Usually, my feeling is that once you start sking these types of questions, it's time to move on from reading comics!

...or start writing for M*****

gee bob, you`re just a little ray of sunshine all of the time aren`t you? i always felt it was fun to try and figure out how certain things in comics worked. like for instance, namor`s wings, while they can support him perhaps a little, i always thought he perhaps had low level telekinesis or an antigravity organ in his body, like watto has in his stomach from star wars.

Overall, the safest answer to the question "How do Superman's powers work" is "Don't ask!"

Superman's a living being, and is probably in the animal kingdom and not the plant kingdom. Solar energy bolsters his biology but he should need to breathe, eat and drink (and excrete-- no biological system is 100% efficient). Don't forget that plants do not live exclusively on sunlight-- take a plant out of the soil (and sources of water and minerals) and they wither pretty darn fast.

As JB said above, it makes better sense if his abilities are largely psionic, with solar power as the battery. JB's take on kryptonite was (IIRC) that kryptonite radiation is toxic to Superman; his body's ability to act as an energy sponge betrays him, because it rapidly absorbs radiation that is poisonous to him. Fortunately, his body seems to be equally efficient at purging the effects of kryptonite poisoning.

A bit of trivia -- and not much more than trivia since for the most part, as here, the terms are used interchangably these days -- the term "psi" was coined to cover all the "psychic" gifts people are supposed to have, like telepathy, teleportation, "mind over matter" and such --- while "psionic" (as the name suggests) was coined to describe a machine with such abilities.

(Another bit of trivia: my brief brushes with Hollywood and adjacent millieus have shown me that civilians make one mistake consistently, and that is that they refer to Superman's vision powers as his "supervision". Not only that, but in each instance in which I have encountered this, the person using the term has been genuinely convinced that he is the one who has coined it. That in all the years of Superman's existance, he is the first to think to call the collection of these powers as "supervision". Usually -- if I am in the mood for another pointless go-round -- I will indicate that we tend to refer to the powers individually -- heat vision, x-ray vision, microscopic vision, telescopic vision -- and that if, for some reason, they need to be referred to in the collective, the term is "super vision", two words. "Supervision" is a word that already exists, and has an entirely different meaning.