A Statistical Approach to Estimate the Shadow Effect of Rotating Wind Turbines

Abstract : This paper presents an approach to studying the shadow area behind a wind turbine or a wind farm based on a statistical approach. As has been shown in previous papers, the shadow area behind a wind farm is characterized by a very complex field strength pattern, caused by constructive and destructive interferences from different scattering centers. The exact shape and distribution of field strength maxima and minima highly depends on the blade orientation and consequently is a very dynamic figure. This also means that the EM simulation for a fixed position of all blades of the turbines in a wind farm can only represent a snapshot of the dynamic field distribution. However, in the evaluation of shadow effects caused by a wind farm, e.g., with respect to reduced range operation of an air surveillance radar, such a snapshot result is not very useful, since the data might be completely different for another blade configuration. To mitigate this uncertainty effect, EM simulations are performed over a sequence of time steps. In the post-processing, after averaging the field strengths, a statistical estimation of the shadow area behind a wind farm is possible.