Researchers at Sandia National Laboratories collaborated with blad manufacturer Knight & Carver to develop a wind turbine blade design that promises to be more efficient than current designs. It should significantly reduce the cost-of-energy (COE) of wind turbines at low-wind-speed sites.
Named ‘STAR’ for Sweep Twist Adaptive Rotor, the blade is the first of its kind produced at a utility-grade size. Its most distinctive characteristic is a gently curved tip, termed ‘sweep,’ which unlike the vast majority of blades in current use, is specially designed for low-wind-speed regions like the American Midwest.
The sites targeted by this effort have annual average wind speeds of 5.8mps, measured at a height of 10m. Such sites are abundant in the US and would increase by 20-fold the available land area that can be economically developed for wind energy.
Sized at 27.1m, almost 3m longer than the baseline it will replace, the blade improves energy capture at lower wind speeds. Instead of the traditional linear shape, the blade features a curvature toward the trailing edge, which allows the blade to respond to turbulent gusts in a manner that lowers fatigue loads on the blade. It is made of fibreglass and epoxy resin.
‘This design allows the blade to twist more than traditional designs, relieving some of the effects of gusty turbulent wind on blade life,’ said Tom Ashwill, who leads Sandia’s blade research efforts. ‘This then allows us to grow the blade length for the same rotor, providing for increased energy capture of 5-10 per cent and yet retaining the same expected fatigue life.’
The first STAR blade was tested in January at Knight & Carver’s fabrication facility in San Diego to determine its bending and twist behaviour due to static loads. Natural frequencies were also measured. This data will be compared to design simulations to determine how well the design concept performs.
Four additional blades will be fabricated in the first quarter of 2007, three of which will be flight-tested on a turbine in Iowa.