First you have to consider photosynthesis converting CO(2) to O(2). In a greenhouse place where the trees don't shine, would be where such a person is content. Also, you need light. It does not matter if it's from the sun (though that would be optimal), or if its from a lightbulb. But mere lightbulbs to a phoyosynthetic-person is like eating just only a bag of pretzels.. per week.
Of water, your hero needs to drink lots, and lots of this if he is going to get enough energy for a day. Perhaps the other processes can substitute other compounds (such as arsenite) for water in the electron-supplying role. Do remember your hero (if he is a human[like]) needs much more energy than the usual tree or flower, especially moving around and thinking.
Then you need the nutrients — like nitrogen, potassium, those found in fertilized soil. I think your hero can eat dirt. Or a suitable nutrition pill, if these exist in your story.
edited 6th Mar '11 1:44:25 PM by QQQQQ