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Chapter 12: Non-Conventional Sources of Energy

The lights go out at four in the afternoon. Inside the classroom the fans slow, stop, and the room grows warm within a minute. Outside, nothing has changed at all. The sun is still standing over the playground, hard and bright. On the ridge beyond the school the wind is still bending the grass in long waves. Somewhere down the coast the tide is still climbing the shore, as it does twice every day, on time, whether anyone is watching it or not. This is the strange thing about energy. It never stops arriving. Sunlight lands on the roof of the school through most days of the year. The wind crosses the ridge whether a machine is standing there or not. Heat leaks slowly upward from hot rock far below the floor of the classroom. Behind the school, in the cattle shed, bacteria are breaking down dung at this very moment and giving off a gas that will burn. None of it is electricity yet. Energy has to be caught, turned into movement, and made to spin something. This chapter is about the machines that do the catching, and about why each one works in some places and not in others.

Diagram

Fig. 12.A1 Caption: Six sources, one grid — each machine catches energy that was arriving anyway. Brief: One wide landscape reading left to right — solar panels on a rooftop, windmills on an open ridge, a tidal barrage across a coastal inlet, a geothermal plant beside a hot spring, a nuclear power plant with cooling towers, a village biogas plant beside a cattle shed; label each and draw a thin power line linking all six to a single grid pylon on the right.

NoteCuriosity Corner

Q1. Why does India receive so much more solar energy than many other countries? Q2. The tide rises and falls twice a day without fail. How is that turned into electricity? Q3. How can cattle dung give a family cooking gas and good manure at the same time? Q4. Heat lies in rock far below the ground. How is it brought up and used? By the end of this chapter you will be able to answer all four.

12.1 What Non-Conventional Sources Of Energy Are

Non-conventional sources of energy are the sources that have been developed only in the recent past, as an alternative to the conventional sources on which the country has long depended. They are called new not because the energy itself is new. Sunlight and wind are far older than any coal seam. What is new is the set of machines that catch them and turn them into electricity.

Six such sources are studied in this chapter, and each one draws on something the earth or the sky is already doing. (a) Solar energy comes from the radiation the sun pours onto the earth’s surface every clear day. (b) Wind energy comes from moving air, which can be made to push a blade round. (c) Tidal energy comes from the rise and fall of ocean water, which happens twice a day at a coast. (d) Geothermal energy comes from heat held in the rock and fluid inside the earth’s crust. (e) Nuclear energy comes from energy stored in the nuclei of atoms of radioactive elements. (f) Biogas comes from animal and plant waste that bacteria break down.

The six sit together as one family, and the branching chart below sets them out with the raw material each one begins from.

Flowchart

Fig. 12.A2 Caption: Six non-conventional sources, and the thing each one begins from. Nodes: non-conventional sources of energy → six branches → solar energy → sunlight; wind energy → moving air; tidal energy → rise and fall of sea water; geothermal energy → heat in rock inside the earth’s crust; nuclear energy → splitting of atoms of radioactive elements; biogas → animal and plant waste broken down by bacteria

Why These Sources Are Different

Most of these sources are renewable, which means the supply is replaced as fast as it is used. A renewable source is therefore inexhaustible — it cannot be used up, however long we draw on it. The sun rises again tomorrow and the tide returns tonight, whether or not a machine was waiting for either of them.

Three further qualities follow from this. These sources are non-polluting, they are less expensive to run once the machine is standing, and they are easy to maintain.

Q. The book says most of these sources are renewable, not all. Which one is the exception?

A. Nuclear power. It runs on radioactive minerals dug out of the ground, and a mineral once used is gone. The other five draw on flows that keep arriving.

The Resources Of The Future

These sources are considered the energy resources of the future. Because of the benefits just listed, many countries of the world, India among them, have begun producing energy from them on a large scale rather than in small experiments.

The work is not finished. Research continues in this field, with two aims — to bring down the cost of production, and to make these sources more cost-effective, so that the energy they give is worth more than the machine that catches it.

12.2 Solar Energy

The sun is the ultimate source of energy. Long before anyone thought of turning sunlight into electricity, people were already using it directly, and those older uses are still with us. (a) Clothes and food-grains are spread out to dry, because the sun’s heat drives the moisture out of them. (b) Eatables are preserved by drying, since food that has lost its moisture spoils far more slowly. (c) Salt is obtained from sea-water in shallow pans, where the sun evaporates the water and leaves the salt behind.

India is fortunate enough to receive a higher amount of solar energy than most countries — an amount equivalent to 5,000 trillion kWh per year. This is because of India’s location on the Tropic of Cancer, the line of latitude that runs across the middle of the country, so the midday sun stands high in the sky over most of India for most of the year.

Two figures show how steady that supply is. Most parts of the country have 300 clear sunny days in a year, and the availability of solar energy is between 5 to 7 kW per hour per square km. A kilowatt is a thousand watts, a measure of how fast energy is being delivered, so this is a rate of arrival rather than a stock lying in the ground waiting to be dug up.

Q1. Why does India receive so much more solar energy than many other countries?

