I'm getting well outside of my depth here, but some starting points: Rain drops have been calculated to charge up to about 1/50 of an esu (electrostatic charge

I'm getting well outside of my depth here, but some starting points: Rain drops have been calculated to charge up to about 1/50 of an esu (electrostatic charge unit): https://agupubs.onlinelibrary.wiley.com/doi/10.1029/TE040i001p00079 https://agupubs.onlinelibrary.wiley.com/doi/10.1029/TE040i00... Their paper is reporting 70V, so Joule/drop is on the order of 3.7E-11 J https://www.wolframalpha.com/input?i=%282.65E%E2%88%9211%29%2F50+coulomb+*+70+Volt https://www.wolframalpha.com/input?i=%282.65E%E2%88%9211%29%... (many, many orders of magnitude below the kinetic energy per drop) It's important to note most of the research they've published is not using real rain, but laboratory generated droplets that is intended to push the harvester to the maximum.