Comparing cost per mile using total energy from trip screen metrics vs wall charger metrics and compared with ICE

[honor_the_driv]

Yesterday I updated the Tesla app so and connected my wall connector in the app so that I could get a sense on the true energy usage. Then I did a little math to figure out my cost per mile:

1. Miles driven yesterday: 56 mi
2. Approximate electricity cost rate for my last billing cycle (including base charge, taxes, etc): $0.1513/kWh
3. Metrics from Tesla Trip Screen
   1. Miles driven since last charge: 56 mi
   2. Energy used since last charge: 16 kWh
   3. Average efficiency since last charge: 285.7 Wh/mi (0.2857 kWh/mi)
4. Tesla Wall charger reported charge amount to get the car back to 80% (this was the charge limit for the previous night and most nights): 20.7 kWh
   1. Average efficiency since last charge using the energy the wall charger reported to get back to 80%: 0.3696 kWh/mi
5. Approximate average mileage for the previous ICE compact SUV I was driving: 27 mi/gal
6. Current cost of regular gas at the gas station I would normally fill up at: $3.69/gal

Results:

Average ≈ cost per mile Electric (based on in-car trip screen metrics)	$0.0432 / mi
Average ≈ cost per mile Electric (based on wall charger metrics + distance traveled)	$0.0559 / mi
Average ≈ cost per mile ICE	$0.1366 / mi

So we can see that there is a significant difference in the energy the car reported having used for the day's drive vs the amount that it took to recharge to the same point. Regardless of which energy metric I used though the cost per mile was far less than with my previous ICE car. The percentages are either 31% of the cost per mile or 41% of the cost per mile compared to gas.

As a bonus I checked and to get the same cost per mile from an ICE car the mileage would need to be ≈ 66mpg, lol.

In case anyone is wondering how I calculated the approximate average cost per mile, or they want to double check my work (I have done much of this since college) here are the formulas I used:

 

[jcanoe]

The Wall Connector utilization (20.7 kWh) includes charging losses (~5%) and energy used while parked including Standby mode/Sentry mode, Cabin Overheat Protection and Preconditioning. Subtract the16kWh consumed driving 56 miles @ 285Wh/mi from 20.7kWh = 4.7kWh (22.7% of the 20.7kWh). For reference, Standby mode will use 5 kWh to 6 kWh over 24 hours when Sentry mode is active. Part of the 4.7 kWh may be attributed to Standby mode with and without Sentry mode active.

 

[honor_the_driv]

The Wall Connector utilization (20.7 kWh) includes charging losses (~5%) and energy used while parked including Standby mode/Sentry mode, Cabin Overheat Protection and Preconditioning.

Yup I realized that. If I want to know the true cost of operating the vehicle and getting around town this is still the figure that gives me the more accurate number.

I included both so people could see the significant difference.

 

[jcanoe]

If you take a road trip in your Model Y you can compare the cost of Supercharging (assumed) for the trip with the 27 MPG ICE vehicle (or similar.) On my last trip the average Supercharger cost to charge was $0.44/kWh.

 

[honor_the_driv]

Yea I'll be paying attention to that when I do take my first road trip. The week that I got the car I tested out supercharging at a stall near my house and it was $0.39/kWh.

As I was typing this out I multiplied that rate times the efficiency I mentioned in the original post but then I realized the the efficiency for a road trip would likely be very different and invalidating whatever number I got (I was stuck in really bad traffic yesterday).

