Interpret my MY window sticker WH/MI and Range

[electric_ftw]

Folks,

I just happened to look the window sticker of my Y and noticed the following :
125MPGe combined / 131 city and 117 highway
27 kW-hr / 100 miles and a range of 326 miles.

Is this saying 326 miles at a rate of 27 kW-hr / 100 miles ? I am assuming that they are logically related, but does not seem to square with the battery capacities of 75kW-hr reported ? I am probably missing something obvious - please help

 

[Rocky_H]

27 kW-hr / 100 miles and a range of 326 miles.

Is this saying 326 miles at a rate of 27 kW-hr / 100 miles ?

You know how you hear people talking about Teslas' efficiency in terms of watt hours per mile? That's the same kind of unit, but looking funny.
27 kWh / 100 miles. Divide by 100 to get per mile:
0.270 kWh per mile. But no one likes using decimals, so multiply by 1,000, so it's watt hours instead of kilowatt hours:
270 wh per mile

27 kW-hr / 100 miles and a range of 326 miles.

So yes, that's saying it's the EPA estimated conditions yield 326 total miles at an average efficiency of 270 watt hours per mile.

Neither of those is directly stating the battery pack size in terms of energy, but that can also be approximately calculated from that, with some caveats about unused buffer space, etc.

 

[electric_ftw]

You know how you hear people talking about Teslas' efficiency in terms of watt hours per mile? That's the same kind of unit, but looking funny.
27 kWh / 100 miles. Divide by 100 to get per mile:
0.270 kWh per mile. But no one likes using decimals, so multiply by 1,000, so it's watt hours instead of kilowatt hours:
270 wh per mile


So yes, that's saying it's the EPA estimated conditions yield 326 total miles at an average efficiency of 270 watt hours per mile.

Neither of those is directly stating the battery pack size in terms of energy, but that can also be approximately calculated from that, with some caveats about unused buffer space, etc.

so 326*0.27 implies a 88kWh battery pack. The rated efficiency in the built in energy meter is 240kWh/mile which at 326*0.24 implies ~78kWh battery pack. So I wonder which of the rating is the accurate one and which battery capacity is the correct one ? I am definitely missing something

 

[jcanoe]

The LRMY original range estimate was 316 miles; the total capacity of the battery pack in the Model Y is currently accepted to be 78 to 78.5kWh (using Panasonic's cells) with 74kWh or 75kWh usable capacity. (I have never quite got to the bottom line truth on the usable capacity; my Model Y has a sticker located under the shroud that states 74kWh. I also received a piece of paper from Tesla with my purchase for the purpose of a Maryland EV rebate that states that the capacity of the battery pack in my Model Y is 74kWh so that is the kWh number I use.)

The latest EPA test data shows a slightly larger capacity for the latest battery packs used in the 2021 Model 3P and Model YP, (the only versions of these Tesla vehicles, to date, where the new, larger capacity battery pack using LG cells shows up) of 81kWh to 82kWh. This is the largest capacity battery pack yet offered in any Model 3 / Y.)

316 miles / 74kWh = 234Wh/mile. With the revised range of the LRMY of 326 miles that works out to 326 miles / 74kWh = 227Wh/mile.

1 gallon of gasoline is equivalent to 33.7kWh; 74kWh/33.7kWh = 2.195 gallons; 125MPGe X 2.195 gallons = 274.48 miles; Also,
74kWh /.270kWh = 274 miles. This is to say that 125MPGe is also 27kWh/100 miles or 270Wh/mile.

The difference between 227Wh/mi and 270Wh/mi is 43Wh/mi; an increase of 19%. The additional 19% is the estimate of the charging losses (heat losses, other losses including cooling or heating the battery while charging) when charging the battery. It requires approximately 20% more kWh than the total kWh the battery can store to charge the battery, that you can use for driving. Once you have charged the battery pack to 100% (74kWh) the LRMY, according to the EPA range estimate of 326 miles (combined city / highway) or 74kWh / .227kWh/mile for 326 miles.

