"The Sainsbury's in Gloucester, which opened in June 2009, has several kinetic energy plates installed in their parking lot. Each time a car drives over the plates, the motion of the plate creates energy. The energy is then stored and sent to the store to provide power to the checkout stations. Sainsburys says that the plates can supply 30 kWh of energy per hour."
Used instead of speed-bumps, energy that would just have been lost is harvested.