La Rance Tidal Barrage (Usine maremotrice de la Rance) was built in the 1960’s near St. Malo in France. A dam 330 metres long was build in front of a 22 square kilometer basin. The tidal range (the difference between high and low tides) averages 8 metres and reach up to 13.5 metres.
The plant consists of 24 bulb type turbine generators 5.35 metres in diameter, 470 tonnes in weight, and rated at 10MW each which generate electricity whether the tide is going in or out (developed by Électricité de France). This peak of 240MW of power is sufficient to power 4% of the homes in Brittany – equivalent to the consumption of a town the size of Rennes. The average power generated is 68MW for an annual output of around 600 million kWh units of electricity.
In November 1996 the La Rance tidal power plant celebrated 30 years of active service during which time 16 billion kWh of electricity were generated without major incident or mechanical breakdown. The initial capital cost of the power plant (620 million Francs) has long since been recovered, and the cost of electricity production is now below 0.02 Euro per kWh.