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VW ID.3 Life Pro Performance, MY22 (software v2.3)
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Quick question (I hope!), with apologies if it has been done to death before (the term is so heavily used that a search is unhelpful).

When we talk of miles per kWh, do we mean kWh consumed by the car (and presumably as reported by the car), or kWh reported as delivered by the supply (EVSE or DC charger). We know there are losses in the charging process, so…?
 

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Renault Zoe 50
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It depends who’s quoting them.

Generally speaking if it’s reported by the car it’s from the battery as used by the motor, with or without the HVAC and other losses, depending on the car.

If it’s from something like EPA ratings they do include EVSE losses, as I understand it.

Confusing isn’t it?
 

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The problem is that charging losses are extremely variable, depending on how the car is being charged, and at what rate.

When AC charging there's effectively no loss from the charge point (might be a watt or two to run the contactor and electronics, perhaps), but there are some losses within the onboard charger(s). Generally onboard chargers are pretty good at their max rated current, might be around 90% efficient, maybe a bit more. They tend to be pretty poor at lower current though, so efficiency tails off towards the end of a full charge, as the current tapers off, and efficiency is almost always poorer when using a granny lead to charge, again because of the low current that the charger is operating at.

DC charging is different, as most of the losses are in the charger, rather than the car, so a lot depends on whether you're paying for AC electricity going into the charger, or DC electricity going from the charger to the car, and whether you want to use that as the basis for the calculation. Most rapid chargers seem to charge for AC electricity going in, so you are paying for the inefficiency of the charger, as well as the charge going into the car.

All told, it makes sense to use the measurements the car makes, on DC drawn from the battery to the motor controller. At least that should be more consistent, as a measure, and I believe that's how the majority of EVs actually display energy usage (happy to be proven wrong if anyone knows different).
 

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Renault Zoe ZE50
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My car measures miles per kWhr drawn from the battery. I guess since it doesn't know how much power was drawn from the grid to charge the car. The problem with power drawn from the grid is that charging efficiency varies with speed. Charging from a granny cable is very inefficent (for a Zoe anyway). 3kW charging will be different from 7, from 11 from 22 and from 43kW. DC will be different again.
 

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LEAF N-TEC 62KW
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It's akin to miles per gallon on an ICE's dash display and of course, is an accumulative average, hence it can vary wildly after being zero'd.
 

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It's akin to miles per gallon on an ICE's dash display and of course, is an accumulative average, hence it can vary wildly after being zero'd.
Exactly, but it’s still a very useful insight to how the vehicle is being used/driven, the difference between average usage during summer vs winter can be quite telling, ours gives us just over 4.3mkWh summer to 3.8mkwh winter.
 

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Do people generally find that miles per kWh makes more sense than Wh per mile?

I'm a Wh per mile person, but that goes back nearly 20 years to my first adventures with home made EVs, in the form of building electric bikes. Wh per mile seemed a better fit for a bike, and I've stuck with it as a measure, because, for me, it seems to make more sense, and somehow I can visualise energy usage more clearly with that measure. Curious to know what others think.
 

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Quick question (I hope!), with apologies if it has been done to death before (the term is so heavily used that a search is unhelpful).

When we talk of miles per kWh, do we mean kWh consumed by the car (and presumably as reported by the car), or kWh reported as delivered by the supply (EVSE or DC charger). We know there are losses in the charging process, so…?
if you have energy meter only for car (like me) than you can calculated energy (in kWh) taken from grid. unfortunately most ev car users reporting value from car's com
 

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LEAF N-TEC 62KW
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Do people generally find that miles per kWh makes more sense than Wh per mile?

I'm a Wh per mile person, but that goes back nearly 20 years to my first adventures with home made EVs, in the form of building electric bikes. Wh per mile seemed a better fit for a bike, and I've stuck with it as a measure, because, for me, it seems to make more sense, and somehow I can visualise energy usage more clearly with that measure. Curious to know what others think.
I do wish that a common standard existed as I find it irritating when comparing different EVs. (bit like ICE vehicles Uk and EU fuel consumption figures).
I think I would be happy with either but I'm used to the Leaf's m/kWh
 

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NISSAN LEAF 62Kwh
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I have a general rule with KWh's and KW's, I only use KWh's to refer to the the battery capacity, this is because this is the capacity the battery has and the time it would take to discharge that battery. For example if you had a 40KWh battery, then you would have to discharged that battery at 40 Kw's continuously to deplete it in one hour.

With that out of the way, I refer to all other measurements as KW's so if my EV uses 1 KW to cover 4 miles then it's 4 miles / KW (not 4 miles / KWh).

