Ballistic energy conversion

Ballistic energy conversion is the direct conversion of kinetic energy into electrical energy. Aqueous droplet-based platforms are eminently suitable for this method, as droplets can be conveniently supplied with both kinetic energy and electrical charge. Starting with the 19th century gravity-driven Kelvin thunderstorm and the electrostatic generators of Melcher and Zahn from the 1960s, we describe the recent development of ballistic energy conversion both in experiment and theory. With this method experimental efficiencies of 48% have been reached at 20 kV operating voltage with an extremely simple setup. Theory predicts maximal efficiencies of more than 90%, operation at <100 Volt. Downscaling also promises to remove one of the largest disadvantages of electrostatic generators, namely the low power density: power densities of 1–1000 kW/m2 are predicted.