A. India lies on the Tropic of Cancer, so the sun stands high over it. Most parts get 300 clear sunny days a year, and 5 to 7 kW of solar energy arrives on each square km every hour. That adds up to 5,000 trillion kWh a year.

Where This Energy Is Being Caught

The world’s largest solar park, the Bhadla Solar Park, is located in Bhadla tehsil in Jodhpur, in the state of Rajasthan. The park has a total capacity of 2,245 MW. A megawatt is a million watts, and capacity is the most the park can deliver at one time, not what it delivers at every hour of the day.

India has also used solar panels as a gift. It gifted 193 solar panels — one panel for each member state — and these have been installed on the roof of the UN Headquarters, in what is called the Gandhi Solar Park. The energy generated there would be equivalent to the energy obtained by using 30,000 kg of coal.

The most complete example, though, is a single village that was rebuilt around the idea.

WC 12.1 — India’s First Solar Village At Modhera The situation: Modhera, a village in the Mehsana district of Gujarat, was chosen to become India’s first Solar Village, in order to empower people at the grass root level using the country’s renewable energy prowess. The working: 1000 solar panels were installed on the village houses, generating electricity round the clock for the villagers → the supply was built through a Ground Mounted Solar Power Plant and more than 1300 Rooftop Solar Systems on residential and government buildings → all of these were integrated with Battery Energy Storage Systems (BESS) → the village now meets all its electricity requirements 24×7 through a 6 MW solar plant coupled with 15 MWh of battery storage → the people of the village are able to save 60 to 100% of their electricity bills → at the ancient Sun temple at Modhera, a 3-D solar-powered projection facility now runs on this supply and educates visitors about the history of Modhera.

The battery storage is the part that makes Modhera work. Panels alone stop producing the moment the sun goes down, so a village running on panels alone would still need the grid at night. Storing the day’s surplus and drawing it back after dark is what turns a daytime supply into a round-the-clock one. Now think about whether it is possible and feasible to establish every village in the country as a Solar Village like Modhera — what a village would need in the way of sunlight, roof space, land and money before the same plan could be repeated there.

Diagram

Fig. 12.2 Caption: Rows of ground-mounted panels beside the village at Modhera, in Gujarat. Brief: Source an aerial photograph of the Modhera solar installation showing the panel rows in the foreground and village housing behind; label the ground-mounted plant and the rooftop systems.

12.2.1 Generation Of Solar Energy

Several techniques have been developed in India for harnessing solar energy. Three of them are described below, and they differ in what they do with the sunlight — one turns it straight into electricity, while the other two simply trap it as heat.

Solar Cells

Solar cells are also known as photovoltaic cells. They are made of thin wafers of semi conductor materials from silicon and gallium. When the sun’s radiations strike them, the sun’s energy is converted into electricity directly, with nothing turning and nothing burning.

A single cell gives very little, so solar cells are used where the demand is small. (a) Calculators run on a strip of cells no bigger than a fingernail. (b) Electronic watches keep going on the light that falls on the dial. (c) Street lighting can be run off a cell and a battery, without a cable to the grid. (d) Traffic signals use them for the same reason, since a signal must keep working when the supply fails. (e) Water pumps can be driven by them where the field is far from a power line.

A group of solar cells joined together in a solar panel can give out a large amount of solar energy. A panel can produce electricity enough to run street-lights, irrigation water pumps, and the heating or cooling equipment of a house.

Diagram

Fig. 12.1 Caption: A solar water pump lifting water in the field, driven by the panel standing behind it. Brief: Source a photograph of a panel-driven water pump discharging water into a field channel; label the solar panel, the pump head and the outlet.

Solar Cooker

A solar cooker uses solar heat rather than electricity. Solar radiations are reflected by a mirror on to a glass sheet, which covers a black insulated box. The raw food is kept inside this box.

Every part of the box has a job. The inside walls of the sides are painted black for efficient absorption of light, since a black surface absorbs far more of the light falling on it than a pale one. The box is insulated on the outside so that the heat cannot escape.

The trap then closes. The heated inside of the box emits infrared radiation, and the glass window is opaque to that radiation — light gets in, but the heat radiation cannot get back out. In this way a significant amount of the energy entering the oven is retained. The cooking pot is placed inside the box, and cooking is made possible.

A new design of solar cooker is now available which involves a spherical reflector instead of a plane mirror. A curved reflector gathers the rays towards one place instead of turning them all in the same direction, so it has more heating effect and greater efficiency.

Diagram

Fig. 12.A3 Caption: The cooker lets light in through the glass and does not let the heat radiation back out. Brief: Cut-away view of a box-type solar cooker — hinged plane mirror reflecting rays onto the glass sheet, black inner walls, insulation layer, cooking pot inside; arrows in for sunlight and blocked arrows at the glass for infrared going out.

Solar Water Heater

One of the most successful applications of solar energy has been in the field of water heating. Sunlight is allowed to fall on flat-plate collectors, which are shallow rectangular trays filled with water and properly inclined so that the efficiency of collection is highest. The tilt matters, because a surface facing the sun squarely catches more of its rays than one lying flat.