That the total battery capacity is currently 78 to 78.5 kWh does not factor into the MPGe or the Wh/mi estimate. You can only access 74kWh of the total battery. If Tesla let you use more of the battery then the EPA range estimate would be higher but the efficiency would still be 125MPGe or 270Wh/mil. (Early testing in 2021 Model 3P with the 82kWh battery pack using the new LG cells is that these cells charge more slowly, for the same % of charge, than the current Panasonic battery cells. The efficiency of the Model Y with the new battery pack may be slightly lower, i.e. less than 125MPGe and more than 270Wh/mile lower but without more data this is uncertain.

The 125MPGe and 270Wh/mile efficiency estimates won't hold at the temperature extremes. In winter the battery will take longer to charge and may require supplemental heating (more energy pulled from the grid.) There are fixed charging losses so the longer it takes to charge the larger the loss. This is one reason why Level 2 charging is more efficient that Level 1 charging.

 

[Rocky_H]

so 326*0.27 implies a 88kWh battery pack. The rated efficiency in the built in energy meter is 240kWh/mile which at 326*0.24 implies ~78kWh battery pack. So I wonder which of the rating is the accurate one and which battery capacity is the correct one ? I am definitely missing something

Like I said, it's got some vagueness and some caveats in it. The other things are that these efficiency numbers are talking about kind of different things in different contexts. The window stickers about energy used per miles of distances are not talking about the car's use. Those are measures of the amount of energy passed through the external charging circuit. So that consumption figure is going to look a little bit higher, because there is some small % of losses through the charging process to what actually gets into the battery. So then the consumption constant in the car is going to look a bit lower (more efficient) than that.

 

[Flybuddy]

 

[electric_ftw]

@Rocky_H and @jcanoe - thank you for the details.

To summarize, the sticker lists the power consumed from the wall to go 100 miles. The information it's trying to supply is how expensive it is to drive a given distance from a power perspective given EPA conditions.

OTOH, it looks like the battery capacity (based on prev EPA report) is ~ 78kWh total which taken with the 326 mile rated range gives a rated consumption of ~238Wh/mi. Given that only 74kWh of this is accessible, the actual accessible range at the rated consumption with a displayed 100% SOC until 0% SOC would be ~310 miles for the MY LR.

 

[Uncle Paul]

In the real world, range is usually determined by the way the car is driven, the variables or road conditions plus the comfort level of the owner as to how high they feel comfortable charging and how much reserve the wish to maintain prior to pluggin in.

The math may give totally different numbers. Variances will most always be experienced depending on how much unusable reserve is set aside both at the max charge and max depletion the company programs in.

 

[AlanSubie4Life]

227Wh/mi and 270Wh/mi is 43Wh/mi; an increase of 19%.

This is too high an increase, by about 5-7%. The source of the error is primarily that you're not accounting for the buffer.

That the total battery capacity is currently 78 to 78.5 kWh does not factor into the MPGe or the Wh/mi estimate. You can only access 74kWh of the total battery.

Look at the EPA documents. You'll see the 2021 Model Y AWD non-P used 77.7kWh to accomplish its rated range in the document linked below. So you have to count that buffer capacity of 4.5% (always 4.5% of the full battery energy, for Model 3, and I believe also for Model Y) below 0%. They use it in the EPA test; they drive on the dyno until the vehicle comes to a halt and those miles all count. There is presumably "brick protection" below THAT true 0% - you can NEVER use that, and the EPA test doesn't either.

Once you correct for that small error, everything else in your post seemed correct and it's very informative. You'll see in the EPA document they also give the recharge energy, and the overhead is typically such that about 88% of the input energy makes it to the battery. (The AC-DC converter is a little over 90% efficient, and the other ~2% overhead goes to running various accessories after the AC-DC during the charge, and some heat losses in the battery itself. This is also all explicitly (you do have to do some simple calculations) documented in the document linked.)

This discrepancy just affects your range, not the efficiency, of course - if you drive at the rated efficiency and you only want to go to 0%, you will end up about 4.5% short of the EPA range.

Model Y Performance and Model Y AWD:
https://iaspub.epa.gov/otaqpub/display_file.jsp?docid=51237&flag=1