Cost of Fuel Equivalent

[Daniel in SD]

The short formula below should account for those as well. Vampire drain doesn't appear to be much, nor does the time spent in park (for me YMMV). I guess it would be considerable if I frequented drive-in movies (yes, there is one around where I live).

In cold weather the car starts blasting the heat the second you open the door. If you're taking a short trip it's not an insignificant amount of energy. Vampire drain is about 1kwh per day.

 

[jerry33]

In cold weather the car starts blasting the heat the second you open the door. If you're taking a short trip it's not an insignificant amount of energy. Vampire drain is about 1kwh per day.

If you set the charge start so that it ends about the time you start driving, and preheat the car with the app (on HI) for 15 to 30 minutes before taking off, you typically don't even need to run the heater during a short trip (up to about 25 miles) in cold weather. Of course, it depends on how cold is cold, at -20 not much helps.

 

[AlanSubie4Life]

The short formula below should account for those as well. Vampire drain doesn't appear to be much, nor does the time spent in park (for me YMMV). I guess it would be considerable if I frequented drive-in movies (yes, there is one around where I live).

Modify as:

W' = W + (350kWh/yr)/(Miles/Yr)

And T = W' * (1+K)

If you set the charge start so that it ends about the time you start driving, and preheat the car with the app (on HI) for 15 to 30 minutes before taking off, you typically don't even need to run the heater during a short trip (up to about 25 miles) in cold weather. Of course, it depends on how cold is cold, at -20 not much helps.

The only way to accurately account for this usage is to have a meter on your EV. It's so dependent on your climate that it's hard to include it in any formula. 15-30 minutes of preheat could use 5kWh, or it could use 1kWh, depending on the outside temperature.

 

[srs5694]

If you set the charge start so that it ends about the time you start driving, and preheat the car with the app (on HI) for 15 to 30 minutes before taking off, you typically don't even need to run the heater during a short trip (up to about 25 miles) in cold weather.

Whether it's heated before you leave or en route, it's still electricity consumed providing heat (or cooling in hot weather), and thus counts in any legitimate cost calculation. Pre-heating (or pre-cooling) is a valid strategy for maximizing range, though. Also, there might be a slight advantage to pre-heating/cooling if the electricity is used directly, rather than first being stored in the battery, which of course is not 100% efficient.

 

[Knightshade]

Whether it's heated before you leave or en route, it's still electricity consumed providing heat (or cooling in hot weather), and thus counts in any legitimate cost calculation. Pre-heating (or pre-cooling) is a valid strategy for maximizing range, though. Also, there might be a slight advantage to pre-heating/cooling if the electricity is used directly, rather than first being stored in the battery, which of course is not 100% efficient.

AFAIK the car runs off wall power, not battery power, when plugged in, so you'd indeed be getting the "better" efficiency that way

 

[RaeW]

I'm surprised you're able to get 300Wh/mi in your S85D (I thought it was rated 330Wh/mi?). You stated average rate of 4.3cents/kWh earlier I think? 4.3c/kWh*300Wh/mi = 1.29 cent/mi = 27% of 4.7 cents/mi (Prius)

Anyway.

You are definitely in an area where if the sole objective is to save on energy costs for your vehicle, you'd want to get a large solar array first!

Sadly without massive solar arrays in San Diego, they've moved around the time-of-use hours to minimize the benefit of solar. They do offer good TOU plans (with a small monthly fee to get about 9 cents/kWh at night), but when you move to that plan, then you had better not use AC between 4-9PM in the summer (at 50 cents/kWh). If you didn't get forced into the TOU by your quest for cheap EV charging, you could get either a tiered rate (which would usually be much better but depends on your use) or a different TOU rate plan which provides for twice as expensive (17 cents) nighttime charging, but 27cents/kWh for most AC use, up to a point - so giving up those cheaper AC rates (if you use AC) could be an extra cost of owning an EV if you pay for the the ultra-cheap night rate! It's a dizzying optimization problem and I think there are about 5 main obvious plans to choose from, but I think there are something like 20 different rate plans available.
The solution is to go big or go home on your solar - 8kW should support 1 EV fairly well, as long as you don't use much AC. If you have two Teslas a 10-12kW system could be more appropriate. Obviously all depends on how much driving you do. I'm adding in some margin on the solar sizing here because the last thing you want to be doing is to put a bunch of money into solar and then have to pay through the nose for TOU AC use. Figuring out the exact right optimum is pretty impossible without knowing the exact usage patterns. And also affected by whether you can get a west-facing array.

