What's better than green power? People power, say some forward-thinking engineers. Daily movements like footsteps generate pressure as we walk, and though that vibratory energy may be fairly low-wattage (about eight, to be exact), when you take the aggregate energy expenditure of, say, 30,000 people moving through a crowded train station, that's a significant amount of power.

That's exactly what a London-based architecture firm called The Facility is proposing: new floors, staircases and other surfaces that are equipped with hydraulic generators and can harvest "people power." What kind of power are we talking about here? "Enough to power all of the lighting and audio equipment within the building and beyond," says Claire Price, the firm's director -- or about 6,500 60-watt LED lights per 30,000 people. Their new energy-harvesting "Pacesetter" staircase will appear in South London tube stations sometime in 2007, and if all goes well, further innovations are yet to come.

The possibilities are seemingly endless, from generators under roadways and sidewalks, at gyms and even inside the fabric of clothing. Think of it as the ultimate form of recycling.