Mapping frequencies of icing on structures in Switzerland

Icing of structures is a problem for wind energy production in cold regions and makes careful planning of new projects essential. This study presents and evaluates a method to create a map showing the frequency of meteorological icing in Switzerland. Icing is simulated for two single years using an algorithm which calculates ice accumulation from temperature, wind speed, cloud and rain water content of the atmosphere. The driving meteorology was obtained from analysis runs of the weather forecast model COSMO-2 with 2.2 km grid size. The quality of the icing map is evaluated for the two years and compared to the 10 years average by using measurements of 165 meteorological stations in the Swiss Alps. Icing frequencies of the wind sensors at the stations were detected based on measured temperature, relative humidity and the standard deviation of the lateral movement of the wind sensor. The icing map shows appropriate regional patterns with icing frequencies ranging from zero to more than 100 day icing per year in accordance with our measurements. However, individual stations often showed strong deviations between modelled and measured icing frequency, especially in high alpine regions. These deviations are caused by a strong spatial icing variability due to local terrain features which cannot be captured by the model at 2.2 km resolution. (C) 2012 Elsevier Ltd. All rights reserved.