Expected ice but unexpected stops

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Winter conditions in the southern Swedish fells have set in hard on a trio of Danish/German wind turbines, part of developer Agrivind's pilot project to test commercial potential in arctic and semi-arctic conditions (Windpower Monthly, December 1998). While two of the machines -- a Nordex Balcke-Dürr 600 kW and a NEG Micon 750 kW unit -- have been out of service nearly the entire time, the Bonus 600 kW turbine has generated 180,000 kWh during the first three weeks in November -- far more than turbines of similar size on the Swedish west coast.

On the day the turbines were all connected to the grid in September, a heavy snowfall hit the area. The cranes and trucks used in the construction only just got down from the mountain in time. The blades on all three turbines were quickly coated with ice, caused by a cold fog drifting over the mountain. As a result, the Bonus turbine did not work in the first month until technicians adjusted the electric heating system at the base of its blades until the ice melted.

NEG Micon had also planned to use a new microwave heating system for the rotor from Denmark's LM Glasfiber, but a last minute hitch led to standard blades being installed instead. For its part, Nordex Balcke-Dürr decided to gather reference data in the first winter in order to evaluate heating systems. Since icing only occurs in specific climatic conditions, the two manufacturers were confident their turbines would anyway produce a fair amount of power during the winter. So far, however, each unit has only generated some 30,000 kWh. Frozen anemometers -- preventing the turbines monitoring wind speed or direction -- were the cause, not ice build-up.

Esa Holttinen of Ekono Energy Ltd of Finland, who has been monitoring the project, reports that while all three manufacturers have experience with running turbines in extreme cold and dry conditions, where the temperature can drop to -40 degrees Celsius, Bonus has the most experience with cold and wet climates, where icing is most likely to occur. Meanwhile, in a different project in Suorva in the far northern fells, a Bonus 600 kW unit has been operating and producing well, Holttinen reports.

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