But, alas, I've had some questions about regenerative braking from friends who are intrigued by the concept. I've certainly experienced it enough of it these past few weeks to discuss what it FEELS and ACTS like, but I needed to do some reading to understand how it actually WORKS.
Here are the basics.
Regenerative braking is used mainly by cars with electric motors (either full electric or hybrid) to redirect the energy generated by the braking process back into the battery by charging it during the braking process.
Even though traditional friction brakes work fine when it comes to stopping a car, they are very wasteful in terms of energy. Every time a driver of a fuel-burning car steps on the brake pedal, he or she claps down on the car's wheel's with the force of thousands of pounds of hydraulic pressure. There are different types of brake pads and systems used, but in any case, the vehicle slows down due to the forceful friction that's generated between the pads and discs (or in older cars, shoes and drums). The friction effectively turns kinetic energy (the energy the car possesses due to being in motion) into heat energy (increased particle movement) - sometimes with a lot of noise produced in the process - and the car, as a result, slows down.
As you can imagine, it takes quite a bit of fuel to create all that kinetic energy while the car is getting up to speed. This energy is completely wasted when the brakes turn it to heat.
Regenerative braking recaptures a portion of the kinetic energy, converts it to electricity, and reuses it to charge your battery.
I've seen this in action, actually. There have been a handful of times since owning my Volt when my estimated miles left on the battery, had just lowered by one, and then I did some creeping and braking due to traffic, and the miles went back up by one. And then I clapped with glee like a 2 year old, but that's another story.
Because regenerative braking turns energy into electricity, it is most useful in hybrid or electric vehicles, because of the simple fact that they have electric systems to which the energy can be returned. During normal operation, the electric motor draws power from the battery to power the vehicle. When the brake pedal is pressed, the electric motor is able to reverse the process and feed electricity back to the battery. This helps keep the battery charged without plugging it in or, in the case of a hybrid, using the alternator. The result: increased efficiency.
This is not a perpetual motion solution, however, as only about half of the energy that would be lose in a fully combustion driven car can be recovered using regenerative braking. The other half is still lost in the form of (mostly) heat. The battery discharging process is merely slowed. With current technology, it cannot be completely halted.
These are some of the electric and hybrid cars that currently use regenerative braking:
- Chevy Volt (obviously)
- Nissan Leaf
- Tesla Model S
- Toyota Prius
- Pretty much every EV/EREV/Hybrid out there
Interestingly, there are also some cars without electric motors that use similar technology, such as BMW's 5 and 6 series and a few others. These cars use modified systems that feed the electric regenerated into the electrical system of the car to power climate, entertainment, etc. This can conserve more gasoline for actual vehicle propulsion.
Regenerative brakes have limitations. They only work on the "drive wheels". So in a Volt, that's only the two front wheels. This is not enough braking force to stop the car under "panic" conditions like, someone darting out in front of you, or cutting you off. You need friction brakes as well. There is a limitation on regen also, as the battery can only store so much energy by design. Future designs may enable regenerative brakes to fully stop a vehicle, doing away with the need for (and weight of) a brake controller to keep track of which brake system is doing what, as well as the friction brakes themselves which can be quite heavy.
For those who don't have an EV, most have screens that show you when you are using battery and when you are regenerating. These are not actual photos I took (I try to limit my photography when driving) but rather, downloaded from Google images.
For now, we need two systems - and them's the brakes. Okay, enough puns for one day. Until next time, charge on!
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