In a few months, the first of a new generation of concrete foundations will be installed for the first time in the English Channel. Optimised production methods and easy installation concept opens up the possibility of major deepwater offshore wind turbine parks.
There was applause all round when the base plate for the prototype for a completely new wind turbine foundation was fully cast in France recently. The foundation is in a few months’ time to be installed approx. 17 km out at sea from Fécamp, in water that is 27 m deep. Norwegian Seatower, Danish MT Højgaard and French Eiffage TP are the companies executing the development project related to “Parc éolien en mer de Fécamp for the French energy company EDF Energies Nouvelles, Danish DONG Energy and German wpd Offshore.
The base plate for the new prototype is just over 23 m in diameter and over a meter high. The weight of the completed structure and meterological mast with ballast is an impressive 1,760 tonnes.
- It's the first big milestone in the production of new concrete gravity based foundations and the casting process went exactly to plan. Now it's the next stage, with construction of the conical concrete and steel structure which will be constructed on top of the base slab and in a few months the foundation will be made ready and towed to sea, explains Kim R. Andersen, director of the Offshore & Steel Bridges division of MT Højgaard.
The foundation will be lowered on the seabed using ballasting with water. Before this, the seabed will have been prepared so that the foundation is self-levelling.
Necessary to look beyond traditional foundations
With over 20 years of experience, MT Højgaard is one of the most experienced operators in the installation of both concrete and monopole monopile foundations. Kim Andersen believes the development of the new type of foundation is necessary to ensure the continued development of offshore wind power as a cost-competitive alternative:
- The “Cranefree® Gravity foundation concept” is a big leap forward from the older types of concrete foundations like Middelgrunden offshore wind farm. The new concrete gravity foundation isn't just designed for locations where the seabed conditions make monopile driving impossible. The foundations are also well-suited to deepwater locations, he explains.
Sustainable economy and an installation that is better for the environment
Using tug boats and without the need for large installation vessels, several foundations can be installed in parallel within a short weather window, even when the waves are high. In addition, the method is better for the environment because of the reduced impact on the seabed, with no noise that would otherwise disturb sea life.
"As offshore wind farms move into deepwater locations, it is crucial that the installation costs are minimised. Otherwise it's no longer financially sustainable," says Kim R. Andersen.
Facts about the concrete gravity foundation
- The foundation is the result of a development project carried out by Norwegian company Seatower. A broad range of know-how and technology from the offshore oil and gas industry was used to develop the new prototype and meet the challenges that the offshore wind power industry faces.
- The concrete gravity foundation is a hybrid structure made from concrete and steel; it can be mass-produced efficiently and installed without the use of costly installation vessels.
- Since 2011, MT Højgaard and Seatower have collaborated on supplying concrete gravity foundations to the European market. In connection with the development project at Fécamp, Seatower has designed the foundation and French contractor Eiffage TP has produced it, while MT Højgaard is responsible for the installation.
Offshore in MT Højgaard
MT Højgaard planned and installed the foundations for the world's first offshore wind farm, the Danish Vindeby. Since 1992, MT Højgaard has supplied more than 630 offshore wind turbine foundations, equivalent to more than 2 GW of wind power.