First ever decommissioning of an offshore wind farm

Tuesday, 2 February, 2016 - 11:00
The dismantling of Yttre Stengrund offshore wind farm by Vattenfall was the first ever decommissioning of an offshore wind farm worldwide. (Photo: Vattenfall)
The dismantling of Yttre Stengrund offshore wind farm by Vattenfall was the first ever decommissioning of an offshore wind farm worldwide. (Photo: Vattenfall)

Vattenfall has dismantled Yttre Stengrund offshore wind farm off the coast of Sweden. It is the first ever decommissioning of an offshore wind farm.

Work on dismantling the five wind turbines with a total capacity of 10 MW which made up the Yttre Stengrund wind farm in Kalmar Sound, Sweden, began at the end of November. The wind farm had been in operation since 2001 and had been owned by Vattenfall since 2006. The reason for the decision to dismantle the entire wind farm rather than replacing the turbines with new, more modern ones was according to Vattenfall both, financial and technical.

"The turbines that were installed at Yttre Stengrund were an early model and only about 50 of them in total were actually produced. The difficulty of getting hold of spare parts and the huge cost involved in upgrading the turbines and gearboxes meant that it wasn't financially viable to replace the turbines," says Maria Hassel, who project managed the dismantling operation for Vattenfall. Finally only one of the five turbines of type NEG Micon 72/2000 was in operation as for the others the necessary spare parts were not available any more.

The job of removing and lifting down the rotor blades and the turbine housings fell to regional company Svensk Sjöentreprenad (SSE). They also dismantled the five masts and cut the concrete foundations off level with the sea bed. There were no major issues with the work itself but the operation was delayed by a month due to bad weather, which was a major risk throughout the dismantling process. Underwater cables are planned to be removed in the summer of 2016.

"Yttre Stengrund was one of our first wind farms and we've learnt a lot over the almost 10 years that we've been operating it. That knowledge, combined with the prohibitive cost and technical difficulty of replacing the turbines, made this a relatively straightforward decision. We have locations with better wind conditions in other parts of the country where we can build new wind power and take with us the knowledge we've gained from Yttre Stengrund," says Hassel.

Katharina Garus / Vattenfall

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