Piezoelectric energy harvesting from raindrop impacts

PEH (piezoelectric energy harvesting) techniques can be used to capture vibration, motion or acoustic noise, to be converted in to electrical output. In recent years there has been an increased interest in scavenging energy using alternative sources. This study focuses on the impact of raindrop on a PEH device and the possibility of harvesting energy from this source. Impact of water droplets on a PEH are analysed after having been released from various heights to replicate a rain shower. Detailed experimental results show features which have not been published in the literature before. The results show two distinct stages in the voltage and power output; first, a log growth, then an exponential decay during an impact event. A model is also developed to characterise the output power for one unit device which is then applied to an array of rain impact harvesters. The experimental results show a power output for one unit at around 2.5 μW that is typical of the data produced in other publications. However, there is significant room for improvement as the efficiency of the system is found to be no more than 0.12% of the total kinetic energy in a typical raindrop in freefall.