Sources of Energy

Chapter:- 3

Sources of Energy

Sources of Energy

The law of conservation of energy states that energy can neither be created nor destroyed. It can only be converted from one form to another. Any system which is capable of providing useful energy in a convenient form at a steady rate over a long period of time is called source of energy. Various sources of energy are used for doing work. Conversion of one form of energy into other is called transformation of energy. For example, diesel to run the trains, electricity to run different electrical appliances, etc.

A Good Source of Energy

A good source of energy can be characterized by the following factors

  • Safe and convenient to use
  • Easy to transport
  • Easy to store
  • Large amount of work per unit volume or mass
  • Economical


Renewable Sources of Energy

These are the sources of energy which are being produced continuously in nature are inexhaustible.

Advantages of Renewable Sources of Energy Are

  • These sources will last as long as the earth receives light from the sun.
  • These sources are freely available in nature.
  • These sources do not cause any pollution.

Non-Renewable Sources of Energy

These are the sources of energy which have accumulated in nature over a long time and cannot be quickly replaced.

Disadvantages of Non-Renewable Sources of Energy Are

  • Due to their extensive use, these sources are depleting fastly.
  • It is difficult to discover and exploit new deposits of these sources.
  • These sources are a major cause of environmental pollution.


It is a source of energy used for different household and commercial purposes. e.g., coal, LPG, bio-gas, CNG, etc.

Features of An Ideal or a Good Fuel Are

  • It should have a high calorific or a heat value.
  • It should have a proper ignition temperature.
  • It should not produce harmful gases during combustion.
  • It should be cheap in cost and easily available in plenty for everyone.
  • It should be easy to handle and convenient to store and transport from one place to another.
  • It should not be valuable to any other purpose than as a fuel.
  • It should burn smoothly and should not leave much residue after its combustion.

Conventional Sources of Energy

The sources of energy which are exhaustible and have been formed in nature long ago are known as conventional source of energy. e.g., wood and fossil fuels (coal, oil and natural gas).

Fossil Fuels

The remains of prehistoric plants and animals which got buried deep inside the early millions of years ago and changed into fuel due to excess of heat and high pressure inside the earth, are called fossil fuels. Coal, petroleum and natural gas are the major fossil fuels we are using today. The process of formation of fossil fuels is called fossilisation.

Disadvantage Fossil Fuels

  • The fossil fuels are non-renewable sources of energy and once used cannot be renewed.
  • Burning of fossil fuels causes air pollution.
  • The fossil fuel reserves in the earth are limited and may get exhausted soon.
  • Burning fossil fuels release acidic oxides which lead to acid rain which affects our water and soil resources.
  • Greenhouse gases like CO, (carbon dioxide) are released on burning fossil fuels.
  • Fossil fuels are not burnt completely. They leave ashes after burning

Thermal Power Plant

Thermal Power Plant

In thermal power plants, fuel is burnt to produce heat energy used for heating up water to produce steam which further runs turbine to generate electricity. Many thermal power plants are set up near coal or oil fields. The term thermal power plant is us: since fuel is burnt to produce heat energy which converted into electrical energy.

Hydro Power Plant

The Hydro Power Plants which convert the potential energy ­ flowing water into electricity are called hydro power plants. Electricity produced by hydro power plants called hydroelectricity.

Principle of Generating Hydroelectricity

Due to rise in water level connected in a high rise dam the kinetic energy of flowing water gets converted into potential energy. The water from the high level is carried through the pipe to turbine located near the bottom of the dam, which is connected to the electric generator. When the water turbine rotates, then the armature of the generator also rotates rapidly and produce electricity.  

Advantages of Hydroelectricity

  • It does not cause any environmental pollution.
  • The moving water needed for the purpose is available free of cost.
  • Water is a renewable source of energy which will never get exhausted. Each time when it rains, reservoir of dams gets refilled.
  • The construction of dams on rivers, helps in controlling flood and also in irrigation.

Disadvantages of Hydroelectricity

  • Construction of dams may lead to ecological damage.
  • A large variety of plants, animals and their habitat gets submerged in water.
  • It decreases the fertility of the soil in the downstream area and affects crops.
  • Dams can be constructed only in limited number of places preferably in hilly terrains.
  • The vegetation that gets submerged rots under anaerobic conditions and gives rise to methane (CH4) which is greenhouse gas.
  • It creates the problem of satisfactory rehabilitation of displaced people.

Due to such disadvantages construction of dams are opposed.

For example, Tehri Dam Project (on river Ganga) and Sardar Sarovar Dam (on river Narmada).

