Sources of Energy class ten science NCERT

Sources of Energy

When we use energy in its usable form we convert the form of energy and get our work done during the process. Since we cannot reverse the change involved in this process so we cannot get back the original usable form of energy. Due to this, it becomes important to think about energy shortage and the related energy crisis.

Characteristics of a good source of energy:


Conventional Sources of Energy:

The sources of energy which have been in use since a long time are called conventional sources of energy. Coal, petroleum, natural gas, hydel energy, wind energy and nuclear energy are considered to be the conventional sources of energy. Additionally, firewood is also a conventional source of energy but its usage is now limited to kitchens in rural parts of India.

Fossil Fuels:

Coal: Coal was formed millions of years ago. The plants got buried under swamps and due to high pressure and high temperature inside the earth; they were converted into coal. Coal is the highest used energy source in India. During the days of steam engine, coal was used in steam engines. Moreover, coal was also used as kitchen fuel; before LPG became popular. Now-a-days, coal is mainly being used in the industries.

Petroleum: Petroleum was also formed millions of years ago. The animals got buried under the ocean surface and were converted into petroleum; in due course of time. Petroleum is the third major source of energy being used today. Petroleum products are used as automobile fuel and also in the industries. Natural gas mainly comes from oil wells and is also a major source of energy.

Non-renewable Sources of Energy: It takes millions of years for the formation of fossil fuels. Since they cannot be replenished in the foreseeable future, they are known as non-renewable sources of energy.

Renewable Sources of Energy: Those sources of energy which can be replenished quickly are called renewable sources of energy. Hydel energy, wind energy and solar energy are examples of renewable sources of energy.


Hydel Energy: Hydel energy is produced by utilizing the kinetic energy of flowing water. Huge dams are built over a source of water. Water is collected behind the dam and released. When water falls on urbine; the turbine moves; because of kinetic energy of water. Thus, electricity is generated by the turbine. Electricity; thus generated is called hydel energy or hydroelectricity. Water in the reservoir is replenished with rainwater and so availability of water is not a problem for hydroelectricity.

Diagram of Hydroelectric Power Plant

Drawbacks of Hydel Plant: Building large dams is not good for the ecosystem. When a large dam is built, a vast tract of land in its vicinity gets submerged. This destroys a large part of vegetation and wildlife which does immense damage to the ecosystem. Moreover, when the submerged vegetation decomposes; it produces a huge amount of methane gas. Methane is a potential greenhouse gas and thus is not good for the environment.

Building large dam also affects a huge section of population which lives in the surrounding areas. Many villages need to be evacuated. Although the government comes with some rehabilitation plan for them but the displacement of people from their roots has its own costs involved.

Thermal Power Plant: In a thermal power plant, coal or petroleum is used for converting water into steam. The steam is used to run the turbine; to generate electricity.


Bio-mass: The plants and animals constitute the biomass. Firewood from plants is used as kitchen fuel. If large number of trees can be planted, then a continuous supply of firewood can be ensured. Farm waste; such as stalks of harvested plants and dung of cattle; can be used to generate methane. The decomposition of biomass produces methane; which can be channelized for useful purposes.

Bio-gas Plant: Bio-gas plant can be very useful in solving the energy need of rural areas. A bio-gas plant is a dome-like structure which is usually built from bricks and concrete. In the mixing tank; the slurry is made from cow-dung and water. The slurry then goes to the digester; which is a closed chamber. Since oxygen is absent in the digester, the anaerobes carry on their work of decomposition. The process of decomposition produces biogas. Biogas has about 70% of methane and the rest is composed of other gases. The biogas is channelized through a pipe and can be utilized as kitchen fuel and also as fuel for getting light. The slurry; left behind; is removed. It is used as manure, once it dries.

Diagram of Wind Energy

Wind Energy: Wind energy has been in use since ages. The sail boats of the pre-industrialization era used to run on wind power. Windmills have been in use; especially in Holland; since the medieval period. Now-a-days, windmills are being used to generate electricity. The kinetic energy of wind is utilized to run the turbines; which generate electricity.

At present, Germany is the leading country in terms of wind energy production and India comes at number five. In India, Tamil Nadu is the largest wind energy producing state. The largest wind farm in India is near Kanyakumari; in Tamil Nadu; which generates 380 MW of electricity.

Limitations of Wind Energy: Wind farms can only be established at those places where the wind speed is high enough and is more than 15 km/hr for most parts of the year. Wind farms need to be established on large tracts of land. The fan of the windmill has many moving parts; so cost of maintenance and repair is quite high. The fact, that it has to suffer the vagaries of the nature further compounds the problem. Initial cost of establishing a wind farm is very high. Windmills have the potential to disturb birds in flight.



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