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Photovoltaic Design and Installation. Bucknell University Solar Scholars Program. Presenters: Colin Davies ‘08 Eric Fournier ‘08. Outline. Why Renewable Energy? The Science of Photovoltaics System Configurations Principle Design Elements - PowerPoint PPT Presentation
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Photovoltaic Design and Installation
Bucknell University Solar Scholars Program
Presenters:
Colin Davies ‘08
Eric Fournier ‘08
Outline
Why Renewable Energy? The Science of Photovoltaics System Configurations Principle Design Elements The Solar Scholars program at
Bucknell (walking tour)
What’s wrong with this picture?
Pollution from burning fossil fuels leads to an increase in greenhouse gases, acid rain, and the degradation of public health.
In 2005, the U.S. emitted 2,513,609 metric tons of carbon dioxide, 10,340 metric tons of sulfur dioxide, and 3,961 metric tons of nitrogen oxides from its power plants.
40%
85% of our energy consumption is from fossil fuels!
Why Sustainable Energy Matters
The world’s current energy system is built around fossil fuels– Problems:
Fossil fuel reserves are ultimately finiteTwo-thirds of the world' s proven oil reserves are
locating in the Middle-East and North Africa (which can lead to political and economic instability)
Why Sustainable Energy Matters
Detrimental environmental impacts– Extraction (mining operations)– Combustion
Global warming? (could lead to significant changes in the world' s climate system, leading to a rise in sea level and disruption of agriculture and ecosystems)
A Sustainable Energy Future
Develop and deploy renewable energy sources on a much wider scale
Bring down cost of renewable energy Make improvements in the efficiency of energy
conversion, distribution, and use
Three Methods:
- Incentives
- Economy of scale
- Regulation
Making the Change to Renewable Energy
Solar Geothermal Wind Hydroelectric
Today’s Solar Picture
Germany leads solar production (over 4.5 times more then US production) – Japan is 2nd (nearly 3 times more then US production) – this is mainly due to incentives
Financial Incentives– Investment subsidies: cost of installation of a
system is subsidized – Net metering: the electricity utility buys PV
electricity from the producer under a multiyear contract at a guaranteed rate
– Renewable Energy Certificates ("RECs")
Solar in Pennsylvania
Pennsylvania is in fact a leader in renewable energy
Incentives– Local & state grant and loan programs– Tax deductions– REC’s (in 2006: varied from $5 to $90 per MWh,
median about $20)
Harnessing the Sun
Commonly known as solar cells, photovoltaic (PV) devices convert light energy into electrical energy
PV cells are constructed with semiconductor materials, usually silicon-based
The photovoltaic effect is the basic physical process by which a PV cell converts sunlight into electricity– When light shines on a PV cell, it may be
reflected, absorbed, or pass right through. But only the absorbed light generates electricity.
Electricity
Part 2: Learning Objectives
Compare AC and DC electrical current and understand their important differences
Explain the relationship between volts, amps, amp-hours, watts, watt-hours, and kilowatt-hours
Learn about using electrical meters
Electricity Terminology
Electricity = Flowing electrons
Differences in electrical potential create electron flow
Loads harness the kinetic energy of these flowing electrons to do work
Flowing water is a good conceptual tool for understanding
Electricity Terminology
Voltage (E or V) – Unit of electromotive force – Can be thought of as electrical pressure
Amps (I or A)– Rate of electron flow – Electrical current – 1 Amp = 1 coulomb/second = 6.3 x 1018
electrons/second
Electricity Terminology
Resistance (R or Ω) – The opposition of a material to the flow of an
electrical current – Depends on
Material Cross sectional area Length Temperature
Electricity Terminology
Watt (W) are a measure of Power – Unit rate of electrical energy
Amps x Volts = Watts 1 Kilowatt (kW) = 1000 watts
Electricity Terminology
Watt-hour (Wh) is a measure of energy – Unit quantity of electrical energy (consumption
and production) – Watts x hours = Watt-hours
1 Kilowatt-hour (kWh) = 1000 Wh
Power and Energy Calculation
Draw a PV array composed of four 75 watt modules.
What size is the system in watts ?
