Energy is the power of the physical action system. Energy exists in several ways: heat, kinetic or mechanical energy, light, potential energy, electricity, or other forms. Energy is the ability to do work. The sources of energy are classified as follows :
(i) Renewable sources of energy (or non-conventional sources of energy):
The sources of energy which are in constant supply to us by nature and are inexhaustible are known as renewable sources of energy.
e.g. The sun (solar energy), oceans, tidal energy, wind energy, running water energy, wood, geothermal energy etc.
(ii) Non-renewable sources of energy (or conventional sources of energy) :
The sources which can't be used again and again and are exhaustible are known as non-renewable sources of energy.
e.g. Coal, natural gas, petroleum; fossil fuels etc.
Conventional sources of energy
These sources of energy donot restock within a span of time.These are used extensively and meet a major portion of our energy requirement since ancient times.
Examples of conventional sources of energy are fossil fuels (coal, oil and natural gas), hydro energy, biomass (firewood, animal dung and biodegradable waste) energy, wind energy, etc.
Non-conventional sources of energy are also called Renewable sources of energy. These sources of energy are not used as extensively as the conventional ones and meet our energy requirement only on limited scale.
Examples of non-conventional sources of energy are solar energy, ocean energy (tidal energy, wave energy, ocean thermal energy, etc), nuclear energy, etc.