I have solar panels (since 2010) facing170 degrees and 240 degrees with a total of 9.87 kW (a system above 10 kW cannot be self-reported in MA). As the car sits in the garage right now it shows 310 Wh/mi for the last 5.2 miles and 333 Wh/mi for the last 86, so you are in the ballpark. The Prius generally gets 55 MPG after the first 5 minutes but may get only 35 MPG for the first 5 when cold. If I use 50 MPG the figure would be 24.6%. On the other hand there have been years when electric cost was close to $0.01/kWh ($0.043 was for 2018 off the top of my head, it was actually $0.0411). In one year (1916) it was $0.067. I think about 25% of the fuel cost of the Prius is a reasonable estimate. Solar power advantage is highly dependent on weather; snow, clouds, heat & humidity (AC use) etc.

 

[StealthP3D]

You're missing energy used while the car is in park (seems to be significant for me) and vampire drain.

Yeah, but my food stamps cover those losses 25 times over!

 

[StealthP3D]

15-30 minutes of preheat could use 5kWh, or it could use 1kWh, depending on the outside temperature.

Nope. There is no way a Model 3 cabin heater can consume 5kWh in 30 minutes, even at -20 degrees. It's maximum draw is around 7kW and as the heater element heats up (which doesn't take long) the resistance goes up due to its design and the maximum draw drops to around 5kW. The only way you would need to pre-heat for 30 minutes is if the car was encased in ice and you heated in lieu of scraping. In practice, I've found a 10-minute pre-heat to warm things up nicely when it's 10 degrees below freezing. A gas car, on the other hand, is just starting to put out barely warm air after 10 minutes of stinky idling in those temperatures.

 

[AlanSubie4Life]

Its maximum draw is around 7kW

This 7kW number is incorrect. Please measure with heat set to MAX and get back to me. Data, man. Data. I’ve measured it. So have others. It is possible to draw in excess of 10kW from the wall outlet (closer to 13kW for some). You can either believe me, or you can measure it on your vehicle screen, or with your metering. You are right that the PTC energy draw does reduce somewhat as time goes on. I’ve measured a steady state of 1.5-2kW with the heat set to 72 with an outside temperature of 60 degrees.

As far as the total, the 5kWh number IS a worst, worst case number (extreme cold) and may be a little high (it’s an estimate). That’s why I said “from 1kWh”, which is probably more common for a 30 minute preheat in conditions where people would be preheating.

 

[StealthP3D]

This 7kW number is incorrect. Please measure with heat set to MAX and get back to me. Data, man. Data. I’ve measured it. So have others. It is possible to draw in excess of 10kW from the wall outlet (closer to 13kW for some). You can either believe me, or you can measure it on your vehicle screen, or with your metering.

I'm sorry, but you are jumping to conclusions. The cabin heater itself cannot draw that much. You are seeing total draw, the battery heater and seat heaters could have been on, the 12V battery was likely charging and who knows what else was left on. None of this indicates the 7kW number is incorrect.

 

[Need]

My previous car is a hybrid with close to 50 MPG. I did the calculation before buying the Tesla and I know that it is not going to save me much on fuel cost. But I also drove close to 30K miles a year. Autopilot will save my sanity on my 3 hours round trip commute. And not having to stop by the gas station to get gas will save me about 86 trips a year. And assuming each trip to the gas station took about 10 min (deviating from route and lining up and getting gas), it will save me over 14 hours a year. What did it cost me? By not going to the gas station, I didn't get a chance to buy any PowerBall ticket in the last 6 months... I could have been a billionaire!

 

[AlanSubie4Life]

I'm sorry, but you are jumping to conclusions. The cabin heater itself cannot draw that much. You are seeing total draw, the battery heater and seat heaters could have been on, the 12V battery was likely charging and who knows what else was left on.

