Jean-Luc Achard, research director at CNRS, studies the development of tidal turbines

Keywords: renewable energy, hydropower, hydroelectricity, recovery, use, marine currents, sea, tide, tidal stream, wind turbines

"A potential comparable to that of wind turbines"

Jean-Luc Achard is research director at the CNRS and works within the LEGI (laboratory of geophysical and industrial flows) in Grenoble. In particular, he studied the development of a certain type of tidal turbine (Harvest project).

From the XNUMXth century, the first tide mills were created in Brittany. In the years to come, should we bet on new systems for exploiting underwater currents?

The Rance tidal power plant was a huge project: what blocks this kind of program is the cost of the initial investment, which is considerable. Heavy projects, there have been many. All were abandoned because of the financial weight of civil engineering, that is to say concrete. The problem is always the return on investment. It is also, for infrastructures such as the Rance plant, that of the environmental impact: the watercourse has changed; the fauna and flora are different. The "Tidal Bridge" which was proposed by a Canadian company to the Philippine government it was a bridge connecting the Samar and Dalupiri Islands, with 274 turbines below was abandoned for these reasons of excessive cost of concrete and because the seaway might be more difficult to access. A certain skepticism about the use of tidal energy has therefore set in since the 1970s and many projects have remained in the pipeline.

What projects can we "show" cards?

We are currently, in relation with Ifremer, in the process of considering studies on a site which seems very interesting: that of Raz Blanchard, at the north-western tip of Cotentin, facing the Anglo-Norman island of Chausey. . You can reach tides of 5 meters per second. The difficulty is that, for each site, you have to carry out a very comprehensive assessment. If there is, for example, a risk of upheaval of the tides, it is a whole economy which is at stake, that of the fishermen, of the people who live around the site. In the case of the raz Blanchard, there is a certain amount of energy that can be "taken": we have measurements on the flows supplemented by digital models. But you have to be careful. In 1974, a study was made by the ancestor of Ifremer. For an average current of 2 meters per second, it was planned to equip the tidal wave with 390 tidal turbines 10 meters in diameter. Electricity production would have been equivalent to that of the Rance. At the time, the project was deemed unprofitable and abandoned. The perception of the stakes was different and this involved a heavy investment.
In the United States, another tidal turbine program, called Coriolis, had been studied: it involved placing 242 tidal turbines in the Gulf Stream, off Florida. It was a fabulous and gigantic project: the rotors were 91 meters in diameter. Then its promoters noticed that there were problems of mechanical resistance and they threw in the towel. There was, moreover, a risk of impact on the current of the Gulf Stream.
Today, we can start again with programs of this type, but without dreaming. The figures quoted solely on the basis of the theoretically available kinetic energy are not serious. The potential of tidal currents is probably greater than that of wind turbines, but it remains comparable. At best, by 2050, this will be closer to the large hydraulic sector, which represents 13% of energy in France for example. We must also always keep in mind where we are starting from: the renewable energy sector currently represents only 2% of French energy. But, faced with the explosion in energy demand, in China for example, we should not imagine that we will respond only with renewable energies. It will certainly be necessary to reinvest in a safe nuclear, integrating from the upstream the treatment of waste with long lifespan as well as energy savings. And combine energy sources.

What are the most promising sites in Europe?

Currents must exceed 1,50 meters per second for sites to be usable. For France, they are located around the Cotentin and the north coast of Brittany. The most remarkable sites in Europe are mainly around the British Isles: from south Wales (the north-west and south-west Finistères of this country especially), to the north of Ireland and Scotland . On the other hand, there is not much to hope for in the Mediterranean, despite the interesting attempt of the Enermar project in Italy, to harness the energy of the currents of the Strait of Messina ...

Interview made in 2005