Keeping Weight Down Key to Boosting Turbine Performance

The V90-3.0 MW turbine from Vestas Americas improves on previous designs thanks to lightweight carbon fiber in  blades and stronger steel for a lighter tower. What’s more, a microprocessor controlled pitch regulator and  redesigned nacelle further improve the turbine’s performance. The company says minimizing weight was a matter of high priority.  As weight goes up, so do costs for production, materials, transportation, and installation. The payoff for the V90-3.0  MW: It takes only two to three hours for it to supply an average European family with electricity for a year. Although the  V90-3.0 MW design is not the company’s most recent design, it was a significant step forward when introduced, has  proved itself a workhorse for wind farm owners, and provided a spring board for additional designs.

The blade design is shared with the V90-2.0 MW turbine, also a 90-m rotor. The blade structure is said to differ from  previous designs by using new materials, most notably carbon fiber for the load bearing spars, and a revised blade  profile. Carbon fiber is lighter than the fiber glass it replaces and its strength and rigidity also reduce the quantity of  material needed which further reduces overall weight. Even though the V90 has a 27% larger swept area than the V80,  the new blades weigh about the same. The final blade design, in part due to a collaboration with Risø National  Laboratory in Denmark, features a plane shape and a curved back edge. The resulting airfoil improves energy  production, while making the blade profile less sensitive to dirt on the leading edge, and maintaining a favorable geometric relationship between successive airfoil thicknesses. Blade features include the microprocessor-controlled pitch regulator. OptiTip constantly adjusts the angle of the turbine blades for best position in relation to prevailing winds. This capability is used in all but one Vestas  turbine. Despite the larger rotor and generator, the V90-3.0 MW weighs less than the V80-2.0 MW turbine.

The nacelle represents a radical redesign, says the firm. Even though the 3-MW generator is larger than the unit in the  2-MW design, nacelle weights are almost equal. This was done by combining the hub bedplate directly into the  gearbox, eliminating the main shaft and thus shortening the nacelle. The result is a nacelle that can generate more  power without an appreciable increase in size, weight, or tower load. Tower improvements come from a stronger steel which requires using less of it. Towers are now constructed in fewer sections than previous designs, with significant  savings in material, transportation, and installation.

Since its introduction in 2002, the company says it has installed more than 1,000 V90 3.0 MW units around the world. The design has been a springboard for the V112-3.0 MW unit a recently introduced on and off-shore turbine. The V112,  however, will not see service in the U.S. till about 2011 and later in Canada.

Blade sensors could let turbines adapt faster

Researchers have developed a technique that lets sensors monitor forces exerted on wind turbine blades, a step toward improving their efficiency by letting them adjust to rapidly changing wind conditions. The research by engineers at Purdue University and Sandia National Laboratories is part of an effort to develop a smarter wind turbine. “The goal is to feed information from sensors into an active control system that precisely adjusts components to improve efficiency,” said Purdue doctoral student Jonathan White, who is leading the research with Douglas Adams, a professor of mechanical engineering and director of Purdue’s Center for Systems Integrity.

The system also could help improve wind-turbine reliability by providing critical real-time information to the control system to prevent catastrophic wind-turbine damage from high winds.

The team embedded uniaxial and triaxial accelerometers inside a wind turbine blade as it was built. The sensors measure acceleration in different directions, necessary information to accurately characterize a blade’s bending and twisting and small vibrations near the tip that eventually cause fatigue and possible failure.

The sensors also measure two types of acceleration. One type, dynamic acceleration, comes from gusting winds, while the other, static acceleration, results from gravity and steady background winds. It is essential to accurately measure both forms to estimate forces exerted on the blades. The blade is being tested on a research wind turbine at the U.S. Department of Agriculture lab in Bushland, Texas.

Such sensors could be instrumental in future turbine blades with “control surfaces” and simple flaps like those on an airplane’s wings to change blade aerodynamics. Because these flaps would be changed in real time to respond to changing winds, constant sensor data would be critical.

“The industry is most interested in identifying loads exerted on turbine blades and predicting fatigue, and this work is a step toward accomplishing that,” says White.

“It is useful to control the blade pitch to optimize energy capture by reducing forces on the components in the wind turbine during excessively high winds, or increase loads in low winds. This should also help improve reliability. Turbine towers can be 200 feet tall and more, making it expensive to service and repair damaged components,” says White.

The research is funded by the U.S. Department of Energy through Sandia National Laboratories. Sandia is a multiprogram laboratory operated by Sandia Corp., a Lockheed Martin Co., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.