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Researchers from MIT's School of Architecture and Planning have designed a crowd farm, that is to say a special floor that collects the energy from a walking crowd. It could be very useful in places like metro stations:

A responsive sub-flooring system made up of blocks that depress slightly under the force of human steps would be installed beneath the station's main lobby.

Crowdfarming is producing energy from a moving crowd and its lost energy.

For more read full article on MIT site.