New Reference Turbine Model Accelerates Development of Larger, Cost-Competitive Offshore Wind Systems

Multimegawatt reference turbine expands capabilities to assess technology for ever-larger and lower-cost designs

Improvements to wind turbine designs can range from incremental component enhancements to dramatic innovations that change entire systems. How can researchers collaborate with industry to more rapidly develop new, high-performance, cost-competitive turbines, or modify existing turbines, without compromising proprietary information? Reference wind turbines—open-access designs of complete wind turbine systems with supporting models for simulation and design tools—make it possible to evaluate the performance and cost of proposed modifications, relative to a well-known and understood reference point, before prototype development.

Since its release in 2005, a 5-MW reference wind turbine created by DOE’s National Renewable Energy Laboratory (NREL) has proven invaluable to designers and researchers around the world. Additional reference wind turbines have been released by others since then, but the scale and features of turbine technology currently under development have advanced beyond the limits of these models.

Now, a new open-source reference wind turbine can be used to assess designs for offshore turbines up to 15 MW. This new reference wind turbine was developed by NREL, with funding from WETO, in collaboration with the University of Maine and the Technical University of Denmark through the International Energy Agency Wind Technology Collaboration Programme (IEA Wind) Task 37 on Systems Engineering in Wind Energy. It is available alongside two other open-source reference wind turbines recently completed by the IEA Wind Task 37 effort: a 3.35-MW land-based design and a 10-MW offshore design. 

“As technology continues to evolve, having an IEA Wind task to coordinate international efforts to produce designs that keep up with or ahead of the pace of industry developments is crucial,” said John McCann, IEA Wind chair. “This IEA Wind task enables relevant research on wind turbine systems analysis, component design innovation, controller development, and more.”

In addition to their larger size, today’s turbines have migrated toward lower-speed drivetrains, heavier rotors and nacelles, and lower specific power than those found in other reference wind turbines. Previous reference wind turbine designs were not meeting industry’s current needs given recent trends in blade scaling, floating foundation design, wind plant control, logistic studies, and other capabilities. Offshore wind turbines also face distinct installation and maintenance challenges that were insufficiently addressed by earlier reference wind turbines.

“While there’s been a lot of success over the years with existing reference turbines, they’re no longer representative of the state-of-the-art or near-future turbine technology,” said NREL postdoctoral researcher Evan Gaertner, who led the design effort.

The use of computer-based reference turbine models enables rapid and robust evaluation of new technologies against a well-defined baseline, accelerating higher-risk technology development. The new IEA Wind 15-MW reference wind turbine includes detailed design of major turbine subsystems (e.g., rotor, drivetrain, tower, foundation) and components (e.g., blades, generator, shaft, nacelle), plus mass summaries of smaller components (e.g., pitch and yaw motors), to enable the assessment of innovations at the wind plant, wind turbine, and subcomponent levels.

The IEA Wind 15-MW configuration was chosen to ensure that the new reference wind turbine’s capabilities advance beyond those of the 10-MW to 12-MW turbines already in development by industry, but are similar enough to serve as a baseline for 15-MW to 20-MW next-generation designs and act as a valuable development resource for the foreseeable future.

“Offshore wind turbines have eclipsed the current slate of reference turbines in terms of size and utility,” said Garrett Barter, NREL senior research engineer and project principal investigator. “We needed a new reference turbine to leap ahead of where industry is today—but not so far ahead that you’d need advanced technology to get there.”

Offshore installations can capture high wind speeds close to population centers, with abundant resources approximately two times the combined generating capacity of all U.S. electric power plants. However, complex construction and maintenance logistics for these systems pose challenges to making them cost competitive with land-based systems. The new reference wind turbine lets researchers and designers assess options for a fixed-bottom monopile support and a floating, semisubmersible support structure.

“We’re seeing the first steel go into the water for fixed-bottom foundations,” Barter said. “Hopefully a commercial floating offshore wind project in the United States will come to fruition in the next 5 to 10 years.”

The 15-MW reference turbine accommodates multiple software models and will provide a public domain tool for designing next-generation offshore wind turbines. The new reference wind turbine can be applied to a vast range of projects, making it possible to examine the potential impact of high-level rotor design specifications, such as airfoil profiles, rotor performance, power, pitch, torque, and thrust.

The IEA Wind 15-MW reference wind turbine was developed in partnership with research organizations and industry leaders around the world. NREL led design optimization studies for the rotor, generator, drivetrain, nacelle, tower, controller, and fixed-bottom supports. The Technical University of Denmark and the European Union COREWIND project provided extensive performance and load analysis. The University of Maine contributed design of the semisubmersible floating substructure. General Electric, EDF Renewables, Senvion, Sintef, and Atkins supplied information to calibrate design assumptions and input values.

Through the open-source GitHub portal, members of the broader research and design community can access input files that support analysis tools and contribute design variants. The open-source approach to the 15-MW reference wind turbine gives industry a public-domain baseline to collaborate with researchers without exposing trade secrets. As users provide model inputs, features will be added to the repository, expanding the tool’s capabilities. This approach was also successfully taken for the other two reference wind turbines, the 3.35-MW and 10-MW, recently released by IEA Wind Task 37 and also on GitHub.   

Interest is spreading in the 15-MW reference wind turbine, which has already appeared in multiple proposals and papers. Wind Europe is using the reference wind turbine for a floating wind project, and DOE is using it as a baseline to evaluate next-generation, lightweight drivetrain designs.

“The IEA Wind 15-MW reference wind turbine represents the future of offshore wind in the United States and worldwide, both near shore and in deep water,” Gaertner said.

Spring 2020 R&D Newsletter

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