La Rance, Brittany, France (48°37'5" N, 2°1'24" W) is home to the La Rance tidal power plant, one of only a handful of commercial-scale tidal plants in operation. The site was chosen because of its enormous tidal ranges that can exceed 13 meters. Commissioned in 1966, the plant was indicative of the French government's plant to use tidal power to supply much of its electricity needs. However, France later decided to agressively pursue nuclear power.
The La Rance tidal plant has been in operation for thirty years without a major accident or breakdown. The plant generates 240 MW of power using 24 bulb-type turbine generators, spanning a diameter of 5.35 meters, incorporated in the barrage technology of the operation, each rated at 10 MW. During high tide, the dam at the plant catches the waters of the Atlantic in the bay, and at low tide the water returns back to the ocean. During this flow back to the ocean, the water passes through the 24 turbines, connected to the generators, producing power. The amount of electricity generated by this tidal plant could supply a city of about 300,000 people. In 1997, the plant was upgraded by the installation of turbines able to spin during both the incoming and outgoing tides.
Like any large-scale hydrological alteration, tidal power stations has economic and social impacts. The La Rance plant provided some unique regional development benefits because it was wide enough to support a road that connected two previously isolated communities, and it allowed further development of the local distribution network for raw materials and finished goods. The plant also supports a modest tourist industry.
High capital cost is the greatest barrier impeding further development of tidal power systems. Tidal energy projects require large capital expenditure at the outset, and thus have relatively long construction periods and low load factors, leading to long payback periods. Other limitations include specific location requirements such as a site that has large tidal flows, a significant range between high and low tides, and low costs of building features of natural submarines. The largest environmental threat of tidal dams consists of the flooding caused by the barrages which disrupts natural estuary ecosystem processes.
Tidal Energy Systems (Research Institute for Sustainable Energy)