Offshore wind turbine overturned in Denmark – Tu.nr
On Wednesday afternoon, a 110 meter high offshore wind turbine overturned in Nysted Offshore Wind Farm south of Lolland. The Danish offshore wind giant Ørsted owns the almost 20-year-old offshore wind farm, according to the local newspaper Folketidende.
Why it overturned remains a mystery Ørsted is trying to find out:
– We received an error message when the turbine was disconnected from the mains. When we go out to sea the next day to troubleshoot, we find that the mill is in the water, says Tom Christiansen from Ørsted to TV2 ØST.
According to the local newspaper, there was a strong wind in the area when the rollover happened, but nothing like exactly hurricane. Ørsted also tells TV2 Øst that the accident did not necessarily have anything to do with finding
Rare foundation
It is not just the wind turbine itself that has overturned. Also the huge concrete foundation has gone over. In total, this is a construction of approximately 2050 tons. Ørsted does not know whether the mill is still stuck on the foundation.
Nysted Offshore Wind Farm
Consists of 72 wind turbines from Siemens, each of 2.3 MW, ie a total power of up to 165.6 MW and an annual production of approximately 590 gigawatt hours.
The park was one of the world’s largest when it opened in 2003.
The mill towers are 69 meters high, and each blade is 40 meters. The highest point of the wingtip is thus 110 meters above the water surface.
Source: Ørsted
This type of foundation, called Gravity Base, is rare. They anchor the wind turbines to the seabed just by gravity, and are therefore only suitable for flat seabed down to ten meters. Nysted is the only one of Ørsted’s offshore wind farms in Denmark that has such foundations.
Today, monopiles are the most common way to anchor offshore wind turbines. Monopiles are up to 12 meter thick steel piles in the seabed, a ttechnology that originally became developed for the oil industry.
Millimeter pressure
The concrete foundations outside Nysted were once cast in Poland and transported to Denmark by barge. Before the foundation was lowered into place, it was dug up to ten meters into the seabed for a quick ground. Then a stone fill was laid which was leveled with millimeter precision, before the foundations were lifted into place by a floating crane.
The foundation has a large heavy base plate with a hexagonal, open box filled with stones. Each foundation weighs 1600 to 1800 ton.
There were no service personnel out in the wind farm when the accident happened. Ørsted’s electricity customers on Lolland were not affected either.
Wind turbine collapse on land in Sweden
In November 2020, a 230 meter high wind turbine collapsed near the town of Jörn in Skellefteå municipality in Sweden. The wing probably fell off while the wind turbine was in operation. The skewed load caused the wind turbine tower to give way and go straight to the ground.
The investigations pointed to a specific steel insert that was also found in finder turbines in Norway. The Kjølberget wind farm in Våler was temporarily stopped after the collapse, and the steel inserts were replaced.
The turbines in question in Skellefteå came from the Danish wind turbine manufacturer Vestas.