Not even the technical equipment, made to measure the icing, could withstand the harsh conditions in Åsele in northern Sweden. Severe icing stopped the ice detectors from working properly or broke them completely.
The conclusion from the field tests of five detectors at the site Stor-Rotliden in Åsele is that none of the detectors are reliable enough to mesure icing on the turbines during production.
”Sometimes they mesured no ice when they were covered with ice, other times different detectors showed different levels of icing. Quite often they broke down,” says Helena Wickman, who did the analyzing for Vattenfall as a part of her thesis in engineering physics at Uppsala University.
”The climate was simply to extreme for the detectors. During less extreme icing they showed okey results.”
”If the reliability of the detectors during the more severe icing events could be increase they could be used for site assessment to give a rough idea of the icing climate.”
Wind power in cold climate requires ice detectors both during the prospecting phase, in the site assessment, and during production for controlling of the turbines to help mitigate problems due to ice, like production losses, fatigue loadings, ice throws and increased noise.
Owners of wind turbines want high productivity in order to obtain the required return on investment, but icing can easily lead to a 10 percent loss of production, which can dramatically affect profits.
With multi-megawatt turbines, downtime costs can easily run into hundreds of Euros per hour.
Vattenfall’s field test shows a bleak picture of what the market can offer today.
”But we really put hem through harsh conditions,” says Helena Wickman, who today works as a wind and site consultant at Meventus.
”They might perform better in less cold climate or if you placed them on a heated boom and kept the boom free from other equipment.”
The tested detectors were:
- the T 40 series from HoloOptics (HoloOptics),
- 0872F1 Ice Detector from Goodrich (Goodrich),
- LID-3300IP from Labkotec (LID),
- IceMonitor from SAAB Combitech (IceMonitor)
- IGUS BLADcontrol from Rexroth Bosch Group (IGUS).
- Two different combinations of anemometers, used for wind measurements, were analyzed for ice detection purposes. The first combination consisted of the three anemometers Thies 4.3350.00.0000 from Adolf Thies GmbH & Co.KG (Thies), Vaisala WAA252 from Vaisala Oyj (Vaisala) and NRG Icefree3 from NRG Systems (NRG). The second combination uses three differently heated NRG anemometers.