Sources of Energy

Introduction
Energy comes in different forms and one form can be converted into another.
A source of energy is one which provide adequate amount of energy in a convenient form over a long
period of time.
Need of energy
➢ For making food
➢ For lightning
➢ For transport
➢ For running machines
➢ For industrial activities and agricultural work
Qualities of a Good Source of Energy
➢ Which would be do a large amount of work per unit mass.
➢ Cheap and easily available.
➢ Easy to store and transport.
➢ Safe to handle and use.
➢ Does not cause environmental pollution.
Fuels: The materials which are burnt to produce heat energy are known as fuels.
Example: wood, coal, LPG, kerosene.
Characteristics of a Good Fuel
➢ High calorific value (give more heat per unit mass).
➢ Burn without giving out any smoke or harmful gases.
➢ Proper ignition temperature.
➢ Cheap and easily available.
➢ Easy to handle, safe to transport.
➢ Convenient to store.
➢ Burn smoothly.
Source of Energy

Conventional Sources of Energy Non-conventional Sources of Energy

Fossil fuels (Coal, Petroleum) TSolar energy (example: solar cooker, solar cell panel)
Thermal power plant Energy from the sea (tidal wave, OT energy)
 Hydro power plants Biomass-biogas plant and Wind energy
Geothermal energy Nuclear energy

Conventional Source of Energy

➢ Sources of energy which are known to most of the people.
Example: fossil fuels, bio mass etc.
Fossil Fuels
➢ Fuels developed from the fossils e.g., coal petroleum.
➢ Take millions of years to form.
➢ Available in very limited amount.
➢ These are non-renewable sources of energy.
India has about 6% share in the world reserved coal, that may last 250 years more at the present rate of
consumption.
Pollution Caused Fossil Fuels
➢ Released oxides of carbon, nitrogen and Sulphur (acidic in nature) which causes acid rain that
damages trees, plants, reduces fertility of soil.
➢ Produces large amount of CO2 in the atmosphere which causes green house effect leading to
excessive heating of the earth.
Controlling Pollution Caused by Fossil Fuels
➢ Increasing the efficiency of the combustion process.
➢ Using various techniques to reduce the escape of harmful gases and ashes into the surroundings.
Q. What are the disadvantages of fossil fuels ?
Sol. (i) The burning of fossil fuels produces large amount of carbon dioxide that causes increased
greenhouse effect.
(ii) The burning of fossil fuels (such as coal) produces smoke which pollutes the air.
(iii) The burning of fossil fuels produces acidic gases such as sulphur dioxide and nitrogen oxide.
These acidic gases cause acid rain that affects our water and soil resources.
(iv) Fossil fuels cannot be replenished in short time because it takes millions of years to form
them.
Thermal Power Plants
➢ A power plant which uses heat energy to generate electricity.
➢ Burning of fossil fuels produces steam to run turbines.
➢ Set up (power plants) near the coal and oil fields to minimize the cost of transportation and
production.
➢ Transmission of electricity is more efficient.

Hydro Power Plants

➢ Convert the potential energy of falling water into electricity.
➢ Hydro power plants are associated with Dams.
➢ Around 25% of our country’s energy requirement is met by Hydro Power plants.

