Floating foundation prototype -- Seeking lightweight turbine

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Norwegian energy company Norsk Hydro is drawing upon 30 years of technical experience building offshore oilrigs to design a prototype floating offshore wind turbine foundation. "We started by looking at current offshore construction and soon felt: this we can do simpler, in deeper water and hopefully cheaper, "says Finn Gunnar Nielsen, chief engineer at the company's research centre in Bergen.

Nielsen borrowed Norsk Hydro's widely used floating concrete construction technique and decided to test how it would transfer to an offshore wind installation. The team first built a 1/47-scale wind turbine model atop a floating concrete tube and secured the tube to the sea floor at Trondheim's Sintef Marintek laboratory using ballasts and anchor lines. Preliminary testing and calculations show the floating wind turbine would be able to withstand 100-year North Sea wave and wind conditions -- 15 to 28 metre high waves -- without failing.

The results have encouraged Norsk Hydro to try the technology, dubbed Hywind, at full scale in 2007 using a 3 MW turbine. The demonstration facility will be located about ten kilometres off Norway's west coast at Karmøy extending about 80 metres above the surface of the water and 120 metres below.

Nielsen believes Hywind will allow use of deep water sites of up to 2000 metres for wind power generation at the same cost as nearer-to-shore wind developments. Hywind is designed to be constructed onshore and towed out to the final destination -- a key cost-saving factor.

Norsk Hydro is searching for a turbine for the demonstration project. The company wants manufacturers to design lighter towers for Hywind installations to reduce turbine fatigue and help control costs on the 200-turbine offshore projects it wants to build in the next ten to 15 years. "All manufacturers realise weight is important, so they are all thinking about it," Nielsen says. "But the question is, who can deliver?"

Norsk Hydro has applied for a construction permit for its demonstration project as well as for a NOK 50 million (ยค6.4 million) grant from Norway's ENOVA renewable energy fund. Meanwhile, Norsk Hydro is also planning to erect 20-25 3 MW turbines onshore at Karmøy, a wind station scheduled for completion in 2007.

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