Validation Study of the Use of Wind Shear Exponents in Extrapolating Wind Speeds for Wind Resource Estimations

Data from meteorological towers are used in wind resource estimation for siting and building wind turbine generators. These towers are usually 50 m in height and equipped with cup anemometers at several levels (typically 10, 30 and 50 m). The hub heights of most of the recently installed and planned commercial turbines range from 65m to 80m, heights that far exceed a typical meteorological tower. And so, a logarithmic nondimensional wind shear exponent is derived between a pair of anemometers and is then used in a simple power law equation to extrapolate wind speeds to a desired turbine hub height. The wind speed data is then passed through a power curve to estimate expected energy production. Installed and planned turbine hub heights are increasing, but meteorological towers are not. Increasing the height difference between meteorological measurements and the turbine hub, increases the risk of inaccurately estimating extrapolated wind speeds. In order to mitigate the increase in extrapolation risk, power producers may respond by increasing the height of meteorological towers, or explore other measurement approaches. Doppler sodars may potentially provide non-extrapolated hub height measurements. Wind power producers are beginning to explore this measurement platform in parallel with classic meteorological towers.

This study utilizes on-site data from a meteorological tower and two sodars on a mesa in Texas. The data populations will be validated by using an analysis of variance approach and utilizing a multiple comparison technique. An analysis of variance will be conducted on the extrapolated hub height wind speeds and the sodar hub height wind speeds.