TIME's Best Inventions of 2008

Correction Appended: October 30, 2008

Wasting energy is so 20th century. Power is all around us, if we just know how to use it. That's what motivated Max Donelan, a kinesiologist at Simon Fraser University, to invent a device that harnesses the energy of walking. The 3.5-lb. device wraps around the wearer's knee and generates power using the same principle that allows hybrid cars to recycle energy created by braking. A walker wearing harvesters on both knees could generate about five watts of power — enough to charge 10 cell phones — without hampering his or her stride. Donelan's device is perhaps the most promising in a class of products that harvest energy — all the more important at a time when portable tech, from Blackberries to iPods, is becoming ubiquitous. There's not a watt to waste.

The original version of this article misidentifed the device invented by Max Donelan as a Biochemical Energy Harvester when it is in fact a Biomechanical Energy Harvester.