BEVs

[Biospace]

Regen braking - part of what makes a BEV so energy efficient?

Consider a typical urban driving scenario from one set of traffic lights to the next, with half a mile between them, stopping at each and cruising at 40mph between them. It's a situation where BEVs are very efficient and a situation in which regen braking would be working well, let's say 50% efficient after losses - it would be more from much higher speeds, but then of course more energy would be wasted.

Imagine a 1.9tonne BEV - perhaps a Hyundai Ioniq - with 50% efficient regen after losses compared with a 1.1tonne BEV - the same weight as some BMW i3s - but with no regen braking, each carrying 100kg of driver and shopping. Would the lighter car use more energy, the same as, or more than the car with regen brakes?

[[XAP]Bob]

Heavy isn't the only variable - though it will overall increase consumption.
You also have to factor in aero design, tyre choices, tyre pressures, road surfaces, weather...

But if you look at the leaf data, or the tesla semi data, above... any extended regen means that you get back virtually all the available energy - the basic efficiency of regen is high, very high; but it doesn't reclaim the energy cost of actually moving (i.e. the aero, friction, and deformation losses).

Assuming two otherwise identical vehicles then the half mile of additional rolling resistance (we can ignore aero since the vehicles are identical) will be approximately proportional to the mass of the vehicle, but remains relatively small compared with the energy required to accelerate and decelerate even the smaller vehicle.
Let's assume a target speed of 30mph (13.5m/s), and an efficiency of 4m/kWh for comparison:

- Energy to accelerate a 1 ton vehicle: 1/2 * 1000^2 * 13.5 = 6.7MJ (1.8kWh)
- Energy to move ~.5 of a mile at 4m/kWh is ~0.12kWh (and that's all the losses, not just the mass dependent losses)

The acceleration takes ten times as much energy (twenty times as much for a two ton vehicle) as the journey, and the deceleration makes that same energy available. To not even try to reclaim that energy is *completely bonkers*.

UK average fuel economy (petrol) is somewhere under 40mpg, and petrol contains a little over 30kWh/gallon.
That's ~1.3m/kWh, or about .65kWh ignoring the acceleration, so for a 1 ton vehicle it's ~2.5kWh for the half mile stretch, most of which ends up heating the brakes. An EV without regen would do about the same... it would save .5kWh in terms of the energy cost of moving, but that's all.

With regen - the EV will claw back most of that 1.8kWh... let's be pessimistic and say it only gets 80% of it - that's taken a 2.5kWh ICE cost down to 2kWh just by replacing the drivetrain with electric motors, then down to 0.5kWh by actually using that drivetrain properly.


(PS: Yes, I know that average economy in both cases already accounts for some of the acceleration etc)

[Carlton green]

I’d be glad of some Leaf data, maybe some really good stuff is hidden in this thread but it’s lost to me. I’d also be glad of data on the Zoe too, one might just fit my needs.

[Biospace]

I’d be glad of some Leaf data, maybe some really good stuff is hidden in this thread but it’s lost to me. I’d also be glad of data on the Zoe too, one might just fit my needs.

What is it you're looking for? There are Leaf users active in this thread, I've driven a Zoe for a good few miles...

...
With regen - the EV will claw back most of that 1.8kWh... let's be pessimistic and say it only gets 80% of it
...

I was wondering what people might expect for comparative energy use two BEVs, one weighing 1.1t (like an i3) but with no regenerative braking and the other 1.9t (mid-size BEV) with regen.

Do you have personal experience of 80% efficiency being a real-world figure, after round trip losses - or links to several sources suggesting this? I'm typically finding 70% as a best possible realistic figure in Tesla chatter, which are generally reckoned to be the most efficient in these respects.

I'm aware the definition of regen brake efficiency can be that of simply recharging the battery under braking, but for these calculations do we not need to consider the round trip figure? As in 0.92 wheels to motor * 0.94 on the motor * 0.95 battery (round trip in and out) * 0.94 motor * 0.92 motor to wheels = 0.71.

[[XAP]Bob]

I'm looking at efficiency as a "possible" efficiency.
It takes a certain amount of energy to move a distance at a speed, and that's unrelated to, for instance, distance climbed. There is also a cost to climbing based on work done against gravity, but that's perfectly returned by gravity on the way down (given some assumptions about smooth paths etc) - if we can capture it.