It is possible that the battery heater (which I think has been measured at 2kW) is a contributor to the > 10kW number, but that would be relevant to my original numbers for a cold situation! It’s going to take quite a long period of 2kW heating to warm a battery that weighs 1 ton!

I just measured 9kW from the wall with heat set to MAX. Note that 500W is for the other car functions (no seat heaters...so efficient! ). So 8.5kW for heat. So for the purposes of this discussion it appears the 7kW number is incorrect. It is possible that when drawn from the battery it is “just” 7kW, but the relevant numbers are drawn from the wall (so include any AC/DC conversion losses). I did see it back off to about 8kW after 1 minute. On MAX it won’t back off much I think, but did not take the time to check it for a long period.

It is quite easy to see that when including battery heating, seat heating, etc, you can easily exceed 10kW for a preheat event! (Drawn from the wall of course in most cases.) If you have all the seat heaters on, at 60 degrees, with internal temp set at 72 degrees, you will see a steady state of about 2kW draw. This will give 1kWh in 30 minutes so I kind of think that represents the minimum you would ever see, which is why I quoted that number for the proposed 30-minute preheat mentioned by another poster.

Conditions: 70 degrees overnight in the garage. Sitting in the garage. So no battery heating here for sure.

Thanks. If you have refuting data let me know.

 

[StealthP3D]

This 7kW number is incorrect.

It's only rated to draw 7kW and that's only to heat it up. It quickly dials back after that.

I don't know what other items you had on when you measured higher numbers so I'm not even going to attempt to explain your measurement but I'm positive it wasn't from cabin heating. I bet I could get it higher than that if I tried. I just don't see the huge amounts of electrical consumption you're always talking about as if it is something shameful. It's literally pennies a day.

 

[Daniel in SD]

It's only rated to draw 7kW and that's only to heat it up. It quickly dials back after that.

I don't know what other items you had on when you measured higher numbers so I'm not even going to attempt to explain your measurement but I'm positive it wasn't from cabin heating. I bet I could get it higher than that if I tried. I just don't see the huge amounts of electrical consumption you're always talking about as if it is something shameful. It's literally pennies a day.

I suggest you read the thread title.

 

[AlanSubie4Life]

It's only rated to draw 7kW and that's only to heat it up. It quickly dials back after that.

I don't know what other items you had on when you measured higher numbers so I'm not even going to attempt to explain your measurement but I'm positive it wasn't from cabin heating. I bet I could get it higher than that if I tried. I just don't see the huge amounts of electrical consumption you're always talking about as if it is something shameful. It's literally pennies a day.

You may be right that it is rated at 7kW DC (my guess is that it can peak at a somewhat higher value - it is just a rating, after all). Can you point to definitive info on that? It’s fine, would be good to see the definitive info so I can have something to back up my statements in the future, other than empirical data.
But, that DC rating scales (apparently) to 8.5kW AC from the wall, which is what is relevant for this discussion. (There is also a fan running at max speed, which might be 50-100W - have not poked around to quantify this.) I did not have seat heaters on. I don’t think I had the AC on. There was nothing else on - 2A @240V is a standard baseline draw from the wall. You can do this test yourself if you have a Wall Connector (preferably one that can source 48A - which I do not have, mine is limited to 9.6kW, but I could definitely max it out even without any battery charging taking place). You’ll get the same result. Note that the baseline draw is usually drawn from the battery: once the overall draw becomes low enough, the Wall Connector clicks off. But you’ll briefly see the 2A@240V number before it does so, after you turn off the HVAC.

My original statement was not in regards to the cabin heater specifically:

15-30 minutes of preheat could use 5kWh, or it could use 1kWh, depending on the outside temperature.

This statement stands as accurate, according to all data presented so far. The high end estimate of 5kWh (from the wall) is for a very cold situation when the car is cold soaked, and preheated for 30 minutes.

 

[StealthP3D]

I suggest you read the thread title.

After considering the thread title for about 3 seconds, I stand by my original statement that the cabin heater can only consume a maximum of 7kW and only initially, it will get quickly dialed back after that to around 5kW, even on a very cold morning.

