Wind Turbines Learn to Swim

Up to now, it has only been possible to construct offshore wind turbines in relatively shallow waters because their foundations are fixed to the sea floor. Soon, however, the first Senvion wind turbines on floating platforms will be produced – an innovation that has the potential to give a huge boost to wind power across the world.

Wind turbine generators the height of skyscrapers, gently bobbing in the sea – this is what the future looks like for Ranjit Mene. Mene works for Senvion in London as Head of Offshore Sales UK and is responsible for the “Floating Turbines” project, in which Senvion is collaborating with international partners to construct the first floating wind farm off France’s Mediterranean coast.* “For the pilot project, we are adapting our 6.2M152 turbine type specifically for use on a floating offshore foundation,” says Ranjit Mene. “One challenge, for example, is heavy swell, which causes additional loads and movements to the turbine that have to be controlled. We also need to design a project-specific tower. Precisely which technical modifications are required will be determined in the study that our engineers are launching in the second quarter.” Throughout the process, Senvion wants to work closely with the designers of the floating foundation.

Contrary to what is usual for offshore wind turbines, the foundations of Senvion’s four test turbines will not stand on concrete pillars anchored into the sea bed and project out of the sea. Instead, they will be anchored with cables, like pontoons, and float on the water. “The cables must of course be extremely strong,” says Ranjit Mene, adding that “innovative composite materials are therefore under discussion.”

More sea, fewer costs

If the pilot project delivers on what it promises, it will open up fresh prospects for offshore power generation as it would be possible to install the floating turbines where the sea is deeper than 60 meters. They could also be installed in areas where it is difficult to drive in the solid foundations for the huge turbines due to the composition of the sea floor. Alternatively, locations with better wind conditions, where there are no flocks of birds and where the turbines do not obstruct the view of the sea for locals and tourists, could also be an option. Floating wind farms have the potential to make this clean method of power generation extremely attractive across the world, especially for energy-hungry countries such as the USA and Japan.

In addition to thousands of new sites across the world, the floating turbines also promise other prospects. “Once they are being developed at scale there could also be reduced costs” writes energy expert Sami Grover in the US sustainability magazine Treehugger.com. “The foundations are—at the moment—more expensive to manufacture, but much easier to install. Because their movement with the waves should reduce vibrations, they may also need less maintenance too. As the scale of the projects go up, the capital costs should decrease dramatically.”

A giant attached to a cable

The test wind farm in the Mediterranean is in Gruissan in southern France. Its construction was commissioned by the French Environment and Energy Management Agency (ADEME). The wind farm is set to be installed and in operation by 2021.

Olivier Perot, Managing Director of Senvion France, is delighted with this expansion. “With a globally installed capacity of more than 750 megawatts, Senvion has access to unique experience in the field of high-performance offshore technology. We are happy to be able to provide our innovative capacity for the first floating wind farm, here in France.” The Senvion 6.2M152 wind turbine type that will float here for the first time has a rotor diameter of 152 meters and a swept rotor area larger than three football pitches. With nominal power of 6.15 megawatts, each turbine can supply around 4,000 homes with electricity.

 

* The EolMed project is led by the French renewable energy developer Quadran and includes Ideol and its Damping Pool® concrete floater, the civil engineering leader Bouygues Travaux Publics and Senvion.

© Photo: EolMed SAS / www.eolmed.fr