 

[MrKashima]

Yesterday I updated the Tesla app so and connected my wall connector in the app so that I could get a sense on the true energy usage. Then I did a little math to figure out my cost per mile:

1. Miles driven yesterday: 56 mi
2. Approximate electricity cost rate for my last billing cycle (including base charge, taxes, etc): $0.1513/kWh
3. Metrics from Tesla Trip Screen
   1. Miles driven since last charge: 56 mi
   2. Energy used since last charge: 16 kWh
   3. Average efficiency since last charge: 285.7 Wh/mi (0.2857 kWh/mi)
4. Tesla Wall charger reported charge amount to get the car back to 80% (this was the charge limit for the previous night and most nights): 20.7 kWh
   1. Average efficiency since last charge using the energy the wall charger reported to get back to 80%: 0.3696 kWh/mi
5. Approximate average mileage for the previous ICE compact SUV I was driving: 27 mi/gal
6. Current cost of regular gas at the gas station I would normally fill up at: $3.69/gal

Results:

Average ≈ cost per mile Electric (based on in-car trip screen metrics)	$0.0432 / mi
Average ≈ cost per mile Electric (based on wall charger metrics + distance traveled)	$0.0559 / mi
Average ≈ cost per mile ICE	$0.1366 / mi

So we can see that there is a significant difference in the energy the car reported having used for the day's drive vs the amount that it took to recharge to the same point. Regardless of which energy metric I used though the cost per mile was far less than with my previous ICE car. The percentages are either 31% of the cost per mile or 41% of the cost per mile compared to gas.

As a bonus I checked and to get the same cost per mile from an ICE car the mileage would need to be ≈ 66mpg, lol.

In case anyone is wondering how I calculated the approximate average cost per mile, or they want to double check my work (I have done much of this since college) here are the formulas I used:

View attachment 975982

Thank you for this! I knew something wasn’t adding up. It’s always seemed like the amount of charge never equates with the supposed “energy usage” in the car app.

 

[honor_the_driv]

@MrKashima You might be interested in the insight from some others on an earlier related thread I started on this topic-
Are the Average Energy per mile metrics on the trip screen accurate?

 

[bruce4000]

Of course I’ve been doing some road trips with no extra cost to charge at hotels lately which really helps the cost per mile.

 

[flixden]

You can look at the charging stats on the Tesla app also, instead of the trip consumption (which, as I understand it, only reports back what was used by the motors, essentially).
The consumption from the charging stats is 5-6% below what my Chargepoint Flex reports, so pretty close.

 

[honor_the_driv]

@flixden do you know if the charging stats can be filtered or exported? I see the chart but it looks like you have to estimate the numerical value

 

[flixden]

@flixden do you know if the charging stats can be filtered or exported? I see the chart but it looks like you have to estimate the numerical value

I am not aware of a way to export the charge stats, but you can read the kWh values right from the app: for a given month, year or the last 31 days. No decimals, it's rounded to the full kWh, but should be good enough.
Tap one of the % numbers, and it will switch to kWh.

 

[dcantato]

Tesla::API - Interface to Tesla's API - metacpan.org

Interface to Tesla's API

metacpan.org

Maybe thats a good start to hit an api

 

[supergeek]

Loggers like TeslaFi will capture the energy used/added for every charge session. Below are my 2022 metrics for an S85 that isn’t particularly efficient at charging and phantom drains like crazy.

4666 kwh used for 6610 kWh pulled from the wall. Since TeslaFi measures charge efficiency we can see that about half that loss comes from charging itself and the other half is phantom drain.

Our car is pre-sentry mode and I tend to discount preheating as extra energy use since the car would have to heat up about the same amount while you’re driving.

 

[dn325ci]

Yesterday I updated the Tesla app so and connected my wall connector in the app so that I could get a sense on the true energy usage. Then I did a little math to figure out my cost per mile:

1. Miles driven yesterday: 56 mi
2. Approximate electricity cost rate for my last billing cycle (including base charge, taxes, etc): $0.1513/kWh
3. Metrics from Tesla Trip Screen
   1. Miles driven since last charge: 56 mi
   2. Energy used since last charge: 16 kWh
   3. Average efficiency since last charge: 285.7 Wh/mi (0.2857 kWh/mi)
4. Tesla Wall charger reported charge amount to get the car back to 80% (this was the charge limit for the previous night and most nights): 20.7 kWh
   1. Average efficiency since last charge using the energy the wall charger reported to get back to 80%: 0.3696 kWh/mi
5. Approximate average mileage for the previous ICE compact SUV I was driving: 27 mi/gal
6. Current cost of regular gas at the gas station I would normally fill up at: $3.69/gal

