Wind-generated electrical energy using flexible piezoelectric materials

Electrical energy can be harvested from the wind using flag-like membranes (termed piezoelements or bimorphs) composed of flexible piezoelectric materials. The flapping of the membrane caused by the wind induces bending stresses that generate a voltage across electrodes positioned on the surfaces of the material via the piezoelectric properties of the material. The best results to date using PVDF (polyvinyledene fluoride) as the piezoelectric material are 10 mW of dc power (50 Vdc across 250 kΩ) obtained from a single bimorph element (size about 8''X11''X 0.02'') flapping a frequency of 5 Hz in a wind speed of 15 mph. The overall efficiency was low (estimated at 0.1%) and to improve this figure, three specific areas of improvement are targeted. The efficiency of the piezoelement in converting wind energy into stored elastic energy will be optimized by determining the best geometry and dimensions for the element in conjunction with upwind bluff bodies using wind tunnel tests. A novel circuit, termed a quasi-resonant rectifier, for extracting the electric energy from the piezoelectric has been developed which can extract several times more power from the piezoelement than a conventional full-wave rectifier. A number of piezoelectric and electrostrictive materials including PZT fibers embedded in an epoxy matrix (termed active fiber composites or macro fiber composites) which may have higher generation efficiencies than PVDF will be examined for this application.