Explain renewable and non-renewable sources of energy.

The various sources of energy are classified into two broad categories — renewable and non-renewable sources of energy.

Renewable Sources of Energy — Energy which can be replenished is known as renewable energy. Some examples include:

1. Solar Energy — Energy emanating from the sun. It is naturally and abundantly available, clean and pollution-free. It can be used directly in solar water heaters, solar cookers, solar furnaces or converted into electricity through solar cells.

2. Hydel/Hydro Energy — Energy created by running and falling water. It is used for generating electricity through dams like Bhakra Dam, Hirakud Dam, and Damodar Valley Project.

3. Wind Energy — Energy obtained from air in motion. It is harnessed using windmills installed in 'wind farms'. India has an estimated wind power potential of 20,000 MW.

4. Biogas Energy — Produced from decomposition of organic matter (animal dung, agricultural waste) in the absence of air. Used widely for cooking and lighting in rural India.

5. Tidal Energy — Energy derived from ocean tides caused by gravitational force of sun and moon. India has selected three sites — Gulf of Kutch, Gulf of Cambay and Sundarbans.

6. Geothermal Energy — Heat energy from hot rocks inside the earth, available at hot springs at places like Manali, Dehradun and Gurgaon.

7. Ocean-Thermal Energy — Heat contained in ocean water heated by the sun, converted into electricity by boiling liquids like ammonia.

8. Nuclear Energy — Energy released from atomic nuclei through fission or fusion. Generates huge amounts of energy without carbon emissions.

Non-renewable Sources of Energy — Sources of energy which once used are not available again are called non-renewable energy. Some examples include:

1. Coal — Formed by slow compression of forests 300 million years ago. Coal is a fossil fuel and was a major source of energy worldwide. India has substantial reserves of coal and Coal Bed Methane (CBM).

2. Petroleum Gas — Obtained as a by-product in petroleum refining. Liquified Petroleum Gas (LPG) is used in cooking gas cylinders. Mercaptan is mixed with LPG to detect leakage.

3. Natural Gas — Found with petroleum in oil wells, contains mainly methane. Compressed Natural Gas (CNG) is used as fuel in automobiles. India has only 0.4% of world's natural gas reserves.