 

[StealthP3D]

This statement stands as accurate, according to all data presented so far. The high end estimate of 5kWh (from the wall) is for a very cold situation when the car is cold soaked, and preheated for 30 minutes.

It would have to be drawing a steady 10kW for the entire 30 minutes for your estimate to be considered anything but unrealistically pessimistic. If it were drawing that much, it wouldn't be entirely due to preheating the cabin, as I said, it could be charging the battery, etc.

 

[AlanSubie4Life]

huge amounts of electrical consumption you're always talking about as if it is something shameful. It's literally pennies a day.

The use of energy to heat the car is not shameful, it's simply physics, and the use of a Positive Temp Coefficient resistive heating element.

The purpose of this thread is to compare the cost of running a Tesla to running a gas car. It's AWESOME to be able to preheat the Tesla easily, and it is much better than freezing in an ICE car until the engine warms up. But it comes at a cost (as does preheating an ICE car if you choose to do so).

As the purpose of this thread is to compare to ICE costs, where it is easy to calculate the total fuel used, I simply was stating that to properly assess the energy used by the Tesla, you have to look at the integrated draw from the wall, not look at the meter in the car, etc. There are simply too many variables for an individual user that that is the only way to be accurate. It's really the ONLY way to compare the costs, if that is your SOLE objective. And I provided some APPROXIMATE numbers to give people an order of magnitude they could have in their head for the costs of certain activities, since most people cannot accurately meter their EV energy usage in isolation - my estimates are not set in stone, but I have proven that my numbers are 100% conceivable. Will the actual number USUALLY be closer to 1kWh for a 15-30 minute preheat? Of course! That was clear from my earlier statements!

Look, I love my Tesla, I repeat, I LOVE it. But it's not like it is God's gift to man.

It would have to be drawing a steady 10kW for the entire 30 minutes for your estimate to be considered anything but unrealistically pessimistic. If it were drawing that much, it wouldn't be entirely due to preheating the cabin, as I said, it could be charging the battery, etc.

If I lived in an EXTREMELY cold place it would be quite easy to prove the 5kWh number is in the ballpark. Should I have said 4kWh? Maybe...not really the point. Why anyone would do a 30-minute preheat, who knows, but that's also not the point (30 minutes wasn't my number - but your departure could easily be delayed, obviously). Charging the battery??? The 12V? Do you have a wattage for that? My estimate is that it takes less than 200W and probably closer to 100W to do that - but the question is really the integrated energy that would need to be added, and since we know vampire is about 750Wh/day, a cycle of charging of the 12V is likely considerably less than 250Wh (I think it's likely less than 100Wh since the total vampire drain per day is dominated by other losses (windshield cam heater, cameras, ultrasonics, computer, etc.) during the period of time the car is in idle mode, not while it is in sleep (when it is draining the 12V)).

Much more likely, in a cold, cold place, you're going to see the 8.5kW from the wall for the heater, plus an additional 2kW (scaled up to 2.4kW from the wall), plus seat heaters (let's say 2, for a total of 200W - this is slightly high but maybe not too far off when scaled up to the AC power requirement), so that leaves you at close to 11kW. @eprosenx has measured what he saw over the winter during a preheat as I recall.

In MOST cases, of COURSE it would taper down the heat as the cabin came to temperature. But not so sure how much tapering there would be when it's -20 degrees out. I KNOW it tapers to 1.6-2kW for a 12 degree F difference from ambient (72F vs. exterior 60F). I imagine to maintain a toasty cabin temperature when there is a 100 degree differential the tapering will be considerably less! Plus the battery heater will likely be operating for quite some time at 2kW at -20F, since 1000 pounds of battery & coolant has a lot more heat capacity than the dry air in a cabin. So that's 1.2kWh JUST from the battery heater.

 

[StealthP3D]

The use of energy to heat the car is not shameful, it's simply physics, and the use of a Positive Temp Coefficient resistive heating element.

The purpose of this thread is to compare the cost of running a Tesla to running a gas car. It's AWESOME to be able to preheat the Tesla easily, and it is much better than freezing in an ICE car until the engine warms up. But it comes at a cost (as does preheating an ICE car if you choose to do so).

