Performance of small-scale bladeless electromagnetic energy harvesters driven by water or air

In this work, three different-diameter energy harvesters driven by turbulent air flow and rainwater are designed. Experiments are conducted first on the air-driven harvesters to gain insight on the energy conversion process. Unlike conventional blade-involved systems, the present setup involves using a number of co-rotating compact discs. They are closely spaced and attached to a central shaft, on which a magnet is attached. As the air flow excitations are set to 4 different levels, the harvester performances are measured in both open- and closed-loop electrical circuits. The results show that approximately 0.3 W electricity is produced. Parametric analysis is then conducted to highlight the effect of the system parameters, such as disc diameter, number, exhaust flow rates and inter-disc distance on its performance and to gain insight on its optimum design. Numerical simulations are then conducted to understand the flow physics. Finally, a 40 mm harvester is used to harness energy from rainwater. Compared with the same size air-driven harvester, the rainwater-driven one is working more efficiently in terms of the overall energy conversion efficiency. The maximum electric current is about 4.5 mA. A practical demonstration is then conducted by using the electricity generated to power a red light-emitting diode (LED).