SOURCES OF ENERGY
Characteristics of an ideal fuel/sources of energy:
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It should have high efficiency
It should be eco-friendly or pollution free
It should be easily available
It should be of low cost
It should be easy to store and transport.
Renewable energy: energy which is regenerated continuously. Eg: wind energy, tidal energy,
solar energy etc.
Non-renewable energy: Energy which is not regenerated and its availability is limited. Eg. fossil
fuels such as coal, diesel, petrol etc.
Fossil fuels: fuels formed by the anaerobic decomposition of plant and animal biomass buried
under the earth at high temperature and pressure over a long period of millions of years.
Disadvantages of fossil fuels:
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They are exhaustible and non-renewable
Produce CO2 on burning, which may lead to green house effect
Acidic oxides released during burning of fossil fuels (eg. SO2, NO2 etc.) may cause acid
rain.
Harmful gases released to the atmosphere are harmful to humans, crops and domestic
animals.
Measures taken to prevent air pollution:
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use alternative sources of energy such as solar energy, wind energy,etc.
use more efficient engines
use good quality fossil fuels such as CNG, lead free petrol,etc.
plant trees along road sides which absorb CO2.
Hydro-elctricity: Electricity generated using kinetic energy of flowing water.
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Water is stored in the reservoir of high raised dam(PE)
It is allowed to flow through a pipe to a turbine placed at the base of the dam(KE)
It rotates the turbine of generator(ME)
Rotation of turbine causes generation of electricity in generator.
Advantages of hydro-electricity:
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Water used to generate hydro-electricity is a renewable resource
High efficiency
Less atmospheric pollution
Disadvantages:
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Hydro-electric power plants can be constructed in limited places such as high terrains.
Construction of large dams results in submerging large areas of agricultural lands, forests
and human habitations.
Anaerobic decay of trees under dam water releases methane to the atmosphere, being a
green house gas it may lead to global warming.
Satisfactory rehabilitation of displaced people is a social problem.
Working of a thermal power plant:
Fossil fuel, mainly coal, is burnt to produce heat.
Heat is used to boil water into steam.
Steam rotates turbine of generator.
Rotation of turbine generates electricity in generator.
Disadvantages:
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Fossil fuel used to generate thermal power is non-renewable and exhaustible.
Combustion of fossil fuel produces CO2, which is a greenhouse gas and leads to global
warming
Acidic gases such as NO2 and SO2 released by the combustion of fossil fuel cause acid rain
Incomplete combustion of fossil fuels releases harmful gases like CO to the atmosphere.
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Biomass: Plant or animal matter which is used as source of fuel. Eg. Fire wood. Cow dung.
Advantages of biomass:
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Renewable resource
Cheap and easily available
Disadvantages:
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Low efficiency
Produce smoke and harmful gases on burning
Leaves solid residue after burning
Conversion of biomass into more efficient fuels:
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Cow dung is converted into biogas by anaerobic decomposition in a biogas plant.
Fire wood is converted into charcoal by heating in the absence/limited supply of air. When
wood is heated in the absence of air, volatile substances present in it are lost in the form
of vapour and charcoal is left behind as a black residue.
Advantages of biogas and charcoal:
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High efficiency
Eco-friendly/ Pollution free
Easy to store and transport
Burn completely and don’t leave any solid residue.
Biogas plant- construction and working:
It is a plant in which plant and animal waste, mainly cattle dung is decomposed to form biogas
by bacteria in the absence of air.
It consists of an underground tank called digester, an inlet tank, a gas tank and an outlet tank.
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Cattle dung is mixed with water to form slurry
Slurry is taken in inlet tank
It is then passed into digester where it is decomposed by bacteria in the absence of air to
form biogas ( a mixture of methane, carbon dioxide, hydrogen and hydrogen sulphide)
Biogas is collected in gas tank above digester, from where it is transported though pipe
Left over slurry (sledge) is collected in outlet tank and is used as manure/fertilizer as it is
rich in essential plant nutrients such as nitrogen, phosphorus and humus.
Advantages of biogas plant:
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It converts cattle dung into a very efficient fuel which can be used as a cooking gas,
for lighting lamps etc.
Effective technology for the proper disposal of plant and animal wastes
Left over slurry from biogas plant is used as manure.
Wind energy: kinetic energy possessed by wind / moving air.
Advantages of wind energy:
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Renewable and inexhaustible
Eco-friendly
Available free of cost
Wind mill: An electric fan-like device which is used to convert wind energy into electric energy.
In olden days, it was used to operate water lift pump, to grind grains etc.
Working of wind mill:
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Kinetic energy of wind is used to rotate the blades of wind mill
It in turn rotates the turbine of generator
Rotation of turbine produces electric energy in generator.
Wind energy farm: electricity produced by a single wind mill is very negligible. Hence, a large
number of wind mills are erected over a large area of land which together to produce electric
energy on a commercial scale. Limitations of harnessing wind energy:
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Wind energy farm can be set up only in limited places where the wind speed is high, more
than 15km/h
Wind energy farm can be set up only in limited places where wind blows continuously
High cost of installation
Large area of land is required to set up wind energy farm.
High cost of maintenance.
Advantages of Solar energy:
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renewable and inexhaustible
environment friendly
available free of cost
Limitations:
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lack of technology for harnessing maximum solar energy
available only during day time and sunny whether
Solar cell: device that converts solar energy into electric energy. Silicon is used to make solar
cells.
Solar panel; Electric energy produced by a single solar cell is negligible. Hence, a group of solar
cells are
arranged
electric energy on large scale. It is called solar panel.
on a board to produce
Uses of solar cells/solar panel:
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used in artificial satellite and space probes
used in traffic signals, wireless transmission
used for lighting lamps, operate TV, etc. in remote areas
used in watches, calculators, etc.
