Uncertainty in vertical extrapolation of measured wind speed via shear

This report provides formulations for estimation of uncertainties involved in vertical extrapolation of winds, as well as the total uncertainty incurred when winds observed at one height are extrapolated to turbine hub height for wind resource assessment. This includes new derivations for uncertainties inherent in determination of (wind) shear exponents in both low-shear (offshore) and varying onshore regimes, and subsequent vertical extrapolation of wind speeds. An uncertainty-model validation and check of the constants is also documented, using roughly 80 commercial sites, using objective statistical methods.

A primary motivation for—and part of—this work is the creation of a standard for uncertainty estimation and reporting, which is known as the IEC 61400-15-2. The authors are actively contributing to this emerging standard, and the work herein thus far constitutes (most of) the vertical extrapolation portion of the IEC 61400-15 draft.