One of the benefits of most electric cars (and many hybrid cars) is regenerative braking – recovering the energy created from braking to charge the battery. It’s something that most petrol and diesel cars can’t do, and it allows electric cars to extend their range slightly.
Regenerative braking is something that electric trains have done for many years (indeed most electric passenger trains in the UK have regenerative braking), but it’s something that is probably new to car owners.
The first law of thermodynamics
If you’ve studied physics, you may be familiar with the first law of thermodynamics. This law dictates that energy can’t be destroyed and it can only be changed from one form to another. When you press the brake pedal to slow your car down, the energy from the brake force has to go somewhere.
On a internal combustion engine (ICE) car powered by petrol or diesel, your car will slow down by the friction created when your brake pads are pressed against your brake discs. The energy is therefore wasted as heat, and braking gradually wears your brake pads down over time.
Electric cars brake slightly differently. They still have brake discs and brake pads, but when you want to brake, the electric motor can work in reverse. The resultant kinetic energy can then be converted into electrical energy that is fed back into the battery, rather than being wasted as heat. From what I understand, this is done using magnets; if you think back to GCSE Science, you’ll remember that a magnet, combined with motion, produces electricity.
Additional range
That additional energy flowing back into the battery can therefore extend the range that your car can achieve on a full charge. We’ve actually noticed the charge level go up whilst driving downhill. An example is when we’re heading home from Manchester; to reach Sowerby Bridge, we exit the M62 at its summit point which is 372 metres above sea level, and descend around 300 metres. Typically, the charge goes up around 2% over the 8 miles from the M62 to Sowerby Bridge.
One thing to note is that your battery needs some capacity to accept the extra charge from regenerative braking. Therefore, if your car is 100% charged, there won’t be any regenerative charge. On our car, regenerative braking is limited above 80% charge.
Overall, depending on the types of roads, regenerative braking tends to add between 5 and 10% more range, which equates to between 7 and 14 miles. As well as allowing you to drive further on a full charge, it also saves a bit of money.
Reduced brake wear
Because you’re using the car’s electric motor to slow down, you should also find that your car’s brake pads and brake discs suffer less wear and tear. Again, this will save you money, as the discs and pads won’t need replacing as often as they would in an ICE car. It also reduces your car’s emissions; not only do electric cars not have any tailpipe emissions, but the particulate emissions from your brakes is also reduced compared to an equivalent ICE car.
How much regenerative braking your car will do, will depend on its mode. On our Nissan Leaf, in standard and eco driving modes, it will do a moderate amount of regenerative braking. But if we pop it into e-pedal mode, which is its one-pedal driving feature, the motor brakes more aggressively to regenerate more energy. We tend to keep it in e-pedal mode almost all of the time, although it’s of less use on motorways, for example.
Regenerative braking is a nice bonus feature of electric cars, and helps them be more efficient. It also adds to their lower maintenance costs, through lower brake wear. It’s certainly something to consider when weighing up whether to buy an electric or hybrid car.