T he Rance Tidal Power Station

1. What power plant would you like to tell us about?

I would like to tell you about the Rance Tidal Power Station.

2. Where is the plant located (country, city)?

The facility is located on the estuary of the Rance River, in Brittany, France.

3. Is it a combined heat-and-power plant?

It is an electricity generating facility.

4. What company operates the plant?

The plant is currently operated by Électricité de France. It is a French electric utility company. It is headquartered in Paris, France. EDF is the world's largest producer of electricity.

5. Is it a big power plant?

The Rance Tidal Power Station is the world's first tidal power station and also the world's second biggest tidal power station, in terms of installed capacity after the Sihwa Lake Tidal Power Station in China. The barrage is 750 m (2,461 ft) long. The power plant portion of the dam is 332.5 m (1,091 ft) long. The tidal basin measures 22.5 km² (9 sq mi).

6. What kind of power plant is it ?( What source of energy does it use to generate electricity?)

It is a tidal barrage plant. It uses the energy of tides to produce electricity.

7. Is it clean? Does it produce any gases harmful for the environment?

Energy from the sea is a source of electricity that is safe, inexhaustible, and CO₂-free.

The La Rance tidal plant produces a source of energy that is clean, renewable and sustainable. It has no impact on climate because it does not emit any greenhouse gases.

8. Is it renewable?

Wave energy is renewable energy.

Tidal energy is wave energy which considered to be a renewable source of energy since it only uses the energy from the changing of the tides instead of burning or consuming any form of energy source.

9. Is it an old power plant? When was it built? Why?

The plant was opened on 26 November 1966

10. What do you know about the history of the plant and its construction?

The Rance Tidal Barrage was built in the 1960's near St. Malo in France. The site located near St. Malo, France was chosen for its shape and due to the fact that it has the highest tidal range in France. It has an average tidal range of 8m between low and high tide, while the spring and neap range can be as big as 13.5m.The idea of constructing a tidal power plant on the Rance dates to Gerard Boisnoer in 1921. An early attempt to build a tidal power plant was made in 1925, but due to insufficient finance, it was abandoned in 1930. Construction of the plant commenced on 20 July 1963. Draining the area where the plant was to be built, required construction of two dams. Construction took three years and was completed in 1966. Charles de Gaulle, then President of France, inaugurated the plant. Connection of the plant to the French National Power Grid was carried out on 4 December 1967.The challenge in the construction was designing turbines that would be able to generate power with tidal cycles, special turbines had to be designed to utilize a double cycle of ebbs and direct pumping(where water is allowed to flow from basin to the sea). Those 2 cycles alone account for 80% of total generation; with the high tides accounting for the rest. Turbines also had to be resistant to corrosion due to the sea environment. In order to combat corrosion both the gates and turbines had cathodic protection installed using Imposed Current Cathodic Protection.

11. Did the construction of the plant cause any ecological damage or change?

Construction of the barrage became an environmental shock for the flora and fauna of the Rance estuary, since the tidal barrage construction needed to drain the estuary. The environment has remained healthy but there have been changes due to heavy sedimentation, turbidity (how clear the water is) of the water system and salinity fluctuations caused by the barrage. As a result of progressive silting of the Rance ecosystem., some species of fish have reduced in number or disappeared. However, the pattern of the tides is preserved so that the impact on species living in the estuary is minimal. A new ecological equilibrium has been established since the construction. Now there is an abundance of fish, bird and other wild life. The mean water level in the lagoon is higher than it was before the construction which promoted an increase in boating and sailing activities. The sluice gates and the lock (built to allow boats to get through the barrage) allow a fairly easy transition from one side to the other for all aquatic animals, so this did not have any real affect on species there either. The one impact it did have was that the mud flats were severely diminished so birds that used the mud flats as a hunting ground had to adapt or move elsewhere to feed.

12. What is done to reduce the environmental impact of the plant?

The operator, EDF, monitors the tides and weather forecasts to program the barrage operations on a weekly basis to adjust the tides level and to minimize the biological impact..

13. What investments were made into the project?

In total, the plant cost ₣620 million (approximately €94.5 million). It took almost 20 years for the La Rance to pay for itself.

14. What is the principle of work of this power plant?

There are currently 3 types of technologies which can be used to capture the power of tides. These technologies are known as Tidal Technologies. These technologies are:

1. Tidal Stream Generator

2. Tidal Barrage

3. Dynamic Tidal Power

In the Rance Tidal Power Station, barrage technology was applied. By building a dam, a reservoir was created and turbines were installed. Operating in both directions, the dam creates a difference in the height levels of the water, which can pass through the turbines twice (during the incoming and outgoing tidal flows). When the tide is coming in, the water on the sea side of the barrage is higher than the estuary side; therefore water will flow from the sea side through the turbine into the estuary. When the tide is going out, the exact opposite occurs. The Rance plant uses both the ebb and flow of the tides to create the height difference essential for generating energy. The turbines are similar to wind turbines, but they are submerged and anchored to the sea bed. That means they are underwater. The force of marine tidal currents turns the blades of rotors in the same way that wind turbines harness wind energy. The mechanical energy produced by the rotation of the blades is transformed into electrical energy. The electricity supply is consistent and predictable.