Electricity Terminology
Amp-hour (Ah) – Quantity of electron flow – Used for battery sizing – Amps x hours = Amp-hours – Amp-hours x Volts = Watt-hours
A 200 Ah Battery delivering 1A will last _____ hours 200 Ah Battery delivering10 A will last _____ hours 100 Ah Battery x 12 V = _____ Wh
Types of Electrical Current
DC = Direct Current – PV panels produce DC– Batteries store DC
AC = Alternating Current – Utility power – Most consumer appliances
use AC
Meters and Testing
Clamp on meter Digital multimeter
Never test battery current using a multimeter!
System Types
Part 1: Learning Objectives
Understand the functions of PV components Identify different system types
Photovoltaic (PV) Terminology
Cell < Module < Panel < Array Battery – stores DC energy Controller – senses battery voltage and
regulates charging Inverter – converts direct current (DC )
energy to alternating current (AC) energy Loads – anything that consumes energy
Systems with DC Loads
DC System Options
Battery backup vs. discontinuous use LVD option in charge controller Load controllers
Systems with AC loads
AC System Options
Combined AC and DC loads Hybrid system with back up generator Grid tied utility interactive system without
batteries Grid tied interactive with battery backup
(why might you need this?)
Grid-Tied System(Without Batteries)
Complexity– Low: Easy to install
(less components)
Grid Interaction– Grid can supplement
power– No power when grid
goes down
Grid-Tied System(With Batteries)
Complexity– High: Due to the
addition of batteries
Grid Interaction– Grid still supplements
power– When grid goes down
batteries supply power to loads (aka battery backup)
PV Modules
Part 3: Learning Objectives
Learn how a PV cell produces electricity from sunlight
Discuss the 3 basic types of PV cell technologies
Understand the effects of cell temperature and solar insolation on PV performance
Gain understanding of module specification Identify the various parts of a module
Solar Cells and the PV Effect
Usually produced with Semi-conductor grade silicon
Doping agents create positive and negative regions
P/N junction results in 0.5 volts per cell Sunlight knocks available electrons loose Wire grid provides a path to direct current
Inside a PV Cell
Available Cell Technologies
Single-crystal or Mono-crystalline Silicon
Polycrystalline or Multi-crystalline Silicon
Thin film
– Ex. Amorphous silicon or Cadmium Telluride
Monocrystalline Silicon Modules
Most efficient commercially available module (11% - 14%)
Most expensive to produce
Circular (square-round) cell creates wasted space on module
Polycrystalline Silicon Modules
Less expensive to make than single crystalline modules
Cells slightly less efficient than a single crystalline (10% - 12%)
Square shape cells fit into module efficiently using the entire space
Amorphous Thin Film
Most inexpensive technology to produce
Metal grid replaced with transparent oxides
Efficiency = 6 – 8 % Can be deposited on
flexible substrates Less susceptible to
shading problems Better performance in low
light conditions that with crystalline modules
Selecting the Correct Module
Practical Criteria – Size – Voltage – Availability – Warranty – Mounting Characteristics – Cost (per watt)
Current-Voltage (I-V) Curve
Voltage Terminology
Nominal Voltage – Ex. A PV panel that is sized to charge a 12 V battery, but
reads higher than 12 V)
Maximum Power Voltage (Vmax / Vmp) – Ex. A PV panel with a 12 V nominal voltage will read 17V-
18V under MPPT conditions)
Open Circuit Voltage (Voc )– This is seen in the early morning, late evening, and while
testing the module)
Standard Test Conditions (STC) – 25 º C (77 º) cell temperature and 1000 W/m2 insolation
Effects of Temperature
As the PV cell temperature increases above 25º C, the module Vmp
decreases by approximately 0.5% per degree C
Effects of Shading/Low Insolation
As insolation decreases amperage decreases while voltage remains roughly constant
Other Issues
Surface temperature can be measured using laser thermometers
Insolation can be measured with a digital pyranometer
Attaching a battery bank to a solar array will decrease power production capacity
PV Wiring
Part 4: Learning Objectives
List the characteristics of series circuits and parallel circuits
Understand wiring of modules and batteries Describe 12V, 24V, and 48V designs
Series Connections
Loads/sources wired in series
– VOLTAGES ARE ADDITIVE – CURRENT IS EQUAL – One interconnection wire is used
between two components (negative connects with positive)
– Combined modules make series string– Leave the series string from a terminal
not used in the series connection
Loads/sources wired in parallel:
– VOLTAGE REMAINS CONSTANT– CURRENTS ARE ADDITIVE – Two interconnection wires are used between two
components (positive to positive and negative to negative)– Leave off of either terminal – Modules exiting to next component can happen at any parallel terminal
Parallel Connections
Quiz Time
If you have 4 12V / 3A panels in an array what would the power output be if that array were wired in series?