The collector consists of an insulated box painted black from inside and having a glass lid to collect and store solar heat. Inside the box there is a black painted copper coil through which cold water is made to flow. The coil gets heated, the water in it gets heated in turn, and the hot water flows into the storage tank.

Diagram

Fig. 12.3 Caption: The tubes collect the heat and the tank above them holds the hot water. Brief: Source or draw a labelled solar water heater — horizontal thermal storage tank, storage tank support, evacuated tube collector with integrated heat pipes, inclined frame; arrows showing cold water down into the coil and hot water up into the tank.

Fig. 12.3 The labels name the parts. Read it as a path instead — cold water enters the coil, picks up heat in the inclined collector, and rises into the tank above. The angle of the frame is set to face the sun. It does not tell you how much hot water the heater gives on a cloudy morning, or how long the tank stays warm after dark.

12.2.2 Advantages

Solar energy carries four advantages, and they are of different kinds — one about supply, one about use, one about upkeep and one about cost. (a) Solar energy is a renewable source of energy which can be harnessed in most of the areas of the world, because sunlight arrives almost everywhere rather than being confined to a few deposits. (b) It can be used for diverse purposes — to produce electricity in areas without access to the energy grid, to distil water in regions with limited clean water supplies, and to power satellites in space. (c) Solar energy systems do not require a lot of maintenance, and most reliable solar panel manufacturers give 20-25 years warranty. As there are no moving parts, there is no wear and tear, so after covering the initial cost of the system it requires little spending on maintenance and repair work. (d) It saves fossil fuels like coal and petroleum, which are used to produce electricity, and it also reduces electricity bills.

12.3 Wind Energy

Wind is an inexpensive, reliable and non-polluting source of energy for generating electricity. Moving air carries energy simply because it is moving, and a machine that stands in its path can take some of that movement for itself.

Diagram

Fig. 12.4 Caption: A windmill turns because moving air pushes against the angled faces of its blades. Brief: Source a photograph of a modern three-bladed windmill on a rise, with more windmills of the same cluster behind it; label the blades, the hub and the tower, and mark the wind direction with an arrow.

Fig. 12.4 Read the machine from the ground up — a tall tower, a hub at the top, and long blades set at an angle so the wind pushes them sideways rather than straight back. The other towers stand well apart, so that one does not take the wind from the next. A photograph cannot tell you how fast that wind is blowing, or how many days in the year it blows at all.

12.3.1 Generation Of Wind Energy

Wind energy is obtained by making use of windmills. The blades of the windmill rotate due to the force of the wind, and that turning is the whole point — the machine has converted straight-line movement of air into rotation, which is the kind of movement a machine can be driven by.

The rotational motion of the blades drives a number of machines. (a) Water pumps can be turned directly, so water is lifted without any electricity being made at all. (b) Flour mills can be driven in the same way, with the turning of the blades passed on to the grinding stone. (c) Electric generators can be turned, and it is here that the movement becomes electricity.

Flowchart

Fig. 12.A4 Caption: The wind’s straight movement becomes rotation, and rotation is what a machine can use. Nodes: wind blows → force on the blades → blades rotate → rotational motion is passed on → drives a water pump; or drives a flour mill; or turns an electric generator → generator produces electricity

A single windmill does not amount to much on a national scale, so they are built in groups. A number of windmills installed in a definite pattern in clusters are called wind farms, and they generate a large amount of electricity between them. Wind farms are installed in coastal regions, open grasslands or hilly regions.

The total already built is substantial. Wind power accounts for nearly 10 per cent of India’s total installed power generation capacity, and the Indian wind energy programme is the fourth largest in the world, after China, the USA and Germany.

12.3.2 Areas

In India, the largest wind farm cluster is situated from Nagarcoil to Madurai in Tamil Nadu, a belt running inland from near the southern tip of the peninsula. Besides this, Andhra Pradesh, Gujarat, Karnataka, Kerala, Lakshadweep and Maharashtra have important wind farms.

Wind Farms On Open Ground Factors: coastal regions, open grasslands and hilly regions are the three kinds of site named for wind farms. The decisive one: openness. Wind that has crossed nothing is still moving fast when it reaches the blades. Move it: put buildings, trees or a hill upwind of the towers and the same wind arrives slower and broken up.

12.3.3 Advantages

Wind energy carries four advantages, and the last of them is about the money the land itself can earn. (a) Wind energy is a renewable source of energy which can be produced again and again, because the wind keeps returning whether or not it was used yesterday. (b) It is the cleanest form of renewable energy, as it produces no pollution while generating electricity. (c) It reduces our dependence on the fossil fuels that would otherwise have been burnt to make the same electricity. (d) Land owners can look for additional income by installing wind turbines on land that can even be used for agricultural purposes, since the crop grows on the ground while the blades turn high above it.

The fourth advantage has a chain of savings inside it. The electricity generated by wind power can be used for domestic consumption, which reduces the monthly electricity bill, and the surplus power can be sold back to the local grid, which results in more savings still.

