One program R&D project that shows potential for demonstrating a significant increase in overall system performance is the 2.5-MW Liberty wind turbine developed by Clipper Windpower. Clipper completed its prototype in 2005 after only 3 years of R&D. The new machine’s innovative distributed-path powertrain design incorporates four permanent-magnet generators, and advanced variable-speed controls. According to U.S. Department of Energy Secretary Samuel W. Bodman, “Clipper’s Liberty Turbine is not only one of the most advanced wind turbines ever produced, it may well be the most efficient wind turbine in the world.” Successful field-tests conducted by Clipper with assistance from NREL and intensive component testing at the NWTC helped Clipper put the Liberty series turbine into production in the summer of 2006. Clipper’s 2006 transaction announcements represent firm commitments of 875 MW of turbines and more than 5,000 MW of contingent orders for delivery through 2011.
Northern Power Systems (NPS) produced an award-winning power electronics package that can be scaled for use in a wide range of wind turbines, from small to multimegawatt systems. According to NPS, the new converter improves wind turbine reliability, energy capture, and grid performance. The project team was chosen by the American Wind Energy Association for its 2006 Technical Achievement Award. Tests completed in 2006 on both the converter and a 1.5-MW direct-drive generator, also developed with program support, demonstrated high-quality power output.
Knight & Carver is developing a 27.5-m (90-ft) replacement blade for a 750-kW turbine. The “STAR” (which stands for sweep twist adaptive rotor) blade is the first of its kind ever built. Its most distinctive characteristic is a gently curved tip, which prompts the blade to respond to high winds such that adverse loads are attenuated. This allows the blade length to be extended with no weight penalty and augments energy capture in low-wind-speed resource areas.
Global Energy Concepts (GEC) worked with program researchers to fabricate a 1.5-MW, single-stage drivetrain with a planetary gearbox and a medium-speed, permanent-magnet generator. The simple gearbox design and moderate-sized generator show potential for reducing tower-head weight and drivetrain costs. The company completed initial testing of this drivetrain at NREL’s 2.5-MW dynamometer test facility. The generator is currently being upgraded, and a second phase of testing is planned for 2007.
Genesis Corporation is testing a new tooth form for gearboxes that promises major improvements in power density while reducing the costs of these devices. The company completed the first round of testing with positive results and is now working to refine its design through further targeted testing.