost Converter Th e development of a high-capacity fuel cell boost converter made it possible to increase the voltage of the motor, reduce the number of fuel cell stack cells and reduce the size and weight of the system. Inno-vations to the voltage-boost control and case structure also result in exceptionally quiet operation.

High-Pressure Hydrogen Storage TanksIn modern FCEVs, lighter weight storage tanks show a more favourable ratio of storage mass per tank weight (hydrogen storage density) than in earlier models. Th is has been achieved through innovations based on various layer structures, including a plastic liner to seal in hydrogen, a plastic layer reinforced with carbon fi bre to ensure pressure resistance and a glass fi bre layer to protect the outer surface of the tank.

Hydrogen RefuellingIn response to new hydrogen fuelling standards (Japan, the US, and Europe), fuelling times of approxi-mately 3 minutes can been achieved but vary based on ambient temperature fuelling pressure. Hydrogen fuelling under the new standards (SAEJ 2601) relies on an advanced control system, based on various feedback loops and communication fl ows (Figure 14).

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H2OO2

POWER CONTROL UNITto optimally control both

fuel cell stack output under various operational

conditions and drive battery charging and discharging

E-MOTORpowered by fuel cell

stack and battery

FUEL CELL BOOST CONVERTERis used to obtain an output with higher voltage than the input

BATTERYwhich stores energy recovered from deceleration and assists fuel cell stack output during acceleration

FUEL CELL STACK

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FIGURE 14: HYDROGEN FUELLING CONTROL SYSTEM FOR FCEVS (SIMPLIFIED)


Temperaturesensor

Pressuresensor

TankinformationInfrared raytransmitter

Nozzle

Hydrogen station

H2Hydrogen

Vehicle

High-pressurehydrogen tank Communication

functions given to

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(i) Video: EN - Bosch Regenerative Braking (mp4) (ii) Video: Hyundai Sonata Hybrid Motor Animation (mp4)

Exercises

1. Briefl y explain why electronic control systems are important for EVs.

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3. Briefl y explain the principle of regenerative braking.

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Occupational Health and Safety

Topic Overview

As discussed in the previous two levels of Renewable Energy Technologies (RET), the Occupational Health and Safety Act (OHS) regulates responsibility for health and safety at the workplace. The OHS Act not only outlines the workers’ rights in terms of health and safety, but also indicates the employ-ee’s responsibilities to avoid dangerous situations and to take appropriate precautions, e.g. against the risk of falling from heights. The RET industry segments are growing, and subsequently more and more people will be employed - health risks at the workplace will thereby also potentially increase. It is therefore important that you know and understand the relevant hazards and safe work practices relat-ed to wind turbine, fuel cell and e-mobility technologies.

Topic 3 covers the following units:Unit 3.1 Hazards and Safe Work Practices related to Wind Turbine Technologies Unit 3.2 Hazards and Safe Work Practices related to Fuel Cell TechnologiesUnit 3.3 Hazards and Safe Work Practices related to E-Mobility Technologies

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UNIT 3.1

HAZARDS AND SAFE WORK PRACTICES RELATED TO WIND TURBINE TECHNOLOGIES

Introduction

As the global wind energy industry continues to grow, new challenges begin to emerge. With an in-creasing number of workers now employed in various aspects of the wind energy sector ranging from manufacturing, logistics, installation and maintenance to project management, occupational health and safety (OHS) becomes a prime concern. Many aspects of sitting, erecting, maintaining, servicing and possibly dismantling wind turbines are unique, but the challenges compared to other industries are often the same. New technologies or working processes associated with wind energy however potentially lead to completely new hazards. Considering that wind energy is a relatively new industry sector, some work-ers may not be fully aware of the hazards that exist in this work environment. Especially the new or less experienced workers involved in processes for which they have not been appropriately trained could put their safety and health at risk.

Unit Outcomes

At the end of this unit, you should be able to:(i) Explain workplace hazards related to wind turbine technologies.(ii) Explain practicable steps to ensure employees are safe from any harm related to wind turbine

technologies.(iii) Explain how employees can be involved in health and safety processes and procedures.

Themes in this Unit

Unit 3.1 covers the following two themes:Theme 3.1.1 Hazards related to Wind Turbine TechnologiesTheme 3.1.2 Safe Work Practices related to Wind Turbine Technologies

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THEME 3.1.1

HAZARDS RELATED TO WIND TURBINE TECHNOLOGIES

Introduction

Wind energy is a renewable technology and far less harmful to the environment and climate compared to fossil fuel technologies. Just as in any other type of industry, wind energy workers can be exposed to hazards that could result in fatalities and serious injuries during the various phases of wind turbine projects. Th e objective of this theme is thus to provide an overview of the OHS challenges in the wind energy sector, focussing on small-scale turbine installations, in order to raise your awareness.

Keywords

Risks and hazardsSafety hazardsChemical hazardsTransportation hazardsConstruction hazards

Theme Outcomes

At the end of this theme, you should be able to explain workplace hazards related to wind turbine tech-nologies.


Risks and HazardsOccupational health and safety (OHS) issues associated with wind turbine technologies include work-ing in remote areas, extreme weather conditions, confi ned spaces, awkward postures, electrical risks, falls from height, musculoskeletal disorders, physical and psychosocial loads, various aspects of work organisation and exposure to dangerous substances at the production stage and also during maintenance operations. A risk can be defi ned as the probability of being injured. Hazards comprise the potential of work equipment or processes to cause harm to people or damage to property or the environment.

Safety HazardsWhen working on wind turbines there are various safety hazards that you could face, including:

(i) Electrical hazards: Workers in the wind power industry are exposed to a variety of potentially serious electrical hazards. Oft en, these include electrical shock and severe burns from arc fl ash-es. Falls and also crushing injuries have been reported as a result of these injuries.

(ii) Falling hazard: Workers who erect and maintain wind turbines work at heights and are thus ex-posed to falls with potentially dangerous consequences (serious injuries or death).

Th ese two types of safety hazards, i.e. electrical and falling hazards can result in fatalities and serious in-juries. Th e examples given below illustrate the diff erent fatalities and incidents which can occur:

(i) An excavator was being off -loaded from a trailer. Th e trailer was parked on a rural road adja-cent to an access road for a wind turbine. Th e excavator operator rotated the upper works of the machine prior to moving the machine off the trailer. During the rotation, the boom accidentally made contact with an 11kW power line. At the same time, a worker touched the trailer and re-ceived a severe electric shock. He sustained entry wounds in his hands and exit wounds in his feet and was transported and admitted for observation to a local hospital 200 km away from the work site.

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(ii) A technician was checking the electrical connections of a turbine and came into contact with a bus bar. An arc fl ash erupted, causing severe injury to the victim. He had to be taken to hospital and treated for his injuries.

(iii) A worker and two co-workers were removing and replacing a broken bolt in the turbine nacelle approximately 60 meters above the ground. As they were heating the bolt with an oxygen-acet-ylene torch, a fi re started. One worker retreated to the rear of the nacelle, away from the ladder access area. Th e two co-workers were able to descend the tower. Th e worker that was trapped by the fi re fell to the ground and struck an electrical transformer box. He was declared dead on the scene.

(iv) An electrician descended the ladder that accessed the nacelle when he slipped and fell from the ladder. He was wearing his company-furnished safety belt, but the safety lanyards were not at-tached. Both lanyards were later discovered attached to their tie-off connection at the top of the nacelle.

(v) A site foreman replacing a 400 V circuit breaker turned the rotary switch to what he thought was the open position in order to isolate the circuit breaker. However, he did not test the circuit to ensure that it was de-energised. Unfortunately, the rotary switch was now in a closed position, and the circuit breaker remained energised by backfeed from a transformer. Using two plastic-handled screwdrivers, the foreman shorted two contacts on the breaker and caused a fault. Th e resulting electric arc caused deep fl ash burns to his face and arms and ignited his shirt. He was hospitalised and remained in a specialised burn unit for some time.

Chemical HazardsChemical hazards are present when a worker is exposed to chemical substances be it solids, liquids or gases. Th ese substances can have dangerous health eff ects and could cause illnesses, skin irritation or breathing problems. Most hazardous chemicals routinely referred to in the wind turbine industry are epoxy-based resins and glass-reinforced plastic (GRP). Epoxy resins are synthetic chemicals traditionally used in paints, glue or composite materials. Th ey are oft en used in the manufacture of wind turbine sys-tem components. Th ere is a risk of contracting contact allergy and dermatitis when using these chemi-cals. Wind turbine blades are produced from GRP. Th e GRP manufacturing process is relatively simple, but worker exposure to the solvent (styrene) vapour which is released during the process, is notoriously diffi cult to control.In addition to chemical hazards from exposure to epoxy resins, styrene and solvents, there are also other harmful gases, vapours and dusts created during manufacture, installation and maintenance processes to consider. Dust and fumes from fi breglass, hardeners, aerosols and carbon can cause problems, includ-ing dermatitis, dizziness, drowsiness, sleepiness, liver and kidney damage, blisters, chemical burns and negative reproductive eff ects.

FIGURE 1: PPE REQUIRED FOR WORKING WITH RENEWABLE ENERGY TECHNOLOGIES

Image source: S4GJ/GIZ. Th e above illustrates the minimum PPE required for working with renewable energy technologies.

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OHS Risks associated with the Transportation of Wind Turbine ComponentsTh e movement and handling of some very heavy and/or large wind turbine components is a substantial logistical challenge and bears potential for health risks and/or damage to property. Transportation and handling of wind turbine components to or at the worksite is no small feat and requires considerable planning. Challenges and risks are specifi c to each location. In South Africa for instance, wind turbine installation sites are mainly located in coastal areas or in remote coastal hinterlands where the required wind conditions exist. Oft en, these sites are diffi cult to access and are far away from settlements or towns where emergency personnel and facilities are available. Th e hazards associated with the transport of wind turbine components include:

(i) People and load falls: Unsecured or inappropriately secured loads that shift are diffi cult to un-load. Sending someone up onto the trailer to handle such loads puts them at risk of falling.

(ii) Overturning vehicles: In serious cases of load shift , the vehicle can become unbalanced and overturn.

(iii) Collision with other vehicles: Oft en remote installation locations will require the use of minor roads and tracks for the transportation of wind turbine components. Due to the size of transport vehicles there will be occasions when they have to cross the centre of a road or even move along the wrong side of a roundabout, and this can put other road users at risk.

(iv) Fatigue: Fatigue caused by driving long distances without an appropriate break can potentially result in sleep-related accidents.

OHS Risks associated with the Construction of Wind TurbinesConstruction is seen as the most complicated and possibly the most dangerous stage in a wind turbine’s life cycle, as it involves the installation of major components, among them the foundation and transition pieces and the assembly of the wind turbine. It includes most of the heavy lift ing of turbine components together with the completion of multiple tasks in quick succession, and this could present a number of safety issues. Examples of hazards encountered during construction phases include:

(i) Falling structures, loads or objects during lift ing operations(ii) Falls from heights(iii) Mechanical hazards, such as contact with moving parts(iv) Ergonomic physiological eff ects as a result of heavy lift ing and repeated movements(v) Fatigue from climbing ladders or working in confi ned spaces(vi) Working with dangerous substances(vii) Time pressure(viii) Insuffi cient or lack of safety equipment(ix) Lack of competence or skills(x) Lack of communication between diff erent actors/companies involved in the operation(xi) Exposure to noise and vibration

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(i) Working in the wind safely, Guidelines on emergency arrangements including fi rst aid, Eu-ropean Wind Energy Association, 2013.

(ii) HAZARD IDENTIFICATION CHECKLIST: OCCUPATIONAL SAFETY AND HEALTH (OSH) RISKS IN THE WIND ENERGY SECTOR, European Wind Energy Association, E-Fact 80, 2015.

Exercises1. Explain the OHS risks associated with electrical work on wind turbines.

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2. Explain the OHS risks associated with chemical work on wind turbine components.

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3. Explain the OHS risks associated with the construction of wind turbines.

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THEME 3.1.2

SAFE WORK PRACTICES RELATED TO WIND TURBINE TECHNOLOGIES

Introduction

Every employer is legally required to take every measure that can be reasonably expected to avoid or lim-it all foreseeable hazards and risks to the safety and health of the employee. Employees are also expected to take appropriate measures with regards to fi rst aid for accidents, fi refi ghting and the evacuation of employees and other individuals on site and to maintain contact with the relevant external emergency services. Following industry-specifi c best practices and guidelines will clearly provide a safer work envi-ronment. However, even if industry adheres to all specifi c best practices this does not relieve employees of their duty to ensure compliance with relevant safety guidelines and best practices. Th us, in this theme we will fi rst introduce you to a basic checklist for the prevention of accidents and damage to health in the wind energy sector and secondly, indicate some prevention and mitigation measures for selected hazards.

Please note:

In RET Level 2 we introduced you to relevant safe work practices: in Th eme 3.1.1, 3.1.2, 3.1.3 and 3.1.4 we off ered some generic information on OHS, while Th eme 3.1.5 dealt specifi cally with electrical safety. Please consider consulting these sections again, as their safety information applies to wind energy appli-cations as well!

Keywords

Safety checklistsPrevention and mitigation measures for selected hazardsWorking at height Electrical installationsLift ing operationsWorking in remote locations

Theme Outcomes

At the end of this theme, you should be able to:(i) Explain practicable steps to ensure the prevention of harm to employees working with wind tur-

bine technologies.(ii) Explain how employees can be involved in health and safety processes and procedures.


Safety ChecklistsTh e best way to reduce accidents in the workplace is to be proactive in terms of prevention. Well-in-formed employees who have identifi ed and can control hazards and risks are important for every com-pany. Safety checklists are a great way to determine compliance with industry specifi c standards and to ensure consistency. Many companies use checklists as documentary evidence that they have a system in place to identify and control hazards and risks. Under the exercises you will fi nd a checklist for the prevention of accidents and damage to health in the wind energy sector (small-scale installations only). Th is checklist can be used as initial documentary evi-dence for compliance with relevant standards in a work environment or in a training facility. Th e check-list aims to illustrate some specifi c health and safety aspects and work area arrangements associated with

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the logistics, installation, maintenance and decommissioning of small-scale wind energy applications. Please note that the list is by no means exhaustive. More comprehensive information is available on the CD.

Prevention and Mitigation Measures for Selected HazardsOHS hazards during the construction, operation, and decommissioning of wind turbines are generally similar to those of most industrial facilities and infrastructure projects. Th ey may include physical haz-ards, such as working at heights, working in confi ned spaces or working with rotating machinery and falling objects. We will focus primarily on hazard prevention related to working at heights, electrical in-stallations, lift ing operations and working in remote locations.

Working at Height Working at height occurs frequently throughout all phases of construction and operation and is espe-cially relevant when it comes to maintenance. Th e main focus when managing working at height should be the prevention of a fall. However, additional hazards that may also need to be considered include falling objects and adverse weather conditions (wind speed, extreme temperatures, humidity, and wet-ness). Managing working at height activities requires suitable planning and the allocation of suffi cient resources. Preferred mitigation methods may include:

(i) Eliminating or reducing the necessity of working at height. During the planning and design phases of an installation, specifi c tasks should be assessed with the aim of removing the need to work at height, if practicable. Examples of this would include assembling structures and carry-ing out ancillary works at ground level, then lift ing the complete structure into position to the extent that is feasible and cost eff ective.

(ii) If working at height cannot be eliminated, use work equipment or other methods to prevent a fall from occurring. Collective protection systems, such as edge protection or guardrails, should be implemented before resorting to individual fall arrest equipment.

In addition to the above, the following points should be considered as methods of preventing incidents:(i) Ensure that all structures are designed and built to the appropriate standards.(ii) Wherever possible, suitable exclusion zones should be established and maintained underneath

any activities that are carried out at height to protect workers from falling objects.(iii) Ensure that all employees working at height are trained and competent in doing so and that they

are able to use the rescue systems that are in place.(iv) When working at height, all tools and equipment should be fi tted with a lanyard where possible,

and capture netting should be used if practicable.(v) Avoid conducting tower/pole installation or maintenance work during poor weather conditions,

especially if there is a risk of lightning strikes.(vi) An emergency rescue plan should be in place detailing the methods to be used to rescue workers.

FIGURE 1: FUSES AND SURGE PROTECTION FOR A SMALL-SCALE WIND TURBINE INSTALLATION (OFF-GRID)

Image source: S4GJ/GIZ.

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Electrical InstallationsWind turbine operations include working with electrical components such as generators, transform-ers, batteries and cables. Working with and around these electric components can be very dangerous, as these are capable of delivering high power to loads and thus potentially lethal electric shocks. Electrical work should therefore be carried out by qualifi ed and competent tradesmen only. However, as a general rule and before you start working with any electrical components, you must assume that all power lines are energised, unless you have confi rmed and ensured (lockout/tagout) that the power line has been de-energised. Beware that if you touch an energised power line or energised equipment, electric energy will attempt to travel through your body. When an electric current is conducted through your body, your body is in op-position (resistance) to that current, resulting in dissipation of energy, usually in the form of heat. Th is is the most basic eff ect of electrical energy on living tissue, i.e. skin, muscles, organs etc. If you become part of an electric circuit, your tissue acts as a resistor and consequently the tissue heats up. If the current is strong enough, which is almost always the case in wind turbine installations, the amount of heat gener-ated can be suffi cient to burn body tissue. A high current enters and leaves the body violently, causing burns or even blowing out an exit hole.Another eff ect of electric current on the body is electric shock (electrocution). Th is is perhaps the most signifi cant type of electrical hazard. If the strength of an electric current is suffi cient and is conducted through your body, its eff ect will overload your nervous system and prevent you from being able to ac-tuate your muscles appropriately. If you are triggered by an involuntary external current through your hands, your forearm muscles responsible for bending fi ngers contract, clenching your fi ngers into a fi st. You will be unable to let go of the live wire or conductor. Th us, stopping the current as quickly as possible is essential. However, even when the current has been stopped, victims may not regain voluntary control over their muscles for a while, as the nervous system is still in disarray. Th e muscle controlling the lungs and the heart can also be aff ected by the electric current, a condition known as fi brillation. A fi brillating heart fl utters rather than beats, and is ineff ective at pumping blood to vital organs in the body. Th e con-sequences of this can be fatal.Last but not least, we need to remind you about the danger of an arc fl ash, a short circuit explosion that fl ashes from one exposed live conductor to another or from an exposed live conductor to the ground. Th e ionised air in an arc fl ash creates very hot plasma that is electrically conductive. Oft en, the explosion lasts for only a fraction of a second but its temperatures can easily reach over 1000º C.

FIGURE 2: LOCKOUT/TAGOUT PROCEDURES

Image source: http://www.shutterstock.com/pic-189125360/stock-photo-electrical-breaker-box-locked-out-for-service-inspec-tion-or-installation-lockout-tagout.html?src=Pg62903boBiVDso523piZw-1-1&ws=1

To prevent the DC and AC circuits from inadvertently re-energising during wind turbine installation or scheduled maintenance work, documented lockout/tagout procedures should be followed both on the DC and AC side of the system.

