A newly discovered Apple patent for 'solar cells on portable devices' outlines a plan to embed solar cells into a device to 'charge the batteries [or]... directly power the operations of the device'.
In Apple's plans, the solar cells sit directly behind the LCD screen, so that sunlight on the display will provide power (as well as screen glare).
The patent also outlines a way of displaying information about the amount of solar charge available, as opposed to costly carbon-sourced mains power.
The iPod Touch and iPhone are the most obvious potential beneficiaries of this technology, although it's likely to add to their bulk.Still, with energy prices rising by the second, that might be a compromise we're willing to take.
However, you'd be a blind optimist if you believed the forthcoming 3G iPhone would be solar-powered. These things take time. So don't forget to pick up a few barrels of black gold when you pick up your black iPhone.