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Evaluation of Wind Shear Patterns at Midwest Wind Energy Facilities: Preprint

The U.S. Department of Energy-Electric Power Research Institute (DOE-EPRI) Wind Turbine Verification Program (TVP) has included several wind energy facilities in the Midwestern United States. At several of these projects, a strong diurnal shear pattern has been observed. During the day, low and sometimes negative shear has been measured. During night hours, very high positive shear is frequently observed. These high nighttime shear values are of concern due to the potential for high stresses across the rotor. The resulting loads on turbine components could result in failures. Conversely, the effects of high nighttime wind shear could benefit wind generated energy production in the Midwest by providing a source of greater hub-height wind speeds, particularly for multi-megawatt turbines that utilize tall towers. This paper presents an overview of the observed wind shear at each of the Midwest TVP projects, focusing on diurnal patterns and the frequency of very high nighttime shear at the sites. Turbine fault incidence is examined to determine the presence or absence of a correlation to periods of high shear. Implications of shear-related failures are discussed for other Midwest projects that use megawatt-scale turbines. In addition, this paper discusses the importance of accurate shear estimates for project development.

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