Improving the Efficiency of Piezoelectric Fluidic Energy Harvesters*

Piezoelectric systems can harvest electrical energy from fluid flows. Maximizing the power output and increasing their overall energy conversion efficiency is a formidable challenge. We compare the conversion efficiencies of various harvester configurations. The first experimentally tested configuration is a cantilevered beam in the wake of a circular cylinder. An efficiency of only 0.03 per cent in converting fluidic to mechanical energy (i.e. ``aeroelastic efficiency'') was estimated while the efficiency of mechanical to electrical energy conversion (i.e. ``electromechanical efficiency'') was close to 11 per cent. In our latest experiments, we attached a circular cylinder to the free end of a piezoelectric beam. The aeroelastic efficiency increased to 2.5 per cent and the electromechanical efficiency is increased to 30 per cent. Placing a stationary circular cylinder upstream of this configuration caused a dramatic increase in harvested power and efficiency. Furthermore, attaching a cylinder of a half-circle cross section resulted in a much larger power and efficiency as compared to attaching a circular cylinder to the tip of beam.