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Managing electrical installation work requires suitable planning and the allocation of suffi cient resourc-es. One preferred mitigation method is the lockout/tagout procedure:

(i) Th e circuit or equipment must fi rst be de-energised.(ii) Every person working on the circuit or equipment must verify that the system is de-energised

prior to starting work.(iii) Every person working on the system must employ his/her own lock to isolate the energy.(iv) Th e locked system must be properly identifi ed with tags to indicate that the system must not be

tampered with.(v) As each person completes his/her task, they remove their padlock and tag.(vi) Before re-energising the system, all covers and panels must be securely reattached.(vii) A system cannot be re-energised until the fi nal lock is removed.(viii) People who perform lockout/tagout must be trained.(ix) Employees who work around locked and tagged equipment must be trained on the hazards of

electricity and the importance of leaving the locks and tags intact.

Lifting OperationsLift ing operations are oft en an integral component of the construction of any wind energy facility. Dur-ing the construction phase, components are typically assembled and transported to the site where as-sembly will take place. Th is involves using lift ing equipment to lift loads of varying dimensions and weights numerous times. Th e management of lift ing operations requires the use of competent personnel, thorough planning, eff ective communication, and a high level of supervision when carrying out a lift . Consideration should be given to the following:

(i) Ensure all relevant information is known about the load, e.g. the size, weight, method of slinging and attachment points.

(ii) Ensure all lift ing equipment is suitable, capable of supporting the load, is in good condition, and in receipt of any statutory inspections required.

(iii) Ensure all supervisors, equipment operators and slingers are trained and competent in the op-eration of lift ing equipment and intended lift ing techniques.

(iv) Exclusion zones are to be established and maintained in order to prevent any unauthorised ac-cess to lift ing areas.

(v) When lift ing large loads, ensure weather conditions are favourable for the task.

Working in Remote LocationsWhen operating in remote locations far away from hospitals or other emergency facilities, planning is vital in ensuring the safety of employees. Points to consider when planning to work in remote areas:

(i) Suitability of communication equipment available for the work crew.(ii) Th e training and competence of personnel working remotely and the readiness of all necessary

safety equipment at the location.(iii) Means for managers to track the exact location of the working crew.(iv) Local emergency plan in place.(v) Provision of suitably qualifi ed fi rst-aid-trained personnel in the work crew.

Exercises

1. Sample Hazard Identi cation ChecklistMake use of the following checklist and answer the questions, for example:(i) Does the hazard exist at the workplace?(ii) Are the hazards controlled to minimise negative infl uences on safety and health of all

workers?Answering ‘NO’ or ‘Don’t know’ to one of the following questions indicates a need for improve-ments to be made in the workplace.‘YES’ = Satisfactory‘NO’ or ‘Don’t know’ = Unsatisfactory = Urgent attention needed!

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Questions YES Don’t know NO

Has a competent safety coordinator been appointed to coordinate and oversee safety actions and to update disseminated safety informa-tion?Do supervisors/foremen provide leadership in addressing and promoting OHS? Is access to the work site controlled and are appropriate levels of supervision in place?Are there written emergency procedures and plans in place that consider major incidents, i.e. how the rescue of workers will be undertaken or how the co-ordination with the emergency services will work? Have an appropriate number of first aiders been appointed? Are there sufficient first aid kits available? Is an accident reporting system in place? Are site-specific and task-specific risk assessments being carried-out?Are all workers aware of these risk management mechanisms and procedures?Is the use of sub-contractors appropriately managed?Is there a system that identifies all hazardous substances? Is exposure to chemicals and dust eliminated or, if not possible, reduced to a minimum?Is work arranged so that manual handling operations such as lifting and carrying or repetitive manual handling of even light items, are avoided, and where not possible, reduced to a minimum? Have the frequency and methods of communication between all parties involved in the wind turbine project been considered and agreed on? Do all workers know when work will cease due to difficult weather conditions? Has working at height been considered in an appropriate risk assess-ment? Can working at heights activities be eliminated or reduced? Are all fall prevention provisions and fall arrest equipment suitable and sufficient and are they regularly inspected? Are workers appropriately trained to use these? Are all lifting operations subjected to a full risk assessment? Are workers involved in lifting operations appropriately trained? Is lifting equipment regularly inspected and suitable for the specific task? Have all operational and maintenance activities been risk assessed? Is there a safe system of work procedures in place to manage work activities on or near live electrical systems? Is there a permit to work procedures in place for electrical work? Is the electrical work carried out by qualified and competent trades-men? Are effective safety measures and procedures for electrical isolation and grounding in place?Has the fault level of the generator, transformer and cable layout been appropriately calculated and are adequate circuit breakers installed? Are wind turbines and their associated hardware compatible with the relevant network operator’s distribution code and safety rules?

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Are all electrical tools/equipment approved for work? Are workers provided with suitable PPE? Is appropriate fault protection in place to selectively disconnect faulty components? Are suitable fire extinguishers regularly checked and appropriately located, and are workers trained to use them?

2. Best Practices for Avoiding Electrical InjuryFollowing a list of best practices can protect employees from electrical injury. Score your ex-perience on each item based on your workshop practice, by using the following guidelines:3 = We/I do this consistently and purposefully2 = We/I do this sometimes, but not always - must be more consistent1 = We/I really must improve on this item

Item 3 2 1We never assume a power source is de-energised unless checked personally.We use tools and equipment only for their designed purpose.We have an emergency response plan for electrical emergencies.We periodically practice the emergency response plan for electrical emergencies.We use lockout/tagout procedures. We keep electrical enclosure doors closed and locked. We discard tools and cords that are frayed or damaged. We ground all electrical equipment. We avoid using tools with missing ground prongs. We maintain required clearances from all power lines when working at a turbine construction site.We contact utilities to locate buried power line locations. We identify safe routes where cranes and other equipment must travel.

Do you reach a score of 36?


(i) Occupational safety and health in the wind energy sector, European Wind Energy Associa-tion, 2013.

(ii) Safety and Health in Wind Energy, University of Wisconsin Oshkosh, 2011.

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Uni

t 3.2

UNIT 3.2

HAZARDS AND SAFE WORK PRACTICES RELATED TO FUEL CELL TECHNOLOGIES

Introduction

Th is unit is an introduction to the hazards associated with fuel cells and the fuels that they use. It also gives simple straightforward advice on safe work practices, aiming to minimise and control the potential risks emerging from this rapidly developing technology. We also aim to make you more aware of your responsibility to prevent an incident that could jeopardise the acceptance of these new technologies. Fuel cell vehicles (FCVs) consist mainly of three principal subsystems: the fuel cell stack, a battery and electri-cal propulsion. We will now deal with the latter two subsystems in Unit 3.2 (e-mobility).

Unit Outcomes

At the end of this unit, you should be able to:(i) Explain workplace hazards related to fuel cell technologies.(ii) Explain practicable steps to ensure the prevention of harm to employees working with fuel cell


Themes in this Unit

Unit 3.2 covers the following two themes:Th eme 3.2.1 Hazards related to Fuel Cell TechnologiesTh eme 3.2.2 Safe Work Practices related to Fuel Cell Technologies

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THEME 3.2.1

HAZARDS RELATED TO FUEL CELL TECHNOLOGIES

Introduction

Th e major hazards associated with fuel cell technologies may be divided into the following categories: (i) working with dangerous substances including fi re and explosions, (ii) electric shock, and (iii) general safety hazards, for example manual handling. As indicated in Topic 2, diff erent types of fuel cells have been developed. Th e potential hazards a fuel cell presents are heavily dependent on the nature of the fuel and electrolyte it uses. Our focus in this theme is on polymer electrolyte membrane (PEM) fuel cells (PEMFC) only, and regarding dangerous substances, fi re and explosions, we will mainly focus on hydro-gen- related hazards.

Keywords

How PEM fuel cells workFuels: Fire and explosion hazardsHydrogen properties and related hazardsFuel cells and electric hazards

Theme Outcomes

At the end of this theme, you should be able to explain workplace hazards related to fuel cell technologies.


Brief Review: How PEM Fuel Cells WorkTo better understand the potential hazards PEMFC present, we will briefl y review their basic modes of operation. A fuel cell is a device that harnesses the energy liberated when hydrogen, or a hydrogen-rich fuel, reacts with oxygen to produce water. Normally, when hydrogen and oxygen react in an uncontrolled environment, a hot fl ame and heat energy is released. In the controlled environment of a fuel cell, a fl ame is not produced, but the reaction produces electrical energy and a certain amount of heat. Like a battery, a fuel cell is an electrochemical device where an electric current is produced as a result of chemical reactions that take place at the electrodes. A battery, however, stores electric energy in the form of chemical energy and needs regular recharging or replacement, while a fuel cell continues pro-ducing electric energy as long as it is supplied with fuel. A single PEM fuel cell consists of an electrolyte membrane sandwiched between two thin porous electrodes, the anode and the cathode. Th e anode of the cell is coated with special catalysts which assist in splitting each hydrogen molecule into two protons (H+ ions) and two negatively charged electrons. Th e electrons leave the anode and travel to the cathode, providing an electric current in the external circuit. Oxygen, usually from air, is fed to the cathode of the cell where it reacts with hydrogen protons and the electrons returning from the external circuit, to pro-duce water.

Fuels: Fire and Explosion HazardsAll fuels suitable for use in fuel cells can potentially catch fi re and so present a signifi cant fi re and ex-plosion hazard. Fuels are thus called “dangerous substances” and regulations are in place that include avoiding sources of ignition and the release of dangerous substances into the workplace. All types of fuels, such as hydrogen, petrol, methane, LPG etc. can easily catch fi re and may produce an explosion. However, before an explosion can occur, a fl ammable mixture of the fuel and air must form and a source of ignition must be present to ignite it.Petrol and methane are fuels routinely used by millions of people every day. Most users are aware of the properties of these fuels and what needs to be done to handle them safely. Th e properties and risks of hy-drogen are oft en not so widely known and this can result in the risk of not being properly controlled. Th e

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hazards of hydrogen are thus discussed in some detail below, followed by a brief summary of diff erent or additional hazards of other fuels.

Hydrogen Properties and Related HazardsHydrogen is a very fl ammable gas and can cause fi res and explosions if it is not handled properly. Hy-drogen is a colourless, odourless, and tasteless gas. It is thus very diffi cult to detect a hydrogen leak with our human senses and by the time it is detected, hydrogen concentrations might have already exceeded its lower fl ammability limit. Hydrogen has some unusual properties, and if these are not known or no appropriate measures were taken, then the likelihood of hydrogen escaping and a fi re or explosion occur-ring may be greater than with many other fuels. Some of the most important properties of hydrogen that make it so volatile are:

(i) Very wide fl ammability range(ii) Very low ignition energy required(iii) Possibility of detonation(iv) Low viscosity(v) High diff usivity(vi) Much lighter than air

In the event that hydrogen catches fi re, it burns with a fl ame that is almost invisible and readily forms an explosive mixture with air. Th e range of hydrogen/air concentrations that can explode is extremely wide, much wider than almost any other fuel. Mixtures containing as little as 4% hydrogen, which is the lower explosion limit (LEL), up to as much as 75%, the upper explosion limit (UEL), will readily ignite and ex-plode. If a fl ammable mixture of hydrogen and air is allowed to form, the likelihood of an explosion oc-curring is very high, because the energy necessary to initiate a hydrogen/air mixture is very small. Hydrogen gas has a very low viscosity and it is thus very diffi cult to prevent hydrogen systems from developing leaks. Pipework that was leak tight when pressure tested with nitrogen will oft en be found to leak profusely when used on hydrogen duty. Th is property increases the likelihood of a fl ammable mixture forming. On the other hand, hydrogen is much lighter than air and is also very diff usive. When it escapes it moves upwards very rapidly. If a leak occurs in an open or well-ventilated area, its diff usivity and buoyancy reduces the likelihood of a fl ammable mixture forming in the vicinity of the leak. Almost all hydrogen is currently stored in high-pressure cylinders. Cryogenic storage of liquid hydrogen for fuel cell use may however become more widespread in the future. Hazards resulting from the very low storage temperatures used for liquid hydrogen, around -250º C, include severe cold-burns and the condensation of oxygen enriched liquid air on unprotected pipework. At atmospheric pressure, liquid hydrogen boils at -253º C and should hydrogen leak from cryogenic storage, it will be very cold and thus heavier than air. As a result, leaking gas oft en sinks initially, forming a fl ammable atmosphere at low lev-el before warming up, becoming buoyant and rising. Th is is in marked contrast to a leak of compressed hydrogen, where the accumulation of a fl ammable concentration of hydrogen is always at high level.

FIGURE 1: BASIC STRUCTURE OF A HYDROGEN SAFETY SYSTEM

Image: S4GJ/GIZ

Inci

dent

s

Figure 1: Basic structure of a hydrogen safety system

Leak

Leak detection

Ignition

Flame detection

Safety measures

Safety vents and barriers

Evaporation

Prevention measures

Damage minimisation measures

Risk

ass

essm

ent

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Fuel Cells and Electric Hazards As indicated in earlier sections, electric shock can be a life-threatening hazard and must not be over-looked in the design, operation and maintenance of fuel cells and its associated equipment. Electrical hazards usually arise from two distinct areas within fuel cell installations: the normal single- and/or three-phase AC supply into the system and the high current DC power output of the fuel cell stack. With larger units there may be a third area - the AC output of an inverter connected to the fuel cell stack.Potential and current produced by each cell element in the stack is usually quite small. However, even relatively small stacks could generate an output that may provide large electrical currents, which can be life threatening. Large fuel cell stacks, as those found in FCVs or containerised units (prime power or UPS), certainly provide large and potentially lethal currents.

Safety Issues of Hydrogen in VehiclesWe have now outlined generic hydrogen hazards related to its properties. While these generic hazards certainly apply to FCVs as well, hydrogen on board a FCV may pose specifi c safety hazards. Th e hazards related to FCVs should be considered in situations where the vehicle is inoperable, when the vehicle is in normal operation and in collisions. Hydrogen as a source of fi re or explosion may arise from the fuel storage tanks, from the fuel supply lines or from the fuel cell stack. Th e stack itself poses the lowest risk, although in a fuel cell, hydrogen and oxygen are only separated by a very thin polymer membrane. In case of a membrane rupture hydrogen and oxygen would combine, but here the fuel cell would lose its potential which should be easily detected by a control system. In that case the supply lines need to be im-mediately disconnected. Th e fuel cell operating temperature in PEMFCs is relatively low (60° to 90°C). However hydrogen and oxygen may combine on the catalyst surface and create ignition conditions. Th e potential damage would however be limited due to the small amount of hydrogen present.

In a FCV, the largest amount of hydrogen is present in the tanks. Several tank failure modes could be considered in both normal operation and collision, such as:

(i) Catastrophic tank rupture due to manufacturing defects or caused by abusive handling of the tank, stress fracture, and puncture by a sharp object or even external fi re combined with failure of pressure relief valves.

(ii) Massive leaks due to faulty pressure relief valves or induced faults in the tank wall, or puncture by a sharp object.

(iii) Low leak due to stress cracks in the tank liner, faulty pressure relief valves, faulty coupling from tank to the feed line, or impact-induced openings in the fuel line connection.

FIGURE 2: A FUEL CELL POWERED BUS MANUFACTURED BY TOYOTA (JAPAN)

Image source / Photo courtesy of Wikimedia: https://en.wikipedia.org/wiki/Fuel_cell#/media/File:TOYOTA_FCHV_Bus.jpg

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Several studies conducted on behalf of various automobile companies performed detailed assessments of probabilities of these failure modes. Th e overall conclusion of these studies indicates that most failure modes are highly unlikely. Th e greatest potential risk appears to be a slow leak in an enclosed home or public garage, where an accumulation of hydrogen could lead to a fi re or an explosion if no hydrogen de-tection or risk mitigation devices or measures such as passive or active ventilation are applied. Avoidance or minimisation of failure will be outlined in the next theme. Lastly, various testing of FCVs, hydrogen vehicle fuelling and maintenance stations by national and international agencies such as the Society of Automotive Engineers (SAE), resulted in guidelines and standards for FCV testing, e.g. Recommended Practice for Electric Fuel Cell and Hybrid Electric Vehicle Crash Integrity Testing (SAE J-1766, 2014).

FIGURE 3: HYDROGEN TANKS ON THE HONDA FCX CLARITY PLATFORM

Image source / Photo courtesy of Wikimedia: https://en.wikipedia.org/wiki/Hydrogen_tank#/media/File:Honda_FCX_plat-form_rear_Honda_Collection_Hall.jpg

Your own notes

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Exercises1. List the most important properties of hydrogen.

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2. Explain the hazards related to the properties of hydrogen.

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(i) Safety issues of hydrogen in vehicles, Frano Barbir, Energy Partners (PDF).(ii) Safety Planning for Hydrogen and Fuel Cell Projects, UNITED STATES DEPARTMENT

OF ENERGY, 2016..

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THEME 3.2.2

SAFE WORK PRACTICES RELATED TO FUEL CELL TECHNOLOGIES

Introduction

In this theme, we will give you some basic advice on safe work practices with PEM fuel cells and FCVs, aiming to minimise and control potential risks. We trust that this guidance makes you more aware of your responsibility to prevent any incidents in relation to this technology.

Keywords

Non-FCV safe work practices Hydrogen safety checklistTh e Hindenburg disasterFCV safe work and application practices

Theme Outcomes

At the end of this theme, you should be able to:(i) Explain practicable steps to ensure the prevention of harm to employees working with fuel cell

technologies.(ii) Explain how employees can be involved in health and safety processes and procedures.


Non-FCV Safe Work Practices Hydrogen safety for containerised fuel cell units (prime power or UPS) or under lab conditions, much like all fl ammable gas safety, relies on fi ve key considerations:

(i) Recognise hazards and defi ne mitigation measures(ii) Ensure system integrity, i.e. keep the hydrogen in the system(iii) Provide proper ventilation to prevent accumulation, i.e. manage discharge(iv) Ensure that leaks are detected and isolated/mitigated(v) Train personnel, ensuring that hazards and mitigations are understood and that established

work instructions are followed, i.e. manage operations

Hydrogen Safety ChecklistFor both new and experienced hydrogen users, safety checklists identify considerations necessary to en-sure safe use and installation of hydrogen fuel. Th e following checklist is rather generic and applies to all types of hydrogen systems. However, the checklist is organised using the above-mentioned key consid-erations. Examples are included to help in identifying specifi c prevention measures. Please note that the checklist is kept very basic, as it is not possible in our context to include more variables.

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Key considerations Actions

Hazard recognition and mitigation Identify risks related to hydrogen properties (flammability, ignition etc.). Follow applicable codes and standards.

Identify potential hazards from adjacent facilities and nearby activities.

Address common failures of components such as fitting leaks, valve failures, control hardware and software failures, and power outages.

Hazard isolation Store hydrogen outdoors. Ventilate indoors.

Provide horizontal separation to prevent spreading hazards to/from other systems’ structures and combustible materials.

Consider worst-case scenarios Design and select only compatible equipment capable of maximum credible pressure.

Provide relief devices that safely vent hydrogen to prevent overpressure conditions.

Perform system pressure tests to verify integrity after initial construction, maintenance, bottle replacements etc.

Protect system Mount hydrogen cylinders. Install automatic shut-off. Demobilise supply vehicles before delivery. Protect system against accidental impact and vandalism. Use warning signs. Size storage appropriately.

