A sea of electricity

A sea of electricity

Lena, Manuel

First tidal power plant still going strong after more than three decades

Thirty years ago, France saw a need to expand its economy by creating new energy sources to make up for limited oil and coal supplies.

The result was the La Rance tidal power plant – the first of its kind in the world.

The La Rance plant in Brittany, a western region of France, over the past three decades has generated 16 billion kWh of power throughout 160,000 operating hours. The entire structure from bank to bank across the Rance River is 2,460 ft. (750 m) long.

In 1996, La Rance officials decided that the plant, completed in 1966 after five years of construction, should begin a $78 million facelift. The 10-year ongoing project aims to replace the facility’s giant turbines one by one while the plant continues to generate power.

Three teams of 15 workers are repairing the turbines. The plant’s permanent 58-member staff was enhanced with 30 new employees for the project.

The portion of the plant that houses the 24-bulb turbine generator connections is at the center of the long dam structure. Each bulb generator is composed of a turbine and 10,000 kW alternator to generate electricity. They function whether the tide is rising or falling and can also be used as pumping engines.

Built on a granite foundation, La Rance is the oldest and most powerful tidal plant in the world. Producing 240 MW of power, it generates 600 million kWh annually.

Electricity is generated by taking advantage of the difference in water levels between high and low tides. As the tide comes in, sea water is channeled through 24 turbines, creating electric power. The turbines are based on a horizontal rather than vertical axis and each has four blades. Once the tide is in, the turbine channels are closed.

When the tide is out, the water held behind the barrier is released through the same turbines to create more energy.

Tides ebb and flow into the estuary twice a day at a maximum rate of 18,000 cubic meters per second.

The plant’s power station is managed by a computer but a crew is on call in case of emergency. Lock keepers are on duty 24-hours a day year round to manually control the generators and lock gates if personal safety is at risk.

Electrical generation at La Rance is not directly related to energy needs. Power at non-peak periods can be used to pump water in either direction, which allows the facility to recapture some of the energy later.

Pumping water into the bay at low tide can also facilitate navigation. The La Rance dam includes a boat lock on the left bank. The lock chamber is 212 ft. (65 m) long and 42.5 ft. (13 m) wide. It is operated from a control station in the administrative building on the lock’s east side wall. More than 17,000 boats pass through the lock annually.

Tidal power is one of the least expensive means of generating power in France at 3.7 cents per kilowatt hour. Nuclear plants cost 3.8 cents and thermal plants cost 10.5 cents. Only hydroelectric plants, at 3.2 cents, are more efficient.

La Rance is Brittany’s only largescale electrical generation facility and supplies 90% of the electricity produced in the region. Harnessing tidal flow, it generates power roughly equal to the annual consumption of a town the size of Rennes, with 300,000 inhabitants.

La Rance can be classified in three ways: as an industrial site, as a tourist attraction and as part of a road network.

A four-lane highway with two drawbridges over the plant’s dam reduces the distance between Saint-Malo and Dinard from 28 miles (45 km) to less than 10 miles 15 (km). Each day, an average 35,000 vehicles travel over the plant. But in summer, traffic can increase to 50,000 vehicles per day.

To attract tourists, the La Rance plant created a protected 8.5-mile area in the estuary for nautical sports including sail and motor boating. Visitors may also take free tours of the La Rance facility including its large operations room where technicians ride bicycles inside. In 1994, the plant welcomed 400,000 people, making it France’s most popular industrial site.

La Rance is at the junction of major tourist attractions in France including Dinard, Dinan, SaintMalo and Mont Saint Michel. The Rance Valley’s maritime heritage also appeals to visitors who may choose from various tourist agencies, hotels and restaurants near the dam.

The French National Electric Power Co. (EDF) uses the plant’s estuary and is a member of the Conference of the Elected Representatives and Users of the Rance Estuary (COEUR). This association,. founded in July 1994, developed the Rance Bay Maritime Agreement. Its main goals are to oversee bay cleanup, maritime culture, navigability, silt eradication, beach maintenance and construction work. In 1995, $600,000 was earmarked for studies and trials before the agreement was signed. EDF provided 20% of that funding.

The La Rance facility pays $2.8 million per year in local property and professional taxes. Thirty percent of the outside services used to operate and maintain the installation are contracted to regional companies.

While technology to build the La Rance tidal power facility proved successful long ago, the biggest roadblock to creating similar ones throughout the world is finding suitable sites. A tidal power plant must be built where there is a significant difference in water height between high and low tides. At La Rance, the difference can reach more than 44 ft. during seasonal equinoxes.

Also, a nearby interconnected electrical network must exist for backup because energy generation is not continuous in a tidal power plant.

Even with these limitations, tidal plants are being planned that will create up to 8,600 MW, such as in England, and other sites are being considered throughout the world.

First studied as a proposed project from 1954 to 1961, La Rance cost $740 million to build and its dam was tested with he first cluster of generators in spring 1966. Inaugurated by Gen. de Gaulle in November 1966, the plant began full operation in late 1967.

France remains the only country in the country in the world to date that has constructed an industrialsized tidal plant.

Manuel Lenas of the EDF Service de Presse may be reached at 2, rue Louis Mural, 75384 Paris Cedex 08, France; 011.33 1 40 42 29 49, fax 011.33 1 40 42 72 44. Or for more information contact Alicia Ronan, French Technology Press Office, 401 N. Michigan Ave., Suite 1760, Chicago, IL 60611, USA; 312-222-1235, fax 312-222-1237.

Copyright American Society of Agricultural Engineers Oct 1998

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