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Sources of Energy

“There is enough on Earth for everybody’s needs, but not enough for everybody’s greed”.

– Mahatma Gandhi.

What is Energy?

Energy is the ability to do work or the total power derived from our natural resources like the Sun, the Oceans, Fossil fuel, Wind, etc.

Energy in the usable form, is dissipated to the surroundings (in form of heat) in less usable forms. Hence, any form of source of energy we use, to do work, is consumed and cannot be used again.

Law of Conservation of Energy

The law of conservation of energy states that energy can neither be created nor destroyed – it only can be converted from one form of energy to another.

Sources of Energy

A good source of energy or good fuel is one that

1. Which does a large amount of work per unit volume or mass

2. It can be easily accessible

3. It is easy to store and transport, and

4. It is economical.

How electricity is generated?

  • The simplest turbines have one moving part, a rotor-blade assembly. The moving fluid (steam) acts on the blade to spin them and impart energy to the rotor which in turn rotates the shaft of the dynamo an converts the mechanical energy into electrical energy.

> Sources of Energy can be divided into two broad heads: Conventional Sources of Energy and Non-conventional Sources of Energy.

Conventional Sources of Energy

The source of energy which have been in use for a very long time or have been used extensively worldwide are known as Conventional Sources. For example, coal, fossil fuel, etc.

Fossil Fuel
  • Fossil fuels are formed due to compression of dead organic matter over millions of years, buried deep under the earth. E.g.. coal or natural gas.

  • Fossil Fuels are non-renewable sources of energy as they have limited reserves and hence finding alternative sources is essential to avoid an energy crisis.

Thermal Power Plant
  • The Thermal Power Plant is a power generation station which burns fossil fuels like coal, petroleum etc., to produce electricity.

  • Thermal power plants use steam produced by burning fossil fuels (mainly coal) to move the turbines to generate electricity.

  • The burning of coal heats up the water and forms steam that is used to run the turbine.

  • Usually, Thermal power plants are located near coal or oil fields as it is easier to transmit electricity than transport coal.

Hydro Power Plant
  • Hydro Power Plants converts the kinetic energy of flowing water or the potential energy of falling water at as height to generate electricity.

  • Hydro Power Plant are usually constructed near dams or waterfalls.


The cow-dung, various plant materials like the residue after harvesting crops, vegetable waste, sewerage, animal products are the sources of these fuel.

Since the starting material is mainly cow-dung, it is popularly known as ‘Gobar-Gas’.

Working of Bio-Gas Plant:
  • The plant has a dome-like structure built with bricks. A slurry of cow-dung and water is made in mixing tank from where it is fed into digester.

  • The digester is a sealed chamber, where there is no oxygen with some anaerobic micro-organism that decompose or break down complex compounds of the cow-dung slurry.

  • Once the decomposition process completes, gases like methane, carbon dioxide, hydrogen and hydrogen sulphide are generated.

  • The bio-gas is stored in the gas tank above the digester from where they are drawn through pipes for use.


  • Bio-gas is an excellent fuel as it contains upto 75% methane. It burns without smoke, leaves no residue like ash in wood, charcoal and coal burning.

  • Its heating capacity is high. It is also used for lighting.

  • The slurry left behind is removed periodically and used as manure, rich in nitrogen and phosphorous.

Wind Energy
  • Wind is the natural phenomenon caused by pressure differentials due to unequal heating of land and water masses on the surface of the earth. The kinetic energy of wind is harnessed to do mechanical work.

For example, windmill is utilized to uplift water from well and also to generate electricity.

  • Wind Energy is harnessed by rotatory structures known as windmills.

  • The windmills have huge blades or fans attached very high on a rigid support that is attached to turbines that rotate due to high speeds of wind and generate electricity.

Advantages and disadvantages of wind energy.



1. Environment-friendly and efficient source of energy.

2.No recurring expenses for the production of electricity.

1.)Wind energy farm can be constructed only at places where wind blows throughout the year.

2.)Wind speed must be >15 km/hour to rotate turbine.

3.)There should be back-up facilities for storage in case of no wind.

4.)Requires large area for set-up.

5.)Establishment cost is high.

Non–Conventional (Alternative) Sources of Energy

Non-conventional sources of energy are also known as renewable sources of energy. For example, solar energy, tidal energy, wave energy, geothermal energy, etc.

Solar energy

Light energy and Heat energy from the Sun are known as Solar energy.

(a)Solar Cooker: (Working of solar cooker)
  • Black surfaces absorb more energy than other surfaces and solar cookers and solar water heater use this property by coating their insides black.

  • The reflecting surfaces like mirrors to focus the sun’s rays are used.

