Nathan Stubblefield is worth investigating.
I feel the real secret relies on...
Thermoelectric effect /different work functions of different metals
Magnetohydrodynamics..if i remember correctly..nernst effect or something..bin a long time..lol
Ground currents/ potential difference between earth and sun
The two coils are copper and iron..that gives the thermoelectric effect..but I THINk Stubblefield then SELF RESONATED the two coils.
Small currents ? They said that about thermocouples..but how come the tiny thermocouple in a boiler pilot light keeps a whacking big valve open

16 amps to be precise if memory serves. Thermoelectric current are massive..dont see why earth batteries would not be same. Almost NOTHING published on that anywhere..promise ya !!