MITACS Project Technical Report : Atmospheric stability and wind profiles at a prospective wind energy production site Crawford, Ben; Matangi, Adrian; Griffiths, James; Christen, Andreas; Black, Andrew T.
Atmospheric stability influences turbulence and wind speeds at wind turbine hub heights, yet it is seldom measured or explicitly considered during wind energy resource assessment. In this study, twelve months of data from a 3-‐d sonic anemometer mounted at 58 m on a 60 m wind resource assessment tower are used to characterize atmospheric stability at a prospective wind energy production site. At this site, three distinct stability classes (unstable, neutral, and stable) are identified that follow diurnal and seasonal distributions. These stability classes are distinguished by unique wind speed distributions, vertical wind speed shear profiles, and turbulence characteristics. A comparison is performed to test whether including stability parameters from the sonic anemometer improves modeled predictions of vertical wind speed profiles. Results show that including stability does not improve results at this site, likely because specific assumptions underlying wind profile models are not met. Recommendations from this work are: 1) future wind resource assessment should include analysis of stability, 2) bulk stability can be classified using measured vertical temperature gradient or the wind shear exponent, and 3) future wind resource assessment should include at least two temperature measurements at different heights. Finally, as turbines grow in height and are placed in complex terrain, we are approaching the limits of tower-‐based measurements and traditional shear models to accurately model conditions across the turbine rotor plane. Future wind resource assessments are recommended to also include remotely sensed wind measurements (e.g. Lidar or Sodar) and high-‐resolution non-‐linear models.
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