Repowering plan for Sweden's first offshore wind farm

Modern turbines may replace outmoded machines at Bockstigen

The first offshore wind turbines installed in Swedish waters may be replaced with larger, modern machines within the next few years, Windpower Offshore has learned. If repowering takes place it will be a world first for a commercial offshore wind.

The Bockstigen project is located 3km off the island of Gotland and is nearing the end of its profitable life. Built between 1996 and 1997, Bockstigen features five Wind World 550kW turbines, which are now seriously outmoded.

The wind farm remains profitable, but margins are slipping. "The [future] life of the turbines lies somewhere between two to a maximum of five years," explained Andreas Wickman, chief executive of Wickman Wind, the company that maintains Bockstigen.

"New gears and blades would be necessary to extend the use of current equipment, but the German owners believe repowering with new plant would increase the value of Bockstigen for eventual sale," said Wickman.

Leaving the issue of repowering aside, there will be the cost of dismantling existing turbines and removing foundations. In fact, the cost of decommissioning makes repowering more attractive, in Wickman’s opinion. "The same ships and barges can do both jobs," he said, adding that permitting is also likely to be less costly since the location is already in use.

A Danish utility is interested in the project, wishing to gain experience in offshore repowering, according to Wickman. New environmental studies would need to take into consideration the impact of larger turbines and foundations, as the plan is for around 10 new turbines with a capacity of at least 5MW. This would increase the project’s total capacity from its current 2.75MW to at least 50MW.

One factor that could undermine the business case for repowering Bockstigen is Sweden’s lack of demand for new electricity generation. However, Wickman believes that a repowered Bockstigen could sell its electricity to the Baltic market, via the Nordbalt undersea cable scheduled to connect Sweden and Lithuania from 2016.

Residents on the island of Gotland are accustomed to wind turbines, as the island has a significant onshore capacity. Nevertheless, any new turbines for Bockstigen would stand at least 150m as opposed to the current 50m, and would be much more visible. Some homeowners may object.

Wickman is wary of proposals to compensate local residents via free or cheaper electricity, as this is "difficult to administer". He would prefer to see Bockstigen invest in the island’s village and/or harbour infrastructure.

Looking back on Bockstigen’s history, Wickman recalls that "so much was unknown. In the 1990s the permit was challenged by those who were worried about seals, but today there are lots of seal. In fact, their numbers have increased, and they are not afraid of the maintenance boats. They always swim up out of curiosity when the technicians are at work."

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