Abstract

The European Parliament issued a directive on the promotion of the use of energy from renewable sources on April 23, 2009. According to this directive, renewable energy should represent 23% of the consumed energy in the union by 2020. Since renewable energy resources vary greatly from one location to another, it is important to select and develop the right technology for the right location in order to achieve the set goal.

The significant tidal stream potential (3GW) near the Britanny coast leads us to think that the most appropriate renewable energy to develop in the region is tidal power. Seeing as there are already some ongoing projects in the region by large industrial firms like GDF Suez (around the Ponant Islands) and EDF (at Paimpol-Bréhat), we thought that carrying out a similar study would be a current and suitable subject for our BEI-ERE. Our focus will be on studying the set up of a tidal power farm in the Passage du Fromveur and the effects it would have on the environment an local population.

Eventually, the tidal farm should be able to meet the energy needs of the islands Ouessant and Molène (8424 MWh/year), thus replacing the current oil dependant energy production.
Our team work revolves around three main axes:

  • The location study: regulation, cartography, tidal stream
  • Choice of the appropriate turbine and the optimal spatial configuration of the turbines in the farm
  • The project's impacts and feasability

First of all, it was necessary to define the criteria taken into account to determine the farm location. Among the considered parameters were: the distance from the coast (the farm has to be as close to the coast as possible to reduce the costs); the bathymetry (the farm has to be at a certain depth not to perturb maritime activities), protected areas (environmental restrictions), and the tidal stream intensity.

A study of the tidal stream allowed us to quantify the tidal resource around the islands Ouessant and Molène. This was necessary in order to see if stream velocities were high enough to keep the turbines spinning. Bathymetric data from the SHOM database were used to create the domain, and numerical simulations were run on TELEMAC.
The tidal stream was modeled by a sinusoidal variation of the free surface at the inlet boudary of the domain. Knowing the right boundary conditions, it was possible to study tides corresponding to a 95 tidal coefficient.

A brief review of the different tidal stream turbines was then made in order to select the most appropriate turbine to our tidal resources. Once the turbine was chosen, we were able to study the wake effects to determine the optimal spatial configuration of the turbines in the farm.
TELEMAC was once again used for the numerical simulations. The presence of the turbines was taken into account by adding a drag force to the Saint-Venant equations solved in TELEMAC. The study showed that four turbines were necessary to satisfy the energy needs of Ouessant and Molène.

The last step of our project was the study of environmental, economical, and social impacts of the tidal power farm. For the environmental study, an analysis of the initial and "after-farm" states was done. The analysis  showed that the farm only minimally affects the area. The few undesirable effects can be compensated with the suggested measures. The economical study highlights the many advantages of the project: reducing carbon emissions, creating job opportunities, reducing the costs of electricity production. The profits are substantial enough to validate the high installation and maintenance costs. The impacts on the human activities (fishing, navigation, tourism) are non-existent. The local authorities and population were also very supportive of the project.