Hydro-energy is the cheapest, and cleaner and hence the best source of energy. Water power is developed by allowing water to fall under force of gravity and is used almost exclusively for generation of electric power. Potential energy of water in converted into mechanical energy by using prime movers known as hydraulic turbines. Hydro-energy is quite cheap in places where water is available in abundance (see Fig below). Although, the capital cost of hydroelectric power plants is higher when compared to other types of power plants, their operating costs are quite low, as no fuel is required.
However, obtaining electricity from mega dams has given rise to many controversies in recent times, small hydro plants are emerging viable alternatives. These plants serve the energy needs of remote and rural area where the grid supply is not available.
A natural or artificial water fall is made to turn a modern type of pedal wheel, called a turbine, which upon rotation generates electricity.
Tides in the sea are the result of universal gravitational effect of heavenly bodies like the sun and moon on earth. Tides can be used to produce electric power, which is known as tidal power. The use of tides for generation of electric power is practical only in a few favorably situated sites where the geography of an inlet or hay favors the construction of a hydroelectric plant.
A tidal plant has been completed in France with a rating of 240 MW in 1960. In India, the first tidal energy project with a capacity of 150 MW has been set up at Vizhinjan near Trivandrum. A major tidal wave power project costing Rs 5000 crores is proposed to be set up in the Gulf of Kutch in Gujarat. Other suggested possible sites for tidal power plants are Gulf of Cambay and Sunderbans areas of West Bengal.
Both incoming and outgoing tides are held back by a darn. The difference in water levels generates electricity in both directions as water runs through reversible turbo-generators