The figures upthread for the leaf and the tesla semi both indicate that the round trip up and down a mountain does very little to affect the range of an EV, despite the reported range being *seriously* hammered on the way up each time.
Obviously if you start at the top then you need to make sure you don't fill the battery before you start, else you can't capture any more energy.

My experience, and that of others I know well, is that I get worse milage as I traverse Cornwall than across flatter bits of the country getting there, however something like crossing the Cotswolds has almost no impact despite the range dropping like a stone on the way up.
That's the difference between going up, along and down (which is highly efficient) and going up, down, up, down, up, down, up, down, up, down, up, down, up, down... etc - where the losses add up each time. It's still far more efficient than doing the same in a vehicle without regen, but the sheer count of cycles has an impact, on an individual cycle the efficiency appears to be higher than I would have anticipated.
That might be partly because on the way down a slope you aren't actually using all that energy to charge the battery, some of it is used with almost perfect efficiency to keep the wheels spinning and push the air out of the way (i.e. you aren't spending the energy that the distance normally costs you - that's energy that doesn't go through the drivetrain at all).

[Carlton green]

I’d be glad of some Leaf data, maybe some really good stuff is hidden in this thread but it’s lost to me. I’d also be glad of data on the Zoe too, one might just fit my needs.

What is it you're looking for? There are Leaf users active in this thread, I've driven a Zoe for a good few miles...

For the Leaf, and in support of this thread, I was looking towards regeneration efficiency measurements that were less anecdotal and more rigourous. For the Zoe it’s a case of I don’t know what I don’t know … and there’s a lot to know or at least have some understanding of what you need to find out. I’d been considering a Gen 2 Leaf but really it’s a bit too big for my local roads, etc., and the range (when needed) is marginal on what I’d be comfortable with. The Zoe is just that bit more compact and has a slightly better range; what the Zoe’s battery repairability is I’m uncertain and likewise the rest of the car. Renault seem to like to tie their customers into expensive franchised repairers too …

[UpWrong]

I've been watching some of the Electric Viking videos. He certainly lives and breathes EVs. The latest from him claims that CATL have got there with solid-state battery development. He seems confident about it. He starts of by mentioning 2026 for use in (prototype?) cars, but later mentions 2027 for large-scale manufacturing and sales, in premium cars at first.

He suggests double the energy density with double the recharging speed compared with CATL's best LFP offerings for these sulfide solid-state batteries.

[Biospace]

I've been watching some of the Electric Viking videos.
...

Thanks for that, it would seem to confirm what Toyota has been suggesting. If correct, there will likely be some bargain BEVs in another few years time when those who must have the latest thing replace their "ancient tech" battery cars with the newer variety.

For the Leaf, and in support of this thread, I was looking towards regeneration efficiency measurements that were less anecdotal and more rigourous. For the Zoe it’s a case of I don’t know what I don’t know … and there’s a lot to know or at least have some understanding of what you need to find out. I’d been considering a Gen 2 Leaf but really it’s a bit too big for my local roads, etc., and the range (when needed) is marginal on what I’d be comfortable with. The Zoe is just that bit more compact and has a slightly better range; what the Zoe’s battery repairability is I’m uncertain and likewise the rest of the car. Renault seem to like to tie their customers into expensive franchised repairers too …

Some Zoes have leased batteries, some don't - in general, it's the earlier cars which are more likely to have a battery which is leased. Here's one for sale which does not have a leased battery, https://www.ebay.co.uk/itm/156502414058

I've driven both, they're both good but the French car would be my preference if driving experience alone was the deciding factor. Earlier models for both have air cooling which imo isn't as large a problem as the pub pundit would like to suggest - as cars age, simplicity will come into its own - a failing liquid cooling system could cause damage to the wallet!

Braking regeneration efficiency figures are perhaps not quite as important as can be made out, regen may typically improve the overall range by 10% depending on conditions so the difference between maximum potential figures of 50% or 70% is not going to have very much difference on overall range. As always, it's more efficient not to use brakes unnecessarily, or to have a lighter car.

[UpWrong]

I've been watching some of the Electric Viking videos.
...