Advantages of Hydro power plants

➢ No environmental pollution.
➢ Flowing water is a renewable source of electric energy.
➢ Construction of dams prevents flooding of rivers, provide water for irrigation.
Disadvantages of Hydro power plants
➢ Large areas of agricultural land, a vast variety of flora and fauna, human settlements get
submerged in the water of reservoir formed by the dam.
➢ Large ecosystems are destroyed.
➢ Vegetation that submerged under water rots under anaerobic conditions and produces large
amount of methane which is a green house gas.
➢ Creates the problems of satisfactory rehabilitation of displaced people.
Biomass
➢ The dead parts of plants and trees and the waste materials of animals and man are called Biomass.
(i) Wood: It is biomass and used as a fuel for a long time.
Disadvantages of using wood as fuel
➢ Produces a lot of smoke on burning.
➢ Do not produce much heat.
➢ Thus, by improvement in technology we can improve the efficiency of traditional sources of
energy.
➢ For example: wood can be converted into much better fuel called charcoal.
(ii) Charcoal: When wood is burnt in limited supply of air, then water and other volatile materials
gets removed and charcoal is formed.
➢ Wood on limited supply of Oxygen gas get converted into Charcoal.
Charcoal is better fuel than wood because
➢ It has higher calorific value than wood.
➢ Does not produce smoke while burning.
➢ It is a compact fuel, easy to handle and convenient to use.
(iii) Cowdung: It is biomass but it is not good to burn cow dung directly as fuel because:
➢ Produces lot of smoke.
➢ Cowdung does not burn completely, produces lot of ash as residue.
➢ Low calorific value.
➢ By making bio gas (or gobar gas) from cow dung, we get a smokeless fuel.
(iv) Bio gas: It is produced in biogas plant.
➢ Anaerobic micro organisms decomposes the complex compound of the dung + water slurry.
➢ It take few day for the decomposition process and generate gases like methane, CO2, hydrogen
and hydrogen sulphide.
➢ Bio gas is stored in the gas tank above the
digester from which they are drawn
through pipes for use.
Advantages of Bio gas
➢ It is an excellent fuel as it contains upto
75% methane (CH4).
➢ It burns without smoke.
➢ Leaves no residue like ash in wood & coal burning.
➢ Heating capacity is high.
➢ It is also used for lighting.
➢ Slurry left behind is used as excellent manure rich in nitrogen and phosphorus.
➢ Safe and efficient method of waste disposal.
(v) Wind energy
➢ Unequal heating of the landmass and water bodies by solar radiations generate air movement and
causes wind to blow.
Uses of kinetic energy generated by wind energy
➢ To generate electricity by turning the rotor of the turbine.
➢ To lift water from the well.
➢ To run the flour mills.
➢ The output of a single wind mill is quite small so a number of windmills are erected over a large
area called wind energy farm.
➢ The minimum wind speed for wind mill to serve as a source of energy is 15-20 KmPH.
Advantages of wind energy
➢ Eco-friendly.
➢ Efficient source of renewable energy.
➢ No recurring expenses for production of electricity.
Disadvantages of wind energy
➢ Wind energy farms need large of land.
➢ Difficulty in getting regular wind speed of 15-20 KmPH.
➢ Initial cost of establishing wind energy farm is very high.
➢ High level of maintenance of blades of wind mill.
➢ Denmark is called the ‘Country of Winds’.
➢ India is ranked 5th in harnessing wind energy for the
production of electricity.
➢ In India largest wind energy farm has been established near Kanyakumari in Tamil Nadu and it
generates 380 MW of electricity.
Q. How has the traditional use of wind and water energy been modified for convenience ?
Sol. (i) Wind mill farms are constructed to produce electricity.
(ii) The traditional use of energy of flowing water has been modified by establishing hydro-power
plants. At hydro-power plants, the energy of falling water or flowing water is tapped by using a
water turbine and then made to drive generators.
Alternate of Non-conventional Sources of Energy
➢ Day by day, our demand for energy increases, so there is a need for another source of energy.
Reasons for alternate sources of energy
➢ The fossil fuel reserves in the earth are limited which may get exhausted soon if we use them at
the current rate.
➢ Reduce the pressure on fossil fuels making them last for a much longer time.
➢ To reduce the pollution level and to save the environment.
Solar Energy
➢ Sun is the ultimate source of energy.
➢ Energy obtained from the sun is called solar energy.
Solar constant = 1.4 KJ/s/m2
➢ Outer edge of the earth receives solar equal to 1.4 KJ/s/m2 or 1.4 KW/m2
[….. 1 KJ/s = 1 KW]
Solar energy devices:
(i) Solar cooker
(ii) Solar water heater
(iii) Solar cells
Geothermal Energy
➢ ‘Geo’ means ‘earth’ and ‘thermal’ means ‘heat’.
➢ Geothermal energy is the heat energy from hot rocks present inside the earth.
➢ When underground water comes in contact with ‘hot spot’ steam is generated. Steam trapped in
rocks is routed through pipes to a turbine and used to generate electricity.
Advantages of Geothermal energy
➢ Economical to use geothermal energy.
➢ Does not cause any pollution.
Limitations of Geothermal energy
➢ Geothermal energy is not available everywhere.
➢ Deep drilling in the earth to obtain geothermal energy is very difficult and expensive.
➢ In New Zealand and USA, there are no. of power plants based on geothermal energy are
operational.
Nuclear Energy
➢ The energy released during a nuclear reaction is called nuclear energy.
➢ It can be obtained by two types of nuclear reactions:
(i) Nuclear fission
(ii) Nuclear fusion
(i) Nuclear fission
➢ ‘Fission’ means split up.
➢ The process in which the heavy nucleus of a radioactive atom (such as uranium, plutonium or
thorium) split up into smaller nuclei when bombarded with low energy neutrons, is called nuclear
fission.
➢ A tremendous amount of energy is produced.
➢ U-235 is used as a fuel in nuclear reactor in form of uranium rods.
Working of Nuclear fission
➢ In nuclear reactor self sustaining chain reaction releases energy at a controlled rate, which is used
to produce steam and further generate electricity.
Major Nuclear Power Plants
➢ Tarapur (Maharshtra)
➢ Rana Pratap Sagar (Rajasthan)
➢ Kalpakkam (Tamil Nadu)
➢ Narora (U.P.)
➢ Kakrapur (Gujrat)
➢ Kaiga (Karnataka)
(ii) Nuclear Fusion
➢ When two nuclei of light elements (like hydrogen) combine to form a heavy nucleus (like helium)
and tremendous amount of energy is released is called nuclear fusion.
3
1 H(deuterium) +1 H ⎯⎯⎯ →2 H +10 n + Heat
2 2 fusion

➢ Very-very high temperature and pressure is needed for fusion.

