Sorry, but no such approach. The potential gradient is real and affects the formation of thunderstorms. But the current available is very low. Classroom Van de Graaf generators can produce potentials of up to 400,000 volts, but are driven by a motor that is probably less than 1 horsepower (and the recharge current power will therefore be smaller). If this approach were viable, every house would have an aerial on a mast to provide power.