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| Pelamis wave energy converter | three gorges dam.jpg |
Hydropower
The term hydropower simply refers to the energy in water, either the kinetic energy of moving water or the potential energy of water stored in a place where there is the possibility for that water to flow downhill, thus converting the potential energy of the stored water into kinetic energy in the moving water.
Hydropower has been used over the years to run mills, and it is now used throughout the world to operate turbines to generate electricity.
Dams are a common way to use the energy in stored water. The natural flow of water down a river course is blocked by the dam. With nowhere to go the water level builds up behind the dam creating a reservoir. When the water is released through gates in the dam wall then it emerges at great pressure. The stored energy in the reservoir of water can be used to drive dynamos to generate electricity.
The Pelamis wave energy converter is one of several devices designed to generate electricity from the movements of the waves.
Hydropower can also provide an almost immediate supply of electricity wheras nuclear or fossil fuel power stations take time to increase their output. A pumped storage facility allows water to be pumped to a reservoir on higher ground. This can be done at times of low electricity demand. The water in the reservoir can be released immediately to generate electricity in the event of a demand peak or the failure of a power station or a critical part of the network. This would give the time needed for other power stations to increase their supply of electricity to meet the increased demand.
Tidal barrages, such as the one at La Rance in France, traps the incoming tide and releases it through generators to provide an electricity supply.
Tidal stream generators are used to generate electricity when the tide passes through them. These devices operate in a very similar way to wind turbines.
The use of a trompe utilises the energy in moving water in a different way. In these devices the water is allowed to fall down a tube and through a constriction which results in lower pressure (the venturi effect). An open port sucks in air to equalise the pressure in the pipe. As these air bubbles go down the pipe they are pressurized proportionally to the hydraulic head. The compressed air rises to the top of the separation chamber and can be extracted to be used as a power source.
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