There are four main sources of energy—coal, petroleum, hydroelectricity and atomic energy. Hydroelectricity has special importance as source of energy. It has the following advantages:
- Coal and petroleum deposits will be exhausted sooner or later but the rivers will continue flowing for thousands of years and so long as the rivers flow there will be no dearth of hydroelectricity.
- While producing hydroelectricity water is not lost. Hydroelectricity is produced by moving turbines with the help of fast-flowing water. The water is afterwards used for irrigation.
- It is not easy to transport coal or petroleum from one place to another and it costs a lot but hydroelectricity can be taken hundreds of kilometres away by wires only.
- Hydroelectricity is cheaper than coal or petroleum.
