hydroelectric power

Turbine in a hydroelectric dam. Hydroelectric dams are very ‘high-tech’ but simple machines. The dam holds back water, creating a reservoir of potential power. Water is released through a gate on the upper side of the dam, and surges through a tunnel leading to turbines. The water turns the turbines that in turn spin generators to produce electricity. The electricity is then carried through cables to wherever it is needed.

At 223 m/731 ft Hoover is the highest concrete (‘arch and gravity’) dam, and the third highest of all dams in the USA. Behind it lies Lake Mead; this head of water drives hydroelectric generators that produce 1,300 megawatts of 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.

Hydroelectricity is an example of a renewable resource. In the UK, it provides 1.3% of total electricity production; power stations are located in the mountainous areas of Scotland and North Wales where there is fast-flowing water.

Hydroelectric plants have huge generating capacities. The Grand Coulee plant in Washington State, USA, has a power output of about 10,000 megawatts. The Itaipú power station on the Paraná River (Brazil/Paraguay) has a potential capacity of 12,000 megawatts. However, they are very expensive to build and can only be built in a small number of places depending upon relief, geology, river regime, climate, and demand – hydroelectric power stations are often associated with aluminium smelters which use up excess energy.

Work on the world's largest hydroelectric project, the Three Gorges Dam on the Chang Jiang River in China, was officially inaugurated in 1994 (due to be completed in 2009).