Influence of Thermal Stratification on Wind Profiles for Heights up to 140 m

The vertical wind speed profile has to be know for many wind power applications. Although the large effect of the thermal stratification is well known normaly the neutral logarithmic wind profile is used, which leads to large errors in the determination of the needed wind speed. In this work a parameterisation of DeBruin for the thermal stratification is testet with measured data from the 200 m high met mast in Cabouw, Netherlands. This parameterisation is quite generel as it uses wind speeds at two heights (one can be with u=0) and two temperatures for the calculation of the Monin-Obukhov-Length. It is robust to the determination of the roughness length and tolerant for unsteady situations. It can be shown that the calculations of higher levels (up to 80 m) is much more accurate by applying this stability correction. This correction is integrated in the wind power prediction system PREVIENTO. Even here where the large uncertainty are caused by the numerical weather prediction the consideration of the stability effects leads to a significant improvement of the wind power prediction.