Improvements in the Technology

(for Using Conventional Sources of Energy)


The waste material of living things (cattle dung) and dead parts of plants and animals is called bio-mass.

The energy obtained from bio-mass is called bio-energy.

Bio-mass as Fuel

Wood and cow-dung are popular bio-mass used as fuels in our country. These fuels do not produce much heat on burning and produce lot of smoke, so technological inputs are required to improve the efficiency of these fuels.


It is obtained by heating the wood in the, limited supply of air (destructive distillation of wood). Charcoal is a better fuel than wood because it burn without flames and is comparatively smokeless and has a higher heat generation heat efficiency.

Bio-Gas Plant

Advantages of Bio-Gas

  • It burns without smoke, therefore causes less pollution.
  • Its calorific value is high.
  • It is convenient to use and leave no residue (called a clean fuel).
  • The slurry left behind in the digester is a good manure.
  • It gives an excellent method to dispose off wastes which would otherwise create pollution.
  • The large scale utilization of bio-waste and sewage material provides a safe and efficient method of waste disposal beside, supplying energy and manure.

Uses of Bio-Gas

  • It is used as domestic fuel for cooking as well as in industries.
  • It is used to run engines and pumping sets.
  • It is used for generating electricity.

Wind Energy

Wind Energy

The kinetic energy of wind is utilised for doing works like

  • Generating electricity
  • Propelling sail boats in rivers and seas.
  • In water-lifting pump to pump out water from ground.
  • Grinding grain to obtain flour.


It is a machine which works with the energy of blowing air or wind.

Principle of Windmill

When the blowing wind strikes across the blades of a windmill, it exerts a force on them due to which the blades of the windmill start rotating. This rotational motion of the blades can be used to drive a large number of machines like water pumps, flour mills and electric generators.

Wind Generator

Windmill used for generating electricity is called wind turbine. The wind rotates the blades of a wind turbine which in turn rotates the armature or coil of a small electric generator to produce electricity. 

Advantages of Wind Energy

  • It is an environment-friendly and efficient source of renewable energy.
  • It requires no recurring expenses for the production of electricity.
  • It does not cause pollution.

Limitations of Harnessing Wind Energy

  • It can be established only at those places where wind blows for most of the part of the year.
  • The minimum wind speed necessary for satisfactory working of a wind generator is 15 km/h, that is not always so.
  • Wind energy farm requires quite area of land nearly 2 hectares land needed for 1 mW generator.
  • The setting up of wind energy farm very expensive.
  • As the blades are exposed to vagaries nature like rain, sun, storm and cyclone they need high level of maintenance.
  • Wind energy farms disturb rain fall pattern.

Solar Energy

It is the energy obtained from the sun.

Traditional Uses of Solar Energy

  • For drying clothes.
  • For obtaining salt from sea.
  • For reducing moisture content in food grains after harvesting.
  • For reducing moisture content in food grains after harvesting.

Solar Energy Devices

The various devices which are commonly used for harnessing sun's energy are called solar energy devices. For example,


Solar lower Plant

It is a type of solar concentrator which is used to generate electricity.

Solar Cell

It is a device to convert solar energy into electrical energy. These cells are made from semiconductors like silicon, gallium, Germanium. Solar cells are also known as photovoltaic cells. A typical solar cell consists of a 2cm2 piece of pure silicon and can develop 0.7W of electricity and a potential of 0.5 V – 1 V when light falls on it.

Uses of Solar Cell

  • Provide electricity in artificial satellites and space probes.
  • Used for street lighting, for traffic signals, for operating water pumps, etc.
  • Provide electricity to light houses situated in sea.
  • Provides radio and TV transmission to remote areas.
  • Used to operate electronic watches and calculators.

Advantages of Solar Energy

  • It does not cause any pollution.
  • It is available in abundance in a hot country like ours.
  • It is available free of cost.
  • It can be put to practical appliances.

Limitations of Solar Energy

  • Energy reaching the surface is very much diffused so direct utility is limited.
  • It is not available uniformly all the time and at all the places.
  • It is not available in night.
  • It is not available on a cloudy day.

Harnessing of Solar Energy

Solar energy can be harnessed directly as well as indirectly Direct utilization the direct utilization of solar energy can be done either by collecting it as heat (solar cooker, solar heater) or by converting it to electricity (solar cells). Indirect utilization it can be done by converting solar energy into chemical energy like bio-mass of plants, etc.

Solar Cooker

Solar Cooker

It is device used to cook food by utilizing the energy radiated by the sun.

