kWh delivered from battery after day of driving

[Red5Sean]

During my daily driving yesterday, I used 19.5 kWh and this resulted in a 32% decline in my battery. So 19.5/32% suggests a 60.9 kWh battery. I have a long range Model 3, so it was surprising to see this differential in what should be a 75 kWh battery. The amount of energy delivered to the car related to the drop in SOC seems off, unless I'm not understanding the kWh/mile data. Is this energy displayed ONLY the energy delivered to the car while in Drive?

I was parked for about two hours with Sentry mode on and I did preheat my car (it was 35 degrees) about 10 minutes before leaving my final destination. At the end of the day, I was getting 320 kWh/mile, however if this does not include energy used while parked, this may account for the difference.

 

[Chisale]

So how did you come up with the 19.5 kWh figure. Is that what you calculated based on the total miles driven x average consumption that the car's Energy calculator told you for that drive. If so then the rest ( or about 5 kWh) was defintely used up by Sentry and prewarming the car. Sound about right to me. By the way, I really like that supercharger in Terre Haute. One of my favorites ones. Having that Culver's there now helps a lot.

 

[Wnuk]

Your math only works if the car was charged to 100%

 

[Red5Sean]

So how did you come up with the 19.5 kWh figure. Is that what you calculated based on the total miles driven x average consumption that the car's Energy calculator told you for that drive. If so then the rest ( or about 5 kWh) was defintely used up by Sentry and prewarming the car. Sound about right to me. By the way, I really like that supercharger in Terre Haute. One of my favorites ones. Having that Culver's there now helps a lot.

It is a very nice Supercharger! It showed 19kWh for the day (since last charge). I took miles driven times kWh/mile to get to the 19.5kWh number.

 

[Red5Sean]

Your math only works if the car was charged to 100%

I started with 80% and ended with 48%. That how I came up with 32%.

 

[AlanSubie4Life]

is this energy displayed ONLY the energy delivered to the car while in Drive?

Yes. Energy use is only counted while not in park. There are certain other pathological (bug) cases where you can also miss energy consumption even when in drive, but they are rare and require trying to miss the data (require sitting in drive, stationary, then going to park, then going to drive again).

I was parked for about two hours with Sentry mode on and I did preheat my car (it was 35 degrees) about 10 minutes before leaving my final destination.

Sentry mode used about 250W*2hr = 500Wh. The preheating likely used at least 6kW*10min*1hr/60min =1kWh.

so it was surprising to see this differential in what should be a 75 kWh battery.

If you have a new 2020 vehicle, you likely have about 79kWh of capacity. (Though it could be significantly lower, depending on the age of the vehicle, etc. - you can roughly tell based on your rated miles at 100%.)

Of this, 95.5% is available above 0%. So you can use 79kWh*0.955 = 75.45kWh before hitting 0rmi.

Finally, the trip meter consistently seems to miss about 2% of the energy.

So the max I would expect you to see between 100% and 0% is 75.45kWh*0.98 = 73.9kWh.

If we add in the factors above we end up at 21kWh/0.32 = 65.6kWh.

So it seems like there is still some energy missing. Perhaps 1-1.5kWh. Some of that could be the preheat. Another factor is rounding error on the 32% number (it is better to use rated miles).

But in any case, all you really have to know is your rated miles at 100%. If that number is 322rmi, that means you have a minimum of 77.6kWh available.

So the minimum number you should see (extrapolated) on the trip meter for a 2020 AWD which displays 322rmi at 100% is: 77.6kWh*0.955*0.98 = 72.6kWh

 

[Red5Sean]

Thank you for this detailed reply. My car is a 2020 AWD stealth performance. So 310 rated miles, unless I should be using the new 299 miles standard used for performance.

I use percentage vs. mileage and honestly given how I use my car I never really notice the battery. I'm even able to charge to 90% in 20 degree weather and drive to north Indianapolis 87 miles away and return home on a single charge with 10% left. That is a long drive for me on any given day. It is helpful understanding how the computer calculates energy usage though.

 

[AlanSubie4Life]

My car is a 2020 AWD stealth performance. So 310 rated miles,

Nope; it is 322 rated miles (if you have 18" wheels selected in your wheel configuration menu).

If you use % it is hard to say how much energy your pack has available. It is fine in general to use % of course, but for this specific purpose you would need to use rated miles.

 

[Red5Sean]

Nope; it is 322 rated miles (if you have 18" wheels selected in your wheel configuration menu).

If you use % it is hard to say how much energy your pack has available. It is fine in general to use % of course, but for this specific purpose you would need to use rated miles.

I have 19 inch wheels.

 

[Red5Sean]

UPDATE: This evening I drove to one location and back home. 30 degrees. I turned off Sentry mode and otherwise did not use my battery for anything other than driving to and from destination. The car sat in the cold for 90 minutes.

I used 7% of the battery to generate 4.2 kWh of energy. This gets me to 59.97 kWh total available energy in the battery. So this makes me wonder, does the cold not only cause the car to use more energy per mile AND it takes more SOC to produce the necessary energy required?

 

[AlanSubie4Life]

I used 7% of the battery to generate 4.2 kWh of energy. This gets me to 59.97 kWh total available energy in the battery. So this makes me wonder, does the cold not only cause the car to use more energy per mile AND it takes more SOC to produce the necessary energy required?

To some extent, available energy is reduced a bit in cold temperature. In Tesla's testing of 2018 & 2020 vehicles, they saw a 7kWh reduction in battery energy in their 20F ambient test. That's about 10%.

But you also can't extrapolate accurately from small numbers like this, is another issue. It is compounded by not using rated miles, so it is hard to tell what is going on (subject to rounding error and lack of accuracy when using % - and this will be amplified for small discharges. What if you only used 6.5% of your battery?).

In addition, when the car is cold, there are a lot of factors at play, because the battery changes temperature and can mess up the results from experiments like this. Best to perform them with a battery at thermal equilibrium.