Manage discharge Discharge hydrogen outdoors or into a laboratory ventilation system that assures proper dilution to avoid build-up of hydrogen under ceilings/roofs and other partly enclosed spaces.

Detect and mitigate Provide automatic leak detection and shutdown/isolation. Provide alarms for actions. Detect and mitigate sensor or process control faults.

Appropriate fire protection with extinguishers, sprinklers, etc.

Manage operations Establish safe operating- and emergency proce-dures, and preventive maintenance schedules including lockout/tagout etc.

Train personnel regularly for safe work practices. Monitor incidents, near misses, compliance etc.

The Hindenburg Airship DisasterDespite the volatility of a gas like hydrogen, which combusts far more easily compared to other vehicle fuels, hydrogen FCVs are considered to be as safe as other types of cars with internal combustion engines or EV types. Hydrogen FCVs are however burdened with a somewhat unfortunate reputation, courtesy of Germany's infamous LZ 129 Hindenburg, the hydrogen-fi lled airship (zeppelin) that exploded over Lakehurst, New Jersey in 1937. Th e airship was fi lled with hydrogen for buoyancy and the theory that a hydrogen leak was ignited by a static spark is the most widely accepted crash hypothesis. Th e cause of ignition and the fi re’s initial fuel however, is still unclear and various hypotheses ranging from sabotage, static spark, lightning, engine failure etc. are still making the rounds.

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FIGURE 1: THE HINDENBURG ZEPPELIN DISASTER IN 1937

Image source / Photo courtesy of Wikimedia: https://upload.wikimedia.org/wikipedia/commons/1/1c/Hindenburg_disaster.jpg

FIGURE 2: A MODERN HYDROGEN-POWERED AIRCRAFT

Image source / Photo courtesy of Wikimedia: https://en.wikipedia.org/wiki/Hydrogen_vehicle#/media/File:Boeing_Fuel_Cell_Demonstrator_AB1.JPG - Th e Boeing fuel-cell demonstrator (Diamond HK36 Super Dimona EC-003) on display at the 2008 Farnborough Airshow

FCV Safe Work and Application Practices All safety-engineered hydrogen FCVs, such as the Toyota Mirai, the Hyundai ix35 FCEV and the Honda FCX Clarity, can be considered to be as safe as any other modern types of cars, be it with conventional internal combustion engines or other EV types. Potentially dangerous failure of FCVs in relation to hydrogen storage tanks have been outlined in the previous theme. Avoidance or minimisation of these failures includes:

(i) Leak prevention through proper system design, selection of adequate equipment and testing standards, allowing for tolerance of shocks and vibrations, locating pressure-relief devices, pro-tecting the high-pressure lines etc.

(ii) Automated leak detection(iii) Ignition prevention through automatic elimination of all sources of electric sparks (disconnect-

ing the battery bank etc.); by designing the fuel supply lines so that they are physically separated from all electrical devices as far as possible; by including both active and passive ventilation

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Lastly, there are fairly comprehensive codes and standards promulgated that address FCV fuelling and on-board vehicle safety. Th ese codes and standards include, inter alia, the SAE series of documents such as: Recommended Practice for General Fuel Cell Vehicle Safety (SAE J2578), Fuel Cell Systems in Fuel Cell and other Hydrogen Technologies (SAE J2579), Compressed Hydrogen Surface Vehicle Refuelling Connection Devices (4SAE J2600 and SAE J2601.6).

FIGURE 3: A MODERN HYDROGEN-POWERED SUV

Image source / Photo courtesy of Wikimedia: https://en.wikipedia.org/wiki/Hydrogen_vehicle#/media/File:Hyundai_ix35_fuel_cell._Spielvogel.JPG

Your own notes

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Exercises1. List and explain some key considerations to ensure hydrogen safety for containerised fuel cell units (prime power or UPS) or when working with hydrogen under lab conditions.

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2. List and explain some considerations to ensure hydrogen safety for FCVs.

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(i) Safety issues of hydrogen in vehicles, Frano Barbir, Energy Partners (PDF).(ii) Safety Planning for Hydrogen and Fuel Cell Projects, UNITED STATES DEPARTMENT

OF ENERGY, 2016..

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Uni

t 3.3

UNIT 3.3

HAZARDS AND SAFE WORK PRACTICES RELATED TO E-MOBILITY TECHNOLOGIES

Introduction

As indicated in earlier themes, the major diff erence between electric vehicles (EVs) and conventional combustion-powered vehicles can be found in the three subsystems of EVs: the battery bank (storage and supply), the electrical propulsion system (electric motor and transmission) and their electronic control systems. Regarding hazards and safe work practices, this unit will only focus on the fi rst two subsystems and particularly on high peak currents.

Unit Outcomes

At the end of this unit, you should be able to:(i) Explain workplace hazards related to e-mobility technologies.(ii) Explain practicable steps to ensure the prevention of harm to employees related to e-mobility


Themes in this Unit

Unit 3.1 covers the following two themes:Th eme 3.3.1 Hazards related to E-Mobility TechnologiesTh eme 3.3.2 Safe Work Practices related to E-Mobility Technologies

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THEME 3.3.1

HAZARDS RELATED TO E-MOBILITY TECHNOLOGIES

Introduction

Electric vehicles (EVs) represent a diff erent technology compared to conventional vehicles that are pow-ered by internal combustion engines. Th is means that new safety hazards, mainly related to the charac-teristics of high current energy storage systems and electric powered motors, may be present. While a safety engineered EV can be considered to be as safe as any other modern conventional vehicle, the EV’s unique two subsystems, i.e. the battery bank (storage and supply) and the electrical propulsion system (electric motor and transmission) do present some potential hazards. In this theme we will thus deal with the general electric safety issues in EVs.

Please note:

We already dealt with electric safety in RET Level 2, particularly in Th eme 3.1.5 and in earlier sections of this textbook. Please consider consulting these sections again as they apply to EV components and sys-tems as well!

Keywords

Battery safety hazardsElectrical hazardsChemical hazardsCumulative chemical and electrical eff ects

Theme Outcomes

At the end of this theme, you should be able to explain workplace hazards related to e-mobility technolo-gies.


Brief Review: Dangers Involved in Working with High Peak Current SystemsAs indicated in earlier sections of this textbook all your muscle reactions, conscious ones like moving your body or subconscious ones like your heartbeat, are controlled by electrical (neutral) stimulation. Th ese stimulations are conducted inside your body through nerve pathways in a similar way to currents in electrical circuits. If you come into contact with live electric components, current can fl ow through your body. Even low direct currents (DC) above approximately 30 mA can potentially cause temporary heart pulse disturbances. If higher currents enter your body, serious external and/or internal burns can occur and in some cases dangerous ventricular heart fi brillation can result. If components of an electri-cal system are short-circuited the risk of arcing (arc fl ash explosion) appears. Th is can cause serious ex-ternal burns on your body, particularly to your eyes.

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FIGURE 1: EV WARNING DECALS

Image source: S4GJ/GIZ EV warning decals are usually located on or next to high ‘voltage’ components.

Battery Safety HazardsAs discussed in previous sections, electrifi cation is the most viable way to achieve clean and effi cient transportation that is crucial for sustainable and global development. In the near future, electric vehicles (EVs) including HEVs, PHEVs, FCVs and BEVs will dominate the clean vehicle market. Key EV compo-nents are powerful battery systems designed to provide suffi cient electric power for traction. Due to their purpose (traction) these traction batteries are very diff erent compared to the ordinary rechargeable 12 V lead–acid batteries in conventional vehicles with internal combustion. Th e latter ones, so-called SLI bat-teries, are mainly required for starting, lighting, and ignition. Traction batteries on the other hand are required to power the propulsion systems of EVs. Traction bat-teries are thus designed to have a high capacity. Please note that Ah or Wh (or kWh) capacity is used to represent a battery’s capacity, while Wh/kg is used to represent specifi c energy, also called gravimetric energy density, to defi ne how much energy a battery can store per unit mass. Th ese traction batteries need to be rechargeable and thus various lithium-ion battery cathode and anode materials are available. With diff erent EV sizes, their associated battery systems diff er as well. PHEVs, for example Toyota’s Prius, are furnished with relatively small batteries, i.e. less than 10kWh. Subcompact EVs are usually equipped with 12 – 18 kWh capacity, mid-sized family sedans may have 20 – 40 kWh capacity, and luxury models are boasting 60 – 90 kWh to provide extended driving range and high performance.Th us, the amount of power EVs require for their propulsion is realised by battery-powered high ‘volt-age’ systems. EVs with high ‘voltage’ systems have components that work with voltages above 60 VDC or above 25 VAC. In fact, some luxury high performance EVs, such as Tesla’s S Model, require very high levels of electrical power, i.e. direct currents between 400 V and 650 V and very high peak currents. Considering all of these facts, we can understand that these high ‘voltage’ components, apart from on board electrical energy storage (battery), also high ‘voltage’ cables, protective relays and electric loads (e.g. motors), represent not only potential electric hazards, but also mechanical and chemical hazards.

WARNING: HIGH VOLTAGE VEHICLE

AVERTISSEMENT: CIRCUITS HAUTE TENSION DU VÉHICULE

TO REDUCE THE RISK OF POSSIBLE SERIOUS INJURY (SHOCK OR BURN) OR DEATH:

COMPONENTS MARKED WITH THE HIGH VOLTAGE SYMBOL CONTAIN HIGH VOLTAGE AND HIGH TEMPERATURESAND SHOULD BE AVOIDED, SERVICE MUST BE PERFORMED BY QUALIFIED PERSONNEL ONLY.

POUR RÉDUIRE LES RISQUES DE BLESSURES GRAVES (CHOCS OU BRULURES) OU MORTELLES:LES ÉLÉMENTS ACCOMPAGNÉS DU SYMBOLE HAUTE TENSION ONT UNE TENSION ET DES TEMPÉRATURES ÉLEVÉESET DOIVENT ÈTRE ÉVITÉS.

LA RÉPARATION ET L‘ENTRETIEN DOIVENT ÉTRE EFFECTUÉS PAR UN TECHNICIEN QUALIFIÉ SEULEMENT.

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FIGURE 2: HIGH ‘VOLTAGE’ COMPONENTS OF A TYPICAL BEV (SCHEMATIC)


Electrical HazardsCurrent fl ow through the battery and all conductive material creates heat. Th us, the heat generated by an electric current during charge/discharge processes needs to be managed by electronic thermal manage-ment systems. Th e battery also has to be protected against high electrical currents and short circuits cre-ated by internal, external or by mechanical damage. Depending on the battery design, the heat created by these high currents may exceed the global battery cooling effi ciency or create a local hot spot. Lastly, the state of charge of the battery needs to be controlled. Overcharge and over discharge generates unwanted reactions which could accelerate temperature increases in the battery. In addition, overcharge creates more chemical instability of some battery materials. Th is is the reason why electronic protection devices, generally based on potential thresholds, are required for lithium-ion batteries.

Chemical HazardsTh e substances contained inside the battery may present some chemical risks. Even though the lithium-ion battery will most probably not release any substances during normal conditions of use, a case of accidental exposure has to be considered, in particular the possibility of rupture of the casing due to me-chanical damages or internal pressure. In this case, the following hazards can be observed:

(i) Spillage: Hazards linked to the corrosive and fl ammable properties of the electrolyte(ii) Gas emission: Hazards linked to the fl ammable properties of volatile organic substances

Cumulative Chemical and Electrical EffectsIn the case of on-board energy storage systems there is a potential cumulative eff ect of chemical and electrical hazards. In some specifi c circumstances it leads to so-called ‘thermal runaway’ conditions, for example, in case of a short circuit, heat accumulation will increase the cell temperature to the point where the organic solvent leaves the cell via the vent. At this time, any hot spot may induce a fi re. Th us, the possible consequences of cumulative chemical and electrical eff ects are:

(i) Fire(ii) Toxic or harmful gas emissions: carbon monoxide (CO), organic electrolytes etc.(iii) Ejection of parts

Front drive unit (if equipped)

A/C compressor

Battery coolant heater

Cabin heaterFront junction box

DC-DC converter

High voltage cabling

Rapid splitter

Charge port Rear drive unit

Charger

High voltage battery

Figure 2: High „voltage“ components of a typical BEV (schematic)

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Exercises1. Explain electrical, chemical and cumulative hazards related to EVs!

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(i) Electric Vehicle Safe Design Checklist, Electrical Safety Working Group (ESWG), 2014.(ii) INFORMATION FOR FIRST AND SECOND RESPONDERS RESCUE AND TRAINING

MANUAL, HIGH VOLTAGE (HV) LITHIUM-ION BATTERIES, CTIF, 2014.

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THEME 3.3.2

SAFE WORK PRACTICES RELATED TO E-MOBILITY TECHNOLOGIES

Introduction

Th roughout EV development and life cycle, care must be taken to minimise potential risks for all who come into contact with these new technologies including developers, assembly line workers, service technicians, vehicle occupants and fi rst responders. In this theme we thus describe some basic on-board safety systems of EVs, focussing on vehicle service and operation.

Keywords

Recognising EVs and their safety hazardsServicing EVs safelyService tasks on EVs

Theme Outcomes

At the end of this theme, you should be able to:(i) Explain practicable steps to ensure the prevention of harm to employees related to e-mobility

technologies.(ii) Explain how employees can be involved in health and safety processes and procedures.


Recognising EVs and their Safety HazardsTh e main dangers in EV service and operation appear to be electrocution and the possibility of the car turning on accidentally while work is being performed. Th ese serious risks make safety training a prior-ity. Most EVs are easily recognisable, but some models are not necessarily distinguishable from their in-ternal combustion counterparts. In addition, some EV models, Hyundai’s Ioniq for example, come with three diff erent powertrains: HEV, PHEV and BEV. A mix-up could create serious problems for workers who are not able to tell the diff erence. To address safety concerns, most car manufacturers have devel-oped certain indicators that can help workers identify the specifi c type vehicle model. In addition, colour coded high voltage cables in EVs warn of their potential danger. Usually these are orange but some mod-els have blue cables instead.

Servicing EVs SafelyIdeally, workers should avoid contact with ‘high-voltage’ cables and components, unless the high-voltage battery has been disconnected. Many EV manufacturers have installed a safety switch or mechanism to disconnect the battery from the vehicle’s electrical system. Th e location of this will depend on the model. If working on a live electrical system cannot be avoided, proper personal protective equipment (PPE), including heavy rubber Class 0 rated gloves are required. Ordinary latex or neoprene gloves are not suf-fi cient enough to protect against a high ‘voltage’ shock. Even the Class 0 gloves need to be inspected to make sure they do not have any pin holes or cracks that would potentially allow direct contact between skins and live electric components. Other precautions include:

(i) Turning the ignition OFF and making sure that the key or key fob is away from the vehicle be-fore it is serviced or repaired.

(ii) Ensuring the READY light is not on.(iii) Waiting 15 minutes before working on the vehicle aft er the battery has been disconnected.

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FIGURE 1: LITHIUM-ION BATTERY PACK OF AN EV

Image source / Photo courtesy of Wikimedia: https://commons.wikimedia.org/wiki/File:Nissan_Leaf_012.JPG A lithium-ion battery pack of an EV with colour-coded high ‘voltage’ cables.

Service Tasks on EVsTh e following generic service tasks indicate the type of work which might need to be performed during a service of an EV:

Battery System:(i) Perform high voltage disconnect procedures.(ii) Select, test and use proper safety gloves.(iii) Select, qualify and use proper electrical testing equipment and leads.(iv) Retrieve and detect diagnostic trouble codes (DTCs), determine repairs.(v) Diagnose problems caused by damaged or failed harnesses, connectors, terminals and fuses.(vi) Diagnose high voltage battery pack malfunctions.(vii) Remove and reinstall high voltage battery pack.(viii) Test, diagnose and repair high voltage leaks/loss of isolation.(ix) Test, diagnose and repair high voltage battery pack heating and cooling systems.(x) Test, diagnose, repair or replace high voltage battery pack internal components.(xi) Test and diagnose charging problems when using EV supply equipment.(xii) Reconnect/enable high voltage system.

Drive System:(i) Perform high voltage disconnect procedures.(ii) Select, test and use proper safety gloves.(iii) Select, qualify and use proper electrical testing equipment and leads.(iv) Retrieve and detect diagnostic trouble codes (DTCs), determine repairs.(v) Diagnose problems caused by damaged or failed harnesses, connectors, terminals and fuses.(vi) Remove and install rotor from stator.(vii) Diagnose motor-rotor position sensor (resolver or encoder type).(viii) Diagnose drive/traction motor-generator assembly for improper operation, such as an inopera-

tive condition, noise, shudder, overheating, etc.(ix) Diagnose improper electrically actuated parking pawl operation, determine repairs.(x) Identify transmission fl uid and coolant fl uid requirements, verify fl uid levels.

Power electronics/controllers:(i) Perform high voltage disconnect procedures.(ii) Select, test and use proper safety gloves.(iii) Select, qualify and use proper electrical testing equipment and leads.(iv) Retrieve and detect diagnostic trouble codes (DTCs), determine repairs.

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(v) Diagnose problems caused by damaged or failed harnesses, connectors, terminals and fuses.(vi) Identify procedures necessary to establish the proper vehicle operational power mode during

service (OFF, ACCESSORY, POWER ON, READY TO DRIVE). Please note the typical operational power modes:

OFF All systems are OFF. The engine and electric drive system are powered off.

ACCESSORYSame as ACC on a conventional vehicle.In this mode the engine will not run, nor will the vehicle move under electric power.

POWER ON Equivalent to KOEO – Key ON/Engine OFF

READY TO DRIVEEquivalent to KOER – Key On/Engine Running In this mode the vehicle is ready to drive. The engine is running, or is OFF and ready to run if so commanded. The electric drive system is also ready for a drive command.

(vii) Diagnose the cause of a hybrid system warning displayed on the instrument panel and/or a driveability complaint.

(viii) Diagnose impact sensor problems, determine repairs.(ix) Diagnose AC/DC inverter overheating, determine repairs.(x) Diagnose AC/DC inverter failure, determine repairs.(xi) Replace AC/DC inverter cooling pump.(xii) Remove and install AC/DC inverter.(xiii) Diagnose failures in the data communications bus network, determine repairs.(xiv) Locate and test the ‘voltage’ level of capacitors.(xv) Diagnose, locate and safely disable/enable safety interlocks.(xvi) Diagnose failed DC/DC converter, determine repairs.(xvii) Remove and install DC/DC converter.(xviii) Test high ‘voltage’ cable integrity and loss of isolation.(xix) Perform 12-volt battery testing.(xx) Diagnose system main relay (SMR)/contactor malfunctions, determine repairs.

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Exercises1. Explain the practicable steps to ensure safe EV servicing.

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2. List and explain the relevant service tasks for the EV battery and drive system, and electronic controllers.

