Wind energy production in cold climate (WECO)

This report introduces main results and recommendations of the research project “Wind Energy Production in COld climates” WECO (JOR3-CT95-0014), which was partially supported by the European Commission DG XII Non Nuclear Energy Programme aiming at the investigation of wind turbines under cold climate operation.
It is shown experimentally and by numerical simulations that icing of rotor blades or other components lead to decreased production due to ice accretion or safety demands. The icing effect is directly related to the climate of the site of the wind turbine, and varies strongly from region to region in Europe. Extreme low air temperature again arises new demands for design parameters. Icing of anemometers and other wind gauges typically lead to wrong estimation of wind power potential and operational problems of wind turbines.
The icing map over Europe, based on meteorological observations from 120 synoptic stations, show that icing and cold weather conditions occur in large regions in Europe, not only in the Nordic countries but also especially at mountainous regions in Northern Europe, Germany, UK, Alps, Spain and central Italy. On the other hand new megawatt turbines are high enough to encounter in-cloud icing even in lowlands. Following the method used to construct the European wind atlas, icing data is presented to show how it affects on-site wind power production.
Experimental data, wind tunnel simulations and numerical analyses were used to describe the ice formation on wind turbine blades, to produce the C l, Cd values, to calculate the power curves for iced wind turbines, and to study the loads. Ice on blades usually decreases the power production. At harsh sites the annual power loss may be up to 20-50 %. The project also produced a preliminary method to combine the European Wind Atlas method, iced power curves and statistics of in-cloud icing to estimate annual or monthly losses due to icing at desired site.
For environmental safety icing is a significant design parameter. New theoretical study in ice throw from the rotating blades was verified to observations. As preliminary results it is recommended that for sites with high probability of icing (1) to keep distance 1.5 (hub height + rotor diameter) between the turbines and nearest objects, and (2) to stop the turbines during the icing period and wind coming from unfavourable directions.
Conventional and ice-free anemometers were tested at several sites in Europe. It was shown that at ice en-dangered sites ice-free anemometers have to be used to avoid measurement errors of wind speed. Due to use of non heated anemometers the wind potential is now underestimated at many regions in Europe. Icing of anemometers also lead to false operation of wind turbines causing losses in power production. Thus it is recommended that all wind turbines operating under cold weather conditions ought to be equipped with ice free wind gauges. Turbines sited in mountains and in the far north have to have very strongly heated wind gauges. The intercomparisons and the market survey showed that there are some ice free gauges suitable for sites with less heavy icing are available today, but there is a need to produce accurate and reliable anemometers for heavily iced regions.