I certainly am not considering electrified roads as a panacea. As a kid I rode many of the trolley cars around Pittsburgh. While the ozone created a sweet odor, the traffic problems created by overhead lines were substantial. We also should not downplay the problems with the current crop of batteries in EV cars. Fires, floods (especially saltwater), and the mining of rare materials cannot be ignored. I’m afraid the word is out among mischief makers that EV cars are a good target for arson.
Looking overall, it’s difficult to ignore the obvious problem of over-population—with everyone believing they have a valid reason to be traveling often and far. We need more reasons to be happy staying at home.
Do they use rare materials?
And something I don’t recall seeing addressed, not that I’ve gone out looking for it either, is how much of the battery can be recycled and reused (feasibly)?
RMI points out that trends between battery efficiency, recycling, more efficient vehicles and extended lifetimes point to peak demand for lithium being somewhere in the mid 2030s at about triple the current level, then descending to zero by 2050. The report gives a current number of recycled content of 90-94%, and presumes some increase of recycling efficiency over time.
IMHO they’re pretty optimistic about eliminating all losses post-consumer, so there’s going to be some mining of battery minerals even after the recycling “loop” is closed, and of course there will be more non-transport applications for batteries over time, but the report paints a pretty bright picture.
One thing it points out is that the total amount of lithium ore extracted to get to the “full recycling point” in their model is less than the tonnage of one year of oil extraction for fossil fuel-powered transport.
They also note associated minerals like cobalt and nickel, and show one graph that shows cobalt mineral demand (in excess of recycling) having already peaked (or possibly peaking this year).
It’s not actually that significant on a high-performing EV. It’s not like an ICE where you have to dump loads of gasoline and air into the cylinders to generate power.
Given an ideal circuit, the only losses due to EV acceleration are hitting wind resistance faster, which really isn’t a factor if you consider already travelling at the target speed.
Since we don’t have ideal circuits, the only real losses are heat which is a function of current and conductor size. Accelerating heats the conductors which is heat loss, but also to maintain the rate of acceleration means you pull more current to have the same useful current – the excess is heat again – until the point where you have to limit current and acceleration, or treat those conductors are fusible links.
All in all, it’s significant if you need every mile of range, and it’s significant in the math sense, but in the practical sense, there’s no real penalty to just flooring it at every opportunity, and certainly nowhere on the scale of an ICE.
There’s also the effect that using the friction brakes at all is a waste on an EV. You should be using regeneration almost all the time.
This isn’t directly affected by high acceleration, but the kind of person that drives between stoplights by flooring it and then slamming on the brakes will see an efficiency hit. If you floor it but still manage full regeneration, it’s not so bad.
I found my cmax fun and responsive, And also almost never used the friction brakes. Basically, they were there for emergency situations. Red light? I’ll stop entirely with regen.
I think a lot of people must enjoy cars with soggy handling.
In terms of cost per mile, flooring the accelerator on an electric vehicle is going to have more impact on the longevity of the tires than losses internal to the motor. And at least for mine electric cars (with cheap solar energy and high-end tires), the cost per mile is more tire than energy.
I’d challenge that … to heat “things” up electrically (so that you now have created a mass of - say - 20kg that is noticable warm/hot, that consumes a lot of energy, easily expressed in BTU (energy needed to heat 1L of water (your mass) by 1°C) …
Also, the Beukert effect is a real thing and your enemy (sloppily formulated: the more power you use from your battery (pedal to the metal) … the smaller your battery becomes, due to voltage sag) …
those are very real things, and you can’t just smart-engineer physics away - you can of course disguise those effects, by putting a very big battery in your system (that is the reason why rather modestly sized EVs weigh nearly 2 tons today).
I as one who uses light EVs to a great degree (e-scooters and e-bikes) know darn well, that when I run low on battery I rather walk the scooter up a short but very steep 200m incline on my way home and have energy for the remaining 5km that come after the incline… or I can power ride up the incline and use the energy in those 200m and then have to walk the scooter for the remaining 5km. That is your rate-of-exchange, so to speak.
tires are a - highly visual - issue, I’d even call them “EV-abuse-indicator” (but that’s a low/medium cost, low complexity “repair”) … your controller and (partially) your battery also take a good (thermal) hit for every 10 sec. where you floor it. Those are high cost / high complexity repairs.
Will those break? chances are, no … but then again, electronics thermally stressed/cycled many times per day … they might call it quits after some 10,000 cycles. A EV that is mostly driven “conservatively” might never see those thermal cycles, whereas a drive-it-like-you-stole-it EV might see a couple of 1000s of those cycles per year
I bow to your superior expertise. Thank you for the thorough explanation.