Thanks for that, it would seem to confirm what Toyota has been suggesting. If correct, there will likely be some bargain BEVs in another few years time when those who must have the latest thing replace their "ancient tech" battery cars with the newer variety.

Maybe, it depends on the price of cars with solid-state batteries and it will take a while before such cars are available to buy on the used market. A reasonable guess might be solid-state appearing in budget new cars in 2030, and being available at good discounts 3 years later. Which does at least fit with the timeline of banning new ICE cars. This all depends on the UK/EU not shoving massive tarrifs on the superior Chinese EVs.

[Biospace]

I was left wondering just whether a Dacia Spring will be up to the cut and thrust of many British driving conditions having watched the latest "Fully Charged Show" video. RL said this: "This feels like a light car just gliding across the road" and "because of its lack of enormous weight I feel I'm really in control of where it goes" but also "I'm having to be a bit careful, since it feels like it's skipping along the road like a dainty rabbit". Speeds were not high, judging by the footage.

I'm not sure what this adds up to in the real world, does it sound like the new stiffer springing over the more compliant ride of the previous model isn't altogether successful? Smaller, lightweight French cars have traditionally worked so well because of their tremendous suspension qualities. However, Autocar seemed to suggest it may well be good enough.

The concensus is that it's aimed at sity driving, which might lead you to wonder why not spend a little more for the style of a Microlino.

Here's Autocar's 90 second review -



and Robert Llewellyn's review - https://www.youtube.com/watch?v=hjoIUg_uu8c

[Carlton green]

I watched the Llewellyn video - thank for the link - and thought it interesting. It will be interesting to see how the second hand prices do and whether the battery capacity is increased.

[UpWrong]

I've watched many Spring videos and most are very positive although comments on the steering are inconsistent. I believe it was remote on the old version and got tightened up on the new. I think it looks stylish. I would have a lot more confidence buying a Spring than a Microlino in terms of reliability and support.

[UpWrong]

So, what do we think of the Renault Mobilise Duo? Half the price of a Microlino with similar performance, https://www.autocar.co.uk/car-review/mobilize/duo

Edit: another review https://www.autoexpress.co.uk/mobilize/duo

[[XAP]Bob]

So, what do we think of the Renault Mobilise Duo? Half the price of a Microlino with similar performance, https://www.autocar.co.uk/car-review/mobilize/duo

Edit: another review https://www.autoexpress.co.uk/mobilize/duo

The Twizzy was always great, assuming you had a raincoat with you...
Assuming Renault have done their normal quirky genius then it should be excellent for the applications it's designed for.

[Biospace]

I've watched many Spring videos and most are very positive although comments on the steering are inconsistent. I believe it was remote on the old version and got tightened up on the new. I think it looks stylish. I would have a lot more confidence buying a Spring than a Microlino in terms of reliability and support.

It's not clear whether criticsm of the steering on the pre-facelift model was due to its softer suspension which many testers will not be used to, or if it's the steering mechanism or front suspension geometry itself. But it has been mentioned by all those who've driven it, in some form or other, which suggests it may not feel quite 'right'. Although I would expect Autocar to have said so, had they felt it was genuinely a problem.

Better for reliability and support even though it is a rebadged car built in China by Jiangling, intended for the Chinese and Indian markets? I suppose coming under the Renault umbrella should help. In contrast, a Microlino is made in Europe and the company will be very keen to establish its brand identity. It's probably impossible to tell until some obscure part is required.

So, what do we think of the Renault Mobilise Duo? Half the price of a Microlino with similar performance, https://www.autocar.co.uk/car-review/mobilize/duo

Edit: another review https://www.autoexpress.co.uk/mobilize/duo

It will make Microlino think hard about pricing, although it's possible the vehicles will attract quite distinct customer bases. Looks a little claustrophobic, visibility doesn't look the best, beyond that - what a great little car for the money. Good news that the battery isn't rented.

However, I can't help but think the Chinese have products which are better placed to satisfy the mass consumer with products like BYD's Seagull - a 'proper' car but diminutively sized - aiming to offer what a 1980s Renault 5 or its replacement Clio offered. Other than the Spring, European offerings seem to be aimed at a niche market sector.