Optimization of structural parameters for rotary freestanding-electret generators and wind energy harvesting

Electret generators have been invented as a promising technology to harvest ambient mechanical energy for powering electrics. This paper discusses the structural optimization of rotary freestanding electret generators (FEGs) for enhancing the output power. The influences of the structural parameters on outputs including the maximum average output power and the matched load resistance are investigated theoretically, with and without the consideration of the parasitic capacitance. The theoretical results are verified through experiments. In addition, a figure-of-merit (FOM) is proposed to evaluate the output performance of rotary electrostatic generators including electret generators and triboelectric nanogenerators. The maximum average power of the optimum FEG achieves 18.3 mW at 1000 rpm, which is 31% higher than that of the previous unoptimized FEG with the same diameter and net charge density. The FEG with a wind turbine can be activated at the wind speed of 0.8 m/s and works continuously at speed of 0.6 m/s. The generator produces an average power of 9.1 mW at the wind speed of 2.7 m/s, indicating the potential of the FEG for wind energy harvesting, especially in low-speed wind.