Defective bearings in wind turbines powering the first floating offshore floating wind farm, located off the coast of Scotland, have been replaced, according to the Norwegian wind farm operator Equinor.

The Hywind Scotland wind farm had to be shut down for months so that the main bearings on the five wind turbines could be replaced, the company told AJOT.

The announcement that the Equinor project had to be temporarily shut down raised questions about the longevity of floating wind turbines and the reliability of power generation from those turbines when operating in challenging sea state conditions.

Equinor has told AJOT that lessons learned from the Hywind Scotland wind turbines resulted in upgrades that will make new wind turbines more durable.

In January, it was reported that Norwegian energy giant Equinor would temporarily remove all five floating wind turbines from the pioneering Hywind Scotland after discovering a need for “heavy maintenance” on the Siemens Gamesa machines deployed there, according to Recharge.

Recharge reported that the 6MW turbines were towed back to Wergeland on the west coast of Norway as part of a maintenance program “that is likely to take around four months and will disrupt power output from the project operating 24 km (kilometers) off Peterhead (Scotland) since 2017. All units will be reconnected back.”

However, Equinor has told AJOT that the repairs were much more substantial than ‘heavy maintenance’ and required the replacement of the main bearings on each of the floating wind turbines.

Equinor said Hywind Scotland was a pilot project and lessons learned from the original Hywind turbines have resulted in the installation of new bearings that will require less repair work: “The need to replace the main bearings is not usually needed and the fact that we have to do it for the turbines on Hywind Scotland is limited specific reasons that are identified and mitigated with relevant measures. Hywind Scotland is a pilot project and serves as a learning platform for future floating offshore wind farms.”

In an email sent on July 2, 2024, Magnus Frantzen Eidsvold, Press Spokesperson, Renewables, Equinor ASA provided AJOT with responses to the following questions:

AJOT: Will all floating wind turbines in a farm have to be shut down for 9 months every 7 years or so for maintenance as with Hywind Scotland?

Equinor: “No, this is not something we foresee will be necessary on floating offshore wind farms. The need to replace the main bearings is not usually needed and the fact that we have to do it for the turbines on Hywind Scotland is limited specific reasons that are identified and mitigated with relevant measures. Hywind Scotland is a pilot project and serves as a learning platform for future floating offshore wind farms. For future floating wind farms Equinor have initiatives in place to reduce heavy maintenance events and to develop on-site repair solutions.”

AJOT: Will newer wind turbines recently have deployed at the Hywind Tampen wind farm face a similar replacement regime after 7 years of operation?

Equinor: “No, we have no indications that this will be needed for Hywind Tampen.”

AJOT: What are the dynamics that are driving long maintenance and repair regimes for floating wind turbines as opposed to fixed and land-based wind turbines?

Equinor: “Floating offshore wind has the potential be a key part of the solution in the energy transition, opening up new areas for energy supply. All offshore wind farms require heavy maintenance of turbines, so this isn’t isolated to floating wind farms. When it comes to Hywind Scotland it is conceptually performing very well and has for many years delivered record high-capacity factors. It is operating within its design parameters and within expected loads. This operation will give Equinor and its partners valuable experience to further develop maintenance methods and improve operational efficiencies for maintenance of commercial scale floating offshore wind projects in the future.”