Using the power of the sun to generate electricity is something that is in use in some commercial products already. Lots of research is being put into making more efficient solar panels to enable us to harvest more of the suns free energy for all sorts of devices.
Researchers at the University of Pennsylvania have unveiled the world's first circuit that can be powered by light. Right now, the amount of power the circuits generate is far from enough to power consumer electronic devices, but the researchers believe that may change.
As technology improves, the researchers see the devices being able to power all manner of electric devices and serve other purposes as well. If the researchers can get more than the 10% of the photovoltaic cells on a slide to work, they could generate more power. In the future a one amp, one volt circuit could measure the diameter of a human hair and only an inch long.