Accueil géoportail > Find out > discovery > The Rance tidal power plant
11/01/2010
The Rance tidal power plant
The Rance tidal power plant in Brittany turns tidal power into electricity. Although the principle is eco-friendly, it has nevertheless had an environmental impact that designers did not foresee. The Rance estuary has now found a new environmental equilibrium.
Location and operating principle
Located between Saint-Malo and Dinard en Ille-et-Vilaine, l’usine marémotrice in the Ille-et-Vilaine department in Northern Brittany, the tidal power station blocks off the estuary of the river Rance. The project was first mooted in the 1920s and preliminary studies began in the1940s.
The site is perfect for such a project: the amplitude between low and high tides is extremely high and up to 18,000 m3 of water per second can flow through the estuary, ten times more than the maximum flow of the river Rhone.
However, actual work on this unique project was not begun until the 1960s, when France, seeking to increase its energy independence, decided to try and diversify its energy sources without yet resorting to the mass production of nuclear energy. The plant was inaugurated by General de Gaulle in 1966.
When the tide is rising, the reservoir behind the dam wall fills with sea-water. The difference between the water level in the reservoir and that of the sea drives the turbines as the reservoir fills and when it is emptied.
Electricity is generated by these special turbines (called ‘bulb sets’), which work in both directions (as the reservoir fills and again when it is emptied).
Effects on the environment
While there is no doubt that the tidal power plant was a resounding technical and industrial success, it entailed consequences that were not foreseen 50 years ago. No longer able to plan their work according to the tides, since the 1960s fishermen have had to fit in with the operating schedule of the lock to the west of the dam.
The artificial river-mouth has disrupted the estuary’s eco-system, resulting in the quasi disappearance of some species of fish, while only ‘good swimmers’ manage to pass the estuary.
Moreover, since the plant was built, the estuary has become increasingly silted up.
Human development of a protected site
Today, the site is both hydroelectric power plant, tourist attraction and communication route:
- the plant can supply the electricity requirements for a town the size of Rennes;
- it is one of France’s most visited industrial sites;
- people travelling from Saint-Malo to Dinard have had their journey cut by 45 kilometres, or 65%, thanks to the road built on the dam wall.
The Rance estuary remains a site of particular environmental interest and is part of the Natura 2000 network.
A preliminary study is currently underway into the possibility of establishing a “Rance Emerald Coast” Regional Nature Park.
|
|
Find out more
> Rance Estuary - Site Natura 2000
|