is defined as the ability or a capacity to perform a work.


On the basis of their form they are used. There are two types of energy sources:


The primary sources of energy are:

These are the sources of energy that are being used in their natural form .Wood, coal, crude oil, natural gas, solar energy.

The secondary sources of energy are:

They are derived from the secondary sources of energy. Coal gas, biogas, kerosene, petrol, diesel, charcoal are the examples of the secondary sources of energy.


On the basis of replacing period energy can be classified into two types:


Non-Renewable sources of energy: Non renewable source of energy are found to be accumulated in the nature over a very long time and cannot be quickly replaced when exhausted at their origin place. For example: Coal, natural gas, petroleum, nuclear energy etc.


Renewable sources of energy:

The sources of energy that can be replaced if they are exhausted at their origin place are called renewable sources of energy. They are being produced continuously in nature and cannot be exhausted. They are:


Bio fuel

Tidal energy

Wind energy

Geo thermal energy

Solar energy


Sun as the ultimate source of energy

The sun is the ultimate source of almost all kinds of energy on earth, either directly or indirectly. Fossil fuels (coal, oil and gas) are the transformed forms of plants (and animals) which once lived on the earth and grew capturing the energy of the sun. Biomass is a product of photosynthesis where the sun has the major role. Hydro-electricity depends upon the water cycle which again is dependent on solar radiation. Similarly, wind energy, tidal power, wave power all, in some way or other, and dependon the sun.


Energy /fuel crisis:

The future scarcity of the energy sources on the earth due to the over population,urbanization and industrialization is called energy crisis. Since the non-renewable resources of the energy will not last long and cannot be regained, the world is going to face the problem of energy crisis in near future. The only solution of energy crisis is energy saving .It can be done in following ways:

By reducing the use of renewable sources of energy.

By developing the alternative source of energy.

By controlling the population growth.


Alternative source of energy:

The source of energy, which can be used instead of non- renewable sources of energy is called alternative source of energy. E.g. nuclear energy

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