TUAW reader Maaz sent in this link to a Forbes story about a possible solar-powered iPhone. We recently posted about Apple's new Solar Energy patent so it's not a big jump to start seeing articles speculating on how that new technology will be used and expressed in Apple's product line.
I have nothing against solar power--the Sun is the source of most of the Earth's human-usable energy but I'm not sure that the iPhone is a particularly good match to solar refueling.
As the Forbes article points out, the iPhone is small and is built to radiate light from a large part of its surface, not collect it. Unlike low-powered calculators, the iPhone is a pretty power-hungry device and is going to get hungrier if the (likely) move to 3G occurs. And what the Forbes article does not point out and should be highlighted is that for the most part, iPhones live in our pants, which isn't a very sunny place (for most people).
So do the math. Small surface + pants-based existence means a Solar-powered iPhone is not very likely to debut.