I am not saying that I am totally correct, but it is the convention I have personally adopted and it seem to work well for me, not confessing to be an expert in these matters :rolleyes:
 

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NISSAN LEAF 62Kwh
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When I first started posting, I was always getting my KWh's and KW's mixed up, and I was often being corrected, so I adopted my convention and it seems to work, like I say I am no expert, just trying to rub along with a little friction as possible :oops:
 

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How can you have miles per kW? You can have miles per kWh, as that's a measure of distance for a unit of energy, the same as miles per gallon of fuel essentially (as a gallon of fuel has a given amount of energy), but miles per kW doesn't mean anything, as it's miles per unit power. Power will vary massively over a mile driven, could be anything from minus a few tens of kW to plus tens (or hundreds) of kW.

I used to have a bit of software running on a Raspberry Pi (Teslamate) that would interrogate Tesla's servers, using the API, and provide all sorts of interesting data. One plot was power used for any trip, with a route map, showing the bits of road where he power was used. I used to play a daft game on one regular trip, to see just how long I could max out the power (around 300 kW or so). Never managed more than 3 seconds at that power before I had to lift off, and as soon as I lifted off there was a massive negative power spike as the motors regeneratively braked and shoved a few tens of kW back into the battery pack.

I might have gone a tenth of a mile at ~300 kW, followed by another tenth of a mile at minus 70 or 80 kW, followed by the rest of the trip at anything between minus 50 kW or so to plus 200 kW or so.
 

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LEAF N-TEC 62KW
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How can you have miles per kW? You can have miles per kWh, as that's a measure of distance for a unit of energy, the same as miles per gallon of fuel essentially (as a gallon of fuel has a given amount of energy), but miles per kW doesn't mean anything, as it's miles per unit power. Power will vary massively over a mile driven, could be anything from minus a few tens of kW to plus tens (or hundreds) of kW.

I used to have a bit of software running on a Raspberry Pi (Teslamate) that would interrogate Tesla's servers, using the API, and provide all sorts of interesting data. One plot was power used for any trip, with a route map, showing the bits of road where he power was used. I used to play a daft game on one regular trip, to see just how long I could max out the power (around 300 kW or so). Never managed more than 3 seconds at that power before I had to lift off, and as soon as I lifted off there was a massive negative power spike as the motors regeneratively braked and shoved a few tens of kW back into the battery pack.

I might have gone a tenth of a mile at ~300 kW, followed by another tenth of a mile at minus 70 or 80 kW, followed by the rest of the trip at anything between minus 50 kW or so to plus 200 kW or so.
Yes, on reflection you are of course, correct.
 

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Yes, you are right, I should have stated m/kw.
Sorry but you are wrong. A KWh is a lump of energy. A KW is a measure of power i.e. a rate of delivering energy. So a KWh is a KW of power delivered for an hour.

So the Miles per KWh is the number of miles you get for your standard lump of energy.

Having said all that, I'm fairly sure I am using the capital's and lower case letter k, w and h all wrong in the units. Happy to be corrected on that.
 

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Measuring miles per gallon with internal combustion doesn’t consider the energy used for extraction of the fossil fuel. Likewise miles per kilowatt hour doesn’t consider the energy used for getting that electrical energy into the battery.
 

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LEAF N-TEC 62KW
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Sorry but you are wrong. A KWh is a lump of energy. A KW is a measure of power i.e. a rate of delivering energy. So a KWh is a KW of power delivered for an hour.

So the Miles per KWh is the number of miles you get for your standard lump of energy.

Having said all that, I'm fairly sure I am using the capital's and lower case letter k, w and h all wrong in the units. Happy to be corrected on that.
Yep, already been correct by JH!
 

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Call a 'kilowatt hour' a 'unit' of electricity' as we all used to once upon a time.

Thus, 64 Units in a battery and 4 miles/unit, charging at 7 units an hour and 14.5p/unit.

A time honoured, understandable measure.
 

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Renault Zoe ZE50
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Do people generally find that miles per kWh makes more sense than Wh per mile?
It depends what you're trying to do. I have a 50kWhr battery and the dashboard says I have 50% remaining - 25kWhr. The car also tells me it has averaged 4 miles per kWhr, so I have 100 miles of range left.

Or, I'm planning a 400 mile round trip. My car uses 0.25kWhr per mile. So I need 100kWhrs to make the journey. My battery holds 50kWhr, so I need 2 full charges. Or more realistically, 2 charging stops.

I prefer the former. Others may differ.
 

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Yes, on reflection you are of course, correct.
Perhaps this helps:

kW is POWER, kWh is ENERGY.

So you load up the battery with energy and then consume it over time as power doing useful work moment by moment.

Your energy supplier supplies you with kWh.

My own preference is for miles per kWh typically expressed to 1 decimal place. Expressing Wh per mile implies an accuracy equal to the precision. The less precision of miles per kWh is better aligned to the accuracy of measurement.
 
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