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High Specific Power High-voltage Variable Capacitance Generator with Resonant Pulse Excitation to Enable the Next Generation of Offshore Wind Turbines

Juan Rivas-Davila, Electrical Engineering and Claudio Rivetta, SLAC 

We plan to develop a novel electrical generator design for use in wind turbines that will offer key transformative benefits over conventional drivetrain architectures, and has the potential to enable the next generation of low-cost offshore wind farms. Wind turbine drivetrains (which include the generator and gearbox) account for roughly half the total cost of the wind turbine. Additionally, drivetrains are massive, which further escalates costs of the supporting structure. Drivetrains also contribute to a large percentage of the total energy losses, and geared mechanical systems have short lifespans which require signficant maintenance. The proposed concept addresses all of these issues simultaneously. Our novel electrostatic generator design is lighter and more efficient than state-of-the-art geared systems, with all the maintenance and lifespan benefits of direct-drive systems, while utilizing low-cost, readily available materials. Furthermore, the direct high-voltage generator eliminates a number of power conversion steps to the transmission system, signficantly improving over-all efficiency. This will result in substantial reduction in the levelized cost of electricity (LCOE), enable wind turbines to increase in scale beyond what is capable with conventional drivetrains, and open low-cost access to currently untapped deep offshore wind resources.

The specific objective of this project is to develop a proof-of-concept prototype to demonstrate the feasibility of high-voltage variable capacitance generators (VCG). The goal for the prototype is 1 kW at 100 kV, the development of which requires research and innovation in high-voltage electrostatics. Modeling indicates that the VCG system will increase drivetrain specc power by nearly 200%, improve efficiency by over 3%, and reduce transmission costs by 10-30%, together resulting in a signficant reduction of LCOE. If proven in the lab, this technology has the potential to completely transform how wind turbine drivetrains are designed. This high-voltage variable capacitance generator could reduce the weight of state-of-the-art geared drivetrains by over 30%, while retaining all the maintenance and longevity benefits of much heavier direct-drive drivetrains. Decreasing drivetrain weight results in a cascade of cost reductions, from decreased structural requirement for the tower, to decreased shipping and fabrication costs. The high-voltage VCG technology also eliminates a number of conversion steps from the turbine to the transmission system. By eliminating the step-up substation, wind farms using VCG drivetrains will result in reduced transmission costs, enabling installations further offshore where there are significant wind energy resources. Furthermore, the light weight VCG drivetrain decreases the cost of floating platforms. All combined, our VCG technology will enable deep offshore floating installations at substantially lower cost. Currently, over 95% of California’s offshore wind resource potential is at depths greater than 60 meters, where conventional foundations become cost-prohibitive.

Awarded 2019