LEAF 2018 151 Mile Range Mystery

[SageBrush]

EPA numbers usually vary.

Same car, same test, same conditions.

Not much variance

[alozzy]

Folks,
The MPGe are a given from the EPA -- regardless of the hows and whys.

Alright then, back to your original comment...

We should expect the 40 kWh Model to have (4/3)*107 = 142.6 miles of range, yet it is rated for 151 miles. The extra 8.4 miles is close to 3 kWh

Improvement in Cd fully explains that...

[SageBrush]

Folks,
The MPGe are a given from the EPA -- regardless of the hows and whys.

Alright then, back to your original comment...

We should expect the 40 kWh Model to have (4/3)*107 = 142.6 miles of range, yet it is rated for 151 miles. The extra 8.4 miles is close to 3 kWh

Improvement in Cd fully explains that...

The difference in Cd does not explain the discrepancy.


Consider this thought experiment:
EV A:
Has a specific MPGe on a drive cycle with C kWh capacity that results in R range.
Nothing else is known about the car.

EV B:
Has the same MPGe on the same drive cycle, but has 1.33*C battery capacity
Nothing else is known about the car.

Can you calculate the range of Car B in terms of R on this drive cycle ? To what accuracy ?

[DaveinOlyWA]

1) EPA actually tests 1 in 7 new cars on average each year which means 85% of the EPA ratings are taken directly from the Manufacturer's mouth (which probably accounts for several lawsuits past and present over MPG claims)

2) Generally DoD for LEAF has been roughly 93.6-94% for more durable 24 kwh packs (btw, they have changed slightly in size) or nearly 95% for the less capable 30 kwh packs.

3) If using the 30 kwh LEAF as a guideline and its 29.6 kwh pack; with the 28.1 kwh usable we are seeing 3.8 miles per kwh. If using that same figure that equates to 39.7 kwh usable which is not realistic.

4) Using a realistic DoD of 94% along with prelim LEAF Spy measurements putting pack at roughly 40.68 kwh AND a 4 mile per kwh average which should be easy to do since we have better aero, etc we get about 38 kwh usable AND the 151 mile estimate.


I think this is a low ball figure.

[DaveinOlyWA]

Folks,
The MPGe are a given from the EPA -- regardless of the hows and whys.

Alright then, back to your original comment...

We should expect the 40 kWh Model to have (4/3)*107 = 142.6 miles of range, yet it is rated for 151 miles. The extra 8.4 miles is close to 3 kWh

Improvement in Cd fully explains that...

So why didn't the MPGe change?

[alozzy]

It is odd that the MPGe doesn't match the range, but MPGe is really only useful for comparing ICE cars to EVs. Converting MPG to MPGe assumes each gallon of gas is equivalent to 33.7 kWh of energy.

EVs should really be rated based on a stated miles per kWh efficiency, and the total useable kWh pack capacity, to arrive at a useable range.

For example, if the 2018 LEAF averages 4 miles per kWh on a standardized track loop, and the total useable pack capacity is 37.5 kWh, then the range rating should be 150 miles. It would be pretty easy for the EPA to measure actual KWh efficiency, rather than is MPGe nosense.

[DaveinOlyWA]

It is odd that the MPGe doesn't match the range, but MPGe is really only useful for comparing ICE cars to EVs. Converting MPG to MPGe assumes each gallon of gas is equivalent to 33.7 kWh of energy.

EVs should really be rated based on a stated miles per kWh efficiency, and the total useable kWh pack capacity, to arrive at a useable range.

For example, if the 2018 LEAF averages 4 miles per kWh on a standardized track loop, and the total useable pack capacity is 37.5 kWh, then the range rating should be 150 miles. It would be pretty easy for the EPA to measure actual KWh efficiency, rather than is MPGe nosense.

MPGe is a standardized measure of energy. We "should" be able to compare it from EV to EV.

Maybe the LEAF Spy reading was low and we have a 42-43 kwh pack? I'd rather go with that!

[SageBrush]

EVs should really be rated based on a stated miles per kWh efficiency, and the total useable kWh pack capacity, to arrive at a useable range.

The combined EPA city/highway efficiency result for both the 30 kWh and 40 kWh models is 301 Wh per mile.
In your preferred units, 3.32 miles per kWh

How do I know this ? It says so, right on the window sticker. But it as written as miles per 33.7 kWh instead of miles per one kWh
----
The EPA does its testing as follows:
The car is charged to full;
Driven on the test cycles until it stops;
then the kWh at the meter to charge it to full is measured.
The distance driven divided by the energy (kWh) at the meter consumed, multiplied by 33.7 gives the MPGe

You should feel quite free to divide the MPGe by 33.7 to get your miles/kWh rating.

---
Which brings us back to my original question:
Since both models have the same 3.32 miles per kWh rating,
one might expect that the "40 kWh" model to have 4/3rds (133%) the range as the "30 kWh" model
But it actually has 141% the range.

Presuming the efficiency label is correct, there is unstated capacity differences.
By my arithmetic,
The '30 kWh' Model has 28 kWh usable
The '40 kWh' Model has 39.7 kWh usable

If we presume that both batteries have ~ 2 kWh reserved against bricking and over charging, the actual capacities are
30 kWh in the '30 kWh' model
and 41.7 kWh in the '40 kWh' model

[alozzy]

@DaveinOlyWA I agree that MPGe is the current standard, I just differ with you on whether it should be the standard. I don't think it makes any sense to use MPGe as a comparison between EVs. Why convert kWh efficiencies to MPG equivalent when neither vehicle burns gasoline? Especially when kWh/mile or miles/kWh comparisons are so much easier to derive for EVs...

If the EPA focused on kWh/mile or miles/kWh instead of MPGe for EVs, it would provide EV buyers with better information. For example, if they stated that an EV ended up with an efficiency of 4.2 miles/kWh on their test rack, and that the usable pack energy was 58 kW, educated EV buyers wouldn't just think "Ok, it'll have 244 miles of range" - they would extrapolate from that efficiency rating, based on their own experiences driving an EV (i.e. I drive more/less conservatively than most EV drivers, I have to deal with harsh winters or hot summers, etc), and would have a good sense of what "real world" range would be for their circumstances.

[LeftieBiker]

The MPGe figure is to help non-EV-experts compare cars, and for that it is useful. It should remain, but the M/KWH number should be given with it.