Sources of Energy

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GOOD SOURCE OF ENERGY

1. a good source of energy would be one

(i) large amount of work per unit volume or mass,

(ii) easily accessible,

(iii) easy to store and transport, and

(iv) economical.

2. We can classify energy sources in different ways. One

classification is based on:-

(i) the reserves (supply) of an energy source [ Conventional

and non-conventional sources of energy]

(ii) Another is based on how long we have been using it.

[Renewable and non-renewable sources of energy]

3. Renewable sources of energy are those which can be

generated by us or which are constantly being generated by

natural processes or whose supply is unlimited. Wood is a

renewable source of energy although its supply is limited.

Nuclear fuels such as uranium are required in very small

quantities to generate electricity. So, their reserves will last for a

long, long time. Therefore, they are classified as renewable

sources of energy.

4. Non-renewable sources of energy are those which were

produced in the past by natural processes, whose supply is limited

and which we cannot generate ourselves. Coal, natural gas

and petroleum are non-renewable sources of energy.

5. Sources of energy that have been in use for centuries are called

conventional sources of energy. Conventional sources include

wood, coal, petroleum and flowing water. Conventional

sources like coal and petroleum are non-renewable, while sources

like flowing water are renewable.

6. Sources of energy that we have started using in new ways or only

in recent times are called non-conventional or alternate

sources of energy. These include energy from the sun, the heat

inside the earth (geothermal energy), tides, ocean

waves, etc. Nuclear energy is also a nonconventional source.

Noon-conventional energy sources are renewable. We have been

using wind and biomass (like cow dung) for energy for ages.

However, they were not used conventionally to do tasks like

electricity generation, which has now been made possible with

improvement in technology. In that sense, they can also be called

nonconventional sources of energy.

CONVENTIONAL SOURCES OF ENERGY

1. Fossil Fuels are Coal and Petroleum.

(i) about 25% of our total energy consumption comes from coal.

More than 90% of this coal is used for electricity generation

in thermal power plants.

(ii) In most thermal power plants, coal is burnt to heat water for

producing steam. The steam falls on the blades of a special

kind of wheel called a turbine. A turbine is a device that

rotates when steam, water or wind falls on its blades. The

turbine turns the shaft of an electric generator to which it is

connected. In this way electricity is produced.

2. The burning of most fossil fuels causes air pollution. The pollutants

produced include carbon dioxide, carbon monoxide, oxides of

nitrogen, sulphur dioxide and unburnt particles.

(i) Burning of fossil fuels produces carbon dioxide leading to

greenhouse effect and global warming.

(ii) carbon monoxide is produced by incomplete combustion of

coal and petrol. Excessive inhalation of this poisonous gas

can cause death.

(iii) During the combustion of coal sulphur dioxide and oxides of

nitrogen are formed combine with oxygen at the high

temperatures inside a running automobile engine to form

sulphuric acid and nitric acid. These fall on the earth with

rain, which we call acid rain. Acid rain damages soil, water

bodies, crops, living tissues and structures like the Taj Mahal.

(iv) The unburnt particles produced during the combustion of

fossil fuels are carried by smoke. They affect our lungs, and

blacken clothes and buildings.

3. Burning fossil fuels has other disadvantages too. The oxides of

carbon, nitrogen and sulphur that are released on burning fossil

fuels are acidic oxides. These lead to acid rain which affects our

water and soil resources.

4. Hydro Power Plants – Another conventional source of energy

was the kinetic energy of flowing water or the potential energy of

water at a height. Hydro power plants convert the

potential energy of falling water into electricity. A

quarter of our energy requirement in India is met by hydro power

plants.

5. Advantages of hydroelectricity: -

(i) The source of energy (water) is free and renewable.

(ii) Harnessing the energy of flowing water is a pollution-free

process, with no smoke, chemicals, etc., being produced.

(iii) The cost of electricity generation is low as compared to

electricity generated from other types of power plants.

(iv) Flowing water is a more reliable source of energy than wind.

(v) Hydroelectricity can be generated on a large scale from a

single plant.

(vi) Dams built for hydroelectric plants also help in flood control

and irrigation.

(vii) Small hydroelectric stations are one of the best options for

generating electricity from renewable sources, as they do not

affect the environment much.

6. To produce hydel electricity, high-rise dams are constructed on

the river to obstruct the flow of water and thereby collect water in

larger reservoirs. The water in the reservoir would be refilled

each time it rains (hydro power is a renewable source of

energy). But, constructions of big dams have certain problems

associated with it.

(i) Large areas of agricultural land and human habitation are to

be sacrificed as they get submerged.

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(ii) Large eco-systems are destroyed when submerged under the

water in dams.

(iii) The vegetation which is submerged rots under anaerobic

conditions and gives rise to large amounts of methane which

is also a green-house gas.

(iv) It creates the problem of satisfactory rehabilitation of

displaced people.