What if it were wired in parallel? Is it possible to have a configuration that
would produce 24 V / 6 A? Why?
Dissimilar Modules in Series
Voltage remains additive – If module A is 30V / 6A and module B is 15V / 3A
the resulting voltage will be?
Current taken on the lowest value – For modules A and B wired in series what would
be the current level of the array?
Dissimilar Modules in Parallel
Amperage remains additive – For the same modules A and B what would the
voltage be?
Voltage takes on the lower value.– What would the voltage level of A and B wired in
parallel be?
Shading on Modules
Depends on orientation of internal module circuitry relative to the orientation of the shading.
SHADING can half
or even completely
eliminate the output
of a solar array!
Wiring Introduction
PV installations must be in compliance with the National Electrical Code (NEC)
– Refer to NEC Article 690 (Solar Photovoltaic Systems) for detailed electrical requirements
Discussion points– Wire types, wire sizes– Cables and conduit– Voltage drops– Disconnects– Grounding
Wire Types
Conductor material = copper (most common) Insulation material = thermoplastic (most common)
– THHN: most commonly used is dry, indoor locations– THW, THWN, and TW can be used indoors or for wet
outdoor applications in conduit– UF and USE are good for moist or underground
applications
Wire exposed to sunlight must be classed as sunlight resistant
Color Coding of Wires
Electrical wire insulation is color coded to designate its function and useAlternating Current (AC) Wiring Direct Current (DC) Wiring
Color Application Color Application
Black Ungrounded Hot Red (not NEC req.) Positive
White Grounded Conductor
White Negative or Grounded Conductor
Green or Bare Equipment Ground
Green or Bare Equipment Ground
Red or any other color
Ungrounded Hot
Cables and Conduit
Cable: two or more insulated conductors having an overall covering
– As with typical wire insulation, protective covering on cable is rated for specific uses (resistance to moisture, UV light, heat, chemicals, or abrasion)
Conduit: metal or plastic pipe that contains wires– PVC is a common conduit used– Using too many wires or too large of wires in a given conduit
size can cause overheating and also causes problems when “pulling” wire
Wire Size
Wire size selection based on two criteria:– Ampacity– Voltage drop
Ampacity: current carrying ability of a wire– The larger the wire, the greater its capacity to carry current– Wire size given in terms of American Wire Gauge (AWG)
The higher the gauge number, the smaller the wire Voltage drop: the loss of voltage due to a wire’s
resistance and length– Function of wire gauge, length of wire, and current flow in the
wire
Safety Considerations
Unsafe Wiring– Splices outside the box– Currents in grounding conductors– Indoor rated cable used outdoors– Single conductor cable exposed– “Hot” fuses
Disconnects Overcurrent Protection (Fuses & Breakers)
Safety Equipment
Disconnects– Allow electrical flow to be
physically severed (disconnected) to allow for safe servicing of equipment
Overcurrent Protection– Protect an electrical
circuit from damage caused by overload or short circuit
Fuses Circuit Breakers
Grounding
Limit voltages due to:– Lightning– Power line surges– Unintentional contact with higher voltage lines
Provides a current path for surplus electricity to travel too (earth)
Two types of grounding:– Equipment grounding (attach all exposed metal parts of PV
system to the grounding electrode)– System grounding (at one point attach ground to one current
carrying conductor) DC side of system => Negative to ground AC side of system => Neutral to ground
Batteries
Part 4: Learning Objectives
Battery basics Battery functions Types of batteries Charging/discharging Depth of discharge Battery safety
Batteries in Series and Parallel
Series connections– Builds voltage
Parallel connections – Builds amp-hour capacity
Battery Basics
Battery A device that stores electrical energy (chemical energy to
electrical energy and vice-versa) Capacity
