Conventional and Non-Conventional Sources

of Energy

1. Electricity generation from Conventional Sources of Energy

Conventional energy sources are the sources which are abundantly used for power generation. The sources

mainly include coal, petroleum, natural gas, water and nuclear sources. This energy sources are exhaustible

except water which is renewable source of energy. Electricity generation from some important conventional

energy sources are discussed below:

1.1 Thermal Sources (Coal)

Thermal energy is the energy released on combustion of fossil fuels (e.g. coal, natural gas). This energy is used to turn

water to steam and rotates steam turbines which drives an electric generator.

Figure 1.1.1: General Layout of Coal-fired Station

Figure 1.1.1 shows layout of a typical coal-fired power station. Continuous source of coal is a prerequisite for thermal

power generation. Coal is fed to the boiler through coal handling plant where impurities are removed and pure coal is

pulverised to fine powder. This is done to increase efficiency of boiler as pulverised coal undergoes complete

combustion. The mixture of pulverised coal and preheated air is burnt in combustion zone in boiler. [1] The ash

produced as a result of combustion is removed to ash storage through coal handling plant. The heat energy released

on combustion is utilised to convert water into steam at high temperature and pressure. Steel tubes run along the

boiler walls in which water is converted to steam (figure 1.1.2). The flue gases exchange their heat in superheater,

economiser and air preheater as they get exhausted to the atmosphere. High pressure superheated steam (through

superheater) is expanded in series of turbines namely high pressure, intermediate pressure and low pressure turbines

coupled to an alternator. As a result alternator rotates and electrical energy is generated which is stepped up with the

help of a transformer for transmission. The expanded low pressure steam is exhausted in condenser to be condensed

to water and reused.

Figure 1.1.2: Schematic of Coal-Fired Thermal Power Plant

1.2 Nuclear Sources

Nuclear energy is a result of nuclear reaction viz. fusion and fission reactions. The nuclear fission reaction involves

breaking down heavy nucleus to stable lighter nuclei while fusion reaction combines lighter nuclei to heavy stable

nucleus towards Iron (Fe) (most stable element). The figure 1.2.1 shows the stability of various nuclei. Both type of

nuclear reactions are accompanied by mass deficit and is directly proportional to the amount of energy released. [1]

Figure 1.2.1: Binding Energy per Nucleon vs Mass Number Curve

Figure 1.2.2: Schematic Arrangement of Nuclear Power Plant [2]

Nuclear power plant uses the same technology as that of conventional steam power generation with nuclear reactor

for heat generation instead of coal furnace and boiler. [2] Figure 1.2.2 shows the schematic arrangement of nuclear

power plant. Most nuclear power stations use Uranium as fuel. When bombarded with neutrons, Uranium undergoes

fission reaction in 35 ways one of them is as follows:

Each of the neutrons produced in the reaction strikes with another Uranium nucleus, thus causing nine subsequent

reactions and so on to form a chain reaction as shown in figure 1.2.3. The tremendous amount of heat energy

Figure 1.2.3: Chain Reaction of Uranium-235

produced in fission of Uranium or other heavy elements in nuclear reactor is extracted by pumping fluid or molten

metal like liquid sodium or gas through the pile. The heated metal or gas is then allowed to exchange its heat to the

heat exchanger by circulation. [2] Atomic power plants usually employ a double folded heat removal scheme shown in

figure 1.2.4. First, heat from reactor(R) is transferred from the fission reaction by the coolant. In next stage, in heat

exchanger (H), coolant transfers its heat to water. This produces steam in heat exchanger. Steam passes through

turbine (T) connected mechanically with the generator. The turbine rotates due to expansion of high pressure steam

and electrical power is generated from generator coupled to the turbine. After losing its energy in the turbine, the

steam is converted into water in the condenser (C) which is again delivered to the heat exchanger. [1]

Figure 1.2.4: Heat circuit in an atomic power plant [1]

This video explains functions of different parts of nuclear power plant.

