Hello! This is just an idea which has come to my mind after reading this http://www.hcrs.at/ELWALZ.HTM (http://www.hcrs.at/ELWALZ.HTM) about a usable electrostatic motor. The website is in german language, but I will explain:
Basically if someone puts a balloon some 100meters in the air: the potential between earth and ballon is multiple kilovolts. It is fact that the electrostatic field of earth grows 100V/meter. Now it is said in the description that someone (not the author) has build a setup with this balloon and a "Walzenläufer" and this motor rotated about 12.000 rpm. Obviously they have measured the power produced by this motor (I don't know how, maybe they attached a simply dynamo) and the output was 70 Watts. Free energy for nothing.
Now if you read on the website they have tried to simulate the high potential between balloon-earth with a simple Wimshurst device. The result however showed the Walzenläufer did not rotate so fast, because the amperage was too low. Therefore the authors connected a simple transformer powered by household electricity which delivered 20kV with 150µA (20*0.000150 = 3 Watts) at 50 Hz and got about 7.000 rpm as you can see on the table on the website. So they put in 3 Watts and got 7.000 rpm.
Now that we remember the 12.000 rpm motor delivered 70 Watts, we could say that by rule of the thumb that 7.000 rpm would deliver 40 Watts. Wouldn't this be a huge overunity? Or am I missing some points in here?