Reported energy consumption [kWh/100miles] is utterly completely totally wrong - Page 2 - Jaguar I-Pace EV400 Forum
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post #11 of 57 (permalink) Old 02-17-2019, 12:21 PM
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Your second graph is interesting and indicates that the SOC (I assume this was taken from the car and not from the charger) is fairly linear during charging in the 30-65% interval range.

However, even if we assume linearity between 0-99% your calculation in the table will not be correct without accounting for the much larger 100%(full)-99% and 0%-empty slots.

If we account for these 6kWh then each percentage used in the interval 99-0% will have a size of (84.7-6)/99 = 0.795 kWh.
If we do the same calculation as in the table using these numbers we will get:
29*0.795 = 23.06kWh. If we account for roundoff errors in the displayed values for SOC the range of consumed energy will be [22.26kWh-23.85kWh].
In other words, these seemingly 29% of battery actually represents somewhere between 26.3 and 28.2% of the net battery capacity.

I agree there is still a discrepancy in the numbers, but I'm not really willing to conclude that the reported average consumption is the bad guy here.
There are at least two other alternatives.
- Reported SOC could be inaccurate
- There is less energy in the battery than the claimed 84.7kWh. We know that the colder it gets, the less energy can be harvested due to increased internal resistance.
If we assume that the reported average consumption does not include the extra heat generated due to this increased resistance (which I guess is logical) then
we can only make sensible measures at fairly warm battery temperature.
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post #12 of 57 (permalink) Old 02-17-2019, 12:40 PM Thread Starter
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The battery is a nominal 90kWh and the usable range (i.e., the 0-100% range) is supposedly 84.7 kWh. I think it's actually less but not 6 kWh less. I agree that there are confounders but they can't explain the results.

Regardless of SoC, I recommend the following to convince yourself that something weird is going on with the consumption calculation: drive hard for a few miles, watch the real time kWh/100miles figure in the Eco Data view. Then get off the freeway and watch the kWh/100miles drop precipitously even though you've only covered a tiny fraction of the total distance driven on this 'journey'. Don't need SoC to see that something is awry.
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post #13 of 57 (permalink) Old 02-17-2019, 01:07 PM
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I looked at these screens on my LEAF back in 2011. Lost interest. It is what it is.
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post #14 of 57 (permalink) Old 02-17-2019, 01:39 PM
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Quote:
Originally Posted by sciencegeek View Post
The battery is a nominal 90kWh and the usable range (i.e., the 0-100% range) is supposedly 84.7 kWh. I think it's actually less but not 6 kWh less. I agree that there are confounders but they can't explain the results.

Regardless of SoC, I recommend the following to convince yourself that something weird is going on with the consumption calculation: drive hard for a few miles, watch the real time kWh/100miles figure in the Eco Data view. Then get off the freeway and watch the kWh/100miles drop precipitously even though you've only covered a tiny fraction of the total distance driven on this 'journey'. Don't need SoC to see that something is awry.
When 0-100% is used like this a lot of people tend to misunderstand. The net capacity of 84.7% is measured from where the BMS stop any further charging (real net 100%) until the BMS will stop any further draw of current (real net 0%). These levels are not the same as the displayed SOC 0 and 100%. There is about 3kWh between a full battery and when the meter starts showing 99%. In other words the car can show 100%, but still lack 3kWh of charge compared to a full battery.

Also, we all know that the car does not come to a halt as soon as the display show 0%. There is more energy there to use.

The usable capacity and the EPA and WLTP ranges are measured between these two extremes.
In addition, there is a brick protection ofr 90-84.7 = 5.3kWh which you cannot use. This buffer is there to prevent damage to the battery.
(disclaimer : It seems to be possible to add some energy through the regen system into this brick protection buffer)

You might be correct that there are weird short term fluctations. I really haven't done much analysis over short distances. I have made a lot of observations over longer trips though, and the average cnsumption displayed has looked fairly reasonable. Also the 100%(full battery) to low number SOC looks OK and do not conflict with average consumption. It's only when I perform measurement in the mid range of SOC I get into this discrepancy.
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post #15 of 57 (permalink) Old 08-24-2019, 12:20 AM Thread Starter
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Here's a preview of actual consumption calculation based on battery SoC in kWh reported by the API and made accessible by WattCat.

Prepare to be shocked.

Mostly suburban driving, fairly aggressive because I have zero patience in traffic and make full use of high-regen one pedal driving. A little bit of freeway.

Regardless of driving style, it's crazy and in fact embarrassing that the JLR computation off by this much.

I will keep posting on this until JLR figures this out.
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post #16 of 57 (permalink) Old 08-24-2019, 01:08 AM
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Quote:
Originally Posted by sciencegeek View Post
Here's a preview of actual consumption calculation based on battery SoC in kWh reported by the API and made accessible by WattCat.

Prepare to be shocked.

Mostly suburban driving, fairly aggressive because I have zero patience in traffic and make full use of high-regen one pedal driving. A little bit of freeway.

