[Tristan Lall]

Well, I'd have to say that many robots are solar-powered. But that's just because the Sun provides light that feeds photosynthetic organisms, which die, fossilize, and are converted into oil, gas and coal (with the help of a little heat and pressure).

One might also argue that these same robots are nuclear-powered, since heat from radioactive decay contributes to the internal heat of the Earth (which "cooks" the fossilizing matter).