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(i) Ford Focus Electric Emergency Response Guide, 2013.(ii) Ford Focus Electric Battery Removal Guide, 2016.(iii) Tesla Model S Emergency Response Guide, 2016.(iv) Coda Emergency Response Guide, 2012

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Application of Wind Turbine and Fuel Cell Systems and Batteries

Topic Overview

is textbook has covered a wide range of renewable technologies and their principal backgrounds. In Topic 4 we will combine some basic mathematical skills and engineering science, and focus on experi-ments and practical work. In other words, we will be focussing on technology application and problem solving with an emphasis on practical skills, because whatever eld you as an aspiring artisan or tech-nician choose to go into, you will need to have a sound basic understanding of these skills for successful further learning, be it manufacturing, servicing or repairs. To make this RET training programme truly e ective, it is necessary to practically apply your knowledge in hands-on experiments or real-world in-stallations. Given that the latter is o en di cult to realise in some TVET colleges, we o er you modular experiments designed to demonstrate most of the aspects of small-scale wind turbine and fuel cell sys-tems covered in this textbook, albeit on a limited scale.

Topic 4 covers the following units:Unit 4.1 Connect Wind Turbine Components using Didactical Training Kits or Small-Scale

Industrial Components Unit 4.2 Connect Fuel Cell System Components using Didactical Training Kits Unit 4.3 Explain the Operation and Performance of Batteries for Renewable Energy Systems

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UNIT 4.1

CONNECT WIND TURBINE COMPONENTS USING DIDACTICAL TRAINING KITS OR SMALL-SCALE INDUSTRIAL COMPONENTS

Introduction

In Unit 2.1 we introduced you to the basic underlying principles of wind power technologies, covering some elementary aspects of kinetic and electrical energy and the laws of electromagnetism. In this unit you need to practically apply your knowledge in hands-on experiments and Do-It-Yourself (DIY) activ-ities, or even real-world installations if your college installed a small turbine, for example Kestrel’s 1 kW island system. However, given that only few colleges installed the latter, this unit will focus on modular experiments using didactical training kits.

Unit Outcomes

At the end of this unit, you should be able to:(i) Identify the components of wind turbine training sets (IKS or leXsolar respectively).(ii) Determine the output power of a generator at di erent wind speeds.(iii) Determine the output power of a generator depending on the number of blades, blade position/

pitch and blade shape.(iv) Record the V/I characteristic line of a generator at a constant number of revolutions. (v) Record the V/I characteristic line of a generator on the resistor with drive rotor at constant wind

speed.(vi) Charge an accumulator using a wind generator.(vii) Set up an isolated network.(viii) Perform testing and fault nding on all of the above setups. If available, perform testing and

fault nding on installed small-scale installations and, in hypothetical context, large-scale in-stallations.

(ix) Re ect on the installation, commissioning and servicing of electrical equipment and cabling on turbines, transformers and substations, high-voltage switchgear and erection of high- and low-tension power lines.

Themes in this Unit

Unit 4.1 covers the following two themes: eme 4.1.1 Experiments with Wind Turbine Training Sets eme 4.1.2 Build your own Wind Turbine

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THEME 4.1.1

EXPERIMENTS WITH WIND TURBINE TRAINING SETS

Introduction

e components required for building and experimenting with simple HAWT models are available in two commercial training kits, the IKS Windtrainer Junior set or the leXsolar-Wind training set. At least one of the two types of training kits need to be available at your college for RET Level 4.

Keywords

Wind power (input) Generator power (output) Blade numberBlade shapeBlade position / pitchI/V characteristicsChargingNetwork setupTesting and fault ndingInstallation, commissioning and servicingHigh-voltage switchgear High- and low-tension power lines

Theme Outcomes

At the end of this theme, you should be able to:(i) Identify the components of wind turbine training sets (IKS or leXsolar respectively).(ii) Determine the output power of a generator at di erent wind speeds.(iii) Determine output power of a generator depending on the number of blades, blade position/pitch

and blade shape.(iv) Record the I/V characteristic line of a generator at a constant number of revolutions. (v) Record the I/V characteristic line of a generator on the resistor with drive rotor at constant wind

speed.(vi) Charge an accumulator using a wind generator.(vii) Set up an isolated network.(viii) Perform testing and fault nding on all of the above setups. If available, perform testing and

fault nding on installed small-scale installations and, in hypothetical context, large-scale in-stallations.

(ix) Re ect on the installation, commissioning and servicing of electrical equipment and cabling on turbines, transformers and substations, high-voltage switchgear and erection of high- and low-tension power lines.


Training Kit ComponentsIdentify which type of training set is available at your college - either the IKS Windtrainer Junior set or the leXsolar-Wind training set. Familiarise yourself with the respective training kit and identify all in-dividual components before you start with the practical activities/experiments. As already indicated in eme 2.1.4, you need to consult the student manual of your respective training set for more information and descriptions of the components, particularly for operating instructions and experimental setup.

Please remember that all components, particularly the wind machines and the rotor parts, need to be handled with care!Please note that the rotor must not be touched during rotation/movement due to the risk of injury!Consider all safety instructions as outlined in the respective student manuals!!

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FIGURE 1: THE IKS WINDTRAINER JUNIOR SET (LEFT) AND THE LEXSOLAR-WIND TRAINING SET (RIGHT)

Image source: Dörthe Boxberg

FIGURE 2: EACH TRAINING KIT USES DIFFERENT COMPONENTS


e individual components of each training kit - either the IKS Windtrainer Junior set or the leXso-lar-Wind training set - are rather di erent regarding their design and their speci cations. Compare for example the wind machine from IKS (le ) with the one from the leXsolar (right). It is thus important that you familiarise yourself with the respective training kit and all of its individual components before you start with the practical activities.

Activity 1:Wind power input und generator output

Please consider that you may have either the IKS Windtrainer Junior set or the leXsolar-Wind training set available at your college! In the IKS Windtrainer Junior set this activity is called Experiment 1!In the leXsolar-Wind training set this activity is called Experiment 1.2. Also, see and perform the follow-ing related Experiments 1.1 and 1.3!Regarding the required components and setups, please consult the student manual of your respective training set!

Objective is activity is designed to determine the relationship between wind machine input and generator out-put, i.e. what kind of correlation exists between wind speed (input) and generator output. In other words, we want to nd out if generator ‘voltage’ (output) is indeed a function of wind power input.

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Background information In eme 2.1.2 we explained the three most crucial factors relevant to determine wind power (input) and obtained the following formula:

According to this formula wind velocity (v) is the most crucial factor for input power, followed by the swept rotor area (A) and air density (ρ). erea er, we introduced the power coe cient (Cp) as a measure of overall wind turbine e ciency. e Cp is de ned as the ratio of power output (watt, W) produced by a wind turbine divided by the total power input. When de ned in this way, the Cp represents the combined e ciency of the various turbine system components, including the turbine blades, the sha bearings and gear train, generator and power electronics. e output power of a wind turbine generator can thus be described as:

Ideally, all kinetic input energy can be converted to mechanical and subsequently electrical energy. Aero-dynamic, mechanical and electrical power losses however make this impossible - thus the introduction of the power coe cient (Cp) as a measure of overall turbine e ciency. In other words, due to aerodynamic, mechanical and electrical power losses, overall turbine e ciency is limited and optimisation of all wind turbine elements is crucial. As explained under aerodynamic e ciency in eme 2.2.1, rotor blades are crucial and elementary parts of a wind turbine. Rotor blades extract the linear kinetic energy present in the wind and convert it to rotary sha motion which again drives the generator. Much experimentation has been carried out to optimise turbine rotors regarding to blade number, blade shape, and blade posi-tion/pitch.

FIGURE 3: INSERTING THE ROTOR BLADES (IKS WINDTRAINER JUNIOR)


Pwind = (v3)

Poutput = (v3) Pwind =

x x x (v3)

Poutput = x

x x x (v3) p

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FIGURE 4: WIND TURBINE AND ROTOR BLADE SETS (LEXSOLAR)


HypothesisIt can be expected that generator output is indeed directly proportional to wind power input: the higher the wind speed, the higher the rotational rotor speed and subsequently the generator output. Conse-quently, a linear correlation between output ‘voltage’ and power input (wind speed) can be assumed.

FIGURE 5: SCHEMATIC SETUP OF ACTIVITY 1 USING IKS WINDTRAINERJUNIOR


Multimeter

Volt (U)

Ampere (I)

DCV

DCA

OFF

Powersupply

Speed control W

ind

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giea

nlag

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Gene

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Figure 5: Schematic set-up of activity using IKS Windtrainer Junior

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FIGURE 6: SCHEMATIC SETUP OF ACTIVITY 1 USING THE LEXSOLAR-WIND TRAINING SET

Image source: S4GJ/GIZ.

SetupPlease note that the rotor con guration for this activity is di erent for each training kit. IKS for example uses a rotor con guration of 4 at blades adjusted at a 45º pitch angle (see also Activity 4). e leXsolar kit requires a 3-blade con guration (air foil type blades) adjusted at a 25º pitch angle (see also Activity 4).

Conducting the activityFollow the instructions for this experiment according to your respective training set as indicated under “Assignment” in the IKS workbook (Experiment 1), and under “Execution” in the leXsolar manual (Ex-periment 1.2) and perform testing and fault nding as required. Ensure that the rotor blade locking bolts (Figure 7) are tightened with caution, not more than hand-tight. Consider that the rotor might need some time to produce consistent output values for each setting - record your measurements only when the readings on the multimeter no longer uctuate. Further, en-sure that you use the predetermined charts for speed readings (v in m/s or rpm).

FIGURE 7: CAREFULLY TIGHTEN THE ROTOR BLADE LOCKING BOLTS


Figure 5: Schematic set-up of activity 1 using the leXsolar-Wind training set

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MeasurementsUse the respective tables to document your measurements (generator ‘voltage’) for each knob division (IKS) or wind machine setting (leXsolar). Consult the predetermined charts to determine the corre-sponding wind speeds (v in m/s).

Result interpretation Enter the measured ‘voltage’ values against their respective speed values (m/s) into your respective chart. Connect the dots by drawing a line for each ‘voltage’-/ wind speed pair. Interpret the resulting line in your chart by answering the following three questions and the questions in your respective workbook:

(i) Describe the relationship between the two variables ‘voltage’ and ‘wind speed’!

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(ii) Explain the correlation between the two values!

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(iii) Can you accept the hypothesis or must you reject it? Explain your views!

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FIGURE 8: HYPOTHETICAL PROGRESSION OF THE OUTPUT CURVE IN THE LEXSOLAR CHART


FIGURE 9: HYPOTHETICAL PROGRESSION OF THE OUTPUT CURVE IN THE IKS CHART


Figure 8: Hypothetical progression of the output curve in the leXsolar chart

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5

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3

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1

0

Output in volt (V)

Wind speed in m/s

0 1 2 3 4 5 6 7 8

Figure 8: Hypothetical progression of the output curve in the IKS chart

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00 1 2 3 4 5 6 7 8 9 10

Divisions on ‚voltage‘ knob

Wind speed in m/s

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Activity 2:Generator output as a function of blade number

Please consider that you may have either the IKS Windtrainer Junior set or the leXsolar-Wind training set available at your college! In the IKS Windtrainer Junior set this activity is called Experiment 3!In the leXsolar-Wind training set this activity is titled Experiment 9.2. Also see and perform Experiment 9.1!Regarding the required components and setups, please consult the student manual of your respective training set!

Objective is activity is designed to determine whether generator output power is indeed a function of blade numbers. We want to nd out whether the number of blades, i.e. 2, 3 or 4 blades, has an in uence on the output power of the generator.

Background information Each rotor design has its unique purpose. Let us consider two extremes, the iconic multi-blade windmill rotor and the modern three-blade HAWTs. e multi-blade windmill has been and is still used to pump water. ree-blade HAWTs are used to generate electrical power. Rotor design thus depends on what you want to do with the turbine, i.e. pumping water or generating electrical power. e important aspect here is that the number of blades dictates the relationship between rotational speed of the rotor hub/sha and the torque that is produced by the rotor. e swept area of a multi-blade windmill rotor is almost fully covered with blades. As soon as wind reaches the rotor, each blade produces an angular momentum on the rotor sha (torque). Since we have a lot of blades, this momentum is multiplied. However, as the rotor begins to turn, each blade will create drag which in turn limits the rotational speed of the rotor. A mechanical pump needs a lot of torque. In this case, rotational speed is secondary and what you are really a er is creating as much torque as possi-ble - a rotor with lots of blades is thus the best choice for the job.

FIGURE 10: DIFFERENT HAWT TYPES


Today, almost 90% of installed HAWTs have three rotor blades. As we could see in multi-blade windmill rotors, with more blades on a rotor the torque would be higher, i.e. the force that creates rotation, and the slower the rotational speed because of the increased drag caused by wind ow resistance. But we can also recall that turbines used for generating electrical power need to operate at high speeds and actually don't need that much torque. us, rotors require a compromise regarding high rotational speed, minimum

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One blade Two blades Three blades Multi-blade

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stress, and the number of blades suited for a particular turbine to produce the optimal amount of power.A one-bladed turbine is the most aerodynamically e cient con guration. However, it is not very prac-tical because of stability/stress problems. Turbines with two blades o er the next best design, but are af-fected by a wobbling phenomenon. Since wind turbines must ideally always face into the wind, the blades will have to change their direction vertically when there is a shi in wind direction. is is referred to as “yawing”. In the case of a two-bladed system, when the blades are vertical, i.e. in line with the tower and the axis of rotation, there is very little resistance to the yawing motion. But when the two blades are in the horizontal position, the blades span a greater distance from the axis of rotation and experience maxi-mum resistance to yawing. As a result, the yawing motion starts and leads to stress on the turbine due to blade chattering. A turbine rotor with three blades on the other hand shows very little vibration or chatter. is is due to the fact that when one blade is in the horizontal position its resistance to the yaw force is counter-bal-anced by the two other blades. A three-bladed turbine usually represents the best combination of high rotational speed and minimum stress, and is thus a good compromise for power generation. e number of blades can thus be considered as a trade-o of many aspects which the designer has to be concerned about.

HypothesisIt can be expected that generator output power is indeed in uenced by the number of rotor blades. e higher the number of blades, the higher the torque, but, the slower the rotational speed. To produce a high amount of electric power however, turbines need to operate at high speeds. One could assume that a compromise regarding high rotational speed and minimum stress would o er the best rotor design. Consequently, a compromise of 3 or 4 blades might be the ideal rotor con guration.

FIGURE 11: THE IKS WINDTRAINER JUNIOR SETUP FOR ACTIVITY 2, 3 AND 4


SetupBoth training kits use 2, 3 and 4 blade rotor con gurations to investigate potential e ects of blade num-bers on generator output.

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FIGURE 12: SCHEMATIC SETUP OF ACTIVITY 2, 3 AND 4 USING IKS WINDTRAINER JUNIOR


FIGURE 13: SCHEMATIC SETUP OF ACTIVITY 2, 3 AND 4 USING THE LEXSOLAR-WIND TRAINING SET


Figure 13: Schematic set-up of activity 2,3 and 4 using the leXsolar-Wind training set

VA

Multimeter

Volt (U)

Ampere (I)

DCV

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Figure 12: Schematic set-up of activity 2,3 and 4 using IKS Windtrainer Junior

Multimeter

Volt (U)

Ampere (I)

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FIGURE 14: ENTER THE MEASURED VALUES INTO THE TABLES PROVIDED


Conducting the activityFollow the instructions for this experiment according to your respective training set, i.e. as indicated under “Assignment” in the IKS workbook (Experiment 3), and in the leXsolar manual (Experiment 9.2). Perform testing and fault nding as required. A certain number of blade arrangements are required and you need to make sure that the locking bolts are tightened with caution - not more than hand-tight. Consider that the individual rotor arrangements, i.e. 2, 3 and 4 blade rotor con gurations might need some time until they produce consistent output values for each setting, i.e. potential di erence (‘voltage’, V in volt, V) and current (I in milliampere, mA). Record your measurements only once the readings on the multimeters no longer change/ uctuate. Further, ensure that you use the predetermined charts for speed readings (v in m/s or rpm). Lastly, maintain similar blade shape and pitch arrangements for each rotor con guration, i.e. 2, 3 and 4 blade rotor setups.

MeasurementsUse the respective tables to document your measurements for each rotor con guration, i.e. a 2, 3 and 4 blade rotor design (Figure 14). Calculate the power output (P = V x I, in mW) and consult the predeter-mined charts for speed readings (v in m/s or rpm).

Result interpretation Enter the respective power values (mW) against their respective speed values (either m/s or rpm) for each rotor con guration (a 2, 3 and 4 blade rotor design) into your chart. Connect the dots by drawing a line for each rotor con guration. Use di erent colours for each rotor con guration, e.g. use a red pen for a 2-blade con guration, a blue pen for a 3-blade con guration and a green pen for a 4-blade con guration. If you do not have di erent colours available, mark each of the three lines with a di erent symbol, e.g. a triangle, a circle and a square. Each rotor con guration is now represented by a separate line. Each of the three lines illustrates the de-pendency of power output on rotor speed. Interpret the three resulting lines in your chart by answering the following three questions and the questions in your respective workbook:

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(i) Which rotor con gurations/rotor speeds generated the highest power outputs (mW)?

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(ii) Explain the correlation between rotor con gurations, i.e. number of blades and generated output power!

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(iv) Consider and re ect on your ndings in context of large-scale installations.

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FIGURE 15: HYPOTHETICAL PROGRESSION OF CURVES IN DIFFERENT CHARTS


e top image is a leXsolar chart example, below is an IKS chart example. Both charts show hypothetical results (power vs speed) for the three di erent rotor con gurations.

Figure 15: Hypothetical progression of curves in different charts

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Activity 3: Generator output power as a function of blade shape

Please consider that you may have either the IKS Windtrainer Junior set or the leXsolar-Wind training set available at your college! In the IKS Windtrainer Junior set this activity is called Experiment 2!In the leXsolar-Wind training set this activity is titled Experiment 13.3. Also perform Experiments 13.1 and 13.2!Regarding the required components and setups, please consult the student manual of your respective training set!

Objective is activity is designed to determine whether generator output power is indeed a function of blade shape. In other words, we want to nd out whether blade shape (i.e. near air foil cross-section, or less op-timised pro les, e.g. at or level blades), has an in uence on the output power of the generator.

FIGURE 16: CURVED ROTOR BLADES (CONCAVE / CONVEX) FROM IKS’S WINDTRAINER JUNIOR SET


Background informationModern, high capacity wind turbines typically have rotor blades with a cross-section very similar to an aeroplane or bird wing. is type of shape is also known as an air foil. An air foil has air owing around it and, as a result, is subject to aerodynamic forces which create movement. Wind turbine blades experi-ence mainly two aerodynamic forces: li and drag which appear perpendicular to each other.

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FIGURE 17: AIR FOIL CROSS-SECTION AND AERODYNAMIC FORCES


In an air foil, the upper surface of the blade is more rounded than the lower surface. A simpli ed ex-planation of li is when wind travels over the upper curved surface of the blade, it has to move faster to reach the end of the blade in time to meet the wind travelling under the lower at surface of the blade. Since faster moving air tends to rise in the atmosphere, the curved surface ends up with a low-pressure area above it and creates an e ect known as li (see the three videos provided on the resource CD on the Bernoulli’s principle). As explained in eme 2.2.1 and already in RET Level 2 ( eme 2.1.1), it is essentially the li force that creates the angular momentum in the rotor blades. Opposing the li ing force is the drag force, perpen-dicular to li and parallel to the direction of motion. Drag causes turbulence around the trailing edge of the blade as it cuts through the air. is turbulence has a braking e ect on the blade - thus we want to make this drag force as small as possible. e combination of li and drag causes the rotor to spin.