Improvements in the Technology for using Conventional Sources of

Energy

7. Bio-Mass - When fuels are plant and animal products the source

is said to be bio-mass. These fuels do not produce much heat

on burning and a lot of smoke is given out when they are burnt.

Therefore, technological inputs to improve the efficiency of these

fuels are necessary.

(i) Cow-dung, various plant materials like the residue after

harvesting the crops, vegetable waste and sewage are

decomposed in the absence of oxygen to give bio-gas.

Since the starting material is mainly cow-dung, it is popularly

known as ‘gobar-gas’.

(ii) Bio-gas is produced in a plant. The plant has a dome-like

structure built with bricks. A slurry of cow-dung and water is

made in the mixing tank from where it is fed into the

digester.

(iii) The digester is a sealed chamber in which there is no

oxygen. Anaerobic micro-organisms that do not require

oxygen decompose or break down complex compounds of

the cow-dung slurry.

(iv) It takes a few days for the decomposition process to be

complete and generate gases like methane, carbon

dioxide, hydrogen and hydrogen sulphide.

(v) The bio-gas is stored in the gas tank above the digester from

which they are drawn through pipes for use.

(vi) Bio-gas is an excellent fuel as it contains up to 75%

methane. It burns without smoke, leaves no residue

like ash in wood, charcoal and coal burning. Its heating

capacity is high. Bio-gas is also used for lighting.

(vii) The slurry left behind is removed periodically and used as

excellent manure, rich in nitrogen and

phosphorous. The large-scale utilisation of bio-waste and

sewage material provides a safe and efficient method of

waste-disposal besides supplying energy and manure.

8. Advantages of Biogas Plants

(i) Reduces burden on forests and fossil fuels

(ii) Produces a clean fuel - helps in controlling air pollution

(iii) Provides nutrient rich (N & P) manure for plants

(iv) Controls water pollution by decomposing sewage, animal

dung and human excreta

9. Limitations of Biogas Plants

(i) Initial cost of installation of the plant being high, and is

beyond the reach of an average rural Indian

(ii) Number of cattle owned by an average family of farmers is

inadequate to feed a biogas plant

RENEWABLE/NON-RENEWABLE SOURCE

10. Wind Energy - Unequal heating of the landmass and water

bodies by solar radiation generates air movement and causes

winds to blow.

(i) The kinetic energy of the wind can be used to do work. This

energy was harnessed by windmills in the past to do

mechanical work. Today, wind energy is also used to

generate electricity.

(ii) The output of a single windmill is quite small and cannot be

used for commercial purposes. Therefore, a number of

windmills are erected over a large area, which is known as

wind energy farm. The energy output of each windmill in

a farm is coupled together to get electricity on a commercial

scale.

11. Advantages of wind energy

(i) The source of energy (wind) is free.

(ii) Harnessing wind energy is a pollution-free process, with no

smoke, chemicals, etc., being produced.

(iii) A small wind-electric plant can be set up near a factory to

provide pollution-free power for its use.

12. Limitations of wind energy

(i) Wind energy cannot be harnessed at places where wind does

not blow regularly. A wind-electric generator works only on

winds of at least 15 km/h.

(ii) Wind is not a dependable source of energy because

sometimes the air is absolutely still and at other times there

are storms.

(iii) It is expensive to set up a wind farm for generating electricity

because wind farms need a large area.

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(iv) Moreover, since the tower and blades are exposed to the

vagaries of nature like rain, Sun, storm and cyclone, they

need a high level of maintenance.

ALTERNATIVE OR NON-CONVENTIONAL SOURCES OF ENERGY

13. Solar Energy is radiant light and heat from the Sun.

14. A solar heating device is one which allows collection of a large

amount of heat from the sunlight in a given region and restricts

the loss of heat to the surrounding in the form of radiation.

15. The following facts help us to design an efficient solar cooker

and solar water heaters:

(i) A black body absorbs maximum heat

(ii) Loss of heat by convection can be restricted in a closed

system

(iii) Radiation losses can be avoided by reflecting the rays inside

the body with the help of reflecting object like a plane mirror

(iv) Conduction can be reduced by using poor conducting

materials

16. Advantages of Solar Cooker-

(i) high performance

(ii) no fuel

(iii) eco-friendly

(iv) one-time investment

17. Disadvantages of Solar Cooker-

(i) can't be used in cloudy weather

(ii) take longer to cook

(iii) need to learn special methods to cook

18. Solar cells are the devices where solar energy is directly

converted into electricity. A large number of solar cells are,

combined in an arrangement called solar cell panel that can

deliver enough electricity for practical use.

19. Advantages of using Solar Cells

(i) They have no moving parts and hence require little

maintenance and work quite satisfactorily without any

focusing device

(ii) It does not cause any environmental pollution like the fossil

fuels and nuclear power

(iii) Solar cells last a longer time and have low running costs.

(iv) They can be set up in remote and inaccessible hamlets or

very sparsely inhabited areas

20. Disadvantages using Solar Cells

(i) The entire process of manufacture is still very expensive as

silver is used for interconnection of these cells in the panel,

which is a very expensive metal.