Amount of electrical energy the battery will contain State of Charge (SOC)
Available battery capacity Depth of Discharge (DOD)
Energy taken out of the battery Efficiency
Energy out/Energy in (typically 80-85%)
The Terms:
Functions of a Battery
Storage for the night Storage during cloudy weather Portable power Surge for starting motors
**Due to the expense and inherit inefficiencies of batteries it is recommended that they only be used when absolutely necessary (i.e. in remote locations or as battery backup for grid-tied applications if power failures are common/lengthy)
Batteries: The Details
Primary (single use) Secondary (recharged) Shallow Cycle (20% DOD) Deep Cycle (50-80% DOD)
Types:
Unless lead-acid batteries are charged up to 100%, they will loose capacity over time
Batteries should be equalized on a regular basis
Charging/Discharging:
Battery Capacity
Amps x Hours = Amp-hours (Ah)
Capacity:
100 amps for 1 hour
1 amp for 100 hours
20 amps for 5 hours
Capacity changes with Discharge Rate The higher the discharge rate the lower the capacity and vice versa The higher the temperature the higher the percent of rated capacity
100 Amp-hours =
Rate of Charge or Discharge
Rate = C/T
C = Battery’s rated capacity (Amp-hours)T = The cycle time period (hours)
Maximum recommend charge/discharge rate = C/3 to C/5
Cycle Life vs. Depth of Discharge
Depth Of Discharge (DOD) %
# of Cycles
Battery Safety
Batteries are EXTREMELY DANGEROUS; handle with care!– Keep batteries out of living space, and vent battery
box to the outside– Use a spill containment vessel– Don’t mix batteries (different types or old with new)– Always disconnect batteries, and make sure tools
have insulated handles to prevent short circuiting
Battery Wiring Considerations
Battery wiring leads should leave the battery bank from opposite corners– Ensures equal charging and discharging;
prolongs battery life
Make sure configuration of battery bank allows for proper connections to be easily made
Controllers & Inverters
Part 5: Learning Objectives
Controller basics Controller features Inverter basics Specifying an inverter
Controller Basics
To protect batteries from being overchargedFunction:
Maximum Power Point Tracking– Tracks the peak
power point of the array (can improve power production by 20%)!!
Features:
Additional Controller Features
Voltage Stepdown Controller: compensates for differing voltages between array and batteries (ex. 48V array charging 12V battery)– By using a higher voltage array, smaller wire can be
used from the array to the batteries Temperature Compensation: adjusts the charging of
batteries according to ambient temperature
Other Controller Considerations
When specifying a controller you must consider:– DC input and output voltage– Input and output current– Any optional features you need
Controller redundancy: On a stand-alone system it might be desirable to have more then one controller per array in the event of a failure
Inverter Basics
An electronic device used to convert direct current (DC) electricity into alternating current (AC) electricity
Function:
Efficiency penalty Complexity (read: a component which can fail) Cost!!
Drawbacks:
Specifying an Inverter
What type of system are you designing?– Stand-alone– Stand-alone with back-up source (generator)– Grid-Tied (without batteries)– Grid-Tied (with battery back-up)
Specifics:– AC Output (watts)– Input voltage (based on modules and wiring)– Output voltage (120V/240V residential)– Input current (based on modules and wiring)– Surge Capacity– Efficiency– Weather protection– Metering/programming
Solar Site
Part 6: Learning Objectives
Understand azimuth and altitude Explain magnetic declination Describe proper orientation and tilt angle for
solar collection Describe the concept of “solar window”
Site Selection – Panel Direction
Face south Correct for
magnetic declination
Orientation and Tilt Angle
Sun Chart for 40 degrees N Latitude
Site Selection – Tilt Angle
Year round tilt = latitudeWinter + 15 lat.Summer – 15 lat.