Advantages of Solar Cooker

  • It saves fuel.
  • It does not cause air pollution.
  • Since, the food is cooked slowly in the solar cooker; the nutrients do not get destroyed.
  • It can cook four food items at a time.

Energy from the Sea

Sea acts as a renewable source of energy. The energy from sea is available in different forms. These are Tidal Energy, Wave Energy, Ocean Thermal Energy.

Tidal Energy

The rise of sea water due to gravitational pull of the moon is called high tide whereas the fall of sea water is called low tide.

The enormous movement of water between the high tides and low tides provides a very large source of energy in the coastal areas of the world. The tidal energy can be harnessed by constructing a tidal barrage or tidal dam across a narrow opening to the sea.

Limitation of Tidal Energy

The rise and fall of water during tides is not high enough to generate electrical energy on a large scale. These are very few places suitable for building dams. That is why tidal energy is not likely to be a major source of energy.

Wave Energy

Due to the blowing of wind on the surface of ocean very fast sea waves are generated, which have a lot of kinetic energy in them. This energy, with the help of various devices can be used to rotate the turbine of generator and electricity is generated.

The three most common devices that are utilized for harnessing ocean wave are

  • Surface-followers, using floats or pitching devices
  • Oscillating Water Columns (OWC)
  • Focusing devices

Ocean Thermal Energy

The difference in temperature with water and surface and deeper section is exploited to obtain energy is known as ocean thermal energy.

The warm surface water is used to boil a volatile liquid like ammonia used to run the turbine of the generator. The cold water from the depths of the oceans is used to condense vapour again to liquid. The devices used to harness this form of ocean energy are known as Ocean Thermal Energy Conversion (OTEC) power plants.

Geothermal Energy

The heat from interior of the earth can be utilized as a source of energy. Underground water when comes in contact of hot spots, it gets converted into steam due to heat of molten rocks. This steam can be used to run turbines connected to electric generators.

Geothermal Energy

Advantages of Geothermal Energy

  • Available at all times.
  • It is clean.
  • It is environmental-friendly.
  • It brings down the cost of production of energy to almost half of that produced from other conventional sources.

Nuclear Energy

Nuclear Energy

Energy contained in the nucleus of atoms is called nuclear energy.

Nuclear reactions occur in the following two ways

  • Nuclear Fission
  • Nuclear Fusion

Nuclear Fission

The reaction in which a heavy nucleus splits into two or more smaller nucleus, with the evolution of large amount of energy when it is bombarded with slow moving neutron is called nuclear fission.


Nuclear Fusion

A reaction in which two or more lighter nuclei fuse to form a heavy nucleus and large amount of energy is given out is called nuclear fusion reaction.

Nuclear Power Plant

Principle the heat produced in a controlled nuclear fission reaction is utilised for producing steam. This steam is used to run turbines connected to the generators and electricity is generated.

Nuclear Power Plant

Components of Nuclear Power Plant

  • Nuclear Reactor Here, a controlled nuclear fission of a fissionable fuel such as 92U235 is carried out.
  • Heat Exchanger the heat produced in the reactor is transferred to water by circulating a coolant through a coiled pipe. The water gets converted into steam. The coolant is pumped back to the reactor.
  • Steam Turbine The steam generated in the heat exchanger is used to run the steam turbine.
  • Electric generator The shaft of the steam turbine is connected to an electric generator (or dynamo) electricity so produced is sent for transmission.

Nuclear Fusion vs Nuclear Fission


  • Nuclear fusion produces more energy than nuclear fission.
  • The products of nuclear fusion are not radioactive.
  • The fuel needed in the fusion reaction is hydrogen, which is available in abundance. On the other hand, uranium needed for fission reaction, has limited availability.


  • It requires very high temperature to occur, which is not possible in a laboratory.
  • It cannot be controlled by the existing technology.
  • It is difficult to fix a suitable material for carrying out fusion reaction.

Hazards of Nuclear Power Generation

The major hazard of nuclear power generation is

  • Storage and disposal of spent/used fuels and the uranium continuously decaying into harmful subatomic particles.
  • Improper nuclear-waste storage and disposal may lead to environmental contamination.
  • There is also a risk of nuclear accidents causing due to leakage of nuclear radiation.

Environmental Consequences

The environmental consequences of the increasing demand for energy are

  • The combustion for fossil fuels is producing acid rain and damaging plants (crops), soil and aquatic life.
  • The burning of fossil fuels is increasing the amount or greenhouse gas carbon dioxide in the atmosphere.
  • The cutting down of trees from the forest (deforestation) for obtaining fire-wood is causing soil erosion and destroying wildlife.
  • Nuclear power plants are increasing radioactivity in the environment.