As electric cars firmly enter the mainstream, more and more debates are opening up about these vehicles and what they can and can’t do, which kinds of technology are best, which brands offer the best combinations of features, and more. Popular debates include recommendations on where to maintain daily battery charge, the pros and cons of autopilot and self-driving features, and also on one other key bit of tech: regenerative braking.
When it comes to regen braking, the main points of discussion are:
- Is regenerative braking really as effective as companies like Tesla claim?
- Is regenerative braking really a good alternative to simply coasting in the car in order to slow down?
In today’s blog, we want to focus our attention on the second question, and consider the ongoing debate between regen braking and coasting.
Background: What is Regenerative Braking?
In short, regenerative braking is a technology whereby excess energy is recaptured from the standard braking process whereby it is then turned into kinetic energy that is transferred back to the car’s main battery system. The idea first emerged in hybrid cars as a way of extending their overall electric range and allowing for even greater fuel efficiency. It has since become popular in battery electric vehicles, especially Tesla models, and the Nissan Leaf.
As time went on, the technology advanced even further to the point where the driver didn’t need to press on the brake pedal in order to activate the effect. Releasing the accelerator pedal would simply cause the electric motor to spin in the opposite direction automatically, and the car could apply the hydraulic brakes itself when it required the vehicle to come to a complete stop.
Some OEMs like Tesla and Nissan have been great champions of this technology, encouraging its use and in the case of Tesla even limiting driver options to ensure that it is used more (see further below for more on that). Others, however, have tended to offer regenerative braking, but have allowed much greater flexibility in its use.
In a regular gasoline car, people would use their gathered momentum to keep the car moving forward — albeit slowing continuously — instead of putting or keeping their foot on the gas pedal. This coasting has long been known as a fuel-saving method, and very useful when driving on highways, or when dealing with very slight forward downhill slopes. Let gravity do some of the work, right?
As it happens, the practice is continuing for electric cars, and the discussion about why is centered on the same issue: efficiency. So-called “hypermilers” are people who know how to maximize their EV range, and arguably the key weapon in their arsenal when trying to get this done is coasting. Coasting doesn’t work in quite the same way, depending on which kind of electric car you’re driving, but we’ll get more into that in the sections below.
Regen Braking Vs. Coasting – Which Is Better (Short Answer)
The simplest answer to the question is that if you need to slow the car and/or come to a complete stop more easily, then regenerative braking is the better choice. If, on the other hand, you are traveling at higher speeds and longer distances — on a highway, for example — with a lot less traffic around, then coasting options are better and overall more efficient when it comes to saving on wear and tear and saving battery energy.
Despite the apparently fierce debates that rage about this topic, it should be well understood that this is not a debate where one side is “good” and the other side is “bad” for you or your electric car. If regenerative braking were genuinely bad for electric vehicles, then it wouldn’t be in there, and the same goes for coasting. Both have clear pros and cons, but it’s still an important thing to understand what they are and therefore which would work best for your particular driving situation.
When Is it Best to Use Regen, and When Coasting?
The key to understanding this is to know the pros and cons of each, and most importantly the kinds of energy losses that occur when using regen versus when using coasting. There are three types of energy loss that you will experience regardless, whether you are coasting or using regenerative braking, namely:
- Frictional losses
- Rolling resistance
- Wind resistance
The reason that coasting is considered overall as the somewhat better option is the fact that when coasting, one only experiences these three types of energy loss. When using regenerative braking, however, there are some additional sources of energy loss on top of the above three, namely:
- Through the inverter
- Through the gearbox
- Through the battery
- Through the wire
So, when looking at the overall effect, it quickly becomes clear why it is that so many people do favor coasting as the best all-round energy-saving method when compared to regenerative braking. However, that doesn’t mean it’s always appropriate to use it. What even the most ardent supporters of coasting have to admit is that it really only works when you have the speed, momentum and physical space to do it. Highways are the best place, of course, where there are few times when you have to do any sharp braking at all.
