Tidal Power History and Arguments For and Against
About the history of tidal power as an alternative energy source as well as arguments for and against its use.
HISTORY AND DEVELOPMENT
Mills powered by tidal energy have been known along the coasts of Brittany, France, since the 12th century. Much later, American colonists built tidal-powered mills in New England. The early tidal mills used the great mechanical force of the tides to turn waterwheels connected to grindstones.
By 1967, tidal energy technology had so advanced that engineers were able to complete the world's first tidal electric plant. Not coincidentally, the plant was again situated in Brittany, this time at the Rance River. The maritime estuary formed where the Rance meets the English Channel is known for its exceptionally large tidal range, which reaches 44.3 ft.
The 240-megawatt La Rance facility is essentially a huge dam with a hydroelectric power plant inside. The dam completely seals off the Rance estuary from the sea, impounding up to 6 1/2 billion cu. ft. of water.
When a rising tide comes in to shore, water passes through sluice gates in the dam, filling the estuary and powering hydroalternators. By closing the sluice gates, the plant operators can trap huge masses of water in the tidal basin behind the dam until the height of the water on the sea side of the dam has dropped considerably. Then the sluice gates can be opened again, allowing the water to spill back across the turbines to the sea. Through the use of specially developed reversible turbines for La Rance, electricity can be generated each time water traverses the dam.
As with other hydroelectric units, the tidal power plant needs no external source of fuel and its operation is essentially pollution-free. Tidal energy is therefore a natural, renewable energy source that can be a significant source of power in a few areas of the world.
Tidal power plants require extremely large tidal ranges in narrow-mouthed bays or inlets in order to make competitive electricity. Only about 15 suitable tidal power plant sites exist in the world, and the total power obtainable from them would equal only a small percentage of the world's electrical capacity. The most promising site for a tidal plant in North America is the Bay of Fundy, on the southeastern Atlantic coast of Canada.
Use of tidal power requires building massive and expensive dams to impound immense volumes of water. Serious disruption of marine ecology may result from construction of the plant; subsequently, plant operation could interfere with normal tidal cycles, and with the life cycles of some marine organisms. The presence of a large dam and its high-voltage lines also might be objectionable to some people.
As the price of fossil fuels continues to rise, tidal power will become relatively cheaper, and existing tidal sites will be progressively more attractive. For example, a U.S. tidal plant project at Passamaquoddy Bay on the Bay of Fundy was studied in the 1930s and found economically unattractive. The Canadians are restudying the Bay of Fundy today, and preliminary indications are that they may opt to build an 800 megawatt plant on one of nine possible sites.
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