HypothesisIt can be expected that generator output power is indeed in uenced by the blades’ shape. Compared to blades with a at shape, one could assume that blades with a cross-section similar to an air foil (concave/convex) would receive more li and less drag (Bernoulli principle). us, an optimised angular rotor momentum and higher rotational speed at equal wind conditions subsequently results in higher power outputs.

SetupTo investigate potential e ects of blade shape on generator output, both training kits use two blade shapes: blades with optimised shapes (air foil type, concave/convex types) and at blades. e experi-mental setup is the same as described in Activity 2 (see Figure 11, 12 and 13).

Conducting the activityFollow the instructions for this experiment according to your IKS workbook assignment or the leXsolar manual. Perform testing and fault nding as required.Consider that the IKS assignment requires a two-blade rotor arrangement, while the leXsolar manual re-quires a three-blade arrangement. A certain number of blade arrangements are required and you need to make sure that the locking bolts are tightened with caution - not more than hand-tight.Mount the at blades rst and maintain the given angle of attack (60º). Set the given wind speed and ensure that you use the predetermined charts for speed readings (v in m/s or rpm). A er measuring ‘volt-age’ (V in volt) and current (I in milliampere) for the at blades, mount the concave/convex blades (IKS) or the air foil type blades (leXsolar) and take similar measurements in accordance to the rst round of settings.Consider that the di erent con gurations might need some time until they produce consistent output values for each setting - record your measurements only once the readings on the multimeters no longer change/ uctuate.

Figure 17: Air foil cross-selection and aerodynamic forces

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MeasurementsUse the respective tables to document your measurements (V in volt and I in milliampere) for each shape con guration. Calculate the power output (P = V x I, in mW) and consult the predetermined charts for speed readings (v in m/s or rpm).

FIGURE 18: ENTER THE MEASURED VALUES INTO THE TABLES PROVIDED AND ANSWER ALL QUESTIONS


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FIGURE 19: HYPOTHETICAL CURVE PROGRESSION (POWER VS WIND SPEED)

Image source: GIZ/S4GJA chart example for the leXsolar training kit

Result interpretation e IKS workbook requires you to answer only two questions. e leXsolar manual on the other hand requires you to enter the respective power values (mW) against the respective speed value (either m/s or rpm) of each blade type into a chart. Connect the dots by drawing a line for each rotor con guration. Use di erent colours for each of the two blade shapes, e.g. use a red pen for a at-blade con guration and a blue pen for air-foil con guration. If you do not have di erent colours available, mark each of the three lines with a di erent symbol, e.g. a triangle and a circle. Each rotor con guration is now represented by a separate line. In other words, each of the two lines illustrates the dependency of power output on blade shape. Interpret the two resulting lines in your chart by answering the following four questions and the questions in your respective workbook:

Figure 19: Hypothetical curve progression (power vs wind speed)

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(i) Which blade shapes / rotor speeds generated the highest power outputs (mW)?

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(ii) Explain the correlation between blade shape and generated output power!

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(iv) Consider and re ect on your ndings in the context of large-scale installations.

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Activity 4: Generator output power as a function of blade position/pitch

Please consider that you may have either the IKS Windtrainer Junior set or the leXsolar-Wind training set available at your college! In the IKS Windtrainer Junior set this activity is called Experiment 4!In the leXsolar-Wind training set this activity is titled Experiment 12.3. Also perform Experiments 12.1, 12.2 and 12.4!Regarding the required components and setups, please consult the student manual of your respective training set!

Objective is activity is designed to determine whether generator output power is indeed a function of blade pitch. We want to nd out whether blade pitch, i.e. the angle of attack, has an in uence on the output power of the generator.

Background information e angle of attack of a rotor blade is the pitch/tilt angle between the direction of the apparent/oncoming wind and the chord line of the blade. Tilt or pitch is the angle of incidence with respect to the oncoming wind (represented by α in the gure below).

FIGURE 20: ANGLE OF ATTACK, ANGLE OF INCIDENCE OR PITCH ANGLE


e angle of attack determines the amount of li and drag. As the pitch angle becomes larger, more li is created. As the angle becomes even larger, usually between 20º - 30º, the blade will begin to stall, thus decreasing li . If the rotor blades are in stall position (the lower at part of the blade would be facing into the wind), the blades would not be rotating.

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Figure 20: Angle of attack, angle of incidence or pitch angle

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FIGURE 21: RELATIONSHIP BETWEEN LIFT, DRAG AND ANGLE OF ATTACK (PITCH)


FIGURE 22: PITCH CONTROL ADJUSTMENTS ALONG THE CORD LINE OF ROTOR BLADES


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Figure 21: Relationship between lift, drag and sngle of attack (pitch)

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ere is an ideal range of wind speeds to produce optimal output power for each turbine type. However, wind o en uctuates in and out of this speed range, making it hard to reach a consistent power output from a turbine. us, if a rotor could adjust the pitch of its blades based on the speed of the incom-ing wind, it would be possible to produce close to ideal amounts of power across a large range of wind speeds. e relationship between wind speed, rotation rates of the turbine and the power output of the turbine is therefore critical. Consequently, it is important to keep the rotor blades at an optimum angle of attack, increasing li and e ciency. Large blades therefore o en show a twisted design throughout their length. In addition, the pitch control mechanism allows for the adjustment of pitch angles so that the blades can be turned in or out of alignment with the wind, permitting optimum power generation at di erent wind speeds.Please consider that it is certainly generally important to improve e ciency of machines and processes, but cost reductions are usually more important than pure e ciency. us, in industry the objective is usually to achieve the most economical design. Many possible solutions for an application may exist, however high e ciency with expensive designs cannot win in a cost-concerned economy.

HypothesisIt can be expected that generator output power is indeed in uenced by blade position/pitch. One could assume that the ideal stationary angle of attack corresponds strongly with a certain wind speed.

SetupUse an experimental setup as described in Activity 2 (see Figure 11, 12 and 13). To investigate potential e ects of blade position/pitch on generator output, both training kits use a three-blade con guration with various angles of attack. However, the settings of each training kit are di erent: IKS uses two di er-ent wind speeds (6 and 8 m/sec) and seven di erent angles of attack, from 0º to 90º in increments of 15º, with only one blade shape type, i.e. at blades. leXsolar on the other hand requires only one wind speed setting with ve di erent angles of attack with irregular increments, but compares two blade shapes (air foil type versus at blades) at the same time.

Conducting the activityFollow the instructions for this experiment as indicated in the IKS workbook assignment or in the leXso-lar-Wind manual. Perform testing and fault nding as required. A certain number of blade arrangements are required and you need to make sure that the locking bolts are tightened with caution - not more than hand-tight.Mount the at blades rst and start with the minimum angle of attack (IKS = 0º and leXsolar = 20º). Set the given wind speed and measure ‘voltage’ (V in volt) and current (I in milliampere). Consider that the di erent con gurations might need some time until they produce consistent output values for each set-ting. Record your measurements only once the readings on the multimeter no longer uctuate.

MeasurementsUse the respective tables to document your measurements (V in volt and I in milliampere) for each wind speed and angle of attack con guration. Calculate the power output (P = V x I, in mW).

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FIGURE 23: HYPOTHETICAL PROGRESSION OF CURVES IN DIFFERENT CHART TYPES

Image source: GIZ/S4GJ e top image is a leXsolar chart example and below is an IKS chart example. Both charts show hypo-thetical results (power vs pitch angle).

Result interpretation Both IKS and leXsolar require that you enter the respective power values (mW) against their respective angles of attack (angle of incidence) into a chart. Connect the dots by drawing a line for each wind speed (IKS) or blade pro le type (leXsolar). Use di erent colours or indicate the dots/lines with a di erent symbol, e.g. a triangle and a circle. Each of the two lines illustrates the dependency of power output on blade position/pitch. Interpret the two resulting lines in your chart by answering the following four questions and the questions in your respective workbook:

Figure 23: Hypothetical progression of curves in different chart types

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(i) With which pitch angles and at which wind speed was the highest power output (mW) generated?

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(ii) Explain the correlation between pitch angle and wind speed!

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Activity 5: I/V characteristics of generators (DC)

Please consider that you may have either the IKS Windtrainer Junior set or the leXsolar-Wind training set available at your college! In the IKS Windtrainer Junior set this activity is called Experiment 5. Also perform Experiment 6!In the leXsolar-Wind training set this activity is titled Experiment 10!Regarding the required components and setups, please consult the student manual of your respective training set!

Objective is activity is designed to record the I/V characteristics of a generator at a constant number of revolu-tions. is will allow you to determine the internal resistance at maximum power output of the genera-tor.

Background informationCurrent–voltage characteristics or I/V curves show a relationship, typically represented as a chart or graph, between the electric current (I) which ows through a circuit, device, or material, and the corre-sponding potential di erence (V) across it. e simplest I/V characteristic involves a resistor, which ac-cording to Ohm's law exhibits a linear relationship between the applied ‘voltage’ and the resulting electric current (Figure 24 and charts in Figure 26). However, factors such as resistor temperature or characteris-tics of the resistor material can produce a non-linear relationship as well.

FIGURE 24: RELATIONSHIP BETWEEN ‘VOLTAGE’ (V ) AND CURRENT (I ) IN A CIRCUIT

Image source: GIZ/S4GJ e relationship between ‘voltage’ (V) and current (I) in a circuit of constant resistance (R) would pro-duce a straight line and a slope equal to the value of the resistance.

e relationship between potential di erence (V), current (I) and resistance (R) forms the basis of Ohm’s law. us, an increase of potential di erence in a linear circuit of xed resistance will cause an increase of current. Similarly, if we decrease potential di erence, current values will increase as a result. Likewise,

Figure 24: Relationship between „voltage“ (v) and current (I) in a circuit

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if we increase resistance, current decreases for any given ‘voltage’ and if we decrease resistance, current values will increase. Consequently, we can see that current ow around a circuit is directly proportion-al (V) to potential di erence (V↑ causes I↑), but inversely proportional (I/∝) to resistance (R↑ causes I↓).Similar to larger industrial generators, our mini-DC-generator in the turbine has internal resistance due to the resistance of its winding (and if it is not brush-less, the resistance of the brush contacts). When current ows through the generator, ‘voltage’ will drop due to its internal resistance and will consequent-ly reduce the available power output. Maximum power output of a generator can be achieved when load resistance equals internal resistance. is statement is expressed by the maximum power transfer theo-rem stating that to obtain maximum external power from a source (whether a battery or generator/dynamo) with a nite internal resistance, the resistance of the load must equal the resistance of the source as viewed from its output terminals.

HypothesisConsidering the above proportionalities between potential di erence (V), current (I) and resistance (R), we can expect that maximum power output of a turbine generator depends, among other things, on load resistance.

SetupFor the IKS training kit, use the experimental setup as indicated in Figure 11, 12 and 13 (identical to activity 2, 3 and 4 setups). IKS uses a 4-blade rotor, at blades with 60º angles of attack and a constant wind speed of around 1000 rpm, i.e. at a generator ‘voltage’ of 1.5 V. Current and ‘voltage’ are measured at di erent load settings (resistance, R in ohm, Ω) from 0 Ω up to 100 Ω and the power output calculated (P = V x I, in mW). e leXsolar setup (Figure 25) requires a 3-blade rotor with air foil type blades and a 25º angle of attack. Initially, set the potentiometer to maximum (∞) by using the 1 kΩ and the 100 Ω knob. By using the po-tentiometer module, set di erent potential di erence values, i.e. start your measurements at a ‘voltage’ setting of 5.3 V and reduce ‘voltage’ in steps of 0.2 V, i.e. 21 steps from 5.3 V to 1.4 V and three 0.5 V steps from 1 V to zero volt. Measure current (I) and calculate load resistance (R = V/I in Ω) and power output (P = V x I, in mW) based on your current measurements and ‘voltage’ settings.

Conducting the activityFollow the instructions for this experiment as indicated in the IKS workbook assignment or in the leX-solar-Wind manual. Perform testing and fault nding as required. Keep in mind that the multimeter readings might need some time until they produce consistent output values for each setting. Record your measurements only once the current and ‘voltage’ readings on the multimeters are more or less constant.

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FIGURE 25: SCHEMATIC SETUP OF ACTIVITY 5 USING THE LEXSOLAR WIND TRAINING SET


MeasurementsUse the respective tables to document your measurements (V in volt and I in milliampere). Calculate the power output (P = V x I, in mW). Enter the respective current (mA) and ‘voltage’ (V) values into a I/V chart. Connect the dots by drawing a line. Next, enter the calculated power output values (mW) versus the measured ‘voltage’ (V) values into the chart. Connect the dots by drawing a I/V regression line and a power output curve. Use di erent colours for the I/V characteristics and the power output curve.

Result interpretation Both IKS and leXsolar manuals require that you interpret your results, i.e. the charts. Try to do this by answering the following ve questions and the questions in your respective workbook:

(i) Do your I/V measurements allow drawing a regression line into the chart? Explain the correla-tion between your I/V measurements!

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(ii) Explain why generator ‘voltage’ decreases by decreasing resistance. Consider in your answer that reduced resistance increases current, which again results in an increase of self-induced ‘voltage’ (emf) which opposes the generator ‘voltage’.

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Figure 25: Schematic set-up of activity 5 using the leXsolar-Wind training set

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(iii) If you have drawn a bell-shaped curve representing the power output, depending on generator ‘voltage’, map the point of maximum output and then determine load resistance at this point. You can calculate internal resistance by relating your point of maximum output to your I/V line. us, internal resistance (R = V/I in Ω) for the IKS generator is: 720 mV / 80 mA = 9 Ω and internal resistance of the leXsolar generator is around 35 Ω. Compare the load resistance values, the point of maximum output, with your generator’s internal resistance.

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(iv) Can you accept the hypothesis or must you reject it? Explain your views!

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FIGURE 26: HYPOTHETICAL PROGRESSION OF I/V LINES AND OUTPUT CURVES IN DIFFERENT CHART TYPES

Image source: GIZ/S4GJ e image on top is a leXsolar chart example and below an IKS chart example. Both charts show hypo-thetical results for an I/V line and a power output curve.

Figure 26: Hypothetical progression of I/V lines and output curves in different chart types

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Activity 6: Charging/discharging using accumulators and designing a DC island system

Please consider that you may have either the IKS Windtrainer Junior set or the leXsolar-Wind training set available at your college! In the IKS Windtrainer Junior set this activity is called Experiment 10. Also perform Experiments 11 and 12!In the leXsolar-Wind training set this activity is titled Experiment 6.1. Also, perform Experiments 6.2, 7.1 and 7.2!Regarding the required components and setups, please consult the student manual of your respective training set!

Objective is activity is designed to examine storage and discharge characteristics of an accumulator using a wind generator.

Background informationSpecial application of energy storage in connection with wind energy systems can be found in so-called island systems. In this case, the electrical energy generated by wind turbines, for example with the rel-atively small Kestrel 1 kW turbine, is stored in large accumulators - in the case of the Kestrel setup in a 102 Ah, 48 V battery bank - to be available for consumption in case insu cient wind power limits imme-diate power generation. us, wind energy island systems, o en in combination with PV systems, allow independent power supply. ese type of systems are most o en used in remote areas where grid power is not at all or not easily available, for example on isolated farms, for telecommunication or medical sta-tions, on drilling platforms, or in inaccessible mountain regions. In the following experiments capacitors are used as accumulators to illustrate the principle of charging and discharging via a wind energy sys-tem.

HypothesisWind energy systems are suitable as island systems to supply power either immediately or via stored power in accumulators (capacitors).

SetupFor the IKS training kit, use the experimental setup as indicated in Figure 27 and 28 (charging and dis-charging). IKS uses a 4-blade rotor, convex blades with 60º angles of attack and a constant wind speed of around 8 m/s. IKS uses a so-called GoldCap capacitor which is a device with high capacity. e leXsolar setup (Figure 29) requires a 3-blade rotor with air foil type blades and a 25º angle of attack, the capacitor and the LED module. Observe the polarity when setting up the experiment. Consider that at the start of the experiment, the LED is not connected to the setup. Ensure that cable 1 and cable 2 are plugged into the respective sockets (Figure 29).

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FIGURE 27: SCHEMATIC SETUP OF ACTIVITY 6 USING IKS WINDTRAINER JUNIOR


Figure 27: Schematic set-up of activity 6 using IKS Windtrainer Junior

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FIGURE 28: DETAILED VIEW FOR ACTIVITY 6 CONNECTIONS USING IKS’S CAPACITATOR MODULE


FIGURE 29: SCHEMATIC SETUP OF ACTIVITY 5 WITH THE LEXSOLAR WIND TRAINING SET


Figure 28: Detailed view for activity 6 connections using IKS´s capacitator module

Connections for step A, B and C Connections for step D

Gold cap Gold cap

1 2

Figure 29: Schematic set-up of activity 5 with the leXsolar-Wind training set

10 cm

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Conducting the activityFollow the instructions for this experiment as indicated in the IKS workbook assignment or in the leXso-lar-Wind manual. Perform testing and fault nding as required. Consider that the multimeter readings might need some time until they produce consistent output values for each setting. Record your mea-surements only once the current and ‘voltage’ readings on the multimeters are more or less constant.

MeasurementsOnly IKS requires measurements (in Step F). Use the respective table and chart to document and plot your measurements (V in volt, I in milliampere and t in min).

Result interpretation Both IKS and leXsolar manuals require that you interpret your results by answering the questions in your respective workbook. A er you have answered these questions review the hypothesis. Can you ac-cept or must you reject it? Explain your views!

………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………


(i) IKS workbook(ii) leXsolar manual

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THEME 4.1.2

BUILD YOUR OWN WIND TURBINE (DIY)

Introduction

As indicated in earlier sections such as eme 2.1.4, we can distinguish between di erent wind turbine types. Based on one of the most common criteria, the position of the rotor axis, we can for example distinguish between horizontal axis wind turbines (HAWT) and vertical axis turbines (VAWT). In this theme we will introduce you to the idea of building your own wind turbine. Given that we would like to encourage you to build a fully functional model which gives you the chance to apply your knowledge and practical skills, we suggest building a VAWT, more speci cally a model that resembles a Savonius type of model. is design is based on the Finnish engineer S.J. Savonius’ (1922) idea of mounting two half-cylinders on a vertical sha . is type of turbine can accept wind from any direction and its aerodynamics operates on the basis of drag: one half-cylinder creates more drag in moving air than the other, causing the sha to spin. One advantage is that you can quite easily design and build all major parts for both the mechani-cal components (frame, sha and half-cylinders) and the electrical components (stator and rotor plate).

FIGURE 1: DIY – BUILDING A HAWT AND/OR A VAWT (SAVONIUS MODEL)


Theme Outcomes

At the end of this theme, you should be able to:(i) Understand the design for a VAWT (Savonius model). (ii) Construct all required components for a Savonius model using basic tools and materials.(iii) Assemble all components into a functional model.(viii) Perform testing and fault nding on the proposed setups.

