Hydro-electric power station

Hydro-electric power stations use the energy from falling water to make electricity. Running water is a very powerful source of energy. For hundreds of years it has been used to drive machinery.

Waterwheels
Waterwheels, like the one in the photo below, were once used to power machines for grinding wheat. Water from the river turned the giant waterwheel, which was connected to cogs. The cogs turned the machinery inside the building. Large stones ground the wheat into flour. Waterwheels are an old-fashioned way of using water to drive machinery.

To understand how water can drive machinery, try this simple experiment.

1) Cut the foil lid from a yoghurt pot. Make a small hole in the middle of the lid.

2) Fold the lid into half, half again, and finally half again. There should be 8 creases. Open out the lid and cut two thirds the way up the line made by each crease.

3) Push a pencil through the hole (in the middle) and hold the wheel under a gently running tap. The wheel should spin around.

Hydro-electric dams
It is best to build a dam across a narrow part of a river. The ideal place is in a gorge, where water flows fast. In countries with many deep valleys such as Norway and Japan, high dams are built to store water. The force of the falling water is used to turn large engines called turbines. In a gorge, water travels faster, so the turbines spin faster. The momentum (spinning) from the turbines turns the generators in the dam to make electricity. Dams with in-built generators are called hydro-electric dams.

The Hoover Dam

Names of some hydro-electric dams

• The Hoover Dam, completed in 1936 on the Colorado River.

• The Aswan High Dam, completed in 1971 on the River Nile.

• The Itaipu Dam, completed in 1982 on the Parana River.

• The Snowy Mountains hydro-electric dam scheme (16 dams in total) in Australia.

• The Tunguska dam in Russia.

Hydro-electric dam under construction
The massive Three Gorges hydro-electric power scheme is being built across the Xiling Gorge on the Yangtze Rriver in China. The dam will be about 2 kilometres long and 100 metres high. The Three Gorges dam will supply electricity to Shanghai and large areas of China. The reservoir will stretch 6 kilometres behind the dam. The project is planned to finish in 2010.

The Xiling Gorge