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Prototype design exonerated -- Improved blade delayed

The basic design of the advanced prototype downwind turbine being developed by The Wind Turbine Company (WTC) is not at fault for a blade failure in May (Windpower Monthly, August 2002). The failure temporarily shut the research project down, according to an unpublished technical report by the National Renewable Energy Laboratory (NREL). While the arrival of a new blade at the project site in California this month should get the turbine back in operation, says WTC's Larry Miles, a redesigned blade intended to boost output has been delayed to August.

Sandy Butterfield of NREL says the federal research agency is still supportive of WTC's design and is not alarmed by the temporary setback. "There is nothing unique to that particular machine design that caused the problem," he says. "It was a control system error and easily fixed." Miles, too, says he is not worried that the agency could withdraw its support any time soon.

But after two years testing the downwind design, NREL financial support is running slim and WTC's next hurdle is to pony up more cash to keep the project moving. "It is a cost-sharing contract and we need to come to the table with a little more of the cost-sharing," says Miles. While his search for new investors has yet to bear fruit, he says a number are becoming more interested.

Finding backing for a prototype poses its own difficulties. One issue is how to provide a product warranty on a machine still not in commercial production. Miles is hoping a small demonstration project, such as a project still in the engineering and siting stages with Klickitat County in Washington, would prove the value of the downwind design. "We need to get the turbine into a commercial operating mode as quickly as we can," Miles says. To get to that point, WTC needs investment capital, but there are few investors willing to "do much beyond the current three blade upwind machine," he says. "Finding someone willing to take a risk on a hardware demonstration project is proving to be challenging."

Upsizing delay

The problem that shut down WTC's 500 kW prototype was caused by a data signal converter failure, resulting in an erroneous signal to the pitch control drive causing one blade to strike the tower, breaking off about one-eighth of the blade. "We got our hands slapped over that and now have a contractor specifically looking at the control system," Miles says.

WTC ordered in August an identical turbine blade from French blade manufacturer ATV to replace the broken carbon fibre-based blade. After NREL's testing of the new blade in December, Miles hopes to install it on the California prototype and get the turbine back into action early this month. Installation of new, prototype blades is pushed back to August, Miles says. He expects the new blades to boost the turbine's capacity to 750 kW.

NREL wants WTC to reinstall the smaller blade now rather than jump directly to the redesigned blades to gain more information about the turbine's performance and its ability to stand up to stresses first, Miles says.

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