Background information

In Unit 2.1 we introduced you to the basic underlying principles of wind power technologies, covering some elementary aspects of kinetic and electrical energy and the laws of electromagnetism. In this theme you need to practically apply your knowledge in hands-on Do-It-Yourself (DIY) activities. is model uses a relatively simple and e cient way to generate electric power: it uses a stator (stationary eld) and a rotor (the rotating eld or armature). e model is thus a simple machine that operates through the interaction of magnetic ux and electric current, based on the fundamental principle of electromagnetic induction (see eme 2.1.3). is is the same basic principle used in almost all wind turbines, even in the large-scale commercial ones.

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DurationIf all materials are available, you will most probably need around 4 hours to complete the model.

Safety! Some of the required tools, e.g. utility knives and jigsaws, can be potentially dangerous. So please use them with caution! e blades of most utility knives can be extended and locked into place. Extend the blades only far enough to cut all the way through the material, no further, and make sure they are locked into position while cutting. Also, remember that hot glue can cause serious burns when coming in con-tact with your skin. e permanent magnets you will be using can cause serious damage to electronic devices. Be sure to keep them away from credit cards, USB sticks or any other devices on which informa-tion is stored magnetically/electronically.

Tools and materialsFor this activity a number of tools (Figure 2) and materials (Figure 3) are required. For each construction step we will indicate the required materials.

FIGURE 2: SOME OF THE TOOLS YOU WILL NEED FOR THIS ACTIVITY


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FIGURE 3: THE MATERIALS YOU NEED


FIGURE 4: THE TWO VAWT DESIGNS ONCE ASSEMBLED


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Construction Step 1: Building the frame As you can see in Figure 4, 11 and 12, our VAWT (Savonius) model requires only a simple frame consist-ing of a baseplate, two stands, a cross-beam and a central axis. e latter functions as the sha for the turbine blades (two half-cylinders) and the vertical- and cross-beams can be built by using three 22 mm x 22 mm square dowels. e baseplate will not only function as a foundation, but also as the stator (sta-tionary eld).

TABLE 1: MATERIAL REQUIRED FOR STEP 1

Quantity Item Description and Sources

1 Wooden base Any type of wood, e.g. plywood or pine boards with 150 mm x 300 mm x 20 mm dimensions can serve as the VAWT base.

3 Square dowelsThese should be around 22 mm x 22 mm and are required to build the frame. You need two 300 mm pieces for the vertical parts and one 200 – 250 mm piece for the cross-beam.

4 Wood screws Required for joining the frame elements to the baseplate.

1 Round dowel The dowel Ø 6 mm serves as the central shaft for the two half-cylinders and thus forms the turbine’s rotor blades.

2 WasherThe washers aim to keep the central shaft in place and are fixed to the central beam and the baseplate. The washer hole diameter shall not be more than 7 - 8 mm.

1 Hot glue One cartridge should be sufficient.

Read the following instructions carefully before you start working:(i) Prepare the baseplate: Use a pencil, ruler and compass and draw the following pattern onto the

plate (Figure 5).

FIGURE 5: PATTERN ON THE BASEPLATE

Image source: GIZ/S4GJ Draw this circular pattern onto the base board for coil positioning and vertical square dowels

(ii) Sharpen one end of the round dowel (6 mm) using a pencil sharpener. Place a short wood screw into the centre of the baseplate circle so that its head can accommodate the pointed end of the round dowel (central sha ).

Figure 5: Circular pattern on base board for coil positioning and vertical square dowels

80-100 mm

140-160 mm

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(iii) Drill a Ø 8 mm hole into the centre of the cross-beam (22 mm x 22 mm square dowel). Using hot glue, join a washer exactly over the cross-beam hole.

(iv) Position the two 300 mm vertical square dowels onto the baseplate as indicated on the base board in Step 1. Ensure a 90º angle between the vertical beams and the baseplate by using a framing square. Once you are con dent that the beams are correctly positioned, carefully use hot glue to x them onto the baseplate

(v) Once the glue has cooled and hardened you can start assembling all frame elements, i.e. the vertical pieces and the cross-beam. Do not use glue to x the cross-beam onto the vertical ones - use wood screws as you might later want to remove the cross-beam so that you can work on the turbine.

(vi) Insert the round dowel (central sha ) through the hole of the cross-beam into the indentation/head of the wood screw. Ensure a 90º angle between the central sha and the baseplate using a framing square. Ensure that the central sha (round dowel) turns freely. Use only wood screws to nally assemble the cross-beam onto the vertical beams.

FIGURE 6: IMPROVED STATOR COIL DESIGN


Construction Step 2: Fabrication and assembly of stator coils As shown in Figures 8 and 9, our VAWT (Savonius) model can work with di erent stator designs, i.e. three, four, six or eight coils. All designs will produce a functional model on condition that all instruc-tions are carefully followed. Based on our experience however, the eight coil design is the most rewarding one and we will thus focus on this design.



1 PVC pipe To build a winding jig we recommend using a 22 mm PVC pipe up to 100 mm long.

1 Magnet wireYou require a reel of enamel-coated magnet wire. Wire diameter is ideally between 0.2 – 0.5 mm. The total length required for the 0.2 mm wire is 120 m and 80 m for the 0.5 mm wire.

1 Masking tape 10 mm width.

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Read the following instructions carefully before you start working:(i) Prepare the winding jig: You are required to use a saw to cut a 5 – 10 mm slot along the whole

length (100 mm) of the 22 mm PVC pipe. (ii) Winding the coils: Carefully wind the indicated wire length (120 m/0.2 mm wire or

80 m/0.5 mm wire) around the winding jig for each individual coil. Ensure that around 50 mm of wire is kept uncoiled at both ends (see Figure 6).

(iii) Once a coil is completely wound, remove it carefully from the jig and maintain its shape by wrapping masking tape around the coil. Work thoroughly, as maintaining the shape, its thick-ness and the number of turns for each coil will later pay o by optimising the generator’s output.

(iv) Indicate the winding direction on all eight coils using a pencil or felt pen. (v) Carefully scrape around 10 – 15 mm of the enamel insulation from the wire ends. (vi) Test all coils with a multimeter to ensure current ow. Choose an appropriate resistance range

on the tester, for example 100 or 200 ohm. Connect the free ends of the coils with each other by ensuring that a current can ow through the coils in a clockwise direction. Continue with the next steps if your reading is appropriate.

FIGURE 7: CLOCKWISE CONNECTION OF EIGHT COILS

Image source: GIZ/S4GJClockwise connection of eight coils. Test for current ow with a multimeter.

FIGURE 8: ROTOR AND STATOR OPTION FOR VAWT DESIGN #1

Image source: Dörthe Boxberg Rotor and stator option for VAWT Design #1 (half-cylinders made out of PET bottle)

Figure 7: Clockwise connection of eight coils. Test for current fl ow with a multi-meter.

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FIGURE 9: ROTOR AND STATOR OPTION FOR VAWT DESIGN #2

Image source: Dörthe BoxbergRotor and stator option for VAWT Design #2 (half-cylinders made out of PVC pipe)

Construction Step 3: Stator assemblyAs indicated in Step 2 and shown in Figures 8 and 9, our VAWT (Savonius) model can work with di er-ent stator designs, i.e. three, four, six or eight coils. All designs will produce a functional model on condi-tion that all instructions are carefully followed. However, based on our experience the eight coil design is probably the most rewarding one and we will thus focus on this design.



1 Baseboard with frame See Step 1

8 Coils See Step 3

1 Solder + flux A basic solder station will do.


Read the following instructions carefully before you start working:(i) Position all eight coils equally onto the baseboard using the circular pattern you have drawn in

Step 1. (ii) Ensure that all free ends of the coils are still connected with each other and that a current can

ow through the coils in a clockwise direction (see Step 2). (iii) Use solder to permanently x the connections between the eight coils. Test the connections us-

ing a multimeter. Ensure that two ends are free to connect the multimeter and later the recti er to the coil/stator arrangement (see Step 2).

(iv) If you are con dent that the coils are equally positioned and current ow is ensured, carefully hot glue them onto the baseplate.

(v) Using a multimeter, test the stator arrangements (coils) again.

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Construction Step 4: Fabrication and assembly of rotor plate/diskAs indicated in Step 3 and in the previous gures, our VAWT (Savonius) model can be built by using dif-ferent rotor disk designs, i.e. up to 8 magnets can be used (Figure 9). All indicated designs will produce a functional model on condition that all instructions are carefully followed. However, based on our experi-ence, the eight magnets/eight coil design is the most rewarding one and we will thus focus on it.



8 MagnetsRound neodymium-iron permanent magnets with a diameter between 10-25 mm and a thickness of between 2.5 - 4 mm are ideal.

8 Washer Diameter slightly larger than the magnet diameter.

1 Cardboard An A4 size cardboard sheet is required to build a rotor disk.


Read the following instructions carefully before you start working:(i) Prepare the rotor disk: It is very important that the diameter of the rotor disk corresponds with

the stator diameter positioned on the baseboard. It is thus recommended to use a similar circu-lar pattern for the rotor disk as we have used for the stator. Figure 10 illustrates the pattern and the position of the magnets.

FIGURE 10: CIRCULAR PATTERN ON CARDBOARD FOR ROTOR DISK


(ii) Draw two circles with the same diameter onto the cardboard. Cut the two circles out and glue them together so that you produce a single circle.

(iii) Position the eight washers as indicated in Figure 10. is arrangement is important as it ensures that the position of the magnets corresponds with the arrangements of the coils.

(iv) If you are con dent that your magnet/coil arrangement is correctly aligned, carefully hot glue the washers onto the rotor disk.

(v) While the glue cools and hardens, you need to determine the polarity of your magnets using a magnetic compass. Indicate the polarity (N or S) on each side of each magnet.

(vi) Once the washers are in their correct position and the glue has cooled and hardened you can start placing the magnets onto the washers. Use the alternating polarity arrangement as indicat-ed in Figure 11.

(vii) Punch a little hole into the disc’s centre to accommodate the central sha (6mm round dowel).

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FIGURE 11: MAGNETS NEED TO BE PLACED IN AN ALTERNATING POLARITY ARRANGEMENT


Construction Step 5: Fabrication and assembly of rotor blades As you can see in the Figures 13 and 14, our VAWT (Savonius) model can be built by using di erent rotor blade designs, i.e. two half-cylinders can be made out of a plastic bottle or by using a PVC pipe. Both de-signs will produce a functional model on condition that all instructions are carefully followed.



1 Plastic bottleMost soft drinks are sold in plastic bottles made from polyethylene terephthalate (PET). You can reuse an empty bottle for your model. Clear water bottles with a uniform shape and diameter are the most suitable ones.

1 PVC pipe As an alternative to the plastic bottle design you can also use a PVC pipe (80 - 100 mm) to build the rotor blades.

1 Cardboard Two or three A4 sized cardboard sheets are required to build two top and bottom covers (end pieces) for the rotor blades.

Read the following instructions carefully before you start working:(i) Prepare the top and bottom covers: Glue the two or three cardboard sheets together so that you

produce a single sheet with an approximate thickness of 10 mm.(ii) Use a pencil, ruler and compass and draw the following pattern onto the cardboard (Figure 12).

Ensure that the circle’s diameter (80 – 100 mm) or radius (40 – 50 mm) corresponds with the diameter of your plastic bottle or PVC pipe.

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FIGURE 12: CIRCULAR PATTERN ON CARDBOARD FOR TOP AND BOTTOM COVER OF TURBINE BLADES


(iii) Using a utility knife, cut the two covers (end pieces) out and punch a small hole into its centre so that the central sha could pass through it.

(iv) Mark one cover as top end piece and the other as bottom end piece. (v) Using a utility knife, cut the top and base part of the water bottle so that what remains is the

central cylinder of the plastic bottle. e length of the cylinder can be between 250 - 150 mm.(vi) Cut the plastic cylinder in the middle so that you produce two equal half-cylinders. Each

half-cylinder shall function as a turbine blade. (vii) Use sand paper to carefully bu all edges of the two half-cylinders. Sanding will avoid skin cuts

and also improves adherence of the glue.(viii) Apply hot glue around one half circle of the top end piece. Quickly position one side of the top

end piece to the half-cylinder. Hold both components in position until the glue cools and hard-ens.

(ix) Apply hot glue around the other half circle of the top end piece. Quickly position the second half-cylinder onto it. Hold both components in position until the glue cools and hardens.

(x) Repeat the instructions given in (viii) and (ix) for the assembly of the bottom end piece so that both end pieces are glued to the half-cylinders.

(xi) Glue the assembled rotor disk onto the bottom end piece. (xii) Once the glue has cooled and hardened, place the almost completed turbine into the frame, i.e.

over the coils, and push the round dowel (6 mm) with the sharpened end through the top end piece ( rst from the horizontal beam) and then through the bottom end piece.

Construction Step 6: Final turbine assemblyIf you have followed the recommended steps, all your turbine components are now ready for assembly.



1 Wind machine Use the IKS or leXsolar wind machine for testing.


Read the following instructions carefully before you start assembling the turbine:(i) Test that the central sha with the turbine blades turns freely between the cross-beam and the

baseboard.(ii) Once you are con dent that your assembly turns freely in the frame, set the distance between

the magnets on the rotor disk and the coils on the stator/base board to approximately 3mm.(iii) Connect a multimeter to the stator coils. (iv) Position the wind machine around 150 – 300 mm away from the turbine and test for current

Figure 12: Circular pattern on cardboard for top and bottom cover of turbine blades

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ow. You should be able to measure between 1 – 3 VAC.(v) If you are not satis ed with the output of the spinning turbine, carefully adjust/reduce the dis-

tance between the rotor disk and stator coils until you are satis ed with the output.(vi) Finally, hot glue the central sha to the rotor blades and the rotor disk, keeping the position set

in the previous step (v).

FIGURE 13: ASSEMBLED VAWT DESIGN #1

Image source: Dörthe BoxbergHalf-cylinders made out of a PET bottle

FIGURE 14: ASSEMBLED VAWT DESIGN #2

Image source: Dörthe BoxbergHalf-cylinders made out of a PVC pipe

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Construction Step 7: Rectifi er fabricationOur current turbine design functions as an alternator, subsequently producing an alternating current (AC). To turn this alternating current (AC) signal into a strong enough constant ‘voltage’ (DC) signal, devices called ‘recti ers’ can be used. In other words, the conversion of an alternating current (AC) into a continuous current (DC) is called recti cation. Small signal diodes can be used as recti ers in low-power, low-current applications. ese semi-conductor signal diodes will only conduct current in one direction - from its anode to its cathode (forward direction). Our VAWT model must be considered as a low-power application and for these, half-wave recti ers are most o en used. However, they have the disadvantage of their output amplitude being less than the input amplitude. is is due to the fact that there is no out-put during the negative half-cycle, so half the power is not available and the output is pulsed DC result-ing in excessive ripple. To overcome these disadvantages, a number of diodes can be connected to produce a full-wave recti- er. An ideal type of circuit is, for example, a full-wave bridge recti er. is type of recti er uses four individual rectifying diodes connected in a closed-loop con guration to produce the desired output. Although we can use four individual diodes to make a full-wave bridge recti er, pre-made bridge recti -er components are available o -the-shelf in a range of di erent sizes that can be soldered directly into a prototyping circuit board.Lastly, in order to produce a steady DC current from a recti ed AC source, a lter or smoothing circuit is very useful. is can be done by using a capacitor placed across the DC output of the recti er. e full-wave bridge recti er gives us a greater mean DC value with less superimposed ripple, while the output waveform is twice the frequency of the input supply frequency. We can therefore increase the average DC output level by connecting a suitable smoothing capacitor across the output of the bridge circuit as shown in Figure 15. Please note that a diode bridge can also be designed to rectify poly-phase AC inputs. For example, for a three-phase AC input, a half-wave recti er consists of three diodes, but a full-wave bridge recti er consists of six diodes.

FIGURE 15: CIRCUIT DIAGRAM OF A FULL-WAVE BRIDGE RECTIFIER AND SMOOTHING CAPACITOR




4 DiodesSmall standard 2 pin rectifier diodes will do. They usually come in assort-ment kit sets. Please note that the silver ring on the diodes indicates the cathode side of the diode.

1 Capacitor A small smoothing capacitor (3900 µf) will do.

1 PCB A small prototyping circuit board will do.

1 Solder + flux A basic solder station will do.

Figure 15: Circuit diagram showing a full-wave bridge rectifi er and smoothing capacitor

AC Input

Smoothingcapacitor

DC Output

D4 D1

D2 D3

Bridge rectifi er

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Read the following instructions carefully before you start working:(i) Complete the electrical circuitry of the full-wave bridge recti er according to Figure 15 or use

any other suitable circuit. (ii) Test the recti er unit with your assembled VAWT design (set 6). Use di erent loads, such as

LEDs or buzzers that already activate in the millivolt range.

FIGURE 16: SIMPLE STATOR PLATE BASED ON 3 COIL DESIGN WITH A SIX DIODE RECTIFIER UNIT


FIGURE 17: CONNECTING/SOLDERING THE COILS TO A RECTIFIER UNIT


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Testing and fault fi ndingWe have continuously indicated that all proposed designs will produce a functional model on condition that all instructions are carefully followed. However, during assembly or due to lack of appropriate ma-terial, construction mistakes may occur causing a dysfunctional setup. In the following section we thus o er you some hints for troubleshooting.

TABLE 8: TROUBLESHOOTING

Problem Causes Recommended Solutions

Turbine turns too slowly or only with difficulty.

The pointed end of the dowel is binding in the wood screw posi-tioned in the centre of the base board.

Re-sharpen the dowel, or smooth it with sandpaper.

Wind machine too far away from the turbine.

Bring the wind machine closer to the turbine or replace it by a blower with a higher power rating.

No or not sufficient output readings.

Magnetic force too weak. Substitute with stronger magnets.

Magnets are not positioned in accordance with coils.

Re-check and correct magnet orientation on rotor disk.

Coils are not positioned clockwise. Re-check and correct coil orienta-tion on stator/baseboard.

Turbine turns too slowly or only with difficulty. See above.

Poor multimeter/load connections. Ensure proper insulation free connections.

Multimeter setting. Set to low AC (before rectifier) or DC (after rectifier).

Multimeter readings are sufficient but loads (LEDs, buzzer etc.) do not function.

Use different loads such as LEDs or buzzers that already activate in the millivolt range.

Further Information

Further information and inspirations for the design and assembly of functional VAWT models can be found at http://www.picoturbine.com. PicoTurbine is generally a good source of ideas and resources for renewable energy education and STEM projects.

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UNIT 4.2

CONNECT FUEL CELL SYSTEM COMPONENTS USING DIDACTICAL TRAINING KITS

Introduction

In Unit 2.2, eme 2.2.2 we introduced you to the basic underlying principles of fuel cell technologies, covering some elementary aspects of electrochemistry. One of the most important applications of elec-trochemistry appears in context with energy storage and conversion of energy. In this unit you will apply your knowledge in hands-on experiments using the didactical hydrogen training kit.

Unit Outcomes

See theme outcomes.

