Abstract
The importance of characterizing the wind-shear at a given site for a utility-scale wind turbine cannot be overemphasized. Such characterization is needed for an accurate prediction of its power output. Thus, the objective of this work based on the use of several US tall tower wind data sets was to determine the accuracies of different wind-shear enumeration methods, especially when used at sites having hills and/or forests. In addition, average wind-shear variations with respect seasonal and annual effects and data length are presented for various long data sets, recorded to between 1995 and 2005. Wind direction and atmospheric stability were not a factor in the analysis. At some of the sites the greatest average wind-shear was found during the summer. For the site with the most complex terrain, the average annual all-direction wind-shear varied by up to 7% between different years; this was partly due to year-to-year variations of the direction distribution. There was found to be no significant difference between the performance of the log and power laws; using either may give inaccurate predictions of hub-height mean wind speeds.