The size and generating capacity of offshore wind turbines are steadily increasing, underscoring the need to design more efficient and competitive drivetrain systems. As the drivetrain-generator configuration directly affects overall turbine performance and costs, scientists from GE Research and the U.S. National Renewable Energy Laboratory (NREL) sought to determine which drivetrain technology would be the most cost competitive for fixed-bottom and floating foundations.

To determine the optimal designs for more powerful turbines, conceptual designs for three drivetrain technologies were developed and evaluated at five different powers ranging from 15 MW to 25 MW for both fixed-bottom and floating foundations. Wind Plant Integrated Systems Design and Engineering Model software created at NREL was used to generate 30 unique design points.

The design with the lowest levelized cost of energy (LCOE) coupled a medium-speed gearbox to a permanent-magnet synchronous generator (PMSG). The LCOE for this option is estimated to be as much as 7% lower for both fixed-bottom and floating designs compared to a more common direct-drive configuration, provided the system does not significantly increase maintenance costs. A comparison of the PMSG and superconducting direct-drive solutions reveals the latter generated LCOE savings of 2% to 5% depending on the rating. Superconducting generators were more beneficial in floating wind turbines than in fixed-bottom ones.

The study published in Applied Energy indicates that direct-drive low-temperature superconducting generator systems have the potential to lower LCOE by 2% to 3% for fixed-bottom designs and 3% to 5% for floating offshore wind turbines relative to direct-drive interior PMSG designs. This option also offers the added benefit of nearly eliminating rare-Earth metals from the generator supply chain.