Hydro-electric-power is using the movement (kinetic energy) of water to generate electricity. The kinetic energy is a result of the Sun's energy. Sunlight evaporates ocean water (giving it potential gravitational energy) which returns back to the earth in the form of rain. The GPE is changed into kinetic energy as the water flows (another form of falling!) down to the sea. The energy is thus contained within the water and the water is captured in hydroelectric power plants and converted into usable energy

Moving water can be provided by waterfalls, rivers and streams. Hydro-power has been used for thousands of years. The ancient Greeks used water to help move large water wheels, which helped grind up grain which was then turned into flour for bread and there are many working examples of water mills around the world..

To produce a large amount of energy, you need a large volume of water moveing at a good speed. Dams are used to control the flow of large quantities of water so that the output from an HEP station can be matched to need.

When water rushes down a river it has a great deal of natural kinetic energy. As the water is channeled through a dam the energy generated by the water can be made to turn large turbines. The turbines spin and operate electrical generators that can produce large amounts of electricity. This electricity is then stored and sent to cities for use.

Advantages

Hydroelectric schemes are generally very reliable.

They can also be started up very quickly to meet sudden increases in the demand for electricity.

They can be operated in reverse - using surplus electricity from other power stations to pump water from a lower reservoir to a higher one. This means that most of the energy from the surplus electricity is stored rather than being wasted.

Disadvantages and Problems

Sometimes when a river is dammed, it can hurt the wildlife that lives in and on the river. Fish like salmon, for example, need to swim up river to reach their spawning grounds. If the dam blocks their way, they cannot reproduce. The result is less salmon, which hurts the fishing industry.

The lives of people can also be affected by damming as land is flooded to create the reservoir at the head of the dam.