Quick Mileage Cost Calculation

[ahd13]

I've been curious and have run some back of the envelope analyses to evaluate the true cost per mile of our Model 3, but just put some "harder" numbers around it, based on one round trip commute (small sample I know). In particular, I wanted to compare it to my wife's old Prius, which we could run for about $.08 / mile (~42MPG, ~$3.50 / gallon), ignoring other costs and inconveniences of an ICE vehicle, as well as driving experience, etc.

Results of the analysis (table below) put our cost to operate the Model 3 at $.05 per mile, based on an off-peak kWH rate in San Jose, CA of ~$.23. There is a minor non-obvious adjustment in the math to account for a recharge to 243 rather than 250 miles, though it doesn't change the rounded end result. Also, note the 85% ratio of actual to theoretical range (on mostly flat freeway) - would be interested to know if that's a typical result.

 

[rickdogg82]

I can't say if this is normal or not but for a more accurate picture I feel these calculations should be made over a longer period of time (6 months to a year)and a greater distance.

 

[mreynolds767]

I've been curious and have run some back of the envelope analyses to evaluate the true cost per mile of our Model 3, but just put some "harder" numbers around it, based on one round trip commute (small sample I know). In particular, I wanted to compare it to my wife's old Prius, which we could run for about $.08 / mile (~42MPG, ~$3.50 / gallon), ignoring other costs and inconveniences of an ICE vehicle, as well as driving experience, etc.

Results of the analysis (table below) put our cost to operate the Model 3 at $.05 per mile, based on an off-peak kWH rate in San Jose, CA of ~$.23. There is a minor non-obvious adjustment in the math to account for a recharge to 243 rather than 250 miles, though it doesn't change the rounded end result. Also, note the 85% ratio of actual to theoretical range (on mostly flat freeway) - would be interested to know if that's a typical result.

Yeah, if this is a day or two worth of information it really is not that helpful. An analysis after 6 months or so would be far more helpful.
Enough time to work in bad weather days, windy days, mixed driving, etc...
Electric cars will see much more fluctuation based on weather and fast highway speeds than ICE cars do.
I imagine that has done before.

Also, minor note I don't see where you indicated which model, which wheels/tires, etc... which all do matter.

Edit: Your data is of particular interest to me, as I pay the same as you for electricity. My supplier has no off peak options, all hours are the same overpriced amount

 

[Bill Price]

I've been curious and have run some back of the envelope analyses to evaluate the true cost per mile of our Model 3, but just put some "harder" numbers around it, based on one round trip commute (small sample I know). In particular, I wanted to compare it to my wife's old Prius, which we could run for about $.08 / mile (~42MPG, ~$3.50 / gallon), ignoring other costs and inconveniences of an ICE vehicle, as well as driving experience, etc.

Results of the analysis (table below) put our cost to operate the Model 3 at $.05 per mile, based on an off-peak kWH rate in San Jose, CA of ~$.23. There is a minor non-obvious adjustment in the math to account for a recharge to 243 rather than 250 miles, though it doesn't change the rounded end result. Also, note the 85% ratio of actual to theoretical range (on mostly flat freeway) - would be interested to know if that's a typical result.

My cost is just over $.03/mile.............but I drive an S and my electrical rate is substantially lower.....$0.1153/kWh

 

[ahd13]

My cost is just over $.03/mile.............but I drive an S and my electrical rate is substantially lower.....$0.1153/kWh

So your rate is about half mine and cost per mile is just over half mine. Mine is a Model 3 which is probably a bit lighter, and our weather is good for range (and my wife drives the car, and takes it pretty easy (chill setting etc.), so I'd say the results more or less foot...

 

[Knightshade]

This is kinda like comparing insurance rates- it's gonna vary wildly from person to person based on a bunch of factors

At about 12k miles on the car my lifetime average consumption is about 265 wh/m... so 3180 kwh used to go 12k miles.

I pay 2.79 cents per kwh to charge overnight (time of use) so 3180 times 2.79 cents is $88.72 to drive 12,000 miles... or 0.0073935 cents per mile driven.

Obviously this leaves out any power "lost" between plug and car and some other very minor factors... but given 12,000 miles of driving in my previous ICE vehicle (a Lexus IS350) would've cost me about 12.5 cents a mile (~24 mpg average at ~$3/gal for premium average) I'm doing pretty good.