And Regenerative Braking?
So, just as coasting is more useful when there is near to no sharp braking required on the part of the driver, regenerative braking covers the other end of that spectrum. In other words, when you are in an environment with a lot of stopping and starting required, or where distances between you and the car in front close quickly, then regenerative braking is the best solution.
Depending on its settings (see below), you can either have regenerative braking slow your car to as slow as 4- or 5-mph, before then slowing the last moment using your conventional brakes, or you can set it up so that it will slow the car in the same way but then apply the brakes for your automatically. Some don’t like it set up to that strength, so they might use it just to slow the car somewhat, but allow more time for the regenerative side of the system to work before the car stops.
The stronger settings allow for what is known as “one-pedal driving” and that’s certainly a great ally to have when you’re driving in heavy city traffic. It’s not necessarily so useful when you’re trying to maintain speed and momentum on the highway, however.
What Are the Pros and Cons of Regen and Coasting?
The Case for Regenerative Braking
Modern regenerative braking systems, however powerful they are in reality, are being installed in nearly all electric and hybrid vehicles, primarily for the clear safety and comfort advantage they offer to drivers. Most systems are adjustable, which means drivers can tailor automatic braking to their specific needs, and even change it mid journey.
The technology allows for full stops at safe distances from cars in front, and is actively creating energy to pass back to the battery. What’s more, it removes wear and tear from the brakes, allowing brake pads and discs to last longer. Gently lifting one’s foot also allows one to maintain a steady rate of regen when heading downhill, which allows one to maintain safe and appropriate speeds in all conditions.
The Case for Coasting
For those who drive on the highway, there’s really no substitute for coasting. It is the freest, most natural way to let the car run without draining excess energy, and makes for a steady, comfortable ride over greater distances. The sudden feeling of slowing when applying the regenerative brakes can be a bit disconcerting at times, especially when one naturally forgets to lift one’s foot off the pedal slowly, as is recommended.
So long as you are able to keep moving forwards without injecting more power, then coasting is the most efficient option to use, but it should be noted that at any point where one needs to apply to the brakes, regenerative is the better option.
Which EVs Allow for More Flexibility In Braking Vs. Coasting?
Most electric vehicles that come with regen braking as a standard feature include some measure of control over the strength of it. In fact, among the major EV players out there right now, Tesla is seemingly the only one (or at least in a very small minority) of companies that no longer offer any choice.
If you buy an MG electric car, Nissan Leaf, Mustang Mach-e, VW ID.4 — among others — you will have some measure of control over the strength and reactive power of your regenerative braking. One piece on CleanTechnica.com was particularly keen on the balance achieved by VW in their ID.4 electric crossover SUV.
When you set the ID.4 to “D” mode, there is more room for coasting, but when you set it to “B” mode it’s more geared towards regen. This is ideal for those who commute between different driving environments on a daily basis. The Mustang Mach-e also weakens the effects of regen depending on which of the driving modes you choose, from “Unbridled” down to “Engage” and then down to “Whisper” as the gentlest setting.
Tesla owners, on the other hand, were frustrated to find within the last 2 years that Tesla had removed this option from them permanently in a system update. They previously had a weak and strong mode (nothing in the middle), but before long the weaker version was removed, leaving Tesla drivers no choice but to use regen in its strongest form.
Tesla hasn’t openly commented on its reasons for this, but we speculate it’s all part of Tesla’s brand image of efficiency and range that prompts them to favor regenerative braking over coasting. They even go a long way to make their regen effects highly visible to the driver by including it as a blue bar that grows to the left of the screen when no more throttle (shown by a green bar to the right) is being applied.
Drivers of Tesla cars who want to coast have to either put the car in “Neutral” or hold the pedal steady at the point where the blue and green bars meet in the middle. Only then is the car “coasting” — not really the most relaxing experience.