That’s also good news for me personally because once I do make the switch to an EV (probably my next car), it’ll get driven like it was stolen. Nice to know that won’t impact my range much.
Which raises a question. As mentioned in another thread I’ve recently been driving my GF’s Tesla. Which is my only EV experience. In one-pedal driving mode with your foot off the pedal is 100% of the retardation regeneration? Or is some friction blended in there?
My limited knowledge of diesel-electric locomotive design & operation is they largely rely on regen, but regen becomes ineffective at very low speeds (WAG <5-10mph) so they need to use friction to come to a halt. And regen is ineffective at holding position on an incline, so once stopped the friction brakes have to be applied.
How does that map to EV’s in general and Teslas in particular?
My Tesla Model 3 definitely applies friction brakes when the car is at a stop and no pedals are depressed. I can feel the slight stutter when pressing on the accelerator from a stop. I’m not sure if the friction brakes are applied before the complete stop.
Accelerating may not impact your range much, but driving fast does.
I rented an EV recently for a road trip (long story, but i needed a car and that was the only one they would give me) and driving at speed limit (70) on an interstate, it became clear that despite my driving considerably less than the “estimated range” when I’d charged it, i want going to make it to my destination. So i put it on cruise control at 55, and limped to my hotel with 16 miles to spare.
According to my “charging/discharging” gauge on my dash, I get heavy regeneration when I apply the brake. So even “friction brakes” somehow are connected to the regeneration.
I question that rate of acceleration has a negligible impact on energy consumption. For example, this guy tested aggressive versus mild acceleration over 30 miles and found aggressive dropped his charge from 80% to 33%, and slow acceleration dropped it from 80 to 40%. That’s obviously a small battery pack, but still, I think you’re fooling yourself if you think it doesn’t have an effect.
The short answer is to just use one-pedal driving as much as possible and not worry about it.
The longer answer is that, as you surmised, for low speeds the friction brakes get blended in at low speeds due to the regeneration being ineffective. But this isn’t a problem since there’s almost no kinetic energy left (due to KE=mv2). The KE at 5 mph is ~1% of 45 mph. And of course there’s no energy consumed by using the brakes at a stop.
The even longer answer is that you actually reclaim more energy per foot of stopping at high speeds vs. low due to various inefficiencies. So if you’re in the unusual situation where you’ve misjudged the stopping distance but have some flexibility in when you apply the friction brakes, you should wait as long as possible. Get as much regeneration done at high speed as possible.
But really that should be a rare occurrence and the difference is going to be minuscule. So in practice you should just use the friction brake in whatever way feels normal.
And as noted, using the friction brake doesn’t disable regeneration–it just applies some braking force on top of it. So it’s not some disaster if you have to use it, it’s just a degree of waste proportional to how much you use.
Thanks. I was more interested from the engineering end than the operator end. Which you covered nicely.
But as you say, the optimal operator technique is to plan your stopping around regen only and top that up with friction if & only if full regen is insufficient for the time / distance / speed remaining to impact / the stop line.
A recent study found that was not true, which surprised the researchers themselves. Most longevity testing was done with steady rates of discharge, because the testing can be done quickly. These researchers performed longer duration tests comparing steady rates of discharge with brief, high discharge rates, and then recharging a bit, to simulate acceleration, then regenerative braking. They found that the spiky discharge improved battery longevity over steady discharges.
Their interpretation is that normal stop and go driving, even with hard acceleration is better for the lifetime of the battery, than just steady discharging.
To be clear, by battery lifetime, I mean the service life of the battery, not how much range/energy is extracted from a single charge.
They also conclude that battery age is going to be a more important determinant of service life than number of charge cycles. My takeaway is, just drive the car, and don’t worry about it.
Some non-Teslas EVs do blend regeneration and braking, so that when you press the brake pedal, you may be getting only regeneration, depending on speed and how far the brake pedal is pressed. In Teslas, the brake pedal only applies the friction brake. However, because when you press the brake you are not pressing the accelerator, the car will also be under regenerative braking in almost all cases you are using the friction brakes.
I prefer this as a design principle. The brakes are the brakes, and aren’t trying to be too smart. If I press them, it means that I want to slow down badly enough to convert energy into waste heat, rather than save it for use later.
So put a few hundred miles of one pedal driving on the Tesla, and then go on a trip where you start the drive at a 100% charge. That first few miles with no regenerative braking will be startling.
My cmax didn’t do one pedal driving, but certainly did regenerative breaking. The car automagically figured out how much of each to apply. It worked great.
