Performance of a 100 kW wind turbine with a Variable Ratio Gearbox

A Variable Ratio Gearbox (VRG) can be used in the drivetrain of a small to medium-size wind turbine to improve aerodynamic efficiency. Currently, all commercially-available wind turbines operate using a fixed-gear ratio between the turbine rotor and electrical generator. A VRG allows wind turbines, with a constant-speed generator, to discretely vary rotor speed and to achieve greater aerodynamic efficiency. The authors’ previous results demonstrate the viability of the VRG design. This research quantifies the gain in efficiency for a VRG-enabled wind turbine based on wind data from representing all seven wind classifications. A method is also presented to identify turbine sites that provide the VRG with the greatest opportunities to increase production. The overall findings suggest that the VRG can benefit all wind turbines, irrespective of wind class, with some wind profiles in the study experiencing gains greater than 10%.

► A VRG increases the output of small to medium-size fixed speed wind turbines in all wind categories.
► The greatest energy gain due to discrete speed variation is during partial load operation.
► The VRG is most effective for turbine sites with a power density of 400–700 W/m2.