Hywind is a floating wind turbine design based on a single floating cylindrical spar buoy moored by cables or chains to the sea bed. Its substructure is ballasted so that the entire construction floats upright. Hywind combines familiar technologies from the offshore and wind power industries into a new design.
The floating design allows Hywind wind turbines to be placed in waters too deep for conventional bottom-fixed turbines. Offshore winds are typically more consistent and stronger over the sea, due to the absence of topographic features that disrupt wind flow.
Hywind uses a ballasted catenary layout with three mooring cables with 60 tonne weights hanging from the midpoint of each anchor cable to provide additional tension.
Control software on board constantly monitors the operation of the wind turbine and alters the pitch of the blades to effectively dampen the motion of the tower and maximise production. Electricity produced is taken to shore through cables.
After 8 years of testing a full-scale prototype offshore Karmøy in Norway, the Hywind demo has been shown to function well in all wind and wave conditions.
The floating structure consists of a steel cylinder filled with ballast water and rock or iron ore. An updated design has been made based on the experience from the demonstrator prototype. The new design has a design draft of 85-90 m and a displacement of around 12,000 tonnes. The diameter at the water line is about 9-10 m, while the diameter of the submerged section of the buoy is 14-15 m.
Onshore assembly reduces time and risk of offshore operations. The substructures for Hywind Scotland were transported in a horizontal position to the onshore assembly site at Stord on the west coast of Norway. There, the giant spar-structures were filled with close to 8000 tonnes of seawater to make them stay upright. Finally, they were filled with around 5500 tonnes of solid ballast while pumping out approximately 5000 tonnes of seawater to maintain draft.
The structure is moored to the seabed using a conventional 3-line mooring system. In a wind farm layout, common anchor points may be used, reducing the number of anchors per unit. The mooring lines are currently made of steel chains. In future, anchor types will be determined by seabed conditions, and in the case of Hywind Scotland, suction anchors are used.
In 2009 Statoil installed the Hywind Demo offshore Karmøy, Norway. The demonstration unit has a 2,3 MW turbine, while the diameter of the blades is 85 meters. For six years, the demonstration unit performed well, and in 2015 it was decided to proceed to the next phase.
Statoil has a strong cost reduction ambition for Hywind. We will utilize a “Hywind Factory” methodology to realise our amibiton. The “Hywind Factory” is not a physical factory, but rather a systematic approach to mature and industrialize the Hywind concept, to significantly reduce costs and improve the competitiveness of floating wind.
Key focus areas of the Hywind Factory include:
- Optimising the Hywind substructure with respect to material use and production friendliness, adapting it to volume production.
- Design Hywind to be compatible with important trends in the bottom-fixed industry through the use of standard turbines, standard installation vessels and so forth.
- Working to standardize solutions that are common to the floating wind industry, such as mooring and anchoring and export cables.