Technically nuclear came from a different star. The sun won't create those kinds of heavier elements until it burns through its hydrogen and helium fuel to start fusing its way up to lead, and I don't think it's massive enough to actually reach the kind of supernova collapse required to smash lesser elements together into heavier elements than that in any significant amount. So technically, fission is the only the form of energy that isn't based on solar. It's just the still-cooling-embers leftover from someone else's dying star, a whole bunch of billions of years ago. I guess you could say the sun's gravity at least attracted it all into this general vicinity though, at least until the Earth's own gravity started pulling its own weight.