Themes in this Unit

Unit 4.2 covers only one theme: eme 4.2.1 Experiments with Fuel Cell Training Sets

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THEME 4.2.1

EXPERIMENTS WITH FUEL CELL TRAINING SETSIntroduction

e components required for experimenting with simple fuel cell models are available in the hydrogen training kit. At least two training kits need to be available at your college for RET Level 4. In eme 2.2.2 you were already introduced to the training kit components and carried out two experiments: (i) deter-mining the volume ratio of the gases produced, and (ii) measuring the quantities of gas produced per unit time depending on current. In this theme we will continue with more experiments, including de-termination of I/V characteristics of the electrolyser and the fuel cell, and operating the electrolyser with other renewable energy technologies.

Keywords

ElectrolysisHydrogenE ciency factorOverpotentialI/V characteristicFuel cellPhotovoltaic electrolysis systems Load matchingWind power electrolysis systems

Theme Outcomes

At the end of this theme, you should be able to:(i) Identify training kit or industrial components for experiments.(ii) Determine the energy and faradaic e ciency of the electrolyser.(iii) Determine the I/V characteristic line of the electrolyser.(iv) Determine the I/V characteristic line of the fuel cell.(v) Set up an isolated network. (vi) Operate the electrolyser with solar cells.(vii) Operate the electrolyser with a miniature wind turbine.(viii) Operate the electrolyser with solar cells and a miniature wind turbine.(ix) Perform testing and fault nding on all of the above setups.


Training Kit ComponentsBefore you start/continue with the experiments, we recommend that you again familiarise yourself with the training kit and identify all of its components. Please also consult the student manual in the training set for more information and descriptions of the components, as well as the operating instructions. In eme 2.2.2 we already brie y described the components and illustrated them with some images, but please consult eme 2.2.2 again and note that all components, particularly the fuel cell and the electro-lyser, need to be handled with care!

Safety and CommissioningAlways read the notes on safety before starting with the experiments. Use only distilled water to operate the electrolyser and the fuel cell. Ensure that all connections have the correct polarity. Carefully store all tting caps from the sleeves in the correct baseplate compartment. Be careful with the Plexiglas housing of each device as these are sensitive to impact stress.

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Preparation for StorageA er each experiment, follow the recommended steps for storing the training kit components in the case. Also remember:

(i) Water needs to remain in the electrolyser to prevent the membrane from drying out. us, care-fully close the connecting sleeves with the tting caps.

(ii) During operation, humidity buildup in the fuel cell is usually su cient to protect the membrane. us, carefully close the connecting sleeves with the tting caps.

(iii) e gas storage container needs to be completely empty - use the syringe and a micro ber cloth to achieve this.

Activity 1: Electrolyser effi ciency

Objective

is activity is designed to determine e ciency values of the electrolyser as dependent variables of cur-rent intensity (‘amperage’). Please note that in Activity 1 we consider only electric e ciency but not fara-daic e ciency nor faradaic losses. In the IKS training set this activity is called ‘Experiment 3’.

Background information Electrolysis o ers a sustainable hydrogen production pathway. One advantage of electrolysis is that it is capable of producing high purity hydrogen (around 99.99%). However, re nery costs for electrolysis are huge, mainly due to the high amount of electric power needed to produce pure hydrogen. Most common industrial electrolysers have a nominal hydrogen production e ciency of around 70%. Nonetheless, if the required power is supplied via renewable technologies - see experiments ‘Operation of the electroly-ser using PV cells’ and ‘Electrolyser operation using a miniature wind turbine’ - negative environmental impact costs, compared to fossil fuel combustion, could drastically be reduced.

How does an electrolyser work? Electrolysers are electrochemical devices which work like a fuel cell in reverse and can split water into its constituent molecules, hydrogen (H2) and oxygen (O2), by passing an electric current through water (Figure 1). When water is decomposed, the ratio of hydrogen gas to oxy-gen gas produced is 2:1 as stated in the reaction:

Anode 2 H2O 4 H+ + 4 e- + O2

Cathode 4 H+ + 4 e- 2 H2

Total 2 H2O (l) 2 H2 (g) + O2 (g) (E = - 1.23 V)

us, theoretically a potential di erence of 1.23 V is required from an external source to decompose wa-ter into its constituent molecules. In practice however, due to electrical and faradaic losses the potential di erence required to split water always exceeds 1.23 V. e di erence between the theoretical decompo-sition potential, i.e. 1.23 V, and the actual decomposition potential is called ‘overpotential’.For example, if 2.23 V is the actual potential required to cause water to decompose, then the overpoten-tial would be 2.23 V minus 1.23 V = 1 V. e overpotential is a function of the electrode material, the electrode surfaces, the type and concentration of the electrolyte, the current density and temperature. Overpotential is always needed to overcome electrode interactions and is particularly common in elec-trochemical reactions where gases are involved.

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FIGURE 1: ELECTROLYSIS REACTION: 2 H2O (L) 2 H2 (G) + O2 (G)


Energy e ciency (η) is determined as the ratio between useful energy output and energy input. E ciency factors of the electrolyser can be calculated by determining the gas volumes produced and the amount of current used. us, in our case η can be calculated by dividing the amount of chemical energy produced (Ech), i.e. stored in the produced hydrogen gas, by the electrical energy used (Eel).

Chemical energy produced can be de ned as:

Ech = Ho x Vexp

Whereby Ho = Chemical energy / fuel value of hydrogen = 11.7 J/ml (Joule per ml) and

Vexp = Volumes of hydrogen obtained in the experiment.

Electrical energy (in Joule) used can be de ned as:

Eel = U x I x t

HypothesisIt can be expected that due to losses in the electrolyser, such as ohmic resistance and resulting heat, e -ciency is a dependent variable of current intensity.

SetupTo investigate e ciency values of the electrolyser, follow the experimental setup as described in the IKS manual Experiment 3 (see also Figure 2). Conduct two measurements as required with two di erent cur-rent values, i.e. I = 100 mA and I = 500 mA. Perform testing and fault nding as needed.

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FIGURE 2: SETUP FOR ACTIVITY 1


MeasurementsMeasure potential and hydrogen volume levels for each current setting and register the produced hydro-gen volumes (start volume = 0). Use the table in the manual to document your measurements. We indi-cated some hypothetical results in Table 1 and 2 to illustrate the activity.

Result interpretation e energy e ciency factor η has been given as Ech over Eel. Chemical energy produced is de ned as Ech = Ho x Vexp, whereby Ho = 11.7 J/ml (Joule per ml). Electrical energy used has been de ned as Eel = U x I x t, in Joule. We can now calculate the energy e ciency factor η using the hypothetical results from Table 1 for each current setting using Table 2.

TABLE 1: HYPOTHETICAL RESULTS (BLUE FONTS) OF ACTIVITY 1

I (mA) V (V) t (min) H2 Start Volumes (ml) H2 End Volumes (ml) H2 ∆ Volumes (ml)

100 1.5 12 0 8 8

500 2 4 8 23 15

TABLE 2: CALCULATING ENERGY EFFICIENCY FACTOR η USING HYPOTHETICAL RESULTS

I (mA) Ech = Ho x Vexp(J)

Eel = U x I x t (J)

Energy Efficiency Factor η (%)

100 11.7 J/ml x 8 ml = 93.6 1.5 V x 0.1 A x 720 s = 108 (93.6 J / 108 J) x 100 = 86.6

500 11.7 J/ml x 15 ml = 175.5 2 V x 0.5 A x 240 s = 240 (175.5 J / 240 J) x 100 = 73.1

O2H2O2 H2

+ -V

A

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Remember that we introduced you to the concept of proportionality. In engineering, two variables are proportional if a change in one is always accompanied by a change in the other. ink of two variables X and Y. A directly proportional relationship occurs when X and Y both increase or they both decrease. An indirectly proportional relationship occurs when X increases and Y decreases. As calculated in Table 2 by using hypothetical results, the energy e ciency factor η decreases with increasing current intensity. In other words, η appears to be indirectly proportional to I. Consequently, a higher potential di erence is required for electrolysis to compensate for resistance (ohmic) losses (dissipating heat). Interpret your results further by answering the questions in your IKS workbook and by answering the following:

(i) Can you accept the hypothesis or must you reject it? Explain your views!

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Activity 2:Electrolyser I/V characteristics

Objective is activity is designed to determine the electric properties of the electrolyser by interpreting its I/V characteristics. In the IKS training set this activity is called ‘Experiment 4’.

Background informationAs already indicated in eme 4.1.1, current–voltage characteristics or I/V curves show a relationship between the electric current (I) and the corresponding potential di erence (V) across it. e I/V char-acteristics for most electrical loads, such as resistors, motors/generators, bulbs etc. usually show a linear relationship between current and potential.

HypothesisIt can be expected that the electrolyser’s I/V characteristic shows a linear relationship.

SetupWith the exception that you do not need a timer, the experimental setup from Activity 1 can also be used for Activity 2. Follow the experimental setup as described in Activity 1 and perform testing and fault nding as needed.

MeasurementsSeveral measurements are required for current values between 0 to 100 mA. erea er, measurements should be taken in 100 mA steps, i.e. between 100 mA and 500 mA. Measure potential and hydrogen vol-ume levels for each current setting and register the produced hydrogen volumes (start volume = 0). Use the table in the manual to document your measurements. We indicated some hypothetical measurements in Table 3 to illustrate the activity.


I (mA) V (V)

0 1.44

20 1.50

40 1.53

60 1.57

100 1.60

200 1.69

300 1.75

400 1.80

500 1.89

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FIGURE 4: ELECTROLYSER I/V CHART BASED ON HYPOTHETICAL RESULTS OBTAINED FROM TABLE 3


Result interpretation Enter the respective current (mA) and ‘voltage’ (V) values into a I/V chart. Connect the dots by drawing a line. As visualised in the chart and unlike many other loads, a minimum ‘voltage’ value, the so-called decomposition potential, in our case around 1.44 V must be supplied to the electrolyser before electrolysis and current ow can be detected. Corresponding with Activity 1, a directly proportional relationship between current and ‘voltage’ can be observed, i.e. current increases when ‘voltage’ increases. Interpret your results further by answering the questions in your IKS workbook and by answering the following:

550

500

450

400

350

300

250

200

150

100

50

00 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8 2,0

Potential difference (V)

Curr

ent (

mA)

(i) Can you accept the hypothesis or must you reject it? Explain your views!

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Activity 3:Fuel cell I/V and P/I characteristics

Objective is activity is designed to determine the electric properties of the fuel cell by interpreting its I/V characteristics. In the IKS training set this activity is called ‘Experiment 6’.

Background informationSome information on current–voltage characteristics (I/V curves) were already provided in the previous activity. In addition to I/V characteristics, we will also examine the fuel cell’s power maximum deter-mined by its P/I characteristics.

HypothesisIt can be expected that the fuel cell’s I/V characteristics shows a linear relationship, while the P/I characteristics will form a curve indicating the cell’s optimum, i.e. maximum power at reversal point in the curve.



SetupFollow the experimental setup as indicated in Figure 5 and 6, and as described in the IKS workbook. Per-form testing and fault nding as needed.

Measurements e aim of the rst measurement is to determine the open circuit ‘voltage’ (Voc). us, the ammeter should not be connected in the rst measurement. erea er, set the ammeter to 10 A, and take all fol-lowing measurements in 200 mA steps, i.e. between 200 mA and 1800 mA. Measure potential (V) for each current setting and calculate power (mW). Use the table in the workbook to document your mea-surements. We indicated some hypothetical measurements in Table 4 to illustrate possible results.

O2 H2

+ -

O2H2

O2 H2

+ -

V

A

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I (mA) V (V) P (mW)

0 0.91 0

200 0.72 144

400 0.65 260

600 0.58 348

1000 0.51 510

1200 0.45 540

1400 0.32 448

1600 0.27 432

1800 0.18 324

Result interpretation Enter the respective current (mA) and ‘voltage’ (V) values into the chart. Connect the dots by drawing a line. erea er, enter the respective power values (mW) into the chart. Connect the dots by drawing a line. We recommend using di erent colours to di erentiate the I /V line (blue) from the P/I curve (orange) in the chart. Indicate the maximum power point with an arrow.

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FIGURE 7: COMBINED I/V AND P/I CHART BASED ON HYPOTHETICAL RESULTS OBTAINED FROM TABLE 4


1,0

0,9

0,8

0,7

0,6

0,5

0,4

0,3

0,2

0,1

0

Power (W)

0 0,2 0,4 0,6 0,8 1,0 1,2 1.4 1,6 1,8 2,0

1,0

0,9

0,8

0,7

0,6

0,5

0,4

0,3

0,2

0,1

0

Potential (V)

Current (A)

Power optimum

Interpret your results further by answering the questions in your IKS workbook and by answering the following questions:

(i) Why is the value of the fuel cell for open circuit ‘voltage’ (Voc) below the theoretical value of 1.23 V? Explain your views!

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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your views!

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(iii) Determine maximum power (Pmax) of the fuel cell. Recall the proportionality between the energy e ciency factor η and current intensity. Explain your view in context with your Activity 3 results!

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(iv) Can you accept the hypothesis or must you reject it?

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Activity 4:Electrolyser operation using PV cells

Objective is activity is designed to showcase electrolyser operation using renewable energy technologies (RET) as power supplies, in this case PV cells. In the IKS training set this activity is called ‘Experiment 7’. Please note that this activity requires the IKS PV training set (Solartrainer Junior, RET Level 2).

Background informationWe already indicated in the previous sections that hydrogen production can ideally be realised by using renewable energy technologies (RET) as a power source. Hydrogen production via electrolysis powered by RET is a promising approach for storing solar energy. However, for this technology to be economically competitive, it is critical to develop RET-powered electrolysis systems with high e ciencies, so-called solar-to-hydrogen (STH) e ciencies.

In this activity, we aim to demonstrate the potential of photovoltaic electrolysis systems for solar energy storage. e aspect of cost-e ectiveness can unfortunately not be demonstrated by our miniature compo-nents. We thus focus on realising electrolyser operation using the PV modules from the IKS PV training set (RET Level 2). Our miniature photovoltaic electrolysis system needs to produce a large enough po-tential di erence to operate the electrolysers with no additional power input. Subsequently, to optimise system e ciency, the maximum power point of the PV cells needs to complement the operating capacity of the electrolysers. In other words, the electrolyser serves as the load for the PV cells. e technique to determine an optimally matched load is called load matching.

Open circuit ‘voltage’ (Voc) and short circuit current (Isc) of the PV cells need to be determined rst, followed by PV cell I/V characteristics. It is therefore recommended to review Experiment 11 (I-V curve of a solar cell) in the RET Level 2 textbook (Unit 4.2, p. 356). Additionally, the results of Activity 2 are required, i.e. the electrolyser’s I/V characteristics, to discuss and compare the I/V characteristics of the PV cells and the electrolyser. is is due to the fact that an intersection between the I/V characteristics of the two devices is required to power our miniature photovoltaic electrolysis system. In other words, the PV system needs to supply a certain minimum ‘voltage’ and current intensity for the production of hydrogen (electrolysis starting point).

HypothesisUnder the condition that the PV system (2, 3 or 4 PV cells connected in series) supplies the minimum ‘voltage’ and current intensity for the electrolysis, hydrogen production can be expected.

SetupFollow the experimental setup as indicated in Figure 8 and 9 and as described in the IKS workbook. We recommend reviewing Experiment 11 (I-V curve of a solar cell) in the RET Level 2 textbook (Unit 4.2, p. 356). Perform testing and fault nding as needed.

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FIGURE 8: RET LEVEL 2 TRAINING SET: 2, 3 OR 4 PV CELLS CONNECTED IN SERIES


FIGURE 9: THE ELECTROLYSER POWERED BY 2, 3 OR 4 PV CELLS CONNECTED IN SERIES


MeasurementsFirstly, measure open circuit ‘voltage’ (Voc) and short circuit current (Isc) of each PV cell arrangement, i.e. 2, 3 or 4 PV cells connected in series (set up according to Figure 8). Secondly, set the activity up as in-dicated in Figure 9 and start measuring the current values at the electrolyser (I electrolyser ) for each PV cell arrangement, i.e. 2, 3 or 4 PV cells connected in series. Observe the buildup of hydrogen gas. We indicat-ed some hypothetical results for these measurements in Table 5 to illustrate the activity.

Multimeter

Volt (U)

Ampere (I)

DCV

DCA

OFF

Multimeter

Volt (U)

Ampere (I)

DCV

DCA

OFF

Cell inclination 90°!

Spotlight(Halogen)

O2 H2

+ -Multimeter

Volt (U)

Ampere (I)

DCV

DCA

OFF

Cell inclination 90°!

Spotlight(Halogen)

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Result interpretation Use the values you have registered in Activity 2, i.e. the electrolyser’s I/V characteristics, and transfer them into the chart (Figure 10). Next, draw the electrolyser’s I/V characteristics of the di erent PV cell arrangement, i.e. 2, 3 or 4 PV cells connected in series, into the chart. Lastly, consider how hydrogen pro-duction could be increased, e.g. by using additional PV cells.


PV cells 1 2 3 4

Voc (mV) 0.5 1.1 1.65 2.15

Isc (mA) 148 149 150 149

I electrolyser (mA) 0 0 60 140

FIGURE 10: HYPOTHETICAL ELECTROLYSER AND PV CELL I-V CHARACTERISTICS


300

250

200

150

100

50

00 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8 2,0 2,2

1 Solar cell 2 Solar cell 3 Solar cell 4 Solar cellElectrolyser


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Interpret your results visualised in the chart (Figure 10) by answering the questions in your IKS workbook and by answering the following:

(i) Which of the di erent PV cell arrangements, i.e. 2, 3 or 4 PV cells connected in series, pro-vide su cient power to operate the electrolyser? More speci cally: (A) Indicate in the chart the minimum potential di erence value (and number of PV

cells) required to start electrolysis. (B) Indicate in the chart the minimum current intensity (and number of PV cells) re-

quired to start hydrogen production.

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(ii) Can you accept the hypothesis or must you reject it?

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(iii) Could hydrogen production be increased by using additional PV cells? Consider the black PV cell I-V curve in the chart!

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Activity 5:Electrolyser operation using a miniature wind turbine

Objective is activity is designed to showcase electrolyser operation using renewable energy technologies (RET) as power supplies, in this case a miniature wind turbine. In the IKS training set this activity is called ‘Ex-periment 7’. Please note that this activity requires the IKS wind power training set (Windtrainer Junior, RET Level 4).

Background informationSimilar to the previous activity, we aim to demonstrate the potential of wind turbine electrolysis systems for solar energy storage. With our miniature components we focus on realising electrolyser operation us-ing the wind turbine from the IKS wind training set. e turbine needs to produce a large enough poten-tial di erence to operate the electrolysers with no additional power input. e electrolyser thus serves as the load for the turbine; the technique to determine an optimally matched load is called load matching. Open circuit ‘voltage’ (Voc) and short circuit current (Isc) of the turbine needs to be determined rst, fol-lowed by the turbine I/V characteristics. It is therefore recommended to review Activity 5 in eme 4.1.1 (I-V curve of wind turbine generator) in Unit 4.1. Similar to the PV modules in Activity 4, the turbine needs to supply a certain minimum ‘voltage’ and current intensity for the production of hydrogen (elec-trolysis starting point).

