What is regenerative braking

Regenerative braking is the process that takes place when decelerating or braking in an electric or hybrid car, as it uses the kinetic energy that would otherwise be lost and turns it into electricity that is stored in the batteries. Not all hybrid cars sport regenerative braking, though, but from the ones that we've tested so far, they all feature some sort of regenerative braking.

Regenerative braking works as the electric motor can turn clockwise, as well as clockwise, one direction when it's actioning the wheels and moving the vehicle and the opposite when you take the foot of the accelerator. In that moment, the electric motor acts like a generator and it is able to create electricity, which would otherwise be wasted.

Regenerative braking is more efficient than traditional braking, which applies physical force on the disks or the drums via the pads in order to slow the vehicle to a standstill, generating heat in the process.

Technically speaking, regenerative braking is not as strong as traditional braking, meaning that in case of an emergency, the braking pads will still be run up against the disks to slow down the vehicle faster. But, for regular braking situations, when you can predict the traffic, such as when slowing down to an upcoming intersection, regenerative braking can provide more than enough slowing force.

Different types of regenerative braking on hybrid cars

On a technical level, regenerative braking is the same across the board as far as the principle of function is concerned, but there are differences on how this feature actually works, depending on what type of battery-electric vehicle you drive, how old or new it is, as well as how expensive it is.

To start with the basics, mild hybrids are the least-powerful electrified type of vehicles, sporting electric motors that can vary in terms of power from just a few horsepower to about 30 HP. This means that when you lift off the accelerator and the electric motor spins backwards, it is able to generate a limited amount of power.

However, it is worth noting that the limited regenerative capacity will be more than enough, as the traction battery in this kind of a car is fairly small, usually below 1 kWh.

Then we have full hybrids and plug-in hybrids, which come with more powerful electric motors, as well as with larger batteries. Full hybrid cars, which are becoming pretty common these days, sport battery cells that are between 1 and 2 kWh in size, plenty to deliver a few consecutive accelerations and usually, the voltage of the battery is way higher to deliver the required power.

To put things into perspective, the voltage of a mild hybrid car is rated between 12 and 48 volts, while for full hybrids, it raises to around 150V, depending on the car, while the power of the electric motor also increases up to 100 HP on the latter.

Given that, full hybrids can also benefit from an additional regenerative capacity, depending on the manufacturer. So, from what I've tested so far, Renault full hybrid cars offer paddles behind the steering wheels, which can adjust the level of regeneration, depending on how strong you want it to be. Note that a stronger regeneration means that the car will decelerate faster, but will also recuperate more energy.

Other full hybrids also come with a standard level of regeneration, such as the Dacia Duster or Bigster, which can't have their regeneration adjusted, but rather turned on or off via the gear selector.

For plug-in hybrid cars is more or less the same as for full hybrids, with the mention that the battery is way larger, between 15 and 25 kWh generally speaking. This means that, although the regeneration can be adjusted to reach higher values, the amount of electricity stored in the batteries will be limited and for a full charge you will need to plug the vehicle in, as the name suggests.

As an example, for me, using the strong regenerative braking on Renault hybrids, I am usually able to charge nearly half of the battery after a couple intersections, without the petrol engine running.

Regenerative braking on fully electric cars

For EVs, the situation might not be as straightforward as you may think, as there are a few technologies that make EVs even more efficient when it comes to regenerative braking.

Firstly, there's a form of regenerative braking on most EVs, at least those from big brands. And that's because these vehicles have larger batteries, generally speaking, compared to even plug-in hybrids, as well as more powerful electric motors running at higher voltages from the batteries.

From what I've tested so far, Mercedes-Benz offers the most aggressive form of regenerative braking on the electric EQE, which can recuperate as much as 100 kW of power when engaged in the strong regeneration mode, while on normal recuperation, the regeneration rate is lower, although I can't offer exact numbers. There's a coasting mode, which basically disables regeneration but that will drastically lower the range and the intelligent recuperation will use the car's integrated cameras and radar to read the traffic and apply braking force accordingly.

This is a very interesting system, which I also tested on the MINI Aceman, as it basically enables the car to coast when you take the foot off the accelerator and it will start to slow when approaching traffic or even a traffic light. The braking force is adapted depending on how fast you are approaching ongoing traffic and the speed of the vehicle in front of you.

Generally, it does a great job anticipating the flow of the traffic and offers a smooth and safe ride in both cars that I tested the system, but the energy efficiency isn't the best, since it may not engage often or will not apply sufficient braking force to recover significant amounts of energy.

Still, it's a great middle ground for those that want to test it and drive according to the car's own perception, but as with every automation, external factors can and will affect its accuracy.

Two of the EVs that I've tested, namely the Dacia Spring and the Renault 5 E-Tech offer a B more, which means that the car will apply a standard regenerative braking, which can't be adjusted through the paddles.

The standard recuperation rate in both these cases is 20 kW, which is decent, as the batteries aren't huge, but the braking isn't very strong and you might find that you need to press the braking pedal yourself to slow down more, at least until you get used to the system.

Some EVs, as the MINI Aceman, enable one-pedal-driving thanks to the fact that the car can come to a full stop using the regenerative braking system, which isn't the case for the other cars that we've tested so far.

Regenerating braking advantages and downsides

The main advantage of regenerative braking is that this system allows you to recover the kinetic energy that will otherwise go to waste, prolonging the range of your car with no additional cost.

The second benefit of this system is that it will also make your braking pads and disks run for longer, as for most of the braking situations you won't use the hydraulic system, thus reducing the mechanical stress these components are subjected to. So, longer range and lower maintenance costs in the long run.

A third advantage is that you will become more aware of the traffic conditions and you will learn to better predict what's going on in front of you, making you a safer driver overall. For this to happen, you have to constantly use this system and stay consistent with regards to its settings, so either normal or strong recuperation to get used to it properly.

For hybrid cars, the advantage is that the fuel economy will improve, given that the combustion engine will have to work less in order to charge the battery.

As a bonus benefit, regenerative braking can be a sustainable way of driving, as less frequent repairs on the braking system means that we can better conserve our limited resources.

The drawback with this energy recuperation system is that it's not very effective at lower speeds and in the case of rush hour traffic it's nearly useless, as the speed isn't high enough to generate the required kinetic energy to generate enough electricity. This is because below 15 km/h or so, regenerative braking is disabled on most EVs to enable the car to coast at these crawling speeds, unless one-pedal-driving mode is enabled. This will bring the car to a standstill, but without much benefit to regeneration.

Another disadvantage is that this system doesn't provide a lot of braking force in some cases, unless your car has an aggressive recuperation mode like on the Mercedes EQE, which uses quite a bit of force to regenerate those 100 kW. This means that in an emergency, you will have to resort to using the brake pedal yourself, using the car's hydraulic braking system.