nPower PEG Personal Power Generator

[CES 2011] The Personal Power Generator blends a funky concept, with an interesting technology: it harvests the Kinetic Energy that your walking motion generates and feeds it back to your gadgets. The result may vary depending on just how much juice you need. For instance, nPower PEG says that a typical one minute of walk can generate enough energy to power an iPod nano for one minute (not bad, right?), making it “neutral” at that point. Powering a smartphone is a different problem altogether, and is estimated to require 15X more kinetic energy. I’ll leave it to you to estimate how useful the Personal Power Generator can be to you, but I’m much more interested by its clean design than by the electricity  that it can build-up. By the way, the device itself is quite big, so… what’s the energy needed to carry it around?