On 24 June 2010, Danish contractor MT Højgaard installed the first foundation for the Sheringham Shoal Offshore Wind Farm, which is located off the coast of Norfolk in England. Over the next nine months, MT Højgaard will install an additional 89 foundations for the 35 km2 offshore wind farm, which will supply electricity to 200,000 British households.
The foundations consist of monopiles, which are large hollow steel pipes between 44 and 61 metres long, with variable wall thickness typically between 60mm and 100mm and weighing between 375 and 530 tonnes. The monopiles are driven 23-37 metres into the seabed, using a hydraulic hammer on board the large floating crane, Svanen (the Swan). On top of each monopile, MT Højgaard installs a transition piece, which is 23 metres high, weighs around 220 tons and functions as a support structure for the wind turbine itself. The total weight of the steelwork in the foundations is about sixty thousand tonnes.
MT Højgaard is among the world's most experienced companies in installing foundations for offshore wind turbines. There is a substantial amount of development and design and logistics work involved in the project, since the sea depth in the area varies from 15 to 22 metres. Each monopile is unique and designed and fabricated for the precise location where it will be installed. The steel foundations are fabricated in Holland and Belgium and sailed to Sheringham Shoal. The 2 large transition pieces for the Offshore Wind Farm's substations are fabricated in Denmark.
MTH and consultant Rambøll have been working on the turnkey design and fabrication of the foundations for two years, and the design is a synthesis of current best practices for both permanent and temporary works. As part of the installation, MT Højgaard with the assistance of specialist consultants have designed and patented a heave-compensated rail trolley to safely and semi-automatically deliver the 375 to 530 tonne monopiles from the transport ships to the floating crane, Svanen, accommodating the different motions of the 2 vessels.
The Sheringham Shoal project is owned by Statoil (50%) and Statkraft (50%) through Scira Offshore Energy Ltd.
Ed Garvey, ICE representative for Denmark, is manager of MT Højgaard's offshore design and engineering department.