Regardless of driving style, it's crazy and in fact embarrassing that the JLR computation off by this much.

I will keep posting on this until JLR figures this out.
Thanks, Sciencegeek. I just started using WattCat and only have one trip as a data source but I can confirm Sciencegeek's findings. I-Pace/InControl reported numbers were underestimated by 20% compared to actual consumption.
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post #17 of 57 (permalink) Old 08-24-2019, 01:35 AM
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At 100% SoC WattCat shows 82.55 kWh available and if we assume 1 or 2 kWh available below 0% SoC to give the driver a safety net then usable battery is around 84.7 kWh as stated by JLR. Now if they can fix the inaccurate consumption numbers we can finally have an accurate range prediction.

I would like to have available battery kWh and miles driven per kWh used added to the trip bank then I could do the math for range myself.
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post #18 of 57 (permalink) Old 08-24-2019, 11:28 AM
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Quote:
Originally Posted by sciencegeek View Post
Here's a preview of actual consumption calculation based on battery SoC in kWh reported by the API and made accessible by WattCat.

Prepare to be shocked.

Mostly suburban driving, fairly aggressive because I have zero patience in traffic and make full use of high-regen one pedal driving. A little bit of freeway.

Regardless of driving style, it's crazy and in fact embarrassing that the JLR computation off by this much.

I will keep posting on this until JLR figures this out.

I'm not shocked. Something doesn't add up, but your trips are way too short and there isn't enough available information to draw any rational conclusions. There is probably a simple non-nefarious explanation for what you're seeing. For example, the car may be warming the battery and JLR may be excluding energy used for that from the consumption numbers it presents. With such short trips, the effect of something like that could be significant. Another possibility is that the JLR numbers are being misinterpreted. Maybe JLR's consumption numbers are computed entirely based on energy used to move the car forward, so if you're using Max AC with seat coolers on full blast and sitting in traffic a lot, a significant portion of your battery energy may not be factored into the JLR numbers. I'm speculating without any facts or evidence.
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post #19 of 57 (permalink) Old 08-24-2019, 04:04 PM
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I also noticed some time ago that the reported efficiency did not seem to match my rough calculations, so I decided to do a data analysis the old fashioned way: measure how much total energy I put into the vehicle over a long period and then divide it into the number of miles I drove over that period. I used the report from my ChargePoint home charger, which is the only charger I have ever used, to determine the total amount of energy I put into the vehicle. Then I simply divided the number of miles driven over the same period by the total energy. In my case, I chose April 16, 2019 as my start date and August 23, 2019 (yesterday) as my end date. During that period, I put a total of 1,361.4 kWh into my I-Pace. Over that period, according to the Jaguar InControl app, I had driven 2,760.9 miles. The simple math is that my efficiency was 2.03 mi/kWh. There will be a slight error in this calculation because my battery was not 100% full on April 16, nor is it full now. The ideal calculation would start and end at 100%, but it is still quite accurate.

So, how does this compare with what the car tells me? Using the InControl app, you can easily calculate the amount of energy reported by the car per trip. I assume the app reports the same number as reported on the display in the car, but I don't know that for sure. If you divide the miles reported for each trip by the mi/kWh reported for each trip, you will get the kWh used on each trip as reported by the app. In my case, over the same period as I used above, the total energy used was 1,103.9 kWh - clearly a lower number than what ChargePoint tells me I put into the battery. In fact, it is off by 23.32%. This is a smaller error than reported by sciencegeek, but still clearly significant.

My typical driving mission, for your comparison purposes, is around the San Francisco Bay area in a combination of city and highway driving. I typically drive 70-80 mph on the freeways and close to the speed limit when possible on surface streets, however quite a bit of time is spent in stop/go traffic on freeways and city streets. I would estimate about 25% of miles are in stop/go traffic and 75% is at high speed on the freeway. However, if you look at time spent, it is probably more like 60% in stop/go traffic and 40% at high speed. Temperature here since April has averaged between 60 and 90 deg F. and I use AC always set at 72 in the car. Some statistics accumulated from InControl are below:

Average trip length: 11.04 mi
Total miles: 2,760.9
Total energy reported by InControl: 1,103.9 kWh
Total energy reported by ChargePoint: 1,361.4 kWh
Total regeneration reported by InControl: 304.7 kWh
Average efficiency reported by InControl: 2.50 mi/kWh
Average efficiency calculated using ChargePoint data: 2.03 mi/kWh

Note that I assume that the InControl app is taking regeneration into account when it reports energy used per trip. If not, then the reported efficiency is off even more than my calculations state. I intend to keep tracking the data over the first year of ownership and then again in a few years to see if there is any degradation in efficiency over time.
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post #20 of 57 (permalink) Old 08-24-2019, 04:18 PM
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For those of you who prefer the kWh/100mi metric, for my numbers above they are:

ChargePoint data: 49.26kWh/100mi
InControl Data: 40.0kWh/100mi
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