A Turbine On Farmland turbine put up on land still under crops → the owner’s own electricity now comes free → the monthly bill falls → power left over is sold back to the local grid → savings rise a second time, from the same piece of land

12.4 Tidal Energy

The term ‘tide’ is used for the periodic rise and fall of the waters of the ocean, produced by the attraction of the moon and the sun. The word periodic matters here — the sea does not rise when it feels like it, but on a timetable set by bodies far outside the earth.

This rise and fall of water produces a large amount of energy, called tidal energy. The energy is in the movement of an enormous mass of water, not in the water itself.

12.4.1 Generation Of Tidal Energy

Tidal energy can be harnessed by constructing a tidal barrage, which is a wall built across the mouth of an inlet, with gates and turbines set into it and a reservoir behind it.

The barrage earns its electricity twice. During high tide, the sea-water flows into the reservoir of the barrage and turns the turbine, which in turn produces electricity by rotating the generators. The reverse process takes place during the low tide — when the sea level is low, the sea water stored in the barrage reservoir flows out into the sea, and during this process the flowing water turns the turbines again.

Flowchart

Fig. 12.A5 Caption: The barrage takes electricity from the water going in and again from the same water coming out. Nodes: high tide → sea water flows into the reservoir through the barrage → flowing water turns the turbines → turbines rotate the generators → electricity; low tide → stored water flows out into the sea → flowing water turns the turbines again → electricity → back to high tide

Diagram

Fig. 12.5 Caption: A barrage closes the mouth of an inlet, holding the sea on one side and the reservoir on the other. Brief: Source an aerial photograph of a tidal barrage across a coastal inlet, water discharging through the gates; label the sea side, the reservoir side, the gates and the roadway on top.

Fig. 12.5 Look for the line of the barrage first, then for which side the water is being pushed towards. Sea on one side, reservoir on the other, and gates in between where the turbines sit. The photograph freezes one moment, so it cannot tell you whether the tide was rising or falling, nor how far the water level moves between high tide and low.

There are only a few sites in the world where tidal energy can be suitably harnessed. A coast alone is not enough — the site must be shaped so that a barrage can be built across it and a reservoir held behind it.

Q2. The tide rises and falls twice a day without fail. How is that turned into electricity?

A. A barrage is built across an inlet. The rising tide pours through it into a reservoir and turns the turbines, which rotate the generators. When the tide falls, the stored water runs back out through the same turbines and turns them a second time.

12.4.2 Areas

In India, the prospective sites for the exploitation of tidal energy are the Gulf of Kutch and Cambay, both on the Gujarat coast, and the Sunderbans, the low delta coast of West Bengal. Other suitable sites are near the Lakshadweep Islands in the Arabian Sea, and the Andaman and Nicobar Islands in the Bay of Bengal.

12.4.3 Advantages

Tidal energy carries five advantages, and most of them come from the same fact — that the tide is regular. (a) Massive amounts of water in the oceans move in extremely predictable patterns, and this makes it easy to harness the tidal energy, because the plant is never waiting for weather. (b) Tides are controlled by the gravitational pull between the earth, sun and moon. This means that as long as the earth is being orbited by the moon, the tides will continue to be there producing energy, so tidal energy is an inexhaustible source of energy. (c) After the initial construction costs, there are very few additional costs to keep the tidal energy plant running, and it requires little maintenance and minimal personnel as well. (d) Tidal energy can be produced even if the water moves at low speed, so the site does not need a fast current. (e) There are no carbon emissions from a tidal energy plant, making it an energy source that does not negatively affect the global environment.

The Moon Stopped Orbiting The Earth Remove: the moon’s orbit around the earth, and with it the pull that raises the tide. Then: the ocean stops rising and falling on its timetable → the reservoir behind the barrage never fills → nothing flows through the turbines → the plant stands still, though it is undamaged. Which tells us: the fuel of a tidal plant is not the water but the moon’s pull, and that is why the book can call the supply inexhaustible.

12.5 Geothermal Energy

Geothermal energy is the heat energy contained in the rock, and in the fluid that fills the fractures and pores within the rock, in the earth’s crust. The heat is already there, held in the ground beneath our feet, and it does not depend on anything happening at the surface. It is clean and sustainable.

12.5.1 Generation Of Geothermal Energy

Resources of geothermal energy can be generated by using the shallow steam, hot water and hot rock, reached by drilling wells up to thousands of feet beneath the earth’s surface. The deeper the well goes, the hotter the rock it reaches, and the extremely high temperatures in the deeper geothermal reservoirs are the ones used for the generation of electricity. There, high-pressure steam spins a turbine that rotates a generator and produces electricity.

The working of the plant can be followed step by step. Hot water is pumped from deep underground through a well under high pressure, which keeps it liquid even though it is far above the ordinary boiling point. When the water reaches the surface the pressure is dropped, and this causes the water to turn into steam.

That steam spins a turbine, which is connected to a generator that produces electricity. The steam then cools off in a cooling tower and condenses back to water. The cooled water is pumped back into the Earth to begin the process again, so the same water is used over and over rather than being drawn out and lost.

