Wake Effects of Large Offshore Wind Farms - a study of the Mesoscale Atmophere
In DTU Wind Energy PhD, 2014
Abstract
The power production contribution to the power system from offshore wind energy is continuously increasing in the northern European countries. A better understanding of the influence of wind farms to those downstream and to the lower atmosphere will help optimising energy production from large wind farm clusters. Mesoscale models allow the simulation of large domains sufficiently to capture large wind farms and surroundings at reasonable computational costs, but processes below the horizontal resolution remain unresolved and have to be parametrised, such as the effects of the wind turbines to the flow. In the past, several approaches have been introduced, ranging from surface roughness change to drag approaches which usually also add turbulence. A new scheme is implemented in the Weather Research and Forecast (WRF) model. Measurements from Horns Rev I are used to evaluate the new scheme together with that in the WRF model. Results show an improvement of robustness in vertical resolution dependency. Furthermore, the velocity and “turbulence kinetic energy” fields agree better to those of high resolution models. The two schemes are applied to various problems. A hypothetical offshore wind farm in northern California, shows a sensitivity of the velocity field around the wind farm to atmospheric conditions aloft. For a shallow boundary layer capped by a steep inversion, gravity waves were generated, with related anomalies of the atmospheric variables aloft. Dependencies of the wind farm efficiency and the wind farm’s wake recovery to different atmospheric conditions aloft were found in an idealised case study. Moreover, the wind farm efficiency to different climates for wind farm sizes up to 375 km2 was examined. The modelled production varied with wind climate and were well above 1Wm−2, contrary to another study. Finally, wind farm shadowing was studied for the worst case scenario, in which two wind farms are perfectly aligned. For this scenario, considerable production losses of the downstream wind farm are expected, even with a separation of 5 wind farm lengths.
Info
Thesis PhD, 2014
In DTU Wind Energy PhD, 2014
UN SDG Classification
DK Main Research Area
Science/Technology