HypothesisUnder the condition, that the generator in our miniature wind turbine supplies su cient power for the electrolysis, hydrogen production can be expected.

SetupFollow the experimental setup as indicated in Figure 11 and 12 and as described in the IKS workbook. According to Activity 5 in eme 4.1.1, we recommend a setup using a 4-blade rotor and curved blades, but with a 75º angle of attack and a maximum wind speed of around 10 m/s. We recommend review-ing Experiment 4 (I-V curve of a turbine generator) in eme 4.1.1. Perform testing and fault nding as needed.

FIGURE 11: SETUP FOR Voc AND Isc MEASUREMENTS OF THE TURBINE GENERATOR


Gen

erat

orTa

chog

ener

ator

Multimeter

Volt (U)Ampere (I)

DCV

DCA

OFF

Multimeter

Volt (U)Ampere (I)

DCV

DCA

OFF

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FIGURE 12: TURBINE GENERATOR CONNECTED TO POWER THE ELECTROLYSER


MeasurementsFirstly, measure open circuit ‘voltage’ (Voc) and short circuit current (Isc) of the turbine generator (accord-ing to setup in Figure 11). We indicated some hypothetical results in Table 6 to illustrate possible mea-surements. Secondly, set the activity up as indicated in Figure 12 and start measuring the current values at the electrolyser (I electrolyser ). Observe the buildup of hydrogen gas. Reduce the wind speed (vwind) at the wind machine until the electrolyser current reaches zero (I = 0). At this point, document the threshold values of the turbine, i.e. wind speed (vwind in m/s), Voc and Isc. We indicated some hypothetical results in Table 7 to illustrate possible measurements for this limiting case.

TABLE 6: HYPOTHETICAL RESULTS (BLUE FONTS): MEASURING Voc AND Isc OF THE TURBINE GENERATOR

Voc (V) 3.3

Isc (mA) 105

I electrolyser (mA) 105

TABLE 7: HYPOTHETICAL RESULTS (BLUE FONTS): MEASURING WIND SPEED (Vwind), Voc AND Isc OF THE TURBINE AT ELECTROLYSER CURRENT (I = 0 mA)

Voc (V) 1.4

Isc (mA) 10

vwind (m/s) 5

Result interpretation Use the values you have registered, i.e. the electrolyser’s I/V characteristics (see Activity 2 and 4) and the wind turbine characteristics at 10 m/s and the threshold values as documented at the limiting case (elec-trolyser current I = 0 mA), and transfer them into the chart (see Figure 13). Assume, for approximation, a straight line for both wind turbine characteristics.

Gen

erat

orTa

chog

ener

ator

Multimeter

Volt (U)Ampere (I)

DCV

DCA

OFF

O2 H2

+ -

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FIGURE 13: HYPOTHETICAL I-V ELECTROLYSER AND PV CELL I-V CHARACTERISTICS


Interpret your results visualised in the chart (Figure 13) by answering the questions in your IKS workbook and by answering the following:

(i) At which point, i.e. point of intersection between the characteristic lines, does the turbine generator provide su cient power to operate the electrolyser?

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(ii) Can you accept the hypothesis or must you reject it?

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300

250

200

150

100

50

0

0 0,5 1,0 1,5 2,0 2,5 3,0 3,5

I/V electrolyserWind turbine at 10m/sWind turbine at electrolyser current I=0


Curr

ent (

mA)


(i) IKS student workbook Hydrogen Trainer Junior(ii) IKS student workbook Solar Trainer Junior(iii) IKS student workbook Wind Trainer Junior

319

NO

TES

Your own notes

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Uni

t 4.3

UNIT 4.3 CONFIGURING BATTERIES FOR RENEWABLE ENERGY SYSTEMS

Introduction

In Unit 2.2, eme 2.2.1 we introduced you to di erent types of batteries and the basic principles of electrochemistry. In this unit you need to apply your knowledge in practical activities using small sealed lead-acid batteries.

Unit Outcomes

See eme 4.3.1.

Themes in this Unit

Unit 4.3.1 covers only one theme: eme 4.3.1 Experiments with Batteries

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THEME 4.3.1

EXPERIMENTS WITH BATTERIES

Introduction

e tools and components required for experimenting with small sealed lead-acid (SLA) batteries are in-dicated in Figure 1 below. Apart from the batteries, lugs (F1 or F2 terminal types according to your SLA) and cables with a diameter of at least 2 mm, you only need a few tools to prepare the connections, includ-ing pliers for cable cutting, stripping and crimping.

FIGURE 1: REQUIRED TOOLS AND COMPONENTS


Keywords

Series and parallelPolarityCrimpingSealed lead-acid (SLA) batteriesOvercurrentBattery failureBattery handling

Theme Outcomes

At the end of this theme, you should be able to:(i) Connect batteries in series, parallel and measure total ‘voltage’ and current.(ii) State overcurrent and disconnecting requirements.(iii) Explain the requirements for e ective battery storage and maintenance.(iv) List common causes of battery failure (fault nding).(v) List the precautions required when handling, installing, charging and maintaining batteries.


Working with Sealed Lead-Acid BatteriesIn the following four activities we will work with sealed lead-acid (SLA) or gel cell batteries (12 V, 7 Ah) and set them up in parallel and series connections for measurements of potential di erence (V) and cur-rent (I). SLA cells are also called ‘maintenance free’ batteries. Albeit SLAs do not require constant main-tenance, please note that the term ‘maintenance free‘ is misleading. SLA batteries still require cleaning, speci c charging and regular functional testing. However, SLAs have a number of advantages compared to ordinary rechargeable lead acid type batteries, for example they can be mounted in any orientation, e.g. inclined, laterally or even upside-down due to their construction.

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Safety

Albeit SLA cells can be considered as a safe type of battery, working with cell or terminal mismatch may cause overcharge and venting with ame. us, ensure that you are following these guidelines:

(i) Wear safety goggles and know what you are doing, i.e. rst design a circuit diagram on paper to achieve the desired rating for each of the exercises below before you start connecting the batteries!

(ii) Only connect cells that match (same type/specs) and have identical state-of-charge! (iii) Never work with batteries that show apparent physical damage! (iv) Never leave batteries unattended during the activities and secure them in a container or box af-

terwards!

FIGURE 2: PAY ATTENTION TO POLARITY WHEN CONNECTING BATTERIES


Important Preparations for Activities

To carry out the next four activities successfully, consider the following: (i) Complete/redraw the required circuit design for each activity as a circuit diagram on paper.(ii) Always attempt to answer the following rst:

(a) What kind of circuit must be con gured?(b) Based on your battery specs, e.g. 12 V, 7 Ah, which potential di erence (V) and current (I)

values can be expected in each activity? (iii) According to the example design and your circuit diagram, keep the cabling lengths to a mini-

mum. Avoid increased resistance and waste of material (copper is expensive).(iv) Prepare the cable connections for the lug carefully and crimp using the appropriate tools. (v) e positive leads and the negative leads are marked in red (positive) and black/blue (negative).(vi) Remember, when batteries are connected in series, the nominal potential of the battery circuit

is increased and current values remain constant. us, connect positive leads (red) to negative leads (black/blue) to wire battery circuits in series.

(vii) Remember, when batteries are connected in parallel, the nominal current in the battery circuit is increased and potential values remain constant. us, connect positive leads (red) to positive leads and negative leads (black/blue) to negative leads to wire the battery circuits in parallel.

(viii) Combining parallel with series connection will double both nominal ‘voltage’ and capacity (current).(ix) Follow and execute the above eight steps rst! Only connect the battery now!(x) Measure potential (V) and current (I).(xi) Verify your assumptions as indicated in Step 2, 6, 7 and 8.

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FIGURE 3: FOUR SLAs CONNECTED IN SERIES


FIGURE 4: FOUR SLAs CONNECTED IN SERIES AND PARALLEL


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Activity 1: Confi guration 1: Increasing potential, maintaining current

Follow these steps:

1. Consider Figure 5 and draw your circuit diagram next to it (example design, le )

FIGURE 5: DRAW YOUR CIRCUIT DIAGRAM NEXT TO THE ILLUSTRATION

2. What kind of circuit must be con gured?

………………………………... . . . . . . . . . . . . .…………………………………………

3. Based on your battery specs, which potential di erence (V) and current (I) values can be expected in your circuit? Do your calculations below:

………………………………... . . . . . . . . . . . . .………………………………………… ………………………………... . . . . . . . . . . . . .………………………………………… ………………………………... . . . . . . . . . . . . .………………………………………… ………………………………... . . . . . . . . . . . . .…………………………………………

4. Prepare each connection (cable) according to the example design and your circuit diagram. Carefully connect the batteries.

5. Measure potential and current and document your results in Table 1.

TABLE 1: DOCUMENT YOUR MEASUREMENTS (V AND I ) IN THE TABLE BELOW:

V (V)

I (A)

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Activity 2: Confi guration 2: Increasing current, maintaining potential

Follow these steps:




………………………………... . . . . . . . . . . . . .…………………………………………


………………………………... . . . . . . . . . . . . .………………………………………… ………………………………... . . . . . . . . . . . . .………………………………………… ………………………………... . . . . . . . . . . . . .………………………………………… ………………………………... . . . . . . . . . . . . .…………………………………………




V (V)

I (A)

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Activity 3: Confi guration 3: Increase current and potential two-fold

Follow these steps:




………………………………... . . . . . . . . . . . . .…………………………………………

3. Based on your battery specs, which potential di erence (V) and current (I) values can be expect-ed in your circuit? Do your calculations below:

………………………………... . . . . . . . . . . . . .………………………………………… ………………………………... . . . . . . . . . . . . .………………………………………… ………………………………... . . . . . . . . . . . . .………………………………………… ………………………………... . . . . . . . . . . . . .…………………………………………




V (V)

I (A)

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Activity 4: Confi guration 4: Increase current and potential four-fold

Follow these steps:




………………………………... . . . . . . . . . . . . .…………………………………………


………………………………... . . . . . . . . . . . . .………………………………………… ………………………………... . . . . . . . . . . . . .………………………………………… ………………………………... . . . . . . . . . . . . .………………………………………… ………………………………... . . . . . . . . . . . . .…………………………………………




V (V)

I (A)

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Disconnecting and Overcurrent ProtectionYou may recall that we clearly advised you in all earlier sections of this textbook and in all other RET textbooks that working on energised equipment should be avoided whenever possible. But, as you cannot easily de-energise stored electrical energy in functional batteries, you should consider battery systems as always being energised. Accordingly, and based on each speci c battery system, various risk-/hazard assessments are required. To minimise thermal, chemical and shock/arc ash risks, appropriate DC dis-connect devices and overcurrent protection for battery systems are needed. In the following section, we thus o er you a brief overview on DC disconnect devices and overcurrent protection. Please always con-sider that in a direct current system it is important to use fuses or circuit breakers that are rated for DC use. Do not use devices rated only for AC service, as they will not function properly in a direct current system.

Overcurrent and Short CircuitOvercurrent protection usually uses fuses or circuit breakers that are placed between the load, such as an inverter or consumers, and the battery system. ese types of devices will open/interrupt the circuit and shut down the connection in case the load draws more current than it is rated for. In any case, the fuse rating should always be lower than the current rating of the battery cables. Short circuit protection is also based on fuses or circuit breakers, but these devices are usually placed at the positive output terminal of the battery. In case a short circuit appears, the protection device will open/interrupt the circuit on the positive battery terminal, disconnecting the battery from the system.

For a battery bank with four individual batteries connected in series to increase potential di erence, e.g. to 4 x 12 V = 48 V, one appropriately sized fuse will su ce to protect the circuit, since any disconnect in a series circuit stops an overcurrent through all parts of the circuit.

FIGURE 9: OVERCURRENT PROTECTION FOR FOUR INDIVIDUAL BATTERIES CONNECTED IN SERIES


In a parallel connected battery bank aimed at maintaining potential di erence and increasing current, one fuse appears to be adequate to protect the circuit against an overcurrent, i.e. between the paral-lel-connected batteries and the load. ere are however other concerns as well: Batteries can internally short circuit, e.g. due to electrode separator failure, causing potentially very large currents. To guard against this eventuality and in addition to the load fuse, each and every battery can be protected against overcurrent with individual and appropriately sized fuses.

Fuse

Load

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FIGURE 10: OVERCURRENT PROTECTION FOR FOUR INDIVIDUAL BATTERIES CONNECTED IN SERIES


FusesA fuse is a device that has a fusible/smeltable conductor between its ends. When the current exceeds the rating of the fuse, the fusible material melts and opens/disconnects the circuit, i.e. a fuse protects the circuit against fault currents. For most battery systems, three types of fuses need to be considered. e smallest types are automotive fuses. Usually these have glass or ceramic cylinders with metal endcaps or an encapsulating plastic body with connecting tabs. ese types of fuses can for example be used in DC circuits below 5 ampere with one 12 volt battery. Above 5 ampere, cartridge-type fuses would be a good choice to protect circuits with small loads and consumers. ere are various standards for overcurrent protection, but to size / select fuses for small single battery systems (< 100 Wp) in 12 V DC circuits one could use the following calculation as a guide:

(i) 12 V DC circuit with consumers drawing in a total maximum of 90 W(ii) Calculation of maximum current drawn from the battery: P / V = I, 90 W / 12 V = 7.5 A(iii) Increase the calculated current value by 20%: 7.5 A x 1.2 = 9 A(iv) In this example, a 9 A fuse or the next size, usually 10 A should be used. In any case, the calcu-

lated fuse rating should always be lower than the current rating of the circuit cables.(v) We always recommend that you use the instruction manual that came with your inverter and

batteries for the sizing of cables, fuses and circuit breakers.(vi) Calculating overcurrent protection for larger DC applications is more complicated. Use the

above example only for small single battery systems.

In the next category we can place time delay fuses. Here a fuse is called a dual-element fuse. ese types of fuses allow the load to exceed its rating for a few seconds before the fuse blows. e higher the current drawn past the fuse, the faster it will blow. ese types of fuses are used with motors so that the fuse will delay while the motor starts, as a motor can draw the rated current a few times to get started.In the last category are very fast acting fuses with a high arc interrupt rating. ese types of fuses should be put on the positive battery terminal. If properly sized and installed, the fuse will clear the short and remove the batteries from the system in the event of a short circuit. e advantages of using fuses are that they have no moving parts and are more or less una ected by temperature variations. As a rule, fuses have a higher arc interrupt rating than most circuit breakers. Remember that some fuses have a time de-lay before blowing. A disadvantage of using fuses is that they can only provide protection once. Further, very fast acting fuses for arc protection are far more expensive than automotive fuses. However, when a battery bank self-destructs due to inadequate fusing protection, costs hardly matter.

Mainfuse

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Circuit BreakersA circuit breaker is a mechanical protection device that can open/interrupt a circuit in case a current passing through the breaker exceeds its rating. It will trip, i.e. open the circuit in one of two ways, de-pending on its design. A thermal circuit breaker heats up when the current draw exceeds its rating and then trips. A magnetic circuit breaker generates a magnetic eld as the current increases, so that the breaker’s contacts trip apart. A circuit breaker has the advantage that it can be used more than once. When it trips you can x the problem in the circuit and then reset the breaker. However, their heavy, spring-driven mechanisms operate very forcefully and wear out quickly. Circuit breakers are thus not meant to be operated frequently. Rather use a load-break switch to isolate components in a circuit.

Requirements for Effective Battery Enclosure and MaintenanceBattery storage and maintenance are important issues. Battery boxes or containers are vented enclosures made from aluminium, berglass, steel or other materials. ese containers can be used for various pur-poses, i.e. they can be pole- or ground mounted and are suitable for indoor or outdoor application. ese enclosures keep your batteries safe from the and protect unauthorised people against possible electrical or chemical hazards. Batteries in a battery bank should always be clean and cable connections secure and tightened. Many battery problems are caused by dirty and loose connections. Serviceable lead-acid batteries need to have their uid levels checked regularly and only at a full charge. Use only distilled water for re ll as domestic water carries dissolved chemicals and minerals that are harmful to lead-acid batteries. To prevent corrosion of cables and connectors, use a small amount of high temperature grease or petroleum jelly (Vaseline).

Charging BatteriesMost modern battery types require special charging technologies, for example all SLA and most AGM batteries, especially the deep cycle models. Regular and appropriate battery charging ensures maximum performance and longevity. Nowadays, three-step regulated charging with special smart chargers is a common technique. e rst step is bulk charging where up to 80 % of the battery energy capacity is replaced by the charger at the maximum ‘voltage’ and current rating of the charger. When the battery reaches a certain potential, let’s say 14.4 volt, absorption charging begins. With this type of charging the ‘voltage’ is kept at a constant 14.4 volt and the current declines until the battery is 98 % charged. en the oat charging step starts via a regulated potential di erence of around 13.4 volt and a current of less than 1 ampere. e three-step charging technology maintains batteries at 100 % readiness and prevents cycling during long-term inactivity.

Precautions Required when Handling and Maintaining Batteries

In addition to the battery safety instructions given in Unit 3, consider the following:(i) Never work alone. Always have someone near you when working around batteries. (ii) Wear appropriate PPE when working with batteries.(iii) Use proper li ing techniques when working with batteries. (iv) Never use old or untested batteries. Check each battery label for age, type and date to ensure all

batteries are identical. (v) Batteries are sensitive to changes in temperature. Always install batteries in a stable environ-

ment.(vi) Install batteries in a well-ventilated area. Batteries can produce explosive gases. For compart-

ment or enclosure installations, always vent batteries to the outside.(vii) Provide su cient space between batteries in a battery bank to make provision for cooling.(viii) Use appropriate insulated tools at all times.(ix) Always verify proper polarity before connecting batteries. To reduce the chance of re or explo-

sion, do not short-circuit the batteries.(x) In the event of accidental exposure to battery acid, wash thoroughly with water. In the event of

exposure to the eyes, ood them for at least 15 minutes with running water and seek immediate medical attention.

(xi) Last but not least, recycle old batteries.

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Common Causes of Battery Failure (Fault Finding)

Most wet-cell failures are caused by one or more of the failures listed below with water loss and sulfation being the main o enders. However, all batteries will fail at some point in time and need replacement, as their plates shed active material during operation. Consider the following failure list for lead-acid and stationary deep-cycle type of batteries:

(i) Loss of electrolyte due to heat or overcharging(ii) Lead sulfation(iii) Undercharging(iv) Age, i.e. positive plate shedding(v) Freezing or high temperatures(vi) Use of domestic water, causing for example calcium sulfation(vii) Positive grid corrosion or growth due to high temperatures(viii) Fast recharging rates

Lack of preventive maintenance, i.e. sulfation from electrolyte loss, under/overcharging, electrolyte strati cation in batteries larger than 100 Ah, use of domestic water, excessive temperatures, or prolonged periods of non-use all account for approximately 85% of battery failures.

Further Information on the R esource CD

(i) DC distribution system characteristics, Short-circuit currents, Schneider, pdf.(ii) Circuit-breakers for direct current applications, ABB, pdf.(iii) e Truth About Batteries, POWERTHRU White Paper, pdf.(iv) Battery Testing Guide, Megger, pdf.(v) Datasheet GEL and AGM Batteries, Vitron, pdf.

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