United Kingdom

United Kingdom

Technical Digest: Experimental 10 MW unit - Vertical axis offshore

A multi-discipline group of companies within the British offshore wind industry is jointly developing a vertical axis turbine designed specifically for operation at sea.

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At 10 MW, it is twice the size of commercial horizontal axis wind turbines on the offshore market today. The initiative is being led by privately owned VertAx Wind Limited. Converteam of Rugby, UK, is responsible for electrical generation and the control system, civil engineers Gifford is looking at the structural design and Slingsby Advanced Composites is developing the blades with research and development help from Northwest Composites Centre at the University of Manchester. The most recent entrant to the team is offshore consultancy SeaRoc Group, which is developing safe and reliable methods of installing the VertAx 10 MW at sea.

The VertAx's power output will be regulated through stall control, with the three 110 metre blades designed to stall to limit maximum power output.

The rotor, with its three blades attached to the tower in an H format, will be directly attached to two 5 MW inverted permanent magnet generators, each seven metres in diameter, bypassing the need for a gearbox. The tower will be of marine concrete up to the electrical hub. The structure will contain a hydraulic crane to allow maintenance and the tower will be topped by a helipad. The concept has been developed by Steven Peace of VertAx Wind, who says the design will not have the problems encountered in previous attempts at vertical axis wind turbines (VAWTs), which for a variety of reasons have long been abandoned by the mainstream wind industry. In particular, the composite material blades have a constant profile, with no tapers or twists. "The cost savings in using a lighter weight blade structure, together with lower cost materials and much fewer, slower moving parts, will enable VertAx to produce larger machines that will experience less fatigue and a longer life cycle," says Peace. Peter Hunter, also from VertAx, adds that with no yaw motors or pitch control motors, the VertAx does not have many of the elements that can go wrong on a conventional horizontal axis machine. Moreover, he claims that the two permanent magnet generators make control, another Achilles heel of previous vertical axis attempts, much easier.

The next step is to prove the concept, Hunter says, adding that desk studies look promising and the design has worked in wind tunnels and on a 600 kW prototype. VertAx hopes to attract support for development from the UK Government and is being assisted by the South East England Development Agency in its search for funding.

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