An Efficient Piezoelectric Windmill Topology for Energy Harvesting from Low Speed Air Flows

This paper presents a topology for micropower piezoelectric wind energy harvesting useful for developing self-powered wireless sensor nodes. The features of the proposed topology, as compared with the existing piezoelectric/electromagnetic topologies, are as follows: 1) delivering power at high voltage levels, particularly at low-speed air flows; 2) starting operation at low cut-in speeds (about 1 m/s); and 3) robust structure for operating at high-speed wind flows practically tested up to 20 m/s. The proposed topology consists of a small fan with embedded permanent magnets (PMs) and a piezoelectric beam with a PM proof mass, which interacts with the PMs in the fan to harvest wind power. This paper also presents an analytical model and a design procedure to determine the number of PMs in the fan and their arrangements to maximize the captured power and minimize the cut-in speed. Using a prototype of the proposed topology, it is shown that the device starts capturing wind power at the wind speeds above 0.9 m/s. It is also shown that the suggested topology is at least 10% more efficient than the existing topologies in using piezoelectric materials and that its total volume power density is higher than those of the other topologies.