Harvesting Energy from Human Movement
Piezoelectricity is electrical energy produced from mechanical pressure (including motions such as walking). When pressure is applied to an object, a negative charge is produced on the expanded side and a positive charge on the compressed side. Once the pressure is relieved, electrical current flows across the material.
Let's look at how the principle works in a motion such as walking. A single footstep causes pressure when the foot hits the floor. When the flooring is engineered with piezoelectric technology, the electrical charge produced by that pressure is captured by floor sensors, converted to an electrical charge by piezo materials (usually in the form of crystals or ceramics), then stored and used as a power source.
In 2007, two MIT graduate students proposed the idea of installing piezoelectric flooring in urban areas. Dubbed "Crowd Farming," the idea was to install a flooring system that would take advantage of piezoelectric principles by harvesting power from footsteps in crowded places such as train stations, malls, concerts and anywhere where large groups of people move. The key is the crowd: One footstep can only provide enough electrical current to light two 60-watt bulbs for one second, but the greater the number of people walking across the piezoelectric floor, the greater amounts of power produced. It's not beyond the realm of possibility -- approximately 28,500 footsteps generate energy to power a train for one second [source: Christian Science Monitor]. Imagine what the combined power of commuters' footsteps during rush hour could do.
Recently piezoelectric floors have debuted in a handful of innovative dance clubs around the world. These floors represent prototypes of the "Crowd Farm" concept: The movement of a large group of clubbers dancing on energy-capturing floors is collected and used to power LED lights and, in the long-term plan, feed energy into the club's power grid.
The principles of piezoelectricity have been understood since the 19th century but the application in energy-generating floors hasn't yet proven to be a substantial power source. In trials outside of the clubs, a "smart home" student housing experiment at Duke University ditched the idea of installing a piezoelectric floor when the high installation costs and nominal amount of power produced got in the way. In the clubs, initial estimates suggest an individual clubgoer could generate roughly 5 to 10 watts, and on a night where the dance floor is packed with moving bodies, the energy from the floor could supply about 60 percent of the club's total energy needs [source: Daily Mail]. Enough to save us from the world's energy crisis? Not yet.