Design studies of swept wind turbine blades

The growth of wind energy is sustained by innovation that lowers the cost of energy. One recent innovation is the swept blade, which deflects in operation and lowers loads. With sweep, a design rotor diameter can increase, capturing more power, with the loads remaining within limits. This concept has been demonstrated in a U.S. program and is in commercial production. This paper describes a parametric study of swept blade design parameters for a 750 kW machine. The amount of tip sweep had the largest effect on the energy production and blade loads; other parameters had less impact. The authors then conducted a design study to implement a swept design on 1.5 MW, 3 MW, and 5 MW turbines. An aeroelastic code, previously described, was developed to model the behavior and determine the loads of the swept blade. The design goal was to increase annual energy production 5% over the straight blade, without increasing blade loads. Successful designs were developed for the 1.5 MW and 3.0 MW turbines. The swept 5 MW turbine exhibited a twist instability at high wind speeds. Further study is required to determine if sweep can be implemented for larger turbines, which are approaching flutter boundaries in unswept designs.