Regenerative braking is one of the key technologies that makes electric and hybrid cars so much more efficient than their gasoline predecessors. It is an intelligent system that captures energy that would otherwise be lost as useless heat during deceleration and converts it into additional kilometers of range. In practice, it’s a win-win situation – efficiency increases, brake life is extended and the impact on the environment is reduced.
Dual role of the electric motor
The heart of the regenerative braking system lies in the dual nature of the electric motor. When you press the gas pedal, it works like a motor, that is, it uses electricity from the battery to move the wheels and accelerate the vehicle. But the moment you take your foot off the gas or lightly press the brake, technological magic happens. The control electronics reverse its function and the motor becomes a generator.
In this mode, the kinetic energy of turning the wheel now drives the motor, which creates magnetic resistance. That resistance is what you feel as the vehicle slowing down. Instead of this movement energy being dissipated by the friction of discs and plates, the generator converts it back into electrical energy and sends it to a high-voltage battery via an inverter.
Modern cars use sophisticated “brake blending” systems that combine regenerative and classic hydraulic braking imperceptibly for the driver. During slight deceleration, the vehicle will use only the engine, while the mechanical brakes will be activated during a sudden stop, at speeds lower than about 10 kilometers per hour or in situations where regeneration is limited.
How much energy is really returned to the battery?
Although the process of converting energy from kinetic to electric is extremely efficient, with an efficiency ranging between 60 and 70 percent, the actual energy recovery during driving depends on a number of factors. The driving style and the environment are the most important. In city driving, with frequent starts and stops, regenerative braking comes to its full potential and can return between 15 and 30 percent of the total energy consumed.
Data from the US Department of Energy suggest that the average combined cycle return is about 22 percent. On the other hand, on the highway, where you drive at a constant speed, braking is rare and energy recovery is minimal, often below five percent. The greatest potential lies in driving downhill. On long downhills, heavier electric cars can generate significant amounts of power, almost as if they were plugged into a slow charger.
However, it is important to dispel a common myth: although recuperation is useful, it is always more energy efficient to maintain speed (the so-called “coasting“) rather than slowing down and accelerating again. Regeneration is superior only to the use of conventional brakes when deceleration is unavoidable.
Driving with one pedal and optimal use
Car manufacturers have different philosophies about how a driver should manage regeneration. Some, like Tesla, integrate powerful regenerative braking as soon as the gas pedal is released, while others, like Porsche, prefer the car to “sail” freely to take advantage of inertia, mixing regeneration with pressing the brake pedal.
Most modern electric vehicles also offer the driver the ability to adjust the intensity of regenerative braking. The strongest level often enables so-called single-pedal driving (one-pedal driving). In this mode, the car decelerates so strongly by releasing the gas that in city traffic the brake almost does not need to be used. This makes driving in traffic more fluid and less tiring.
For maximum reach, traffic prediction is key. Instead of braking suddenly at a traffic light, it is recommended to release the gas earlier and let the engine do its thing. Limitations should also be kept in mind – regeneration is weaker or completely turned off when the battery is charged to 100 percent (because the energy has nowhere to go) or when it is extremely cold.