1.3 Hydel Sources

The energy of water utilised for hydro-power generation can be kinetic or potential energy. Kinetic energy of water is

its energy in motion and is a function of mass and velocity while potential energy is a function of difference in level of

water between two points called the head. The hydro energy that can be generated is dependent on the quantity of

water available, the rate at which it is available and the head available. [1] The power generated is directly proportional

to the head available as greater head implies greater pressure to drive turbines. [1]

Figure 1.3.1: General Layout of Hydroelectric Plant

The essential requirement for hydro-electric power generation is the availability of continuous source of water. Figure

1.3.1 shows the general layout of hydro-electric plant with an artificial storage reservoir. Artificial reservoir like dam is

built where natural lake or reservoir is not available. Dam ensures that water is available from wet season to the next

dry season. [1] Water from the storage reservoir is carried through penstocks or canals to the powerhouse. Water after

passing through the turbine is discharged to the stream. [1] [2]

The powerhouse is located at an optimal position from reservoir considering the head loss due to friction in penstock.

The powerhouse contains prime movers, generators and transformers. The prime movers convert kinetic energy of

water into mechanical energy. The alternator or generator coupled to turbine converts mechanical energy to electrical

energy. The prime movers can be reaction or impulse turbines classified on the basis of forces used. [2] Figure 1.3.2

shows different types of turbines employed for power generation. Reaction turbines make use of lift forces while

impulse turbines use drag forces. The reaction turbines are employed when head available is low and high flow rate

while it is converse for the impulse turbines.

Figure 1.3.2: Different types of Hydraulic turbines

This video explains how hydro energy is employed for power generation.

2. Electricity generation from Non-Conventional Sources of Energy

Non-conventional energy is considered the energy of the future. Solar energy, tidal energy, geo-thermal energy, wind

energy, biomass energy are some the non-conventional energy sources and can be used effectively to generate

electricity. This sources can be either reused or abundantly available in nature. Hence this are often termed as

renewable sources of energy. Power exploitation from some of these sources is explained below:

2.1 Solar Energy

Solar energy is regarded as an in-exhaustible (hence renewable) source of energy as the sun is expected to radiate at

constant rate for a few billion years. [3] Solar energy reaches the top of the atmosphere at the rate of 1.353 kW/m2.

Part of this energy is reflected back to space and part is absorbed by atmosphere. In full sunlight, the solar energy

reach the ground at the rate of roughly 1 kW/m2. [3] More energy form sun strikes the earth in one hour than all the

energy consumed on the planet in a year. [4] Solar energy, received in form of radiation, can be converted directly or

indirectly into other forms of energy such as heat and electricity.

Solar energy can be converted into electricity in two ways: (1) Concentrated Solar Thermal Energy (CSTE) systems and

(2) Photovoltaic systems. CSTE systems consist of reflecting surfaces which concentrate solar radiations onto boilers

to produce high pressure steam required for power generation. Figure 2.1.1 shows schematic of solar thermal electrical

power plant. Solar thermal collectors used for concentration can be either trough (or parabolic) concentrators or tower

systems or dish systems (figure 2.1.2) differentiated by the temperatures that can be achieved on concentration. [4]

The heat is transferred via heat transfer fluids (oil, molten salt) to produce steam in heat exchanger which then drives

turbines coupled to electric generator.

Photovoltaics or solar cells are devices which convert incident solar radiation to electrical energy. Solar cells in form of

thin cells are semiconductor devices that convert 3% to less than 30% of incident solar energy into DC electricity with

Figure 2.1.1 : Solar Thermal Electrical Power Plant

Figure 2 .1.2 : Different types of Solar Thermal Collectors

efficiencies depending on illumination intensity, solar cell design and temperature. [4] Electricity generation is a result

of photovoltaic effect shown in figure 2.1.3. Since a solar cell gives low voltage hence such cells are connected in

Figure 2.1.3: Photoelectric Effect

parallel-series configurations to permit high currents and voltages of the order of kilovolts, known as a solar module.

The electrical power output of photovoltaic cell is roughly proportional to the rate at which solar radiation falls on its

surface. Hence insolation is increased by tracking compound parabolic (non-focussing) concentrators. The basic

photovoltaic system integrated with the utility grid is shown in figure 2.1.4. [3] Solar array converts solar insolation to

DC electrical power which is then converted to AC signal in DC, AC inverter to integrate with the utility grid. [3] Battery

storage enables electrical energy to be stored from utility feeder through rectifier or directly from solar array to be

used during no insolation times. Blocking diodes ensures the battery does not discharge to array during times of no

insolation. [3]

Figure 2.1.4: Basic Photovoltaic System integrated with power grid [3]

2.2 Wind Power

Wind energy is harnessed via windmills which convert kinetic energy of wind to mechanical energy. [3] A generator

further converts it to electrical energy or is used to run the machine such as for water pumping, mill grain etc. Wind

energy conversion systems uses two types of turbines classified as Horizontal Axis Wind Turbines (HAWT) and Vertical

