If a conventional vehicle decelerates, a large part of the kinetic energy is converted to heat by the friction brake and emitted into the environment without being used.
Hybrid and electric vehicles can recuperate some of the kinetic energy. When braking in a hybrid or electric vehicle, the electric motor switches to generator mode. The wheels transfer kinetic energy via the drivetrain to the generator. The generator turns in a similar way to a bicycle light generator transforming part of the kinetic energy into electrical energy, which is then stored in a high-voltage battery. At the same time, generator resistance produced from the electricity created, slows the vehicle. When more braking torque is required than the generator alone can provide, additional braking is accomplished by friction brakes. The electrical energy stored in the vehicle’s high-voltage battery is available to the electric motor to be used for driving off or accelerating.
In many cases, the generator's braking power is sufficient to slow the vehicle as desired by the driver. The friction brake is used less often, for example, for very rapid deceleration, at very low speeds and when stationary.
Regenerative braking contributes toward increasing the range of electrical vehicles. It helps to save fuel in hybrid vehicles and to reduce emissions of CO2 and pollutants, particularly in urban traffic situations involving frequent braking and acceleration. In addition, using the generator for braking also reduces brake wear and the build-up of brake dust.