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United States

Low wind speed blades being developed in California

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A southern California company mostly known for its custom yachts is developing a wind turbine blade specifically for low wind speed areas. Knight & Carver's Gary Kanaby says the plan is to test the 85-foot blade (26 metres) in 2006 on a Zond 750 kW turbine at the Lake Benton station in Minnesota, owned by FPL Energy. The test blade is two metres longer than the existing blade the Zond machines and will increase the rotor swept area for greater energy capture.

"The turbine will start so much sooner to make power and it will achieve its maximum 750 kW at much lower speeds," Kanaby says. "We're saying that at the normal hub height of 80 metres, there is about a 12-20% increase in energy benefits." The goal is to generate electricity for $26-$29/MWh, he adds.

The longer blade, however, creates a problem: momentary overpowering of the turbine until its control system adjusts the blade pitch. A "scimitar" profile with a "bit of a hook" at the blade's end, along with some additional flexibility, will allow the blade to momentarily twist and dump excess wind to reduce load. Once the control system adjusts the pitch, the blade will automatically resume its original shape.

The technology, once tested, should be transferable to much larger applications, Kanaby says. Development begins this year, with construction of the blades in 2005. The company won a $2 million grant for the work from the US Department of Energy (DOE), one of 21 grants totalling $60 million awarded in April for technology improvements to improve the profitability of lower wind speed sites. DOE defines low wind speeds as up to 7.5 m/s.

Knight & Carver, based in San Diego, has been in the yacht business since 1976 and started repairing wind blades in 1996. Last year it began making replacement blades for old Kenetech 100 kW turbines still turning in California.

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