Axis Wind Turbines (VAWT) on the basis of axis of rotation relative to wind stream. (Figure 2.2.1)

Figure 2.2.1: Wind Turbine Types, VAWT- (a),(b),(c) and (e) HAWT- (d)

HAWT uses vane or wind sensors to point in direction of the wind. [3] HAWT requires gearbox shown in figure 2.2.2

which turns slower rotation of blades to faster rotation suitable to drive an electric generator. VAWT does not need to

be pointed in the wind direction to be effective as it is independent of wind direction. [3] [4] HAWT and VAWT rotors are

either lift or drag devices. Lift devices have higher rotational speeds and more output power can be developed than

by drag devices. The ratio of power extracted by a lift device to that of drag device is usually greater than 3:1 for the

same swept area.

Figure 2.2.2: Wind Turbine showing gearbox

Figure 2.2.3: Basic Components of Wind Electric System

The figure 2.2.3 shows the basic components of wind-electric conversion system. Wind turbines convert wind energy

into rotary mechanical energy. A mechanical interface, consisting of a step-up gear and a suitable coupling transmits

the energy to an electrical generator. The controller senses the wind direction, wind speed, power output of the

generator and necessary performance quantities of the system and initiates appropriate control signals to take

corrective actions. The system also takes care of electrical faults, extra wind energy and protects from excessive

temperature rise of the generator. [3]

Video shows applications of wind energy, working principle of wind power plant and different parts of wind turbine.

2.3 Geothermal Energy

Geothermal energy is an inexhaustible source of energy present as heat in the earth’s crust. [3] Geothermal energy of

the Earth’s crust originates from the original formation of the planet (20%) and from radioactive decay of minerals

(80%). The geothermal gradient, the difference in temperature between the core of the planet and surface, drives a

continuous conduction of thermal energy in form of heat from the core to the surface.

Figure 2.3.1 shows a typical geothermal field. The hot magma (molten mass) near the surface (A) solidifies into igneous

rock (B). Groundwater coming through fissures gets heated up by heat transfer from the rock or hot gases and steam

emanating from the magma [3] [4] and gets collected in permeable reservoir (C). The hot water then escapes through

fissures (E) in solid impermeable rock (D) in form of fumarols (F) or hot springs (G). [3] [4]

Figure 2.3.1: A Typical Geothermal Field

The hot water escaped through fissures is found at surface in following forms:

1) Dry steam at about 200 °C and 8 bar pressure [3] emanating from vapour dominated reservoir. It is passed to low

pressure turbine via centrifugal separator to generate electricity as shown in the figure 2.3.2.

Figure 3: Schematic of Vapour-Dominated Power Plant

2) Wet steam, mixture of hot water and steam which is formed due to flashing of liquid water as it rises to the low

pressure surface (ground) in liquid dominated reservoir with water temperature above 100 °C. Hence it is passed

through flash separator to separate steam and then passed to turbine to generate electricity as shown in figure 2.3.3.

Geothermal resources is also found in form of Hot Dry Rock (HDR) system but no underground water shown in figure

2.3.4. In such cases, a cavity is created by detonating an explosive at the bottom of a well drilled into the rock. Water

is circulated through the cavity to extract heat from the rock. Water-steam mixture thus obtained is utilised for

generation of electricity with binary liquid system using Freon as turbine working fluid. [3]

Figure 2.3.4: Heat Extraction from Hot Dry Rocks

Geothermal resources having temperatures low enough to produce steam are used for heating applications in

industries and households.

The video shows different forms through which geothermal energy rises to earth’s surface in Iceland and gives an idea

to generate power utilising geothermal energy.

Figure 2 .3. 3: Schematic of Liquid - Dominated Power Plant

The video explains the occurrence of geothermal energy, animates different ways to utilise it for power generation

and benefits of geothermal energy and its waste products.

2.4 Biomass energy

Biomass is an organic matter produced by plants, both terrestrial and aquatic, and their derivatives. It includes forest

crops and residues, crops grown for their energy content on ‘energy farms’ and animal manure. [3] Biomass is indirectly

obtained from solar energy through photosynthesis by plants. One of the advantages of biomass fuel is that it is often

a by-product, residue or waste-product of other processes such as farming, animal husbandry and forestry.

Video gives basic idea on power generation from different biomass sources.