Advantages of solar cells/solar panel:
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No moving parts
Eco-friendly
Can be set up in remote, inaccessible areas where laying down of electric transmission
wires is very difficult and economically not feasible
Solar energy, used in these devices, is renewable and inexhaustible
Disadvantages:
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Availability of special grade silicon, required for the manufacture of solar cell, is very
limited
Manufacture of special grade silicon is expensive
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In solar panel, silver is used to inter connect solar cells which makes it expensive
Lack of a backup system/ technology for the storage of electricity
Solar cooker: It is a device in which solar energy is used to cook food.
Construction and working: It consists of a box, which is painted black inside as the black surface
absorbs more heat, a plane glass sheet used to cover open upper side of the box (which helps to
trap heat rays inside the box by letting them to pass into the box and prevent them from
escaping) and a plane mirror to reflect sun light into the box.
Take the food to be cooked in a vessel, which is painted black on outside, and place it inside the
box. Close the box with glass sheet and keep it in sun shine. Adjust the mirror such that it reflects
sun light into the box through the glass sheet. As the glass sheet prevents heat rays that entered
the box from escaping, a lot of heat rays get trapped inside the box. Black surface of the box and
cooking vessel absorbs the heat rays and makes inside the box hot and cooks the food.
Advantages of solar cooker:
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It uses solar energy to kook food, which is renewable and inexhaustible
Eco-friendly or pollution free
Comparatively low temperature is maintained, which helps to retain the nutritive value
of food
It is cheap and easy to make
Disadvantages:
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It works slowly or it takes more time to cook food
It is suitable for cooking only those food items which require low temperature.
It will not work during night and rainy seasons
The position of the mirror has to be adjusted from time to time
Energy from sea/ocean: Three forms of energy are available from sea/ocean- tidal energy, wave
energy, ocean thermal energy.
Tidal energy: High tide (rise in the level of water in sea) and low tide (fall in level of water in sea)
are due to gravitational pull of moon on earth. Energy due to difference in the level of water
during high tide and low tide is called tidal energy. It is harnessed as electricity by constructing
dams across narrow openings to the sea. When water flows through the narrow opening, turbine
of generator fixed in it gets rotated to produce electricity.
Advantages of tidal energy:
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It is renewable and in exhaustible
It is eco-friendly
Disadvantages:
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Locations suitable for constructing tidal dams are limited
Lack of efficient technology for maximum exploitation of tidal energy
Harnessing tidal energy on a large scale is expensive
Wave energy: kinetic energy possessed by waves of sea/ocean. It is harnessed as electricity.
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Renewable and in exhaustible
Pollution free
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Disadvantages of wave energy:
High velocity waves required for generating electricity are available in limited locations.
Lack of efficient technology for maximum exploitation of wave energy.
Harnessing wave energy on large scale is expensive
Ocean thermal energy (OTE ): Temperature of the surface of the ocean is more due to the heat
of sun light when compared to the lower layers. Energy due to temperature difference between
warm water of the surface and cold water of the lower layers of the ocean is called ocean
thermal energy. It is harnessed as electricity in Ocean Thermal Energy Conversion (OTEC ) plant.
Working of OTEC plant:
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Warm water of the surface of the ocean is used to boil a volatile liquid, ammonia
Ammonia vapour rotates turbine of generator
Rotation of turbine generates electricity in generator
Cold water from lower layers is pumped to condense ammonia vapour back to liquid to
use it again.
Advantages:
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OTE used in OTEC plant is renewable and inexhaustible.
Eco-friendly.
Disadvantages:
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A minimum temperature difference of 20 C/ 293K between surface of the ocean and up
to a depth of 2 km is required to operate OTEC plant.
Low efficiency
Harnessing OTE on large scale is expensive
Geothermal energy: molten rocks formed in the deeper part of the earth are pushed upward and
trapped in certain regions called hot sports. This causes boiling of under-ground water and
formation of steam. Heat energy possessed by steam trapped in rock under the earth is called
geothermal energy. The steam trapped in rocks is routed through a pipe to a turbine to generate
electricity.
Advantages:
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it doesn’t cause atmospheric pollution
it is renewable and inexhaustible
low cost
Disadvantages:
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Commercially viable sites where geothermal energy can be exploited are limited.
Nuclear energy: Energy released by the fission or fusion of atomic nuclei.
Nuclear fission:
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It is the process in which heavy nucleus splits to form lighter nuclei with the release of
large amount of energy.
It takes place when heavy nucleus is bombarded by low energy neutron
It is a chain reaction
Products of the process are radioactive.
Eg. U + n ------------- Ba + Kr + 3 n + energy
Nuclear fission may be controlled or uncontrolled. Controlled nuclear fission of uranium
is carried out in a nuclear reactor to generate electricity. Uncontrolled nuclear fission of
uranium takes place in an atom bomb.
Nuclear fusion:
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It is the process in which lighter nuclei fuse to form heavy nucleus with the release of
tremendous amount of energy
It takes place at very high temperature.
It is not a chain reaction
Products of the reaction are non-radioactive
2H + 2 H ---------- 3He + 1 n + energy
In sun, heat and light are produced by the fusion reaction of hydrogen. It also takes place
in hydrogen bomb.
Advantages of nuclear fusion over nuclear fission
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Produces more energy than nuclear fission
Less radiation
Products are non-radioactive.
Limitations of nuclear power plants:
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High risk of environmental contamination from radiations and nuclear wastes.
Limited availability of uranium
High cost of installation.
Production of electricity in a nuclear generator:
Controlled fission of U-235 is carried out in nuclear reactor to produce large amount of
heat. Heat boils water to steam. Steam rotates turbine of generator to produce electricity.