A pair of MIT graduate architecture students are proposing a novel, almost carbon-free way to generate electricity. In crowded buildings and malls when thousands of people are walking around, every step they take puts mechanical energy into the floor. They want to harness that energy by building in a generating system tied to the vibrations of the floor. As people move around the individual energy is small but when aggregated it could potentially produce a significant amount of power.
A system like this wouldn't be practical to retro-fit but if built into new buildings it could reduce the amount of outside power required. Perhaps if they had parking spaces with plugs tied the system, shoppers could recharge their vehicles while they shop.