Offshore Wind Farm Coping with Danish Winter

Winter is for real, and in January, massive frost covered Denmark and the installation area at Anholt Offshore Wind Farm. Danish Meteorological Institute, DMI, is making weather forecasts and preparing satellite photos to follow the ice formation in the Danish waters.

The prognosis for ice formation in the Danish waters issued on 25 January 2013 says: “According to the weather forecast for the coming days, a small increase in the ice formation is expected as the frosty weather continues. It gets warmer again after the weekend, so we don’t expect a severe winter right now.”

In the Danish inland waters, such as the Baltic Sea and the Kattegat, where the sea water is mixed with fresh water from the Golf of Bothnia, there is a risk of ice formation at sea. This is also the case in the waters between Djursland and the island of Anholt where Anholt Offshore Wind Farm is being constructed.

Normally, a severe winter is characterised by large ice-breaking vessels in operation when the Danish inland waters freeze over. Denmark has experienced severe winters 15 times over the past 100 years.

This has been taken into consideration in the dimensioning of the foundations which have been constructed to manage the load from up to 40cm even ice, drifting ice and considerably thicker ice pack.

The calculations are based on international standards and the historically registered conditions during previous severe winters. The calculations also take into account combinations of various weather situations and severe winters, including the risk that a storm may occur during a severe winter and result in large ice floes pounding against the foundations.

A severe winter could really have troubled the installation work, but even though the risk of a severe winter seems to have blown over, the biting cold with temperatures down to minus ten degrees Celsius has complicated the installation work for wind turbine installers and technicians in the wind farm.

Besides the biting cold, water from waves has splashed on the ladders and formed large ice lumps which in some cases have complicated the access to the foundations. Ice cover on the access ladders and the safety lines used to access the foundations is also a safety risk, and in periods with great frost, special focus has been on ensuring safe access.

In periods with great frost, the guard ship Guard 1 has been assigned a new additional task of flushing ice cover from the ladders which are to be used during the day. The flushing is made by high-pressure washers using salt water.

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Press release, February 6, 2013; Image: DONG Energy