what the world is waiting for is a truly efficeint battery. We've got the capaicty issue pretty much solved, the only thing keeping cap'n kirks hand phaser outta production is the lack of a battery with a low enough internal impedance.
solve the battery capaicty/impedance problem, and any one of a large number of cheap charging sources could be utilised.. hydro/electric, tidal, nuclear, solar.. matters not what the source of the cheap energy is, the issue remains how to store and deliver the energy.