Max performance isachieved when panelsare perpendicular to thesun’s rays
Solar Access
Optimum Solar Window 9 am – 3 pm
Array should have NO SHADING in this window (or longer if possible)
Solar Pathfinder
An essential tool in finding a good site for solar is the Solar Pathfinder
Provides daily, monthly, and yearly solar hours estimates
Practical Determinants for Site Analysis
Loads and time of use Local climate characteristics Distance from power conditioning equipment Accessibility for maintenance Aesthetics
Energy Efficiency
Part 7: Learning Objectives
Identify cost effective electrical load reduction strategies
List problematic loads for PV systems Describe penalties of PV system components Explain phantom loads Evaluate types of lighting; efficiency
comparison
Practical Efficiency Recommendations
For every $1 spent on energy efficiency, you save $3-$5 on system cost
Adopt a load dominated approach – Do it efficiently – Do it another way– Do with less– Do without – Do it using DC power– Do it while the sun shines
Typical Wattage Requirements
Appliance Wattage
Blender 350
TV (25 inch) 130
Washer 1450
Sunfrost Refrigerator (7 hours a day)
refrigerator/freezer (13 hours a day)
112
475
Hair Dryer 1000
Microwave (.5 sq-ft)
Microwave (.8 – 1 sq-ft)
750
1400
Appliances to Avoid
Electric oven or stove Electric space heater Dishwasher with heaters Electric water heater Electric clothes dryer
Improving Energy Efficiency in the Home
Space Heating:– Super insulation– Passive solar design – Wood stoves– Propane– Solar hot water– Radiant Floor/
baseboard– Efficient windows
Domestic hot water heating
– Solar thermal – Propane/natural gas– No electric heaters– On demand hot water
Improving Energy Efficiency in the Home
Kitchen Stoves– Solar cookers – Gas burners- no glow
bar ignition – Microwaves
Washing machines– High efficiency horizontal
axis
Cooling – Ceiling fans – Window shades– Evaporative cooling – Insulation– Trees– Reflective attic cover– Attic fan
Phantom Loads
Phantom Loads
Cost the United States:– $3 Billion / year– 10 power plants – 18 million tons of CO2– More pollution than 6 million cars
TV’s and VCR’s alone cost the US $1 Billion/year in lost electricity
Lighting Efficiency
Factors effecting light efficiency– Type of light– Positioning of lights– Fixture design– Color of ceilings and walls– Placement of switches
Incandescent Lamps
Advantages – Most common– Least expensive– Pleasing light
Disadvantages – Low efficiency – Short life ~ 750 hours
Electricity is conducted through a filament which resists the flow of electricity, heats up, and glows
Efficiency increases as lamp wattage increases
FROM THE POWER PLANT TO YOUR HOME INCANDESCENT BULBS ARE LESS THAN 2%
EFFICIENCT
Fluorescent Bulbs
Les wattage, same amount of lumens Longer life (~10,000 hours) May have difficulty starting in cold
environments Not good for lights that are repeatedly turned
on and off Contain a small amount of mercury
Light Emitting Diode (LED) Lights
Advantages – Extremely efficient – Long life (100,000 hours)– Rugged – No radio frequency
interference
Disadvantages– Expensive (although
prices are decreasing steadily)
– A relatively new technology
Mounting
Part 8: Learning Objectives
Evaluate structural considerations
List hardware requirements
Pros and cons of different mounting techniques
General Considerations
Weather characteristics– Wind intensity– Estimated snowfall
Site characteristics – Corrosive salt water– Animal interference
Human factors– Vandalism – Theft protection– Aesthetics
Basic Mounting Options
Fixed– Roof, ground, pole– Integrated
Tracking– Pole (active & passive)
Pole Mount Considerations
Ask manufacturer for wind loading specification for your array– Pole size– Amount of concrete– Etc.
Array can be in close proximity to the house without penetrations to roof structure
Tracking Considerations
Can increase system performance by: – 15% in winter months– 40% in summer months
Adds additional costs to the array
Passive Vs. Active
Passive:– Have no motors, controls, or gears– Use the changing weight of a gaseous refrigerant
within a sealed frame member to track the sun
Active:– Linear actuator motors controlled by sensors
follow the sun throughout the day
Roof Mount Considerations
Penetrate the roof as little as possible Weatherproof all holes to prevent leaks
– May require the aid of a professional roofer Re-roof before putting modules up Ballasted roof mounts work on certain roofs Leave 4-6” airspace between roof and
modules On sloped roofs, fasten mounts to rafters not
decking
Building Integrated PV
Ready for a field tour?
Questions?
If you are interested in anything you have seen today and would like to get involved, please contact any member of the Solar Scholars team:
Colin Davies, Eric Fournier, or Jess Scott (cjdavies, efournie, jpscott)
The END
Thank you for participating in this lecture series
Now lets go out into the field and take a look at the systems that we have already installed.