 

[AlanSubie4Life]

For the OP, should be about 7 cents per mile. Something is off.

Do you have an AWD?

I would calculate:

$0.23/kWh * 46rmi * 0.245kWh/rmi / 0.9 /39 miles

= 7.4 cents/mi

0.9 is the charging efficiency which is a pretty good number for that. But it could be slightly better (maybe 0.92?)

But that is just quick calculations. Could not see the error right away. Maybe there is no error...who knows...if you have an SR+ it would make more sense but the efficiency makes not much sense then... EDIT: Can’t be an SR+ - charge rate too high...

This does not count vampire at all of course.

 

[ahd13]

Yeah, if this is a day or two worth of information it really is not that helpful. An analysis after 6 months or so would be far more helpful.
Enough time to work in bad weather days, windy days, mixed driving, etc...
Electric cars will see much more fluctuation based on weather and fast highway speeds than ICE cars do.
I imagine that has done before.

Also, minor note I don't see where you indicated which model, which wheels/tires, etc... which all do matter.

Edit: Your data is of particular interest to me, as I pay the same as you for electricity. My supplier has no off peak options, all hours are the same overpriced amount

We have a Model 3, dual motor, with 310 mile range, run it pretty easy on chill setting, and don't use auto pilot.

 

[ewoodrick]

Cost is pretty easy, about 0.250 kW/m * price/kWh.
Energy varies across the country, season, and time. But unlike gas, stays pretty consistent, year after year.

Some charging locations are free, while Superchargers are more expensive. And if you have the capability, CHAdeMO is often even more. But still gas competitive

 

[ahd13]

For the OP, should be about 7 cents per mile. Something is off.

Do you have an AWD?

I would calculate:

$0.23/kWh * 46rmi * 0.245kWh/rmi / 0.9 /39 miles

= 7.4 cents/mi

0.9 is the charging efficiency which is a pretty good number for that. But it could be slightly better (maybe 0.92?)

But that is just quick calculations. Could not see the error right away. Maybe there is no error...who knows...if you have an SR+ it would make more sense but the efficiency makes not much sense then...

This does not count vampire at all of course.

Perhaps I'm missing something, but it cost me a total $1.93 (true cost calculated from my grid usage, not from the car) to drive 39 miles. That's about 5 cents a mile.

 

[ahd13]

This is kinda like comparing insurance rates- it's gonna vary wildly from person to person based on a bunch of factors

At about 12k miles on the car my lifetime average consumption is about 265 wh/m... so 3180 kwh used to go 12k miles.

I pay 2.79 cents per kwh to charge overnight (time of use) so 3180 times 2.79 cents is $88.72 to drive 12,000 miles... or 0.0073935 cents per mile driven.

Obviously this leaves out any power "lost" between plug and car and some other very minor factors... but given 12,000 miles of driving in my previous ICE vehicle (a Lexus IS350) would've cost me about 12.5 cents a mile (~24 mpg average at ~$3/gal for premium average) I'm doing pretty good.

You certainly are - that's a really low electricity rate compared to mine!

 

[powaking]

With 16,000+ miles I have averaged 326Wh/mi and since May of this year I'm averaging 294Wh/mi. My rate is .22/kW and this includes all taxes and fees. With that in mind my lifetime average is about 7.2cents/mi and since May (warmer months) its about 6.5cents/mi. The 3 is much more efficient so your numbers should be lower.

 

[AlanSubie4Life]

With 16,000+ miles I have averaged 326Wh/mi and since May of this year I'm averaging 294Wh/mi. My rate is .22/kW and this includes all taxes and fees. With that in mind my lifetime average is about 7.2cents/mi and since May (warmer months) its about 6.5cents/mi. The 3 is much more efficient so your numbers should be lower.

This does not account for charging inefficiency.

 

[AlanSubie4Life]

Perhaps I'm missing something, but it cost me a total $1.93 (true cost calculated from my grid usage, not from the car) to drive 39 miles. That's about 5 cents a mile.

Agreed. That is what I could not figure out. It seemed like the only piece of data that could be in error was the time spent charging. Or the car somehow added some miles on its own (sometimes happens but not usually this time of year). If you have an actual meter on your Wall Connector...showing 8.4kWh...I really could not explain it then, except for possibility of SoC nonlinearity or phantom miles added, as mentioned!

I would try a longer charging interval, monitor charging time carefully.