(ii) A practical problem linked with the use of solar cell panels is

regarding the storage of electricity storage batteries which

give us only direct current. But to operate our devices we

need alternating current. Therefore, we need to convert DC

to AC before using any appliance and thus it increases the

cost of such solar panels as the sources of electricity.

21. Uses of Solar Cells: -

(i) Artificial satellites and in space probes like Mars orbiters

(ii) Wireless transmission systems or TV relay stations in remote

locations

(iii) Traffic signals, calculators and in toys

ENERGY FROM THE SEA

22. Sea Energy can be harnessed through:

(i) Tides

(ii) Sea-waves

(iii) Temperature differences in the water

23. Tidal Energy - Due to the gravitational pull of mainly the moon

on the spinning earth, the level of water in the sea rises and falls.

This phenomenon is called high and low tides and the

difference in sea-levels gives us tidal energy.

(i) Tidal energy is harnessed by constructing a dam across a

narrow opening to the sea.

(ii) During high tide, when the level of water in the sea is high,

sea-water flows into the reservoir of the barrage and turns

the turbines. The turbines then turn the generator shaft to

produce electricity.

(iii) During low tide, the sea-water stored in the barrage reservoir

flows out into the sea. This flowing water also turns the

turbines and generates electricity.

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24. Limitations of Tidal Energy

(i) The tides do not possess enough energy to generate

electricity on a large scale

(ii) Only few sites are suitable for building such barrages (or

tidal dams)

25. Wave Energy - The waves are generated by strong winds

blowing across the sea.

(i) Kinetic energy possessed by huge waves near the seashore

can be trapped to generate electricity.

(ii) A wide variety of devices have been developed to trap wave

energy for rotation of turbine and production of electricity.

(iii) Wave energy would be a viable proposition only where

waves are very strong.

26. Ocean Thermal Energy - there is always a temperature

difference between the water "at the surface of ocean"

and "at deeper levels." At many places in the ocean, this

difference in temperatures of water is up to 20oC. The energy

available due to the difference in the temperature of water at the

surface of the ocean and at deeper levels is called ocean thermal

energy(OTC).

(i) These plants can operate if the temperature dif ference

between the water at the surface and water at depths up to

2 km is 293 K (20°C) or more.

(ii) In one type of OTEC [Ocean Thermal Energy Conversion]

power plants, the warm surface-water is used to boil a

volatile liquid like ammonia. The vapours of the liquid are

then used to run the turbine of generator. The cold water

from the depth of the ocean is pumped up and condense

vapour again to liquid.

27. Advantages of OETC are

(i) A greater advantage of the ocean thermal energy is that it

can be used continuously for 24 hours throughout the year.

(ii) Ocean thermal energy is a renewable source of energy and

its use does not cause any pollution.

28. Limitation - The installation and maintenance of an OTEC

power plant is very high and efficient commercial exploitation is

difficult.

29. Geothermal Energy is that heat energy obtained from hot

rocks present inside the earth. This heat can be used as a source

of energy to produce electricity. When underground water comes

in contact with the hot spot, steam is generated. Such outlets are

known as hot springs. The steam trapped in rocks is routed

through a pipe to a turbine and used to generate electricity.

30. Advantages of Geothermal Energy

(i) Geothermal plants can operate round the clock, unlike those

based on solar and tidal energy

(ii) Geothermal energy is almost pollution-free

(iii) The cost of a geothermal plant is high as compared to a

coal-based plant, but operating costs are lower

31. Disadvantages of Geothermal Energy

(i) Not all areas are suitable for production of electricity in this

way

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(ii) It depends on the structure of rocks

(iii) It creates noise pollution

(iv) very few commercially viable sites where such energy can be

exploited.

32. There are number of power plants based on geothermal energy

operational in New Zealand and United States of America.

NUCLEAR ENERGY

1. Nuclear Energy - In a process called nuclear fission, the nucleus

of a heavy atom (such as uranium, plutonium or thorium), when

bombarded with low-energy neutrons, can be split apart into

lighter nuclei. When this is done, a tremendous amount of energy

is released

2. The released energy can be used to produce steam and further

generate electricity.

3. Advantages of Nuclear Power

(i) Nuclear power is a viable option where fossil fuels like coal

are not available

(ii) If operated properly, nuclear power plants produce less

atmospheric pollution than thermal power plants

(iii) It consumes very little fuel. It can operate for more than a

year without needing new fuel elements

(iv) A sizeable amount of fuel (uranium and plutonium) can be

reclaimed by processing the spent fuel material in contrast to

fuels like coal which cannot be reclaimed

(v) Some radioactive by products in the process are used in

medicine and industry

4. Disadvantages

(i) The high cost of installation of a nuclear power plant

(ii) high risk of environmental contamination

(iii) limited availability of uranium makes large-scale use of

nuclear energy prohibitive

(iv) The disposal of radioactive wastes in the fission process is a

major problem. Expensive long-term storage areas have to

be built