Huh, they are a lot of energies free for the taking, solar energy, etc. Where is the payback if I take a little Sun's energy?

One theory for Tesla's "free energy" I read is that he was using the dynamo energy generated by the interaction of the Sun and the Earth, or something like that. Right or wrong, the idea is that there is a colossal amount of unused energy being wasted around us.

As for why he stopped, it was because he didn't get sponsors. Industrials were still trying to get back their investments by milking his first inventions. Tesla said so himself.