Small-scale experimental study on the optimisation of a rooftop rainwater energy harvester using electromagnetic generators in light rains

This research proposes a new rooftop rainwater energy harvester using electromagnetic generators, which demonstrates better rain-energy harvesting performance than the traditional rainwater energy harvesters that use electromagnetic generators under light rain conditions. Conventionally, the rainwater collected from the roof of a building or a residential attic using the installed roof gutter system is drained directly along a pipe to drive water turbines combined with electromagnetic generators for generating electricity. Such an energy harvesting method has high energy harvesting efficiency under heavy rain conditions but is inefficient under light rain conditions. To improve the energy harvesting efficiency in light rains, a pipe-connected tank including a passive rainwater buffer is introduced and fixed below the rooftop gutters in the proposed structure. The passive rainwater buffer is attached above the pipe-connected tank. After collecting a certain amount of rainwater from the gutters, the passive rainwater buffer automatically releases the rainwater periodically into the pipe-connected tanks. The released rainwater results in a large flow along the pipe, which can drive water turbines with electromagnetic generators to work at a high efficiency for a short period of time. A small-scale experimental prototype was built for validating the energy harvesting performance of the proposed structure. The results show that the intermittent high-efficiency power generation of the proposed structure is better than the continuous low-efficiency power generation of the traditional structure during light rains. The proposed structure can charge a 680 mu F capacitor with at least nine times the electrical energy that is stored in a conventional capacitor for a rainwater flow rate of less than 300 mL/min in the same amount of time. However, with the increase in the rainwater flow, the energy harvesting performance gap between the proposed structure and the traditional one gradually narrows.