Non-renewable sources of energy:

Non-renewable sources of energy are precious as they can never be replenished once consumed. Resources like natural gas, oil, coal and uranium have taken millions of years to form. These are called conventional sources of energy because they are most commonly used for generation of energy across the globe.

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Coal is formed from decomposition of forests which had got buried beneath the earth millions of year, ago. It contains carbon, hydrogen, oxygen, nitroger and sulphur. Coal has been used as a source of energy since very long. In ancient times, it was used to cool and to keep homes warm. Today, it is extensively being used for the generation of electricity. It is also used in paper production and cement as well as iron and steel manufacture.


Oil is another form of fossil fuel that has taken more than 300 million years to form. Oil has been formed due to decomposition of diatoms that were living organisms of the sea and of the size of the head of a pin. These organisms had the ability to directly convert the sunlight into stored energy. Diatoms, which died and got buried under the sea millions of years ago, changed into carbon under the pressure and heat, and eventually turned into oil.

Crude oil or petroleum when refined gives petrol (gasoline), diesel fuel, jet fuel, waxes and lubricants. These in turn are used to make plastic, rubber and detergents. The list of products of oil is endless. Therefore, oil has become a primary source of energy for human existence. If oil is not used judiciously, it can cause severe shortage of petroleum in the future.

Natural gas:

Natural gas is made up of methane (85%), ethane (10%) and other hydrocarbons, which are simple chemical compounds that are made up of carbon and hydrogen. The gas is lighter than air and it is highly inflammable. Natural gas can be liquefied and stored easily in liquid form as it occupies much less space than gaseous form and is used for domestic purposes such as cooking.

Renewable sources of energy:

The renewable sources of energy fall in two categories, i.e. vegetable or wood biomass that can be easily replenished, and the other natural sources, also known as non-conventional sources of energy because they are not used so often. If we start using renewable sources more often, it will be beneficial for the environment because these resources do not emit greenhouse gases and they are easily replaced. They help to reduce the demand for fossil fuels.


Biomass is a low carbon fuel that is produced from wastes of living organisms like wood, agricultural residue, cow dung and sewage. This makes the source easily available. Since India is an agricultural country, it is particularly beneficial because each time waste is generated; it is converted into energy and used for various purposes.

Biomass is a reasonable means of energy generation. It is also environment friendly and can be easily produced each time it is finished. Biomass, as firewood, is the traditional fuel for domestic cooking still in most parts of India. The rural people and the urban poor still prefer wood as their main fuel, because of its easy availability. About 75% of rural population depends on forests for fuel wood.

This is a free mode of energy available to them because they have the right to collect it from forests. But biomass is now being converted to biogas, which is a cleaner and more efficient fuel than firewood.

Biogas is produced in a biogas plant by fermenting a mixture of plant waste and animal dung in the absence of oxygen. The mixture of gases thus produced is mainly methane, along with carbon dioxide, hydrogen and traces of hydrogen sulphide. Biogas is now replacing the ‘chulha’ in many rural areas because it is a cleaner fuel (wood and dung cakes give out smoke which is a health hazard and they are not so energy efficient). It can be used to do cooking as well as to run pumps for irrigation. The residue in the biogas plant is used as manure.


Hydropower or hydelpower is harnessing water sources to produce energy. Flowing water especially if it falls from a higher to a lower level has a lot of energy that can be utilized to produce electricity. When water is stored in a reservoir, it acts as a source of energy. Hydropower is becoming a popular source of electricity generation because water is free, it leaves no wastes, and it does not pollute the environment.

However, huge capital investment is required to construct a dam and the power station. The water which is stored in large quantity in the reservoir also impacts the ecology of the area. Some major hydroelectric projects in India are the Bhakra-Nangal project, Damodar Valley Corporation, Nagarjuna project and Tehri project. About 20 per cent of the power generated in India comes from hydroelectric power stations.

Geothermal power:

When hot rocks under the earth’s surface turn underground water into steam, the steam gushes out from a weak spot on the earth’s surface with great pressure. This steam can be used to drive electric generators. The first geothermal power station was made in Landrello (Italy), followed by the Wairekei Power Station in New Zealand. Iceland, Japan, Philippines and the United States also have geothermal power stations.

Geothermal energy is a renewable source of energy. Since the interior of the earth is going to remain hot for millions of years, geothermal energy is inexhaustible source of energy. It is a clean source of energy as it does not cause any environmental pollution. The cost of production of electricity is not much, i.e. the electricity produced is inexpensive and economical.

There are certain limitations of using geothermal energy. Geothermal hot spots are scattered and not found everywhere. There are very few commercially viable sites where energy can be harnessed.

Wind energy:

Kinetic energy from blowing winds is harnessed and converted into mechanical energy to run a turbine, which is connected to a generator. Thus electricity is generated. High speeds of wind generate energy high enough to run windmills and it has been used for centuries. Wind energy is available infinitely and it produces no pollution.

For these reasons, wind energy is fast becoming a popular form of energy. Wind power stations do not require any raw materials and they do not produce any wastes. Wind pumps, wind battery chargers, wind electric generators and grid-connected wind farms are the primary requirements for generating wind energy.

The limitations of harnessing wind energy are as follows:

i. The wind energy farms cannot be established everywhere.

ii. The wind energy farms need back-up facilities to take care of the energy needs during a period when there is no wind.

iii. The wind energy farms require large area for its establishment.

Tidal energy:

The alternate rise and fall in the water level of oceans and seas is known as tides. The energy obtained from tidal waves is known as tidal energy.

A tidal power plant has a dam built across a bay having a narrow opening to the sea. A turbine is fixed at the opening of the dam. The dam has sluice gates.

During high tides, the sluice gates are opened. Water from the sea falls on the turbine and rotates the blades of the turbine. During low tide, the stored water is allowed to flow back through the turbine again. It again rotates the blades of the turbine resulting in the production of electricity.

Some of the limitations of using tidal energy are as follows:

i. Tidal dams cannot be established everywhere. There are very few sites which are suitable for building tidal dams.

ii. The power can be generated only on a small scale.

iii. It involves high maintenance cost.

India has estimated power potential of about 15,000 MW. Although no tidal energy is being generated in India, the following states have been identified for harnessing tidal energy.

i. Navalakhi and Kandla (Gulf of Kutch) 1000 MW

ii. Bhavnagar (Gulf of Cambay, Gujarat) 7000 MW

iii. Sundarbans 100 MW

Solar Energy:

Thermonuclear fusion reactions that take place in the core of the sun provide a lot of usable energy’. This energy has been harnessed for solar cookers and solar heaters for a long time. Reflectors are also used to collect solar energy that can be used to convert water into steam. Solar cells use the energy of the sun to generate electricity. Solar energy is also used for evaporation, desalination and distillation purposes.

In India, we have access to sunlight throughout the year. This is very beneficial and offers great scope for use of solar energy for our needs.

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