Physics of Atlas Shrugged
A bit of each. It's actually not very difficult - just stick a conductor D meters up in the air, collect charge at 150 D V/m and discharge it through your motor into the ground. The trouble is that the currents you get are extremely small, so you don't have much power.
You could get a lot more current if you could stick your conducting antenna all the way up into the ionosphere where ions are plentful and current flows pretty freely, but the global energy flow is still pretty small by power industry standards - perhaps 800 MegaWatts - about 80% of the output of one of the Fukushima reactors when they were operating.