Which would supply no where near enough energy to do what he does, ergo
it would have to act as a catalyst for a much larger energy source.
I can feel the comic geek being unleashed, anyway...Recently on a visit
to New Genesis this very thing was suggested, sunlight allowed Superman
to tap into The Source for the energy he needed to do his superfeats.
The Source for lack of a better description is the ultimate origin of
everything, a limitless well of untapped energy and potential. A
similar description has been given by some to the Zero Point Field.