Here's an energy source most of us haven't considered tapping: Wi-Fi wireless signals.
At CES 2010, RCA was showing a prototype of a handheld energy-harvesting battery designed to convert energy transmitted in a Wi-Fi signal into DC power, according to a report in OhGizmo.
The device, called the Airnergy, uses an antenna and circuitry to harvest the energy and an internal battery to store the electrical charge. A company representative told OhGizmo that they were able to charge a BlackBerry from 30 percent to full charge in about 90 minutes using the ambient Wi-Fi signal at CES, although the charge time varies depending on how close the battery is to the original signal.
The goal is to have a product that's smaller than a smartphone and has a mini USB port in the market this summer in the range of $40 to $50. Next year, RCA would like to integrate the energy harvesting into a battery that could act as a replacement for cell phone batteries for the same cost as a replacement, a company executive said in the interview. There is no additional information on the Airnergy on RCA's Web site.
There are a number of energy-harvesting technologies, but none have been able to successfully free people from the power cords of their cell phones and music players. The challenge is often getting a sufficient amount of energy. One company,, set out to build motion-powered chargers for small devices but never fully succeeded and its assets were sold to a new investor.