Recent wind farm development has shown a shift towards choosing large windturbine sites well away from habited areas. Offshore sites are becoming increasingly used. The placement of windturbines in harsh offshore environments is an engineering challenge, which requires development of suitable foundation designs as well as dedicated installation methods in order to overcome the access restrictions. This paper describes the development of offshore monopile foundations for the first three major British offshore sites for large wind turbines in the 2 MW class: Blyth (2 foundations), North Hoyle (30 foundations) and Scroby Sands (30 foundations). The paper includes a discussion and evaluation of design and installation of the foundations. Installation tolerances for main components, which are installed separately offshore: pile, transition section, sea access arrangement, J-tubes and access platform are discussed. Seabed scour protection solutions are briefly described.
The three first offshore windfarms offshore the British coastline have been erected. On all three projects, foundations of monopile type were chosen. LICengineering A/S supplied the design of monopile and appurtenance structures for these windfarms.
The locations are Blyth, North Hoyle and Scroby Sands. Allthough the windfarms are situated at locations, which have similar water depth and the windturbines and tower structures are approximately same size (2 MW class), very different designs were developed in order to suit the local geotechnical, hydrographic and environmental conditions, as well as provide solutions to overcome the different access restrictions and installation methods.
The Blyth location is situated on the East coast of England in Northumberland, a site exposed to shore breaking waves from the North Sea. The two windturbines are placed on a bedrock formation with sandy seabed in the area around.
The North Hoyle location is situated North of Wales in relatively sheltered waters, but with very high tidal variations.