I think you’ll find it ends up closer to 7 cents per rated mile (per driven mile depends on the drive of course).

 

[powaking]

This does not account for charging inefficiency.

Nor does it account for the times I supercharged for free during the first 6 months or the times I've charged for free at charge point locations. Its a ball park figure I use. I can multiply it by .83 as thats about the efficiency of charging at home but again I don't charge 100% at home. Its also the reason why I said 'about' in my estimates.

 

[darth_vad3r]

OP, in terms of sources of inaccuracy ...

1) Does your trip home end with any downhill stretches and/or large deceleration stretches shortly before stopping your car?

There can be several miles of added range from regen hidden from you which could translate to you not having used 46 miles off the dashboard. It seems like it’s possible that up to 1 kWh of regen may be hidden from the dashboard gauge’s distance number at any time. It’s not clear to me if this would stay hidden during a recharge event, I would presume not and it would be added back in as the charge progressed which would manifest as your efficiency for that charge session (as measured by increase dashboard range) being better than it actually was.

2) Also, using a trip meter gives better distance accuracy with 1 decimal place versus the odometer with rounded miles introducing as much as a full mile of error.

To quantify these errors:
1) 39 miles added to the range (204 -> 243) while charging is 9.555 kWh (39 mi x 245 Wh/mi). The 1 kWh max regen ‘error’ is up to 10% error here.

2) “39” off the odometer measured from OdoA (7958 +/- 0.5mi) minus (7919 +/- 0.5mi) = 39 +/- 1.0 mi. So that’s up to 2.56% error.

That all said, I agree with @AlanSubie4Life that something still seems off even with above sources of error:

Seems you charged at 240 V, 48 A so the efficiency should be quite high, easily in the 90’s.

8.4 kWh x 0.90 = 31 miles of added range for AWD with 245 Wh/mi internal charge rate constant. That’s 20% off your number of 39 added miles.

Something seems quite off with the numbers. I would repeat test again.
Also, doing it over a few days will capture vampire drain costs as well.

You really have to weight it for seasonality too since colder winter temps decrease the battery’s efficiency.

 

[darth_vad3r]

Nor does it account for the times I supercharged for free during the first 6 months or the times I've charged for free at charge point locations. Its a ball park figure I use. I can multiply it by .83 as thats about the efficiency of charging at home but again I don't charge 100% at home. Its also the reason why I said 'about' in my estimates.

Well, you need to divide by .83, or whatever charge efficiency your average is, to get wall kWh used.

This is assuming the Wh/mi number you mentioned is one pulled from the car’s trip meter (which is measuring DC kWh out of the battery, after losses from DC kWh into the battery, after losses from AC kWh in from the wall (or DC supercharging)).

So if you are trying to calculate a cost in kWh from AC, you should divide the DC kWh used according to the trip meter by anywhere from ~0.6 to ~0.9 (multiply by 1.11 to 1.67) depending on the AC power you charge at.

So saying the Model 3 should be better than your numbers quoted is missing the multiplier, so the final AC kWh cost might actually be higher than the numbers you quoted (~6-7c/mi) for an AWD 3.

 

[AlanSubie4Life]

0.250 kWh/mi * price/kWh.

After correcting units, this is correct for the SR+, but it does not include vampire losses. Use 0.29kWh/mi * Price/kWh for the AWD (not including P3D+) and then add about 10-15% to the resulting cost, if you live in a mild climate and drive 10k miles a year. Might be more like a 40-50% adder in a more extreme climate (but depends on a lot of factors of course). That's the quick and easy calculation and it will be quite accurate.

 

[ahd13]

Agreed. That is what I could not figure out. It seemed like the only piece of data that could be in error was the time spent charging. Or the car somehow added some miles on its own (sometimes happens but not usually this time of year). If you have an actual meter on your Wall Connector...showing 8.4kWh...I really could not explain it then, except for possibility of SoC nonlinearity or phantom miles added, as mentioned!

I would try a longer charging interval, monitor charging time carefully.

I think you’ll find it ends up closer to 7 cents per rated mile (per driven mile depends on the drive of course).

I expect over the longer run you're right. This was a very small sample.

 

[AlanSubie4Life]

I pay 2.79 cents per kwh

This is so ridiculous.

0.0073935 cents per mile driven.

Yes, that is 0.7 cents/mi, not 7 cents/mi! For you, worrying about charging inefficiency and vampire drain really is completely unnecessary!