  • The device is covered with a glass plate thereby establishing the greenhouse effect by trapping heat inside the cooker.

(b)Solar Cells: (Working of solar cell)
  • A device that converts solar energy into electricity is known as a solar cell.

  • A typical solar cell produces a voltage of 0.5 1 V and 0.7 W of electrical power. A large number of such cells can combine to form a solar panel which can generate power large enough for practical uses.

Advantages: (i) no moving parts (ii) require little maintenance (iii) can be set up in remote areas without the hassle and expenses of transmission lines.

Disadvantages: (i) Requires a special grade silicon which is not easily available (ii) Usage of silver for interconnections makes it expensive.

Uses: traffic signals, calculators, artificial satellites and space probes.

Energy from the Sea
(a)Tidal Energy
  • The gravitational pull of the moon on the revolving earth, the level of water in sea rises and falls. This phenomenon is called high and low tides and the difference in sea-levels gives us tidal energy.

  • Tidal energy is harnessed by constructing a dam across a narrow opening to the sea. A turbine fixed at the opening of the dam converts tidal energy to electricity.

(b)Wave Energy
  • The waves are generated by strong winds blowing across the sea and these waves possess huge kinetic energy which can be trapped in wide variety of devices to rotate turbine and generate electricity.

(c)Ocean Thermal Energy
  • The difference in surface temperatures of water and water at a certain depth in oceans is exploited to harness this form of energy.

  • Temperature difference must be 20∘ between the surface and water up to depths of 2 km.

  • Warm water is used to boil volatile ammonia to form vapours that move the turbine. Cold water is used to condense the vapour back to liquid.

Geothermal Energy
  • Due to geological changes, molten rocks formed in the deeper hot regions of earth’s crust are pushed upward and trapped in certain regions called ‘hot spots’.

  • When underground water comes in contact with these hot spots, a steam is generated that finds outlet at the surface known as ‘hot springs’.

  • The steam trapped in rocks is routed through a pipe to turbine and used to generate electricity.

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 spilt apart into lighter nuclei and a tremendous amount of energy is released known as nuclear energy.

  • This energy can be used to produce steam and further to generate electricity.

Difference between Nuclear Fission and Nuclear Fusion.

Nuclear Fission

Nuclear Fusion

In this process heavy nucleus is divided into two fragments along with few neutrons.

In this process lighter nuclei will join together to produce heavy nucleus.

These reactions will take place even at room temperature.

These reactions will take place at high temperature such as 107 Kelvin.

Bombardment of external neutrons is necessary.

No such need for external neutrons.

Energy released per unit mass of participant is less.

Energy released per unit mass of participants id high, Nearly, 7 times high than fission reaction.

Neutrons are liberated in the process.

Positrons are liberated in this process.

This reaction can be controlled, example, by nuclear reactor.

There is no control on fusion reaction.

Atom bomb works on the principle of fission reaction.

Hydrogen bomb works on the principle of fusion reaction.

Famous Nuclear Power Plants in India

Name of Nuclear Power Plant


Tarapur nuclear power plant


Rana Pratap Sagar power plant



Tamil Nadu


Uttar Pradesh





Difference between Conventional and Non-conventional Sources of energy

Conventional source of energy

Non-conventional source of energy

Those sources which have been in use since the early times

those sources that generally have been identified in the recent past.

They are exhaustible

They are inexhaustible

Cause pollution when used as they emit smoke and ash

Generally, these are pollution free

Their generation and use involve huge expenditure

Low expenditure required

Examples- coal, natural gas, firewood, etc.

Example- geothermal energy, solar energy, wind energy, etc.

Environmental Consequences

  • Non-renewable resources such as coal and petroleum cause more harm to the environment when compared to renewable resources, in the form of air and water pollution, generation of toxic wastes, etc.

  • Even renewable resources are not completely eco-friendly. The generation of energy from the wind, the sun, tides, etc. also creates harmful environmental impacts and affects biodiversity to a significant level.


Consequences or Impacts


Emissions of green house gases, particulate matter and SOx.


Flooding to construct dams, altering, downstream river regimes, silting upstream of dams, barrier against fish migration, proliferation of algae, loss of historical and archaeological and tourism, removal of local populations.


Loss of Biodiversity, atmospheric pollution, fish mortality, contamination of groundwater and aquifers.

Wind energy

Noise pollution, death of birds.

Solar energy

Accumulation of toxic residue in environment

Nuclear energy

Risk of accidents, uncertainty in residue management, Danger of proliferation of atomic weapons.

- Sources of Energy can also be categorized as Renewable Sources of Energy and Non-renewable Sources of Energy.

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