Regenerative braking is any technology which allows a vehicle to recapture and store part of the kinetic energy that would otherwise be 'lost' to heat when braking. A simpler technology that only converts the energy to heat but which 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 provided to be used when rapid, powerful braking is required. Estimates currently see 30% efficiency; however, the actual efficiency depends on numerous factors, such as the state of charge of the battery, how many wheels are equipped to use the regenerative braking system, and whether the topology used is parallel or series in nature.

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.

Hydraulic System

This is a patented system currently in development by Permo-Drive , a small Australian company. It is designed to replace the current exhaust braking system on trucks and boasts better efficiency, less noise as well as other benefits over exhaust braking.

The mechanism is attached to the driveshaft of the vehicle and when brakes are applied feeds energy into accumulators and is stored as hydraulic fluid under great pressure. The energy is then released again into the drive shaft when the vehicle is accelerating. This system is claimed to withhold up to 40% of the energy otherwise wasted in braking.