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doesn’t that ignore the fact that you also arrive 1.1667 times quicker at 70 than 60, so you’re using the energy for less time?
The measurement of energy use in this case (miles/kwH) doesn't have a time factor, so time taken is not relevant.
I don't really have a grasp on electric mileage figures, so will switch back to fossil fuel numbers to illustrate the point.
During the recent fuel shortage, I dropped down to 60mph for my commute. It is a 92 mile round trip & I averaged 68mpg; I used 1.353 gallons of fuel (92/68), or 6.14 litres.
Today i was back up to 70mph on the way in, and think I averaged 58mpg (last time I looked it was on 58). Assuming the same on the way home, I will have used 1.586 gallons of fuel (92/58), or 7.20 litres.
If you measured fuel used/min rather than miles/gallon then the time spent travelling would be relevant. But in this case, I think you would find that the fuel used fell more as a proportion than the extra time it took.
The measurement of energy use in this case (miles/kwH) doesn’t have a time factor, so time taken is not relevant.
No, but the measurement of energy required to overcome air resistance does. It's a certain force, for a certain time. Much like mpg numbers, the quoted miles/kwh will also be based on some mix of measurements and speeds, which will already include some allowance for motor and power conversion efficiency, and wind resistance.
No, but the measurement of energy required to overcome air resistance does. It’s a certain force, for a certain time.
No, energy is force x distance moved against that force. It doesn't have a time component.
so will switch back to fossil fuel numbers to illustrate the point.
As Ed points out the situation with ICEs is so different as to be not comparible.
EVs do seem to be more efficient the slower you go. On my wife's commute we can get 5.2 or sometimes over 6 miles/kWh. We have seen 7 on a few occasions on different routes. On the motorway, flat, constant speed it's at most 4.8. So that's best case something like 20-25% more efficient on the local commute than the motorway. The Merc does about 60% better MPG on the motorway than the commute.
I do however see something that surprises me. When I set off from my house in an ICE it's inefficient for the first few minutes, as you'd expect, cos the engine's cold and it needs more fuel to generate the power. However I still see the same effect in the EV, and I did all through spring and summer. I have to drive up a hill on the way out of my street but it's only about 15 or so m of altitude and about 150m of driving.
Do other EV owners who live in flat streets see the same low efficiency at the start of a trip?
No, energy is force x distance moved against that force. It doesn’t have a time component.
It sure does, in the case of air resistance - the force depends on speed!
Do other EV owners who live in flat streets see the same low efficiency at the start of a trip?
In Winter, yes. Over 20°C ambient, no. On the second charge on a long run in Winter the car is as efficient as in Summer. The battery heats up with use and charging and gets more efficient.
Left out overnight in Winter in a ski resort the battery gets so cold I get a warning that regenerative braking won't work and the range drops as you'd expect.
Valve overlap makes engines inefficient before they come on the cam and very high revs are inefficient due to friction losses and incomplete scavenging.
Good point - the efficiency of an ICE over its rev range is well understood and published. I wonder what the equivalent numbers for an EV motor would be?
As Ed points out the situation with ICEs is so different as to be not comparible.
Eh, they're totally comparable. You just need the efficiency data for the vehicle powertrain over its speed and load range, and the drag coefficient for the car.
It sure does, in the case of air resistance – the force depends on speed!
I did some algebra, possibly incorrectly, and found that the cube of distance is inversely proportional to the square of the time taken to do cover it. So yes, the faster you go the less distance you can cover, but I couldn't figure out what that relationship means and how it relates to my earlier statement which I still believe to be correct. I may have made a mistake though.
You just need the efficiency data for the vehicle powertrain over its speed and load range, and the drag coefficient for the car.
Neither of which we have, so in this situation they aren't.
Eh, they’re totally comparable. You just need the efficiency data for the vehicle powertrain over its speed and load range, and the drag coefficient for the car.
Apart from the drag coefficient we don't have any of that though. You need the frontal area too to work out drag.
We just know that electric motors get inefficient at high load and high speed and ICEs are generally most efficient around peak torque under load. We don't have the partial load figures because manufacturers don't publish them.
This is interesting. On this page which is about synchronous permanent magnet motors in general (same construction as in most cars) it shows how the efficiency gets worse at lower outputs:
Going up my street is done very slowly because of parked cars etc so this doesn't help. The instantaneous readout doesn't get much better when we get onto the flat either, because we are still going slowly.