Results:

Average ≈ cost per mile Electric (based on in-car trip screen metrics)	$0.0432 / mi
Average ≈ cost per mile Electric (based on wall charger metrics + distance traveled)	$0.0559 / mi
Average ≈ cost per mile ICE	$0.1366 / mi

So we can see that there is a significant difference in the energy the car reported having used for the day's drive vs the amount that it took to recharge to the same point. Regardless of which energy metric I used though the cost per mile was far less than with my previous ICE car. The percentages are either 31% of the cost per mile or 41% of the cost per mile compared to gas.

As a bonus I checked and to get the same cost per mile from an ICE car the mileage would need to be ≈ 66mpg, lol.

In case anyone is wondering how I calculated the approximate average cost per mile, or they want to double check my work (I have done much of this since college) here are the formulas I used:

View attachment 975982

Love it. Nice analysis, Copernicus. An important discussion, as .0559 is greater than the car's .0432 by 29%. Not trivial, though still a significant savings over ICE.

 

[voldar]

Your Tesla reported 16 kWh used while the Tesla wall reported 20.7 kWh added to come back to 80%. So, the efficiency of charging is 16/20.7 = 77%
To have an accurate report you should charge your Tesla to 100%, drive it then come back and charge to 100% back. Usually the difference between the 2 values is 18-20% for Tesla Model 3. For the Tesla Y it is indeed about 22%. It is believed that it happens because Tesla doesn't count the kWh while parked. Or it really has a shitty on-board charger.

 

[flixden]

Your Tesla reported 16 kWh used while the Tesla wall reported 20.7 kWh added to come back to 80%. So, the efficiency of charging is 16/20.7 = 77%
To have an accurate report you should charge your Tesla to 100%, drive it then come back and charge to 100% back. Usually the difference between the 2 values is 18-20% for Tesla Model 3. For the Tesla Y it is indeed about 22%. It is believed that it happens because Tesla doesn't count the kWh while parked. Or it really has a shitty on-board charger.

I am only seeing a 5-6% difference between what the car (app, charge stats) reports vs what my chargepoint homeflex is saying.

 

[voldar]

I am only seeing a 5-6% difference between what the car (app, charge stats) reports vs what my chargepoint homeflex is saying.

That would be news to me. So to make sure, what you see in the car as kWh used for a trip and the kWh added to bring back the battery state of charge at the same level as before the trip, you see 5% difference ?

 

[flixden]

That would be news to me. So to make sure, what you see in the car as kWh used for a trip and the kWh added to bring back the battery state of charge at the same level as before the trip, you see 5% difference ?

No, as I said: I am comparing what the Tesla charging stat (in the app) reports for a charging session vs what my Chargepoint reports for the same session.

 

[flixden]

No, as I said: I am comparing what the Tesla charging stat (in the app) reports for a charging session vs what my Chargepoint reports for the same session.

Here is an example showing my numbers for the month of September.
At home, it's 247 vs 237 kWh.

Also, Tesla shows 11kWh at work, which is the same charging session listed with 12kWh by Chargepoint (public) We have a Chargepoint Station at work, very convenient. Of course, these numbers are rounded, but over time, it comes down to a 5-6% difference.
BTW: my Chargepoint monthly statement shows 3 decimals for each charging session. The 12kWh session above actually was 11.998kWh. That one I am sure is super accurate, as it's a public charger where people pay, so it must be calibrated.

 

[voldar]

No, as I said: I am comparing what the Tesla charging stat (in the app) reports for a charging session vs what my Chargepoint reports for the same session.

Ahh, so you are talking about the difference between what Tesla and your EVSE reports as sent to the car. Yes, in this case the difference is about 5-6%. I have teslafi.com to confirm this to me too.