[Behind Liberal Lines]

Air, rain and sunlight come to mind. But I'm sure they're working on it.

But even those require some sort of capital outlay to be successfully used.

[DoughtyOne]

Yes, but once the capital outlay is complete, the additional expenditures are minimal. Those who have river front property can sometimes set up a mill too. Same idea. I believe there are natural sources of energy that when understood will one day provide caparitively free energy to everyone.