They've cut off the right side of the graph just before efficiency fell off a cliff. Which is fine if the management of the motor means it can never be exploited outside of its optimum range.
My old Zoé was allowed to just run out of steam but the new one (which has a more powerful motor) feels as though it's limited to the declared maximum speed which is much better for effciency.
lots of graphs and maths here http://roperld.com/science/ChevyBoltRange.htm
That's a graph of the mandated efficiency bands for motors of different rated outputs. However, the graph of % max power output against % max efficiency looks fairly similar, but rises to 100% quite quickly (according to this paper, for ~100hp electric motors).
That's not the whole story though, as the speed the motor is turning at also has an effect on efficiency. Here's a nice graph I found for a Prius motor and inverter:
I'm not sure what a typical EV final drive ratio is, but the e-Niro has 8.2:1. So, that zone of max powertrain efficiency at a motor speed of 6000rpm would equate to a road speed of 37mph.
Above this speed, EV drivetrain efficiency drops, along with rising wind resistance.
A quick search finds this graph for an ICE:
The area of maximum efficiency between about 2500rpm and 3000rpm gives you peak drivetrain efficiency around 45-50mph.
So there we have it. EVs might not have those old-fashioned gearboxes, but the tradeoff is that the most efficient road speed is quite a bit lower than an ICE.
Interestingly, today I learned that AWD Teslas have different final drive ratios for the front and rear motors, and power is directed to each according to road speed, to maximise the efficiency of the electric drivetrain across a wider speed range.
I’m not sure what a typical EV final drive ratio is, but the e-Niro has 8.2:1. So, that zone of max powertrain efficiency at a motor speed of 6000rpm would equate to a road speed of 37mph.
It seems unlikely that Kia would choose a final drive ratio to give max efficiency at such a low speed. Not unreasonable to assume that the motor in the Kia could easily have a different rpm for max efficiency. The graphs I posted were an attempt to understand the shape of the curve not any actual numbers.
So there we have it. EVs might not have those old-fashioned gearboxes, but the tradeoff is that the most efficient road speed is quite a bit lower than an ICE.
I doubt that this analysis is enough to draw those conclusions 🙂
If I were designing an EV I'd probably have the max efficiency at a point that maximises the WTLP range. Even if the 37mph is the most efficient point it would seem that efficiency may not necessarily tail off that fast at higher speeds. So by setting a particular final drive you might lose 3% at motorway speeds but gain 30% at city speeds.
As I pointed out, the graph you posted doesn't mean much without taking the rotational speed of the motor into account. It's not just how much power you are asking the motor to provide, but the speed of the motor while it is doing it. That's why I found the graph of the Prius motor so interesting.
As EVs don't have much stored energy compared to an ICE, and are thus much more concerned with weight and parasitic losses, the decision to not include a gearbox would involve more than just optimising for efficiency at highway speeds.
No, it's not a very rigorous analysis. However, I'm sure the graphs I posted are fairly typical, and it does line up with the real-world observation that the efficiency of EVs drops off more with speed than an ICE car. I don't think it's at all a surprising result.
Even if the 37mph is the most efficient point it would seem that efficiency may not necessarily tail off that fast at higher speeds.
Maybe not, but the efficiency is decreasing, and wind resistance is increasing (and enough to be noticeable to the average EV driver). Unlike an ICE, where drivetrain efficiency continues to rise for a while before reaching a peak.
FWIW, the average speed of the WLTP is 30mph, and if anything favours EVs, which can do regenerative braking.
So there we have it. EVs might not have those old-fashioned gearboxes, but the tradeoff is that the most efficient road speed is quite a bit lower than an ICE.
I think this is why porsche do use a 2-speed gearbox in their cars - so they can give prefferential range at motorway/autobahn speeds whilst still giving poo-yer-pants acceleration from rest. They seem to come very close to the EPA figures during real-world testing (compared to, say, teslas)
it does line up with the real-world observation that the efficiency of EVs drops off more with speed than an ICE car
Did we have graphs for that?
Anecdotally it's hard to testify because in the real world it's hard to separate wind resistance from drivetrain efficiency
No. We have some graphs for selected theoretical data, and some real world observations (provided by others in this very thread). Wind resistance is the same for everyone, so it shouldn't be hard to separate the two. 🙂
Does anyone have any experience of the new Polestar 2? It's available on my company scheme and seems decent value for the range. The ID3 is less, but also smaller and less range.
