Flowing tidal water possess large amount of potential energy. The harnessing the energy of the tides dates back to the eleventh century in England where they used the tides to turn waterwheels to make mechanical power. Today, the rising and the falling of the tides is harnessed to produce electricity.
Tidal energy is a renewable resource which has none of the usual amounts of environmental effects as regular sources of energy like fossil fuels. Changing the flow of the tides can however have a variety of impacts on the water life.
The earth, moon and sun all effect the rise and fall of the tides. The moon and the sun both exert a gravitational force on the earth. The moon exerts a greater amount of force no the earth because it is much closer then the sun. This causes the oceans to bulge along the axis towards the moon. Tides are made by the rotation of the earth under this bulge, causing the rise and fall of coastal ocean levels.
The higher the tides the more energy can be produced, and the lower the cost. Worldwide, around 3000 gigawatts of energy is available fro the action of tides. However, only about 2%, or 60 GW can be recovered for electricity generation.
The first requirement to convert tidal energy into electrical energy is a dam across a tidal bay. The best sites for this dam is where the bay has a narrow opening, reducing the length of the dam, therefore the cost. Along the dam, gates and turbines are built. When the water elevates on the different sides of the barrage, the gates are opened. This creates a hydrostatic head that causes water to flow through the turbines, turning an electric generator to make electricity. (Figure 2)
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