What is Regenerative Braking and How Does It Work?

Rowan Harris 5 minutes Published: 14/10/2021

Driving an electric car is a little different to driving a petrol or diesel car. You’ll need to get used to electric car charging at home, planning longer journeys around charging stations, and brushing up on your electric car charging etiquette. 

There are also some key differences in the way that they handle. Regenerative braking is an innovative technology designed to make braking more efficient, but for those who have never driven a hybrid or an EV before, it might take a little getting used to. 

In this article we explain the ins and outs of regenerative braking, as well as the advantages and disadvantages of relying on these systems.

What is regenerative braking?

Regenerative braking is when kinetic energy from braking is transformed into electrical energy to power the electric battery of a hybrid or electric car.

How does regenerative braking work?

Moving cars have a lot of kinetic energy. But what happens when you brake? All of that energy has to go somewhere. 

In an internal combustion engine, we usually apply friction brakes. While these quickly bring the car to a standstill, they also produce a lot of waste heat energy which wears down our brake pads.

In an electric car, when you decelerate, power is no longer supplied to the electric motor. When the motor stops, it disengages and begins to run backwards. The motor doesn’t reverse the wheels as the transmission is still in Drive.

However, when an electric motor is used in reverse, it will begin to act as a generator, converting kinetic energy into electrical energy. This can then be stored in the battery and sent back to the motor when it’s needed.

Which cars have regenerative braking? 

The first car to boast regenerative braking was a concept car called the Amitron, which was unveiled by American Motors in 1967. Regenerative braking became more mainstream in 1997 with the launch of the original Toyota Prius.

Fast forward to 2021 and regenerative braking is now standard across most hybrid and electric vehicles. 

Hybrid cars, including Mild Hybrid Electric Vehicles (MHEV) and Plug-in Hybrid Electric Vehicles (PHEVs) rely on regenerative braking to recharge the battery, though the latter can also be recharged by plugging into a power outlet. The same is true of Battery Electric Vehicles (BEVs).

Regenerative braking is even used in some of the more conventional internal combustion engines. The Mazda 3 is built on what it calls the ‘M-Hybrid’ system. This isn’t used to drive the car but instead to power the onboard electrical equipment and enable smooth stop-start functionality.

How effective is regenerative braking?

How much of your day to day braking will be using regenerative braking? Well, according to Porsche, that figure could be as high as 90%! Unfortunately, 90% of the energy from braking can’t actually be recovered.

While the efficiency of regenerative braking will vary from vehicle to vehicle, it is usually between 60-70% of the kinetic energy that is recovered through regenerative braking. 

When a battery is fully charged however, it can’t accept any more charge so all regenerative braking power is wasted.

EV manufacturers actually advise that you keep your battery charged between 20-80% rather than fully charged to prolong the life of the battery, so this is another great reason to do so!

How does regenerative braking reduce pollution?

When people think of roadside traffic pollution, they probably think of exhaust pipes. But exhaust pipe emissions are only part of the story. 

According to one study, as much as 55% of roadside pollution is from non-exhaust emissions (NEE). Approximately 20% of all particulate pollution on the roadside comes from brake wear. Recent studies have shown the damaging effect this can have on our immune systems. 

As EVs become mainstream, it’s likely that we will shift our focus from reducing CO2 to cutting down on NEE. In busy urban areas where cars are forced to repeatedly stop and start, regenerative braking can play a big part in helping to reduce the amount of toxic particulate matter in the air. 

Does regenerative braking reduce brake wear and replacement frequency?

According to Elon Musk, the ‘brake pads on a Tesla literally never need to be replaced for the lifetime of the car’.

While Elon Musk could only get into so much detail in 140 characters, it’s worth providing a more nuanced answer here. 

Regenerative braking can reduce the amount of brake wear and the frequency with which you need to replace your brake pads, however, this is entirely dependent on how you drive and what strength of regenerative braking you use. 

Can I turn off regenerative braking?

Some manufactures allow you to set different levels of regenerative braking whilst others have one standard setting.

The Nissan Leaf provides three levels of regenerative braking. Nissan’s ‘e-Pedal’ feature is reserved for the most adventurous, providing strong regenerative braking for true one-pedal driving. 

Before October 2020, Tesla allowed you to switch between “standard” and “low” levels of regenerative braking, but now if you buy any Tesla Model 3, Tesla Model S or Tesla Model X built after June 2020, you won’t be allowed to choose. This is likely to boost range and reduce NEE.

Porsche has a blended braking system instead. The Porsche Taycan has mild lift-off regeneration, so the vehicle does not rapidly decelerate when you lift your foot off the pedal as is the case with ‘one pedal driving’ options. It is well-suited for the autobahn, so it coasts when not accelerating. 

Should I use regenerative braking in snow or ice?

Several new EV owners have expressed concern on forums that regenerative braking might lead to dangerously unpredictable driving in icy conditions. One EV owner even raised a class action lawsuit against Tesla after he lost control of his car and went off a mountain side. 

Because a car needs to ‘coast’ to a stop rather than suddenly brake when driving in icy conditions, it is advisable to either set the regenerative braking to a lower setting, or learn to feather the accelerator. 

Typically, because cold weather reduces the ability of the battery to accept charge, the regenerative braking effect will be greatly reduced regardless.

Conclusion

Regenerative braking is a great way to reduce the amount of energy that goes to waste when braking, improve a vehicle’s range, and cut down on harmful non-exhaust emissions. 

Although most cars offer a selection of regenerative braking ‘levels’ to choose from, Tesla’s recent decision to drop this feature suggests that regenerative braking is here for good and drivers are just going to have to get used to it.

To find out more about EV charging, check out our articles ‘how to charge an electric car’ and ‘how long does it take to charge an electric car’. Or, for a more technical overview, check out our post on EV charger types.