Charge Your Phone By Walking

How much oomph is in your stride? Each step you take releases enough energy to light up a bulb, and rather than let it go to waste, SolePower stores the energy as usable electrical power

Developed by Matt Stanton and Hahna Alexander when they were students at Carnegie Mellon, the shoe insoles consist of similar parts as a mechanically-powered, hand crank flashlight. The duo initially designed the power-generating inserts to light an LED in the shoe for students walking to and from campus late at night.

The energy from each heel strike is converted into rotational energy that spins the small magnetic rotors, which then generate an electrical current within coils of wire. The electricity then travels along a cable into a lithium-ion polymer battery pack for storage. Small electronics can be charged through a USB port on the external battery pack, which is secured onto the shoelaces in a fabric holster.

Together with the external power pack, the device weighs less than five ounces. With the current version, a 15-mile hike can charge a smartphone, although the team is working on a design that can do the same in 5 miles and last about 100 million steps’ worth of wear and tear.

Other power-generating, in-shoe concepts exist. One idea out of University of Wisconsin-Madison, for example, relies on a technique called reverse electrowetting. This converts the energy of metal droplets (in the soles) into an electrical current. When the conductive liquid drops are compressed or sheared by the electrode layer on top, voltage is produced.

The all-weather, removable SolePower inserts can be cut to fit any shoe, and it would be especially useful for backpackers who don’t have room for extra juice packs or as backup for solar chargers on cloudy days and nights. The final product should be out later this year.