New generation turbine foundation makes its debut

Turbine foundations are an area where innovative alternatives to the traditional monopiles dominating current projects are now appearing. As windfarms move further offshore and into deeper water, and as turbines become larger and heavier alternative foundation solutions including gravity base are emerging as one such innovation.

Earlier this year the foundation base plate featuring Seatower’s patented Cranefree Gravity design was cast with the complete structure due to be towed out to its final location in water 27m deep, 17km off Fécamp. Principle partners in the windfarm are EDF Energies Nouvelles of France, Denmark’s DONG Energy and German company wpd group.

MT Højgaard see the development as the first big milestone in the production of new concrete base gravity foundations and the next stage was construction of the conical concrete and steel structure on top of the base slab. The seabed will be prepared to make the foundation self-levelling once lowered by ballasting. The base plate for the prototype foundation is just over 23m in diameter and over a metre high. The complete structure, with a meteorological mast and ballast, will weigh in at 1,760 tonnes. The foundation is a part-scale model of a potentially larger version to accommodate the 6MW Alstom Haliade turbine.

Seatower’s knowledge and expertise in the area of concrete gravity foundations has its roots in the offshore oil and gas industry making the move into offshore renewables a somewhat natural one and they have been collaborating with MT Højgaard in the sector since 2011. This particular project sees Seatower responsible for the design, production will be by Eiffage TP and installation by MT Højgaard. The latter company has, since 1992 supplied over 630 turbine foundations, the equivalent of over 2GW of wind energy.

A feature of concrete gravity foundations is that installation involves towing of the foundation to the site by conventional towing vessels. There is no requirement for an offshore crane or the usual piling which can be subject to restrictions in some jurisdictions including seasons where building has to be stopped for fear of noise interference with mammals.

Seatower CEO Petter Karal said: “Our technology will ease and speed up the construction of offshore wind farms at a time when cutting costs and risks is necessary to help the sector progress to more challenging project sites,” adding: “Cranefree Gravity foundations are generally more cost-efficient, quicker to install and less risky than current methods that use steel foundation designs. They also allow for local construction, which provides welcome economic activities to the coastal communities close to the wind farms.”

By Peter barker