I had a test drive in one a few months ago (the dual motor). Looks quite big on the outside but feels small inside, kind of the opposite of the Tesla Model 3.
Google Maps is great but the rest of the implementation feels a bit half-baked. They've taken steering wheels etc from Volvo but some of the controls are deactivated. Everything a bit plasticky for weight saving. Go-kart element of point-and-shoot driving very good. Boot is enormous. More "normal" to own and drive than a Tesla.
Matt Watson from Carwow reviewed the single-motor version recently and really rated it. I think if you have a relatively short journey to work and can charge there or at home, it's a great choice. If you're relying on the motorway charging network, get a Tesla.
There's been some calling for further incentives to encourage EV uptake. I wonder if we'll see anything in next week's budget. AA are calling for scrapping VAT on some EV sales. That would be quite the incentive.
It's a bit contradictory to the recent reductions in the grants, but the government could do with some help when they go to COP26 and show their non existent homework.
I quite fancied a Polestar 2 but I don't like the idea of buttons from other cars simply deactivated...
Polestar is a weird one. There are several in these parts but, for large cars, they look small. They are also really expensive for what they are and are (as I understand it) largely a Chinese EV trading off the Volvo heritage. Same with Volvo really.
XC40 was on my list of options too, but they are ridiculous money for what it is.
What WLTP range would you want to enable a regular 155mile commute? Mix of A road/M25, with no option to charge at work?
If I occasionally needed to pop into an Ionity on the way home for 10 minutes that would be fine, but I'd like to be able to manage it most of the time.
My missus has an XC40 petrol which she loves. That was her original choice for EV, but as you say, bloody expensive!! Range is poor too.
I'd manage that in my Ioniq, it's about the same as the distance to my parents. We've done it twice and got home with 20-30 miles range left. But you'd have to make sure that you had the option of a charger.
We're pretty good at driving economically however we do set the cruise to 70 on the motorway, you would only lose a few minutes setting it to 65 and you'd probably save a fair bit of range. The thing is that when you are driving home you can run it right down because you know exactly how far away you are from the charger.
Re Polestar:
I quite fancied a Polestar 2 but I don’t like the idea of buttons from other cars simply deactivated
Which buttons are you referring to?
There are several in these parts but, for large cars, they look small. They are also really expensive for what they are and are (as I understand it) largely a Chinese EV trading off the Volvo heritage. Same with Volvo really.
Indeed, it's essentially a "Geely", based on the XC40 platform, with some Volvo parts (seats, steering, etc) and it overall it's reasonably well resolved and cohesive.
Regarding size, I can get a bike in the boot (seats down) with both wheels on. We recently did a 400 mile trip, 5 people with weekend bags and food, which all fitted well - the frunk took a decent sized bag.
Tesla has a more efficient drivetrain, Polestar is arguably more attractive/reliable. It's also more fun to drive hard if that's your thing (particularly with the Performance Pack's dampers and brakes).
I get a reliable 210 miles in summer and 170 miles in winter (YMMV, etc).
Is that the old Ioniq with 193 mile range advertised rather than the I5?
Agreed, once you get to trust/know the range predictions you can be a bit braver. My last charger on the way home is 15 miles from home, so always a chicken option.
Is that the old Ioniq with 193 mile range advertised
Yes, although it's still on sale no?
Which buttons are you referring to?
The ones that Flaperon was referring to 🙂
The ones that Flaperon was referring to 🙂
All the buttons on my steering wheel work and have a purpose; I'd be interested to know which functions/controls are potentially missing. Perhaps he's referring to things like Carplay which aren't yet "enabled" on Android Automotive?
I get a reliable 210 miles in summer and 170 miles in winter (YMMV, etc).
@jacobyte - that's the smaller battery model?
I keep coming back to the eNiro, but I don’t think this is rated for towing.
The eNiro is the one that seems to tick all the right boxes for me - range, performance, spec, ride comfort, luggage space, price.
They don't seem to crop up much, especially on this thread so any reason why?
I think the e-Niro has become the solid fallback benchmark. All the new options need to beat it. Personally I might well, end up with one - the range is just a bit better than the small battery Enyaq.
that’s the smaller battery model?
@Daffy Nope, mine's the full 78Kw launch model with Performance Pack. Most people get 230-240miles or more but I have a heavy right foot!
