Electromagnetic shadow effects behind wind turbines

The development of wind farms may sometimes conflict with Defence interests by degrading the performance of Defence installations such as radars or telecommunications systems. This report has studied the potential problem with electromagnetic shadow effects behind the wind turbines. The analyses have shown that there will be a shadow behind the wind turbine that is narrow (about 10 m wide) close to the turbine, but not very deep. At lower frequencies the shadow is wider and shallower, while at higher frequencies the shadow is narrower and deeper. The shadow increases in width and decreases in depth for increasing distance behind the wind turbine. For distances larger than 10 km the shadow depth is less than 3 dBV/m for all relevant frequencies. The radar’s ability to detect targets will not be significantly affected by the shadow effects, except possibly for small targets that are close to the turbine. The shadow effects calculations can be quite time consuming, especially for higher frequencies. A new set of equations has therefore been derived that can be used to quickly calculate the shadow boundary and depth behind a wind turbine.