| This is not exactly energy of the future, since electric power stations working by tidal energy already exist. The biggest of them is in France, near St-Malo, the tidal
engine plant at
Rance. With 24 turbines and a power output of 240 MW, it accounts for 90 % of the ocean energy exploited worldwide. Three other tidal farms exist in the world, in Canada (20 MW), China (5 MW) and Russia (0,4 MW).
To be profitable, a tidal power plant cannot be installed just anywhere. The tidal range must be very significant: on average, 10 to 15 meters for the best sites. And it must be possible to construct a dam in good conditions. In fact, a tidal power plant works on the same principle as a hydroelectric plant: a waterfall drives a turbine, and the turbine drives an electric generator.
How does a tidal dam work? As the tide comes in, the dam allows the sea water to pass through into a holding basin. As soon as the tide is about to go down, the dam is closed. The water held back in this way will be used to feed the turbines at low tide.
As with the majority of renewable energy sources, tidal electric power is intermittent.
However, there is one major difference: it can be forecast precisely, even years in advance.
The energy potential from tides worldwide is difficult to calculate. It might be between 500 and 1000 billion kWh per year (world hydroelectric production was 2700 billion kWh in 2002). In France, the average annual production of the Rance power plant is 0.5 billion kWh, less than 1% of total electrical energy produced from water.
It is likely that future tidal power plants will work on the principle of “watermills”, that is to say with turbine blades placed in the marine current, because the environmental impact of a plant with a dam, like that at la Rance is very significant and the maintenance costs are very high. Nevertheless, South Korea has started construction of a plant comparable in size to that at la Rance (the Sihwa dam with a power output of 260 MW), for which the planned start-up date is in 2009. |