Ultra-low wind speed piezoelectric windmill

We report an ultra-low start-up speed windmill that consists of a 72 mm diameter horizontal axis wind turbine rotor with 12 alternating polarity magnets around its periphery and a 60 mm × 20 mm × 0.7 mm piezoelectric bimorph element having a magnet at its tip. This wind turbine operates at very low Reynolds number of around 2×10⁴, but still it has reasonably high power coefficient of about 11% at the optimal tip speed ratio of 0.7. It was found to produce peak electric power of 450 μW at the rated wind speed of 4.2 mph. An extremely low start-up wind speed of 2.4 mph was achieved by operating the bimorph in actuator mode.