Bockstigen repowered turbines

Location and History

• The Bockstigen wind farm is situated off the coast of Gotland, Sweden, and it is notable for being the third offshore wind farm established in the world. It was built in 1998.

Original Configuration

• The original project consisted of five Wind World 550 kW wind turbines, each with a capacity of 550 kW. These turbines had been generating electricity since their installation in 1998.

Repowering Process

• By 2017-2018, the turbines were nearing the end of their technical lifespan. To extend the life of the wind farm, Momentum Gruppen undertook a repowering project. This involved replacing the existing turbines with refurbished components:
  • The nacelles, rotors, and transformers from the old wind turbines were replaced with refurbished Vestas V47 nacelles and new DEIF transformers and monitoring systems.
  • The old wind turbines were dismantled, and the refurbished components were installed, utilizing the existing towers, lattice structures, and foundations.

Technical Upgrades

• The repowering process included several key upgrades:
  • The rotor diameter was increased from 38 meters to 47 meters.
  • New blades and control systems were installed.
  • Software updates and new control systems were implemented to improve remote control of the turbines.

Outcomes and Benefits

• The repowering extended the technical lifetime of the wind farm by at least 15 years.
• The project resulted in more than a 100% increase in electricity production, from 5 gigawatt-hours to 11 gigawatt-hours per annum.
• The availability of the turbines after the repowering was over 99%.
• The use of refurbished main components such as gearboxes, blades, and generators was a novel approach, opening up new possibilities for similar projects.

Financial and Ownership

• The repowering process was financed by various banks and the owners’ equity.
• After the successful operation of the repowered turbines, the wind farm was sold to a Danish investor in December 2019.

Environmental and Economic Impact

• The repowering project significantly increased the energy output while minimizing the need for new infrastructure, thus reducing environmental impact.
• The project exemplifies a sustainable approach to extending the life of aging wind farms, avoiding decommissioning and the associated costs and environmental impacts.

The Bockstigen repowering project sets a precedent for the wind energy industry, demonstrating the feasibility and benefits of repowering aging wind turbines to enhance efficiency and extend the lifespan of existing wind farms.