a biologist at the University of Pennsylvania has led the development of a backpack that can generate around 7 watts of electricity, without solar cells, and actually providing a more comfortable backpack in the process.
Seven watts is sufficient to power a handful of electronic gadgets at the same time, including a cell phone, an MP3 player, a handheld computer and a water purifier
Taking advantage of vertical motion, much like some wave generators, the backpack harnesses body movements while hiking. The spring mechanism involved appears to ‘cushion’ the movement of the backpack on the wearer, leaving those who have tried it saying it is more comfortable then standard gear.
The net weight gain of the device only appears to be a few ounces.