Advanced Energy Systems (AES) Inc. conducted a conceptual study of independent pitch control using inflow angle sensors. The control strategy combined input from turbine states (rotor speed, rotor azimuth, each blade pitch) with inflow angle measurements (each blade angle of attack at station 11 of 15) to derive blade pitch demand signals. The controller reduced loads sufficiently to allow a 10% rotor extension and to reduce cost of energy 6.3%. iv ACKNOWLEDGMENTS This study was performed by a team of wind energy consultants, including Tim Olsen of Advanced Energy Systems (project manager), Eric Lang of E3-Design (principal investigator), Craig Hansen of Windward Engineering, Marvin Cheney of PS Enterprises, John VandenBosche and Terrance Meyer of Chinook Wind, and Gene Quandt. Technical and management support were provided by a National Renewable Energy Laboratory (NREL) technical review team, led by Alan Wright and Dave Simms (technical monitors), with Neil Wikstrom serving as contract administrator. David Malcolm and Dayton Griffin of Global Energy Concepts also provided substantial support in establishing and understanding the WindPACT baseline turbine and its associated design and analysis tools. Funding was made possible through the NREL Low Wind Speed Turbine Project, subcontract number RAM-2-31235 (84%), and cost-sharing by the project team members (16%). v

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In work performed under subcontract * to the National Renewable Energy Laboratory (NREL), a preliminary design study and proof-of-concept field test were conducted to evaluate the feasibility of using pultruded blades for wind turbine rotors. A 400 kW turbine was selected for the design study, and a scaled 80 kW rotor was fabricated and tested as a demonstration of the concept. To examine the feasibility of pultruded blades, several issues were addressed, including power performance, tower strikes, yaw stability, stall flutter, fatigue, and rotor cost. Results showed that with proper design, rotors using pultruded blades demonstrate acceptable fatigue life and stable yaw behavior without tower strikes. Furthermore, blades using this technology may be manufactured for approximately half the cost of conventional blades. Field tests of the scaled rotor provided experimental data on power performance and loads while verifying stable yaw operation.

or DOE Information Bridge http://www.doe.gov/bridge/home.html Printed on paper containing at least 50% wastepaper, including 20% postconsumer waste FOREWORDThe National Renewable Energy Laboratory's (NREL's) National Wind Technology Center is supporting the efforts of its industry partners to develop advanced, utilityscale wind turbines. Part of the research being conducted focuses on innovative components and subsystems that eventually may be incorporated into these advanced turbines. PS Enterprises, Inc. (PSE) chose to investigate a flexible, downwind, free-yaw, five-blade rotor system employing pultruded blades.Studies conducted by PSE showed that, for a given rotor solidity, increasing the number of blades reduced the rotor weight. And from previous experience with both helicopter and wind turbine rotors, it was known that the pultrusion process resulted in blades having a very low cost-per-unit-weight. Indeed, pultruded blades were employed on wind turbines by StormMaster, Windtech, Dynergy, and Bergey Windpower. However, in some cases, problems were reported with yaw instability and occasional tower strikes. Furthermore, because pultruded blades are constrained to constant cross sections, without taper or twist, they are known to suffer a degradation in aerodynamic performance. So the challenge of the PSE project was to design and test a dynamically-and structurally-stable rotor that demonstrated the anticipated weight and cost savings while maintaining reasonable aerodynamic performance.PSE assembled a diverse group of consultants from around the United States to work on the project. The expertise of the project participants included aerodynamics, mechanical design, structural dynamics and testing. They worked closely with NREL to accomplish design reviews, modal tests, blade structural tests and field tests. This approach had the effect of adding logistics challenges to the acknowledged technical difficulties.It can be said with virtual certainty that engineering projects of this nature always encounter unexpected difficulties and frequently fall short of the original goals and objectives. In this project, a gearbox failure and subsequent runaway led to an early curtailment of the field-test program. Nevertheless, PSE and its consortium of consultants, completed an exceptional amount of work, the results of which demonstrate great promise for the proposed rotor concept. And to their credit, it was completed within the negotiated budget. PREFACEThis project, supported by NREL under Subcontract No. AAA-4-12272-04, was undertaken to assess the feasibility of using pultruded blades for wind turbine rotors. It represents a more rigorous engineering investigation of pultruded wind turbine blades compared to that performed on the initial rotors using this technology. The early operating experience of these rotors, although it showed pultrusions as a promising new blade technology, was plagued with design and quality control problems. Adequate engineering analysis and component testing had not been performed du...

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