Biomass resources can be found in any of the three forms [3]:

(1) Solid mass in form of wood and agriculture residue

(2) Liquid fuels by converting biomass to methanol and ethanol

(3) Biogas obtained on Bio digestion

Table 2.4.1: Biomass Conversion Technologies [3]

Conversion

Process

Principle Products Further

Treatment

Premium

Fuels Solids Liquids gases

Wet Anaerobic

Digestion

Methane b

and

Carbondioxide

Carbondioxide Removal

Methane

Fermentation Ethanol Distillation Ethanol

Chemical

Reduction

Mixture of

oils

Fractional

distillation

Hydrocarbon

liquids

Thermal

processes

Liquefaction Char Pyroligneou

s acid oils

and tars

Fuel gas b Steam reforming

and/or shift

reaction

Methane

Methanol or

Higher

Alcohols

Gasification

Char Fuel gas a,c

Steam-gasification Char Methane c

Hydrogenation Mixture of

oils

Fractional

distillation

Hydrocarbon

liquids

Oil Extraction Vegetable

oil

Esterification Diesel

substitute

Key: a = low calorific value (5-10 MJ/m3)

b = medium calorific value (10-25 MJ/m3)

c = low calorific value (30-45 MJ/m3)

The table 2.4.1 shows various conversion technologies used to obtain fuel from biomass. Biogas can be produced by

digestion, pyrolysis or hydrogasification and is a mixture containing 55-65% Methane, 30-40% Carbon dioxide and rest

being the impurities (H2, H2S and N2). Biogas is a slow burning gas having calorific value between 5000 to 5500 kcal/kg. [3]

Figure 2.4.1: Fixed Dome type Biogas Plant

The figure 2.4.1 shows fixed dome biogas digester. Slurry is subjected to anaerobic digestion/fermentation using

different types of microorganisms (bacteria, fungi, virus etc.).[3] The gas is collected at the top and can be used for

cooking, water heating and industries. Fuels obtained on biomass conversion technologies having good enough

calorific value can be burnt to produce steam and run the turbines to generate electricity.

2.5 Tidal Energy

Tides are generated by action of gravitational forces of the sun and moon on the water of the earth. [3] [4] The tides are

periodic vertical rise and fall of water. The tidal rise and fall of water is accompanied by periodic horizontal to and fro

motion of water called tidal currents. [4] The amplitude of tides covers a wide range from 25 cm to 10 m because of the

changing positions of the moon and sun relative to earth. The speed of tidal currents is in the range of 1.8 km/h to 18

km/h. [4]

Figure 2.5.1: Principle of Tidal Power Generation

Figure 2.5.1 shows the principle of tidal power generation. The principle is to utilise differential head during high and

low tides in operating a hydraulic turbine. The idea is to hold water in a basin during high tide and then let water back

to sea through a turbine, thus producing power. [3] The power can also be generated by utilising both high and low

tides by double cycle system shown in figure 2.5.2.

Figure 2.5.2: Double cycle system

Tidal power extraction involves construction of a long barrier across a bay or an estuary to create a large basin on

the landward side. The barrier includes dykes, gate-controlled sluices and the power house. [4] The different tidal

power schemes employed for power generation are Single Basin Tidal Power Scheme and Linked Basin Tidal Power

Scheme (figures 2.5.3(a) and 2.5.3(b)). In former type, the power is generated from both tides using double cycle

system but involves only one basin. In the latter type, there are two basins on the landward side with the power

house located in barrier between the two basins. Power is generated by water flowing from high basin to low basin

during high tide when sluice gates of low basin are closed so that sufficient head is available. The water is then let to

sea during the low tide. [3] [4] The typical hydraulic turbine employed for tidal power generation is shown in figure

2.5.4.

Figure 2.5.3: Different Tidal Power Schemes

Figure 2.5.4: Layout of Tidal Power Plant

References

1. Abhijit Chakrabarti, M. L. Soni, P.V. Gupta and U. S. Bhatnagar, A Textbook on Power System Engineering

(Second Edition), DhanpatRai and Sons, New Delhi, 2010

2. JB Gupta, A Course in Electrical Power (Fifteenth Edition), S. K. Kataria and Sons, New Delhi, 2013

3. G.D. Rai, Non-Conventional Energy Sources (Fifth Edition), Khanna Publishers, New Delhi, 2007

4. Tasneem Abbasi and S.A. Abbasi, Renewable Energy Sources Their Impact on Global Warming and Pollution,

Prentice Hall India Learning Private Limited, 2010