Tidal Energy

Background

Tides, the daily rise and fall of ocean levels relative to coastlines, are a result of the gravitational forces of the moon and sun as well as the revolution of the Earth. The principle of harnessing the energy of tides dates back to as early as the Middle Ages, when the phenomenon of tides was not yet explained and were used to turn waterwheels, producing mechanical power. A large amount of energy is stored in tides and it is possible to tap into this renewable resource with tidal power plants. Tidal electricity generation involves the construction of a barrage across a delta, estuaries, beaches, or other places that are affected by the tides [1].

How it works

Specifically, the barrage (dam) blocks the incoming and out-going tides of a coastal basin. The barrage is equipped with sluices and turbines that will permit the retention of water entering at high tide and release it at low tide; normal turbines will produce electricity as the water flows out; reversible blade turbines, however, can produce electricity both as the water enters the basin and when it leaves. The basic difference between a hydraulic power plant on a river and a tidal power plant is this two-directional flow [2]. If navigation to the upper part of the basin is necessary, a ship lock may be installed.
To date, relatively few tidal power plants have been constructed. Of these, the oldest and by far the largest is the La Rance 240 megawatt barrage located near St. Malo, in Brittany, Northern France [3]. This tidal power plant was built for commercial production and came into service in 1966. It is highly automated, requiring only two people to operate it on weekends and in the evening, [4] and furnishes 90% of Brittany's electrical needs. After completing over 30 years of reliable operation, the power plant underwent a renovation. To provide uninterrupted power production, the plant's 24 turbines were upgraded one at a time over a 10 year period [5]. Numbers correspond to References in the See More section.