Impact of wind turbines on the quality of operational weather radar products

Renewable energy production is becoming increasingly important because of economic, political, and environmental concerns. Wind power is an affordable option and numerous groups are now involved in its development. However, several studies have shown that wind farms or even single wind turbines could have a negative impact on the quality of weather radar products. Wind turbines in the vicinity of Doppler weather radars could result in (i) clutter, (ii) beam blockage, and (iii) erroneous radial wind measurements. This might lead to meteorological algorithm errors and mis-identification of thunderstorms in or near wind farm reflectivity signatures. The degree of disturbance depends on many factors, e.g. the radar cross section of the wind turbine and its distance to the radar. Topography and weather conditions need also to be considered.

The Swedish weather radar network consists of 12 C-band Doppler radars covering the country almost completely. At some radar sites wind turbines are already built within a radius of 20 km and the number of applications for new wind turbines increases dramatically. According to the EUMETNET OPERA guidelines no wind turbine should be deployed below 5 km. Between 5 and 20 km projects of wind parks should be submitted to an impact study. Above 20 km there are no restrictions. To facilitate the planning of new wind farms in the intermediate zone (5-20 km), a simple tool for simulating beam blockage caused by wind turbines has been developed at SMHI. The method will be explained and illustrated with some examples.

To study wind turbine related clutter and beam blockage, long-term accumulations of precipitation are very useful while time series of radar reflectivity and spectral width might help to gain insight into the impact of wind turbines on Doppler measurements. Operational weather radar products from the Swedish radar network have been used to study wind turbine clutter. As anomalous propagation is a common problem at some stations, it is planned to investigate the impact of atmospheric conditions on the intensity of clutter.