Regenerative braking or regen braking is a great technological solution with greater limits than you might think.
Regenerative braking has been a key part of electric mobility for decades – as far back as the first commercially available hybrid vehicles. The principle is quite straightforward and elegant – an electric motor can convert electrical energy into kinetic energy to move the wheels – regenerative braking essentially reverses this. The kinetic energy of the wheels is converted back into electrical energy using the motor as a sort of dynamo.
While regenerative braking has been used in pure petrol vehicles (recall the ‘Charge’ meter on recent BMW vehicles), the effectiveness here is secondary. Usually what happens is the recovered energy is used to relieve the internal combustion engine of driving the alternator. This reduces losses and just improves the overall efficiency of the engine, but it’s a bit tough to accurately tell how much fuel you’re saving.
Regen braking is even more relevant to electrified vehicles that use the battery to drive the wheels, but don’t let anyone tell you that it’s more effective than it actually is. We recently came across this tweet that accurately said that regenerative braking “charge the battery”. The impression one might get here is that regenerative braking is puts all the energy back into the battery and that’s far from correct.
The first is that Regenerative Braking does not fully recover all the energy spent getting the car up to speed or up a hill. No machine can be 100% efficient either, so there are losses there too.
The second problem is that the car’s battery is also running loads of other electrical components. The air conditioning, interior and exterior lighting, sound system, data connection, displays, massage seats, wipers… These system use energy that just don’t get recaptured. Interestingly, the petrol (and some earlier hybrid) cars that had regen braking would use the recovered energy to power these items.
So how much does Regenerative Braking help? Electrek did some research in 2018 and found that the upper limit on a Model S was around 32% but the average was around 15-20%. There are more recent studies, but in Malaysian weather the amount of energy recovered probably is outweighed by how much power is drawn by the air conditioning system. In fact, Porsche’s Taycan page has a range calculator that shows the effect of air conditioning on range. We set the slider to full city driving to simulate higher traffic and here’s what we got:
Air conditioning in this instance cuts range by over 100km, or 30%. Even in the most ideal regenerative braking scenario it’s just the air conditioner’s energy requirements that are being met. There’s also evidence that suggests that regenerative braking is even less effective at lower speeds.
Conclusion
Regenerative braking is elegant and a no-brainer in all electrified vehicles. It dramatically reduces wear and tear on your brake pads, it reduces wasted energy and overall does add some range to your EV in certain scenarios. It’s better to have it than not, no question. Every time I take an electric test car I set the regen braking to its maximum level instinctively. However, the public should be aware that it’s not some miracle technology that minimizes the need for a robust public charging infrastructure.
