Regenerative brakingthat allows a vehicle to recapture and store part of the kinetic energy that would ordinarily be lost when braking. A simpler technology that does not recover energy but uses similar principles is known as dynamic braking. Both are most commonly seen on electric or hybrid vehicles. Braking is accomplished by electrically switching motors to act as generators that convert motion into electricity instead of electricity into motion. Traditional friction based brakes must also be used to provide powerful response in rapid situations. Estimates currently see 30% efficiency.
Electric railway vehicles feed the recaptured energy back into the grid, while road vehicles store it for re-acceleration using flywheels, batteries or capacitors. Older dynamic brake systems generally used the electricity to provide heat or just passed it through large banks of resistors to dissipate the energy. New York City subways are about to see this installed.
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