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Although tidal mills had been in popular use in some parts of Europe and the US, still there was no success to harness the tidal energy on a commercial scale anywhere across the world. It was only in the year 1967 that the world’s first tidal power plant went operational in France that a new era was ushered in the utilization of marine tidal energy for onshore use in a major way. But this was not an easy journey since it was the first project of its kind.
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France is a country which depends heavily on nuclear power and rough estimates suggest that nearly 78% of all the electrical power utilized in France comes from nuclear power plants while only 15% from thermal power plants. That leaves very little room for any other source of power but it was really a welcome step when plans were made in 1960 to construct a barrage in order to hold tidal water for use in a power plant.
The construction of the barrage required an area free of water so first of all two temporary dams were built to clear and isolate that area from the sea water. It took nearly two years to complete those temporary dams after which the real work started. Then the power plant was constructed and completed in the year 1966, but it was not till towards the end of the next year that the plant got connected to the French national power grid.
The main reason for choosing Rance as a site for construction of the tidal plant was the fact that it has the advantage of having a huge difference between the ebb and flow of the tide ranging from an average of 8 meters to a maximum of nearly 14 meters.
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Special reversible turbines were developed to be used in the Rance power plant which could produce energy during flow of water both ways so as to increase efficiency and improve utilization of the tidal energy. Two dozen turbines were installed each with a capacity of 10MW which makes for a total peak power of 240MW. Of course since tidal flow is not 100% predictable the plant hardly produces near its peak capacity all times of the year.
Another method to gauge actual production is to multiply the peak power with the capacity factor which depends on the types of water in which the power plant is located. The Rance tidal plant which depends on Scottish waters has a capacity factor of roughly 40% which means that the actual power produced is nearly 96MW. This can be multiplied by the number of hours in a year to give the actual number of kilowatt hours produced by the plant.
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Rance power plant has been successful both as a power generation unit as well as a tourist spot. But there has been some damage to the marine ecosystem as well with lot of silting and the disappearance of certain species of marine life.