The project 'Alpine Test Site Gütsch: meteorological measurements and wind turbine performance analysis' had the goal to expand the knowledge base on atmospheric icing specifically in the Alps. The main topic of the research plan was to carry out a comprehensive experimental study on Gütsch mountain located in the Swiss Alps at 2'300 m a.s.l during the winter periods 2005/06, 06/07, 07/08 and 08/09. The work was carried out in a close collaboration between Meteotest and the Federal Office of Meteorology and Climatology MeteoSwiss. The following steps were achieved during 2006, 2007, 2008 and 2009: - Meteorology: MeteoSwiss participated in this project by providing the test station in Alpine environment, at the Guetsch. For the purpose of the project, this test station has been expanded with numerous measurement systems. On one side, the station was fully equipped with standard instruments as defined for the SwissMetNet network (the new ground-based automatic measurement network of MeteoSwiss). In parallel, a number of new meteorological instruments, especially ice detectors, have been installed by MeteoSwiss and interfaced to the SwissMetNet platform in order to test their robustness to harsh environment for other meteorological applications. MeteoSwiss collected the data from all installed sensors at the test station Guetsch, and set it at disposal for the project. The first installations of the ice detectors already allowed to identify several technical shortcomings of the instruments concerning the suitability for harsh conditions. Due to the poor results obtained in winter 2006/07, 'pressure' was put on the manufacturers in order to improve the situation. The resulting effect was the upgrade of one reference instrument and the installation of a second one: a new version of the Combitech IceMonitor Mk I and a Goodrich ice detector were installed in the fall of 2007. Both instruments behaved in a more or less satisfying way during a major icing event in the second part of November 2007 and during later, less intensive icing periods. During the summer 2008, a new version of the Combitech Mk I was installed in order to solve some of the remaining stability problems: unfortunately, this upgrade proved to be less stable than the older instrument. The manufacturer Saab Security Systems/Combitech delivered a new upgrade in February 2009, unfortunately too late to gather enough measurements for a conclusive outdoor trial. However, this new sensor provided positive results for a few icing events at the end of the winter period, especially when considering the measurements performed at the two other test stations located in Switzerland (Schwyberg in the Pre-Alps and Matzendörfer Stierenberg in the Jura region. The Goodrich ice detector performed good measurements, but not during all icing events: during strong icing events, an 'igloo' builds up around the sensor and prevents it from measuring icing correctly. Wet snow in many cases is not detected at all. A new prototype of the sensor with a stronger heating was installed in the fall 2009 in collaboration with the manufacturer, which will hopefully deliver more stable results. All ice detectors were regularely monitored by an automatic camera which has been upgraded during the summer 2007 with a new model used on the camera network of MeteoSwiss. The quality of the pictures has clearly increased since then. However, due to the extreme conditions and the difficulty to reach the stations in winter, the camera cannot be maintained in operation during all the time. - Wind turbine: Two web cams were mounted at the nacelle of the wind turbine to allow for the investigation of icing on the rotor blades and the performance of the blade heating. În summer 2007 a new, more sensitive camera was installed together with an infrared headlight which allowed taking pictures of the rotor blades also during the night. Ice throw is a significant safety risk at the Gütsch site. The most dangerous areas are near the tower and underneath the blades especially during und shortly after a blade heating process. The ice detection of the Enercon E-40 via power curve seems to work considerably well except for light icing and during periods with low wind speed. However, this ice detection method gives no information if blades are still iced after heating cycle. This makes the automatic restart a safety risk. Often, not all the ice can be melted during one blade heating cycle, especially at the leading edge of the blades. The heat transfer to the leading edge therefore should be optimized. Measurements of temperature, relative humidity and incoming long wave radiation have been installed on the nacelle of the wind turbine in order to set up a simple approach to detect icing conditions based on meteorological data only. - Interaction with Working Group 1 of COST Action 727 (modelling and forcasting of icing): In Working Group 1, a breakthrough has been achieved by use of the numerical weather prediction model WRF operated by the Norwegian Meteorological Institute. Very promising simulations were carried out and compared with the measurement data of the test site Guetsch during an STSM hosted by Meteotest in May 2007. Further icing events could be successfully simulated during the winter 2007-2008 with an enhanced version of the WRF obtained in close collaboration with NCAR, USA. Another 3 STSMs took place in 2008 and 2009, respectively in Switzerland and Norway. The complete results were presented during the IWAIS 2009 Conference. - Interaction with Working Group 2 of COST Action 727 (icing measurements): Six test sites in Europe have been selected to perform icing measurements during the winters 2007/2008 and 2008/2009: Luosto (FI), Deadwater Fell (UK), Zinnwald (D), Studnice (CZ), Sveg (SE) and Guetsch (CH). All sites were equipped with at least one identical reference instrument (Combitech IceMonitor) in 2007. Additionally, the Luosto and Guetsch stations were further outfitted with the Goodrich ice detector. In summer 2008, the remaining 4 stations have been equipped with the missing sensors so that all the sites were equiped with 2 similar instruments. Results obtained during the winter 2008-2009 showed that identical results - and problems - were obtained at all latitudes. The unfortunate, but obvious conclusion is that - at present time - there are no ice detector available on the market suitable for long-term, stand alone operation. - Miscellaneous: The village of Andermatt near the Gütsch station was selected for the organization of the IWAIS 2009 Conference (International Workshop on Atmospheric Icing on Structures) which was held in combination with the Final Workshop of the COST Action 727, September 8 to 11, 2009 (see
http://www.iwais2009.ch for more details). Dr. Alain Heimo has been selected on the December 14, 2007 as Chairman of the COST Action 727 by the MC of the Action in replacement of Dr. Bengt Tammelin who remained Vice-Chair. Though retiring in May 2008, A. Heimo has accepted to chair this Action until the combined IWAIS and Final Workshop Conference in September 2009.
