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NREL Researchers Assess Where to Gear Up U.S. Manufacturing and Supply Chain Capabilities for Advanced Drivetrain Technologies

December 2, 2013

Illustration of an advanced wind turbine drivetrain showing the single-stage gearbox, power electronics, medium-speed generator, and hydrodynamic bearings.

A wind turbine drivetrain featuring advanced technologies. Illustration by Powertrain Engineers Inc.

The drivetrain of a wind turbine converts the power of the wind into electrical energy. Now, innovative technologies, such as medium-voltage and permanent-magnet generators, silicon-carbide (SiC) switches, and high-torque-density speed increasers, have the potential to improve the capacity and operating reliability of conventional drivetrains. Yet, these new configurations may be more advanced than what today’s manufacturing and supply chain processes can handle.

To better understand the impact of advanced drivetrain technologies on the U.S. wind industry’s manufacturing and supply chains, researchers at the National Renewable Energy Laboratory (NREL) conducted a study, An Assessment of U.S. Manufacturing Capability for Next-Generation Wind Turbine Drivetrains, for the U.S. Department of Energy (DOE). The analysis involved a comprehensive literature review, industry expert interviews, and manufacturing facility tours to define possible areas of improvement and growth.

NREL researchers first compiled a list of 80 different drivetrain technologies. They then used a down-selection process to narrow the list to three final technology categories for more detailed analysis: medium-voltage permanent-magnet generators; high-torque speed increasers; and electrical systems (such as full SiC medium-voltage switches).

Based on the study findings, researchers recommended the following priorities for future manufacturing and supply chain investments by private, public, or nonprofit entities:

  1. Medium-voltage and permanent-magnet generators. This technology affects the entire turbine and has the greatest likelihood for reducing mass, improving efficiency, and decreasing the levelized cost of energy (LCOE). However, lower speed designs have the highest risk and possibility to disrupt existing manufacturing activities by requiring new technologies, process capabilities, and manufacturing facilities. Furthermore, medium-voltage and permanent-magnet generators currently have little to no manufacturing and research and development (R&D) activity in the United States. As a result, public investments in this technology area are a top priority because they will help fill the manufacturing and R&D gaps and position U.S. manufacturers for new opportunities.
  2. High-torque speed increaser technologies. These new technologies (such as journal bearings or flex pins in the planetary stages of gearboxes) have solid potential for reducing the cost of energy, but changes are anticipated to have less of an effect on the related manufacturing and supply chain.
  3. Full SiC switch technology. SiC switches are used to convert a variable electric frequency into a constant frequency. In this study, they were indicated by subject matter experts as having the highest potential to reduce LCOE. Another advantage of investing in SiC switches is stated in the report: “The use of SiC switch technology will benefit a variety of industries. For example, the automotive industry is interested in using this technology in electric vehicles for similar reasons as wind turbines (e.g., power quality and small size), and because it could eliminate a separate coolant loop for the power electronics in hybrid vehicles. The wind industry may be able to take advantage of this broader interest.” However, R&D for this technology is already being funded by a number of other industries (such as transportation and defense), therefore it is a lower priority investment for the wind industry.

According to the study, drivetrain manufacturing and supply chain growth can only happen if there is a stable U.S. market. To help improve wind turbine manufacturing and supply chain activities in the United States and boost competition with Europe and Asia, NREL researchers suggest conducting further analysis on the manufacturing and supply chain issues for power electronics, formally vetting the report findings with industry stakeholders, and creating a long-term strategic plan.