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Last month the turbine on its submerged platform was towed out to its site and anchored to the seabed some ten kilometres south-west of Karmoy off Stavanger. Cable laying to connect it to land is scheduled for this month with power being fed into the local grid almost immediately.

The 65 metre turbine and its 82 metre diameter rotor is mounted on a steel jacket filled with ballast. This floating element extends 100 metres beneath the surface and is moored to the seabed by three anchor piles. The technology is designed to be used in water depths of between 120 and 700 metres.

With conventional turbine foundations becoming expensive at depths of 30-50 metres, most offshore development is limited to shallow near-coast waters. "Hywind could open new opportunities for exploitation of offshore wind power, as the turbines could be placed much more freely than before," says Henrik Stiesdal of Siemens. The floating "spar-buoy" system is already used in offshore oil and gas rigs. "We have drawn on our offshore expertise from the oil and gas industry to develop wind power offshore," says Alexandra Bech Gjorv from StatoilHydro.

The full-scale demonstration follows testing of a three-metre-high model in a wave tank in Trondheim in northern Norway. "Floating wind power is not a mature technology yet and the road to commercialisation and large scale development is long," she says. "An important aspect of the project is therefore research and development."

Wave damping

StatoilHydro and Siemens have jointly developed an advanced control system that can deal with the operating conditions particular to floating structures. This takes advantage of the turbine's ability to dampen out part of the wave-induced motions of the floating system. "The wind turbines must work satisfactorily even when subjected to movements, and it must also be possible to carry out necessary maintenance to the highest of safety standards," says Bech Gjorv.

The goal of the pilot project is to reduce costs so that floating wind power can compete with other energy sources. "If we succeed, then we will have taken a major step in moving the wind power industry offshore," says Bech Gjorv. "Floating wind turbines can make a major contribution to providing the world with clean power, but there are major technical and commercial challenges that need to be resolved. If we are to succeed, we will need to cooperate closely with the authorities. As with other technologies for renewable energy, floating wind power will be dependent on incentive schemes to be viable."