As the purpose of this thread is to compare to ICE costs, where it is easy to calculate the total fuel used, I simply was stating that to properly assess the energy used by the Tesla, you have to look at the integrated draw from the wall, not look at the meter in the car, etc. There are simply too many variables for an individual user that that is the only way to be accurate. It's really the ONLY way to compare the costs, if that is your SOLE objective. And I provided some APPROXIMATE numbers to give people an order of magnitude they could have in their head for the costs of certain activities, since most people cannot accurately meter their EV energy usage in isolation - my estimates are not set in stone, but I have proven that my numbers are 100% conceivable. Will the actual number USUALLY be closer to 1kWh for a 15-30 minute preheat? Of course! That was clear from my earlier statements!

Look, I love my Tesla, I repeat, I LOVE it. But it's not like it is God's gift to man.



If I lived in an EXTREMELY cold place it would be quite easy to prove the 5kWh number is in the ballpark. Should I have said 4kWh? Maybe...not really the point. Why anyone would do a 30-minute preheat, who knows, but that's also not the point (30 minutes wasn't my number). Charging the battery??? The 12V? Do you have a wattage for that? My estimate is that it takes less than 200W and probably closer to 100W to do that - but the question is really the integrated energy that would need to be added, and since we know vampire is about 750Wh/day, a cycle of charging of the 12V is likely considerably less than 250Wh (I think it's likely less than 100Wh since the total vampire drain per day is dominated by other losses (windshield cam heater, cameras, ultrasonics, computer, etc.) during the period of time the car is in idle mode, not while it is in sleep (when it is draining the 12V)).

Much more likely, in a cold, cold place, you're going to see the 8.5kW from the wall for the heater, plus an additional 2kW (scaled up to 2.4kW from the wall), plus seat heaters (let's say 2, for a total of 200W - this is slightly high but maybe not too far off when scaled up to the AC power requirement), so that leaves you at close to 11kW. @eprosenx has measured what he saw over the winter during a preheat as I recall.

In MOST cases, of COURSE it would taper down the heat as the cabin came to temperature. But not so sure how much tapering there would be when it's -20 degrees out. I KNOW it tapers to 1.6-2kW for a 12 degree F difference from ambient (72F vs. exterior 60F). I imagine to maintain a toasty cabin temperature when there is a 100 degree differential the tapering will be considerably less! Plus the battery heater will likely be operating for quite some time at 2kW at -20F, since 1000 pounds of battery & coolant has a lot more heat capacity than the dry air in a cabin. So that's 1.2kWh JUST from the battery heater.

There's a lot of speculation there. I just look at the size of the bill every month for our carport electrical meter we had installed last year for charging our two Model 3's. And it's not much. Yes, we pre-heated all through the Arctic spell that lasted most of the winter (but only for around 10 minutes, not 1/2 hour).

The car is a lot more efficient than the numbers I've seen coming out of San Diego. And I'm not sure why anyone in San Diego is so laser-focused on the kind of cold weather that is only experienced by a small fraction of Americans and only for a small portion of the year.

How come I never hear you extolling the high efficiency achievable in a climate like San Diego? During the mild weather here in Washington its easy to best the rated efficiency of the LR RWD Model 3.

I love my Tesla, I repeat, I LOVE it. But it's not like it is God's gift to man.

It's not? Darn! Now I feel like I did when I was 4 and I learned there was no Santa!

 

[Daniel in SD]

There's a lot of speculation there. I just look at the size of the bill every month for our carport electrical meter we had installed last year for charging our two Model 3's. And it's not much. Yes, we pre-heated all through the Arctic spell that lasted most of the winter (but only for around 10 minutes, not 1/2 hour).

This is the right way to measure if you have a meter. What are you results?

The car is a lot more efficient than the numbers I've seen coming out of San Diego. And I'm not sure why anyone in San Diego is so laser-focused on the kind of cold weather that is only experienced by a small fraction of Americans and only for a small portion of the year.

My car is parked in a carport so I got the low regen warning quite a few times this winter. San Diego has the most expensive electricity in the country so it is a concern to some people who live here. I've got solar so it's more of an environmental impact question than an economic one.
I contend that it is almost impossible to achieve the EPA estimates in a Model 3 when you measure wall-to-wheel efficiency.