All the buttons on my steering wheel work and have a purpose; I’d be interested to know which functions/controls are potentially missing.
On the one I took for a test drive the left and right buttons (which on a Volvo cycle between speed limiter / cruise control / pilot assist) weren't activated, and you had to pick the one you wanted from a submenu on the centre screen.
I've just had a look in the online manual and this has been added since I drove one, so you can ignore me on that aspect.
Ah cool, at least I'm not being short changed!
The eNiro is the one that seems to tick all the right boxes for me – range, performance, spec, ride comfort, luggage space, price.
They don’t seem to crop up much, especially on this thread so any reason why?
I've mentioned my e-Niro here a few times. I've had mine 7 months and its been great. We've got rid of our old Merc diesel and are 100% electric and my business with the ICE has been concluded.
Dants is right to say its a benchmark vehicle. Although not built from the ground up as an EV and a 4 year old design even purpose built EVs released in the last year have a problem beating it for efficiency and usability- even HMGs new Ioniq 5 and EV6 vehicles. Kia are refreshing the design for 2022 so if they make it even better it will be a car to beat.
we traded in the petrol yeti for an e-Niro, it the poverty spec with the big battery but its got everything I want (adaptive cruise being number one but also car play so the lack of satnav isnt really an issue).
only took the plunge as the yeti was going for silly money, the niro is costing 100/month more (its a lease) than the yeti was costing us and we'll save that on fuel.
Isn't the E Niro the same as the Hyundai Kona?
Same powertrain but different size. The Kona is pretty much identical to our fiesta in size inside, the Niro is more Focussy. The kona looks bigger in pictures too than it is in real life too.
I test drove a Kona, it seemed plenty bigger than Fiestas I've known.
Anyway. I'm going to Llanbrynmair in Powys at the weekend. Zap Map found no routes. There are four rapid charging stations in the whole of Mid Wales away from the coast - Brecon, Llandovery, Llandrindod Wells and Newtown. Each only has one rapid charger. And the one in Brecon is broken. If I were driving to North Wales maybe two are realistically en route with short diversions. That's the main north-south link in Wales.
That's filtering for 50kW though. If you want 100kW or more, outside the Cardiff/Newport area there's just one, in Aberystwyth, the other two are Chirk and Flint on the English border.
Isn’t the E Niro the same as the Hyundai Kona?
I drove a Kona for 3 monbths before getting my e-Niro. Although they use the same power train the e-Niro is quite different from the Kona. Its usefully bigger inside, the cabin is much better finished and the ride is much smoother and planted. Also the e-Niro uses SK batteries whilst the Kona uses LG batteries so the e-Niro doesn't have the recent battery fire/recall issue that the Kona has had.
Anyway. I’m going to Llanbrynmair in Powys at the weekend. Zap Map found no routes.
Understandable when you look at the National Grid high voltage network and see that mid Wales is bereft of high voltage infrastructure.
nyway. I’m going to Llanbrynmair in Powys at the weekend. Zap Map found no routes. There are four rapid charging stations in the whole of Mid Wales away from the coast – Brecon, Llandovery, Llandrindod Wells and Newtown.
Yes I was near Machynlleth recently and as my mate was in his tesla had a look on zap map and thought the same. Even the Centre for Alternative Technology only had one (7kw?) charger. They have a big car park just off a main N-S route so crying out for a rapid charger provider to come in with a partnership offer.
But seeing high voltage map above explains it a bit if that's a prerequisite for DC rapid charging.
mid Wales is bereft of high voltage infrastructure.
It did occur to me that the grid infrastructure is not necessarily going to be in place where people want chargers, that's an interesting graph thanks.
On the other hand, given the size the country and the road network you have to use, you really only need two or three charging hubs to cover most journeys people are likely to make.
Worth noting there are quite a few 22 and even more 7kW chargers. On holiday in West Wales this year loads of car parks in the small towns had a row of 7kW chargers - this explains why they were weren't any faster ones. I suppose the intent is there from local government.
To be fair I could do a West Wales trip. I could top up rapidly in Carmarthen to get to my destination then rely on destination chargers such as the car park ones to keep ticking over.
There are rapid chargers available now with battery storage so even if the local grid can't deliver the requireed power for 50kW or above charging as long as there's a sufficient delay between charges to allow the battery to charge these chargers can deliver rapid charge power outputs without high voltage grid connections. These would appear to be ideal for mid-Wales.