Wind Turbine Issues in Germany

Wind turbines (WT) have long been known to adversely affect radar measurements. Due to their huge radar cross section, WT cause clutter both from contributions inside and outside the radar main beam and multi-path effects as well as so-called “shading” effects behind the WT. These effects are highly variable in time and space due to varying WT operations and atmospheric conditions. They are reflected in the electromagnetic field distribution around the WT and propagate through the radar processing chain into base data, such as reflectivity, radial wind and dual polarisation moments, and further on into secondary products. The latter comprise rain accumulation, model assimilation, and warning products such as warnings of severe convection, hail, or mesocyclones, just to name a view. Thus, WT effects depend on the application.

Accordingly, several methods have been proposed in order to protect against WT interference. To our knowledge, none of them has solved the problem so far. Particularly, no operational tools are available to identify, quantify and/or to appropriately mitigate these wind turbine effects. As a first step, a realtime wind turbine recognition is necessary as, due to the above mentioned effects, affected pixels are highly variable and data at farther distance to the WT may be affected, too. As a second step, extensive WT sensitivity studies are necessary, in order to know the range of possible error magnitudes and to evaluate the impact of WT and of possible future WT mitigation algorithms on follow-up procedures and final products. So far, case studies have shown that even single WT pixels may impede the detection of hail or meso-cyclones, and WT echoes from outside the main beam may still contribute significantly and even surpass severe weather thresholds.

This contribution is to give an overview of the WT-weather radar challenge in Germany, focusing on the scope of WT impacts as observed by various network radars and on different stages of the radar processing chain. A couple of ideas that have been proposed to cope with existing WT will be discussed as well.