Diagram

Fig. 12.6 Caption: Water is drawn up hot, flashed to steam, used, cooled and sent back down. Brief: Source or draw a cut-away geothermal power plant with the ground in section — numbered stages for the production well bringing hot water up, the steam line, the turbine and generator, the cooling tower, and the injection well returning cooled water; arrows showing the direction of flow at every stage.

Fig. 12.6 The numbers give the order, not the size. Follow them — well up, steam across, turbine and generator, cooling tower, injection well back down — and you have the whole loop, with the same water making the round trip. The section shows the well reaching hot rock, but not how deep that is, how hot, or how far apart the two wells must be sunk.

Flowchart

Fig. 12.A6 Caption: A closed loop — the water that made the electricity is sent back down to be heated again. Nodes: hot water pumped up the well under high pressure → pressure drops at the surface → water turns into steam → steam spins the turbine → turbine rotates the generator → electricity → steam passes into the cooling tower → condenses back to water → cooled water pumped back into the earth → back to hot water pumped up the well

Q4. Heat lies in rock far below the ground. How is it brought up and used?

A. Wells are drilled thousands of feet down to hot rock. Hot water is pumped up under high pressure; the pressure drops at the surface and the water flashes into steam. The steam spins a turbine, then cools, condenses and is pumped back down.

12.5.2 Advantages

Certain general characteristics make geothermal energy of significant importance for both electricity production and direct use. (a) It is easily accessible because of its extensive distribution, so the heat can be reached in many parts of the world rather than in a few places only. (b) It is environment-friendly in nature, with low emission of sulphur, carbon dioxide and other Greenhouse Gases (GHG). (c) It is independent of external supply and demand effects and of fluctuations in exchange rates, because nothing has to be bought from abroad to keep the plant running. (d) It is independent of weather and season, since the heat underground does not change when the sky clouds over or the wind drops.

The last two advantages are what set this source apart from solar and wind. A geothermal plant produces at the same rate at midnight in the monsoon as at noon in summer.

12.5.3 Distribution

India has about 12,000 MW of geothermal power potential that can be harnessed for various purposes. The most promising geothermal energy sites in India are named below, and they are spread across very different parts of the country. (a) Manikaran, in the mountains of Himachal Pradesh in the north. (b) Puga Valley, in Ladakh, in the far north. (c) Tattapani, in Chhattisgarh, in central India. (d) Cambay Graben, in Gujarat, in the west. A graben is a block of the crust that has sunk down between fractures, so the hot rock below it lies closer to the surface. (e) Surajkund, in Jharkhand, in the east.

The surface temperature of the hot springs at these sites ranges from 35°C to as much as 98°C, which is close to boiling. These hot springs have been grouped together and termed as different geothermal provinces.

The provinces are the Himalayan geothermal province, the Naga-Lushai geothermal province, the Andaman-Nicobar Islands geothermal province, and Cambay graben, Son-Narmada-Tapti graben, West coast, Damodar valley, Mahanadi valley and Godavari valley.

There Is Heat Down There Evidence: hot springs reaching the surface, their temperatures measured at 35°C to as much as 98°C, and their positions mapped into provinces. Reasoning: water that comes up hot must have been heated by rock at depth, so a spring marks a reservoir below it. Limit: a surface temperature cannot tell us how hot the reservoir is, how large it is, or how long it would last if drawn upon.

12.6 Nuclear Power

Nuclear power is obtained from energy stored in the nuclei of atoms of naturally occurring radioactive elements like uranium, thorium and plutonium. A radioactive element is one whose atoms are unstable, so their nuclei can break up and release the energy locked inside them.

This makes nuclear power the odd member of the group. The other five sources in this chapter draw on something that keeps arriving, while this one draws on a mineral that has to be mined.

12.6.1 Generation Of Nuclear Energy

When atoms of these radioactive substances react, they split apart. This process of splitting of atoms is called nuclear fission.

Nuclear fission produces heat, and this heat is used to heat water and make steam. The steam powers turbines, which in turn are used to run generators, which produce electricity. From the steam onwards, the plant works like any other steam power station — what is unusual is only the source of the heat.

Diagram

Fig. 12.7 Caption: The tall cooling towers and the reactor building of a nuclear power station beside a river. Brief: Source a photograph of a nuclear power plant showing reactor buildings and cooling towers with vapour rising; label the reactor building, the cooling towers and the water body used for cooling.

The Two Types Of Reactor

Two main types of nuclear reactors are used to generate electricity — the pressurised water reactor (PWR) and the boiling water reactor (BWR). Both use the same heat to make steam, and both reuse their water, but they differ in where the boiling happens.

In the pressurised water reactor, the water is heated by the nuclear reaction but it does not boil, because the water is pressurised. This heated water is circulated through tubes in steam generators, allowing the water in the steam generator to turn to steam, which then turns the turbine. The water that touched the reactor and the water that becomes steam are therefore two separate bodies of water.

In the boiling water reactor, the water comes to a boil due to the heat produced by the nuclear reaction and turns into steam to turn the turbine, so the water from the reactor itself powers the turbine. In both systems, the water is reused.

