hydroelectric power

Electricity generated by the motion (kinetic energy) of water. In a typical scheme, the potential energy of water stored in a reservoir, often created by damming a river, is converted into kinetic energy as it is piped into water turbines. The turbines are coupled to generators to produce electricity. Hydroelectric power provides about one-fifth of the world's electricity, supplying more than a billion people. Hydroelectricity is a non-polluting, renewable energy resource, produced from water that is naturally recycled.

Conventional hydroelectric power stations can provide a constant supply of electricity. They have large dams that can store enough water to last for several years. In pumped storage plants, water flowing through the turbines is recycled. At times of low energy demand, the water is pumped back into an upper reservoir and reused to generate electricity. A tidal power station exploits the rise and fall of the tides.