Owners of Apple devices such as iPods and iPhones may soon be able to charge them up by leaving them out in the sun.

Apple has filed a patent for a technology which would enable a layer of solar cells to be inserted under a touch-sensitive screen of the sort used in the iPhone.

The patent, should it be awarded, has the potential to make the iPhone a truly portable device, dispensing with the need for it to be connected to a power supply by wires.

There is usually little room for solar panels on portable devices, once space taken up by the screen and keypad is taken into account - a fact which has plagued previous attempts to power MP3 players and mobile phones via the sun.

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Apple's patent would get round the problem by stacking the solar cells underneath both the touch-sensitive screen and the LCD, according to The New York Times. That would potentially allow the full 2.4 by 4.5 inch glass face of the iPhone to operate as a solar panel.

If the application, entitled 'Solar cells on portable devices', is successful, it has the potential to increase dramatically the battery life of iPhones and iPods. According to Apple, the existing iPhone battery gives about eight hours of talk time and seven hours of video, but once a faster, 3G version is released, the device will become even more power-hungry.

As concerns about environmentally friendly behaviour have grown, the challenge of fitting consumer devices with solar power capabilities has received greater attention from manufacturers.

Better Energy Systems, a UK company, has released a small, handheld charger that gives 20 minutes of talk time on a mobile phone for every hour of sunlight to which it is exposed, and Sunload, a German company, sells a range of bags fitted with thin six-watt solar panels that can charge a range of portable devices.

The story about Apple's patent for solar-powered devices originally appeared on the MacRumors website.

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