Although Apple has yet to release a solar-powered gadget, its engineers clearly see the potential for solar power in multitouch devices, such as the iPhone and iPad.

A recently surfaced patent application, spotted by Patently Apple, shows that Apple employees filed a patent for a technology to embed solar cells under the touch screens of handheld devices.

Creating a single "stack" that combines the sensors for a multitouch screen and solar cell frees up more surface area, according to the patent description. The patent, which was filed in September 2008, also calls for the use of "light channels" to direct light to a solar cell underneath a touch screen, potentially using a parabolic reflector.

One of the notable aspects of the patent application is that it can be applied to a range of gadgets and could lead to the use of a double-sided solar panel that absorbed light from both the top and a glass-covered backing.

In August of 2008, Apple engineers submitted another patent application relating to the electronics circuitry needed to use a solar cell embedded into a small device. That followed a more general patent application from 2006 called "Solar Cells on Portable Devices."

Standalone chargers for small electronics, including Apple gear, have been around for years. But embedding a solar cell into a device, with a power management system, is a far more challenging engineering job and it's still not clear that can be done without adding significantly to a gadget's cost.

In theory, a solar-powered device could use cells that harvest indoor light, rather than only direct sunlight.