12.6.2 Distribution

Nuclear power is the fourth-largest source of electricity in India, after thermal, hydroelectricity and renewable sources of electricity. India has 21 nuclear reactors in operation in seven nuclear power plants, having an installed capacity of 5780 MW and producing a total of 30,292.91 GWh of electricity. A gigawatt-hour, or GWh, is a thousand megawatt-hours, and it measures energy actually delivered rather than the size of the machine.

The seven plants are spread widely across the country, as the table below shows.

Table 12.1 Caption: The nuclear power plants of India and the states in which they stand. | Power station | State | |—|—| | Kaiga | Karnataka | | Kakrapar | Gujarat | | Kalpakkam | Tamil Nadu | | Narora | Uttar Pradesh | | Rawatbhata | Rajasthan | | Tarapur | Maharashtra | | Kudankulam | Tamil Nadu |

Table 12.1 Two columns only — the station and the state it stands in. Read down the second column and the pattern appears: seven stations in six states, with Tamil Nadu holding two, and most of them near a coast or a large river, since a plant needs water for cooling. The table does not give the capacity of each station, its number of reactors, or the year it began working.

Where The Fuel Comes From

Uranium and thorium, which are available in Jharkhand and in the Aravalli ranges of Rajasthan, are used for generating atomic or nuclear power. The Monazite sands of Kerala, along that state’s coast, are also rich in thorium.

India has a flourishing and indigenous nuclear power programme — indigenous meaning built with the country’s own technology rather than bought from outside — and it aims to supply 25 per cent of electricity from nuclear power by 2050.

WC 12.A1 — Installed Capacity Against Electricity Actually Produced The situation: India’s nuclear plants have an installed capacity of 5780 MW and produced a total of 30,292.91 GWh of electricity, both figures taken from this section. The working: a year has 8,760 hours, so the most the plants could deliver if every reactor ran every hour is \[\text{Maximum output} = 5780 \text{ MW} \times 8{,}760 \text{ hours} = 50{,}632{,}800 \text{ MWh}\] and since 1 GWh equals 1,000 MWh, this is \[50{,}632{,}800 \text{ MWh} \div 1{,}000 = 50{,}632.8 \text{ GWh}\] The share actually produced is therefore \[30{,}292.91 \div 50{,}632.8 = 0.598 \text{, or about } 60 \text{ per cent}\]

About three-fifths of what the machines could deliver was actually delivered. That gap is not a fault in the arithmetic — a nuclear plant needs to refuel every 18 to 24 months, and it must also be stopped for inspection and repair, so no station runs every hour of every year. The wider lesson holds for every source in this chapter. Installed capacity tells you how big the machine is; generation tells you what came out of it, and the two are never the same number.

12.6.3 Advantages

Nuclear energy carries three advantages, and the second one explains much of the third. (a) Nuclear energy reduces the requirement of the amount of energy generated from fossil fuels such as coal and oil, and therefore reduces the use of those fuels and lowers Greenhouse Gas emissions. (b) Fission of one atom of uranium produces ten million times the energy released by the burning of one atom of carbon. In this way nuclear energy saves not only on raw materials but also on transport, handling and extraction of fuel, and the cost of nuclear fuel, overall uranium, is 20% of the cost of the energy generated. (c) Nuclear energy is the most reliable source of energy, as nuclear power plants can run 24 hours a day and seven days a week, and a plant needs to refuel only every 18 to 24 months. This shows that nuclear fuels are less affected by fluctuating fuel prices than the more volatile industries like oil and natural gas.

Ten Million Times The Energy one uranium atom releases ten million times what a carbon atom does → a very small mass of fuel runs a plant for months → far less has to be mined, moved and handled → fuel is 20% of the cost of the energy → a jump in world fuel prices barely moves the cost of nuclear electricity

12.7 Biogas

Biogas is composed of methane, carbon dioxide, hydrogen and hydrogen sulphide. Methane is the part that matters as fuel, because it is the gas that burns.

It is produced by anaerobic degradation of animal and plant wastes in the presence of water. Anaerobic degradation means the breaking down of organic matter by bacteria in the absence of oxygen. The fermentation of the waste products is carried out by bacteria, which produces hydrocarbon gas, predominantly methane, and alcohol.

Nothing is thrown away at the end of this. The residue left behind in the tank is rich in nutrients and can be used as manure, so the same load of waste yields both a fuel and a fertiliser.

The plants which use cattle dung are called ‘Gobar Gas Plants’. These plants have been set up in many villages, and they provide twin benefits to the farmers in the form of energy and good quality manure. The gas is used for cooking, for lighting and for pumping water from wells.

Q3. How can cattle dung give a family cooking gas and good manure at the same time?

A. Bacteria break the dung down in a sealed tank without oxygen. The gas they give off is drawn from the top and piped to the stove. What stays behind in the tank is the residue, rich in nutrients, and it is taken out and spread as manure.

