In November, a Danish asset management group called Momentum Gruppen recommissioned five turbines at a 20-year-old offshore wind farm located 4km (2.5 mi) off the coast of Sweden. Momentum purchased the wind farm and upgraded the nacelles, blades, and control systems while leaving the towers, foundations, and transmission equipment. The turbines were originally rated to produce 500 kilowatts (kW) apiece. The upgrades were done with 600 kW turbine replacement equipment.
According to GreenTechMedia, it's the first such repowering of an old offshore wind farm. As Europe's first offshore turbines age, it represents a possible long-term future for Europe's clean-energy fleet. Although onshore wind farm owners have been repowering their equipment for years, offshore repowering comes with its own technical challenges.
In 2017, Dong Energy dismantled the first-ever modern offshore wind farm, built in 1991 off the coast of Denmark. It had been in operation for 25 years. (One turbine was preserved for display at the Danish Museum of Energy.)
Momentum wrote in a press release that upgrading to better equipment at its Swedish wind farm will increase the lifetime of the existing five turbines by more than 15 years, and the upgrades will more than double the expected yearly output of the farm, from about 5,000 megawatt-hours (MWh) per year to about 11,000 MWh per year.
In Momentum's press release, CEO Kim Madsen was positive about the potential for more repowering: "With the completion of this project, Momentum has proven that we can assist the owners of older turbines with the extension of the lifetime of their assets, also under as difficult circumstances as offshore."
GreenTechMedia wrote that the wind farm's previous owner wanted to scrap the current wind farm and replace it with 10 turbines at five megawatts (MW) apiece. When Momentum bought the project, it modified this plan, hoping to install 12 four-megawatt turbines. But the transmission extension necessary to make that project economically feasible was cancelled in 2017, sending Momentum back to the drawing board. Repowering has allowed the owner to continue making money on its wind farm while working within the existing transmission infrastructure.
As the earliest wind farms age, repowering is an economic and relatively environmentally-friendly way for owners to continue making money on their investments. Wind turbines generally have a lifespan of 20 to 25 years, but another incentive to repowering besides replacing older equipment is that wind turbine technology has improved dramatically in the last two decades, so a single turbine can send much more electricity to the grid than it could 20 years ago.