Regenerative Braking in Electric Vehicles

In a conventional car, braking wastes almost all of the vehicle's kinetic energy, converting it into heat through friction between the brake pads and the rotors, energy that simply disperses into the air and is gone for good. Electric and hybrid vehicles recover a substantial portion of that energy instead, through a system called regenerative braking, which relies on a property most electric motors already have built in: the same motor that spins the wheels to accelerate the car can also, when driven in reverse, function as a generator. When the driver lifts off the accelerator or presses the brake pedal, the vehicle's control system reverses the role of the motor, using the wheels' own momentum to spin it rather than using electricity to spin the wheels. A spinning generator resists being turned, and that resistance is what actually slows the car down, converting the vehicle's kinetic energy into electrical current instead of wasted heat. That recovered electricity is routed back into the vehicle's battery, meaning energy that would otherwise be lost during ordinary braking is captured and made available again for the next acceleration. Regenerative braking alone typically can't bring a vehicle to a complete stop, since the motor's braking resistance weakens as the car slows toward very low speeds, which is why most electric vehicles still include conventional friction brakes as a backup for the final stretch of stopping and for emergency braking. The amount of energy recovered varies considerably depending on driving conditions, with stop-and-go city driving offering far more opportunities to recover energy than steady highway cruising, where the brakes are used only occasionally.