12.7.1 Generation Of Biogas

A digester tank is placed underground. The digester tank receives the dung-water mixture through an inlet pipe, while the other side discharges the spent slurry through an outlet pipe. In the digester tank there is a gas outlet, which is controlled by a pipe, so that the gas is drawn off as it collects.

Diagram

Fig. 12.8 Caption: Dung and water go in at one side, gas is drawn from the top, and spent slurry leaves at the other. Brief: Source or draw a section through a floating gas-holder type biogas plant — mixing tank, inlet pipe, underground digester tank with partition wall, floating gas-holder with gas valve and outlet for bio-gas, outlet pipe, overflow tank for spent slurry; arrows showing the direction of flow through the plant.

Fig. 12.8 Read it left to right at ground level. Mixing tank, inlet pipe down into the buried digester, gas collecting in the holder above, spent slurry out through the far pipe into the overflow tank. The holder rises as gas gathers under it. The section shows the parts and the path, but not how many days the dung takes to ferment, nor how much gas one load gives.

Flowchart

Fig. 12.A7 Caption: One load of dung leaves the plant as two useful things. Nodes: cattle dung mixed with water in the mixing tank → inlet pipe → underground digester tank → bacteria ferment the mixture without oxygen → two outputs → biogas collects at the top and leaves through the gas outlet → used for cooking, lighting and pumping water from wells; spent slurry leaves through the outlet pipe → used as manure on the fields

Waste That Would Otherwise Be A Problem

Waste Recycling and Resources Recovery Programmes (WRRSE) are now being used from the organic plant waste and night soil, night soil being human waste. This helps in improving the sanitary conditions in our cities and villages, because the waste is fed into a sealed tank instead of being left where people live.

The plants generate enriched organic manure, useful for supplementing chemical fertilisers rather than replacing them entirely.

Feeding Waste Into A Digester organic plant waste and night soil sent to biogas plants → less waste left lying in streets, drains and yards → sanitary conditions in cities and villages improve → the tank also turns out enriched organic manure → fields need less chemical fertiliser than before

12.7.2 Advantages

Biogas carries three advantages, and they run from the gas itself to what is left after it. (a) Biogas is clean, non-polluting and cheap, since the raw material is waste that the household already has. (b) There is a direct supply of gas from the plant to the point of use, and therefore there is no storage problem. (c) The sludge left behind is a rich fertiliser containing bacterial biomass, so the plant returns nutrients to the soil.

The spread of these plants has been official policy. The Ministry of Non-Conventional Energy Sources (MNES) has been promoting the Biogas Programme in India, and it has set up a number of biogas plants across the country.

12.7.3 Compressed Biogas

Biogas as it leaves the digester is a mixture, and a mixture is not a good motor fuel. It is therefore purified to remove hydrogen sulphide, carbon dioxide and water vapour, and then compressed, to obtain Compressed Biogas (CBG).

What is left after that cleaning is almost entirely fuel. CBG has a methane content of more than 90%, with a calorific value and other properties similar to CNG, or compressed natural gas. Calorific value is the amount of heat a fuel gives when it is burnt, so a fuel that matches CNG on this count can be used in the same way — which makes CBG a green renewable automotive fuel.

In an attempt to boost the manufacturing and consumption of CBG, it has become mandatory to blend CBG with CNG, and with PNG, or piped natural gas, for households, in a phased manner from 2025-26. The purpose is national as much as environmental — this would reduce the country’s reliance on natural gas imports, since the CBG is made from waste produced within the country.