➢ Hydrogen bomb is based on this phenomenon.
➢ Nuclear fusion is the source of energy in the sun and other stars.
Advantage of Nuclear Fusion
➢ Production of large amount of useful energy from a very small amount of nuclear fuel.
➢ Does not produce green house gases like CO2.
Limitations of Nuclear Fusion
➢ Environmental contamination due to improper nuclear waste storage and its disposal.
➢ Risk of accidental leakage of harmful radiations.
➢ High cost of installation.
➢ Limited availability of nuclear fuel.
Environmental Consequences
➢ Exploiting any source of energy disturb the environment in some way of the other.
➢ The source we would choose depends upon following the factors:
(i) Ease of extracting energy from the source.
(ii) Cost of extracting energy from the source.
(iii) Efficiency of technology available to extract energy.
(iv) The environmental damage caused by using that source.
➢ In other words, no source of energy is said to be pollution free. Some source are cleaner than the
other.
➢ For example, solar cells may be pollution free but the assembly of the device would have cause
some environmental damage.
Non-renewable Sources of Energy:
➢ Sources that will get depleted some day.
For example: Fossil fuel.
Renewable Sources of Energy:
➢ Energy sources that can be regenerated and that will last for ever.
For example: Wind energy, water energy.

Notes End
 Some Important NCERT Questions
Q1. What is geothermal energy ?
Sol. Energy stored as heat in certain regions of the earth (called hot spots) is called geothermal
energy. Hot spots are the locations below earth’s crust where upward moving magma gets
collected due to geological changes. When underground water comes in contact with the hot
spots, steam is generated. This steam is utilised to generate electricity using pipes and turbines.
Sometimes hot water from the hot spot finds outlet at the surface. Such outlets are called hot
springs.
Q2. What are the advantages of nuclear energy ?
Ans: The advantages of nuclear energy are that :
1. It produces a large amount of useful energy from a very small amount of a nuclear fuel
(like uranium-235).
2. Once the nuclear fuel (like uranium-235) is loaded into the reactor, the nuclear power plant
can go on producing electricity for two to three years at a stretch. There is no need for
putting in nuclear fuel again and again.
3. It does not produce gases like carbon dioxide which contributes to greenhouse effect or
sulphur dioxide which causes acid rain.
Q3. Can any source of energy be pollution free ? Why or why not ?
Ans: No source of energy can be pollution free because even if it is clean, its assembly could have
caused some environmental damage.
Q4. Hydrogen has been used as rocket fuel. Would you consider it a cleaner fuel than CNG ? Why
or why not ?
Ans: Hydrogen is cleaner fuel than CNG. This is because the burning of hydrogen produces only
water, which is totally harmless. On the other hand, burning of CNG produces carbon dioxide
gas and water. The carbon dioxide can produce greenhouse effect in the atmosphere and lead to
the excessive heating of the environment in long run.
Q5. Name two energy sources that you would consider to be renewable. Give reasons for your
choices.
Ans: (i) Energy derived from biomass is a renewable source of energy because waste products are
continuously produced. Plants and trees are also grown at reasonable intervals.
(ii) The energy derived from flowing water, wind, sun and ocean are renewable sources because
these sources can be harnessed into energy so long as the present solar system exists.
Q6. Give the names of two energy sources that you would consider to be exhaustible. Give reasons
for your choices.
Ans: Fossil fuels like coal and petroleum are exhaustible sources of energy. The estimated reserves
of these fuels are said to last us for about another 200 years, while it takes millions of years for
these to be formed.
Q7. What kind of mirror – concave, convex or plane – would be best suited for use in a solar cooker?
Why?
Ans: Plane mirror would be best suited for use in a solar cooker. A plane mirror is used as a reflector.
The reflector is used to increase the area over which the solar energy is collected so that more
and more heat rays of the sun may enter the solar cooker.
Q8. What are the limitations of the energy that can be obtained from the oceans?
Ans: The energy from the oceans can be obtained mainly in three forms,
(a) Tidal energy
(b) Ocean waves energy
(c) Ocean thermal energy
The energy potential from sea is quite large, but efficient commercial exploitation is difficult