Envision tests 'partial pitch' turbine

Proof-of-concept trial for 3.6MW two-blade design

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The first prototype of an innovative two-blade, partial-pitch turbine produced by Envision is about to be installed in Denmark.

The 3.6MW machine will be erected in the next three weeks by the Danish-based research arm of the Chinese turbine maker. The test site is an onshore, near-coastal location near Thyborøn.

A "big brother" to the 3.6MW turbine is currently on Envision’s drawing board. There are plans to begin testing this larger machine, likely to have a capacity of at least 6MW, within the next 18 months.

A primary advantage of the E128-3.6MW two-blade turbine is its novel ‘partial pitch’ rotor feature, explained Envision senior project manager, Peter Toft Madsen, speaking with Windpower Offshore.

The first 21m of the blade is a fixed stall section, with no pitching, while the outer 42m are capable of pitching. "We call this partial pitching - it reduces the extreme loads applied to the turbine," said Madsen. This, in turn, translates into measurable weight reductions. "The lower extreme loads have a direct impact on sheet thickness of the tower and on the size of foundation structures."

Envision estimates that the lower-weight design will reduce the cost of a turbine by 10%.

The E128-3.6MW turbine was originally designed with a Chinese offshore site in mind, one that experiences typhoons. As a result, finding ways to reduce extreme loads was a priority, says Madsen.

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