An engineer from Nokia’s UK research labs says that the company is developing technology that can harvest ambient electromagnetic radiation to keep a cellphone going. The device works on the same principles as a crystal radio set or radio frequency identification (RFID) tag: by converting electromagnetic waves into an electrical signal.  TThe group is working towards a prototype that could harvest up to 50 milliwatts of power–enough to slowly recharge a phone that is switched off. He says current prototypes can harvest 3 to 5 milliwatts.

Other researchers have developed devices that can harvest more modest power from select frequencies. A team from Intel previously developed a compact sensor capable of drawing 6 microwatts from a 1.0-megawatt TV antenna 4.1 kilometers away.

I would say it is possible to put this into a product within three to four years. Ultimately Nokia plans to use the technology in conjunction with other energy-harvesting approaches, such as solar cells embedded into the outer casing of the handset.

Source :Technology Review – Wireless Power Harvesting for Cell Phones