12.8 Summary

  1. Non-conventional sources of energy are those developed in the recent past as an alternative to conventional sources, and they include solar, wind, tidal, geothermal and nuclear energy and biogas.
  2. Most of these sources are renewable and therefore inexhaustible, non-polluting, less expensive to run and easy to maintain, which is why they are called the energy resources of the future.
  3. India is well placed for solar energy, receiving the equivalent of 5,000 trillion kWh per year because of its location on the Tropic of Cancer.
    1. Most parts of the country have 300 clear sunny days in a year.
    2. The availability of solar energy is between 5 to 7 kW per hour per square km.
    3. The world’s largest solar park, Bhadla Solar Park, lies in Bhadla tehsil in Jodhpur, Rajasthan, with a total capacity of 2,245 MW.
  4. Solar energy is harnessed in India by three main techniques.
    1. Solar cells, or photovoltaic cells, made of thin wafers of silicon and gallium, turn the sun’s radiation straight into electricity, and joined together they form a solar panel.
    2. The solar cooker traps heat in a black insulated box behind a glass sheet, which lets light in but is opaque to the infrared radiation given off inside.
    3. The solar water heater passes cold water through a black copper coil inside an inclined flat-plate collector, and the heated water flows into a storage tank.
  5. Wind energy is obtained from windmills, whose blades are turned by the force of the wind, and the rotation drives water pumps, flour mills or electric generators.
    1. Windmills built together in a definite pattern are called wind farms, and they are installed in coastal regions, open grasslands or hilly regions.
    2. Wind power accounts for nearly 10 per cent of India’s total installed power generation capacity, and India’s wind energy programme is the fourth largest in the world after China, the USA and Germany.
    3. The largest wind farm cluster runs from Nagarcoil to Madurai in Tamil Nadu.
  6. Tidal energy comes from the periodic rise and fall of ocean water produced by the attraction of the moon and the sun.
    1. It is harnessed by a tidal barrage, which takes electricity from the water flowing in at high tide and again from the same water flowing out at low tide.
    2. The prospective sites in India are the Gulf of Kutch, Cambay and the Sunderbans, with other suitable sites near the Lakshadweep Islands and the Andaman and Nicobar Islands.
  7. Geothermal energy is the heat energy contained in the rock and in the fluid filling its fractures and pores within the earth’s crust.
    1. Hot water is pumped up from deep wells, flashes into steam as the pressure drops, spins a turbine, and is then cooled, condensed and pumped back down.
    2. India has about 12,000 MW of geothermal potential, with promising sites at Manikaran, Puga Valley, Tattapani, Cambay Graben and Surajkund.
    3. The hot springs, whose surface temperatures range from 35°C to as much as 98°C, have been grouped into geothermal provinces.
  8. Nuclear power comes from energy stored in the nuclei of atoms of radioactive elements such as uranium, thorium and plutonium.
    1. The splitting of these atoms is called nuclear fission, and the heat it produces makes the steam that turns the turbines.
    2. The two main reactor types are the pressurised water reactor, in which the water does not boil, and the boiling water reactor, in which it does.
    3. India has 21 reactors in seven plants, with an installed capacity of 5780 MW producing 30,292.91 GWh, and aims to supply 25 per cent of its electricity from nuclear power by 2050.
  9. Biogas is produced by the anaerobic degradation of animal and plant wastes, that is, their breakdown by bacteria in the absence of oxygen, and it is predominantly methane.
    1. In a Gobar Gas Plant the dung-water mixture enters an underground digester tank, the gas is drawn off from the top, and the spent slurry leaves as manure.
    2. The plant therefore gives farmers twin benefits — energy for cooking, lighting and pumping water, and good quality manure.
  10. Compressed Biogas is biogas purified of hydrogen sulphide, carbon dioxide and water vapour and then compressed, with a methane content above 90% and properties similar to CNG, making it a green renewable automotive fuel.
  11. Every one of these sources works the same way at bottom — energy that was arriving anyway is caught by a machine and turned into a form we can use.

Flowchart

Fig. 12.A8 Caption: Six sources, and the path each one takes before it reaches a switch or a stove. Nodes: energy already arriving → sunlight → solar cells → electricity directly, with no moving part; or solar cooker and solar water heater → heat used as heat; moving air → windmill blades rotate → generator → electricity; rise and fall of the sea → water through a tidal barrage → turbine → generator → electricity; heat in rock → hot water flashed to steam → turbine → generator → electricity; fission of uranium atoms → heat → steam → turbine → generator → electricity; animal and plant waste → bacteria ferment it → biogas → burnt for cooking and lighting, or purified and compressed to CBG for vehicles

What This Chapter Cannot Tell You

The figures here are national and they hide almost everything below that level. A country-wide count of 300 clear sunny days says nothing about how many a particular district gets, and 12,000 MW of geothermal potential is an estimate for the whole of India, not a promise about any one hot spring.

The chapter also lists the advantages of each source and stops there. It does not give the costs, the land needed, the waste produced or the disadvantages, so it cannot by itself tell you which source a given village or city should choose.

Finally, capacity is not output. A park of 2,245 MW and an installed nuclear capacity of 5780 MW describe the size of the machines, and only the generation figure tells you what actually came out of them in a year. ## 12.9 Check Your Concepts

  1. Look at Table 12.1.
    1. Which state has two nuclear power stations listed against it?
    2. Name two things the table does not tell you about any of the stations it lists.
  2. Wind farms are installed in coastal regions, open grasslands or hilly regions. What do these three kinds of site have in common, and why does that shared quality matter for a windmill?
  3. A tidal barrage produces electricity twice in one cycle of the tide. Describe the two stages in order, saying what the water is doing in each.
  4. The 193 solar panels of the Gandhi Solar Park generate energy equivalent to that obtained from 30,000 kg of coal.
    1. Work out the amount of coal that one panel replaces, showing your steps.
    2. State one thing this figure cannot tell you about the working of a solar panel.
  5. State two differences between conventional and non-conventional sources of energy.
  6. Give a reason for each of the following.
    1. Solar energy is replacing fossil fuels in India.
    2. Harvesting of solar energy does not require much maintenance.
  7. How is wind energy utilised to produce electricity?
  8. The raw material for nuclear power is a mineral that is non-renewable. Even so, countries prefer nuclear power to conventional energy sources. Why?

12.10 Case-Based Questions

  1. Fig. 12.8 is a picture of a biogas plant. Briefly explain how biogas is generated.
  2. Observe Fig. 12.6 and answer the following.
    1. Identify the type of energy generated and state the advantages of using it.
    2. Which two areas can be well suited for its generation?
    3. Briefly describe the method of generating electricity by this method.
    4. In India this source of energy has been divided into provinces. Name three such provinces.