jcanoe, that is the clearest explanation I have seen to date. Thank you for the thorough run down.
A question comes to mind for the different preconditioning modes. You said that the winter precon can use up to 7kw. Would that be 10 min on say a 30F day, or would that be closer to a 10F temp day? How can you tell what you used? Will it show up on the energy screens or the trip screens under the car symbol?
How much energy for 10 min precon in the summer, on say a 95F day?
Thanks for working this thread with me.
In cold weather the Model Y (also Model 3) use the stator (the part of an electric motor that is fixed) of the front and rear drive units to generate heat for the battery pack, other heating needs. This has been measured to use a little over 3.5kW for each drive unit; ~7.3 kW for both. The Model Y will use ~220W while powered on. Add a coolant pump circulating coolant and the total power draw is closer to 8kW.
There are several temperature thresholds to keep in mind when the battery pack is cold. First, note that you don't absolutely have to precondition to warm the battery in anything like normal winter temperatures (down to 10F (-12C) for example) but if you don't precondition then A) the battery cannot be charged and B) there will be no regenerative braking available, C) maximum power available from the battery may be reduced. So we generally precondition for a period of time because having some regenerative braking is preferable not having any. The first temperature threshold is 50F (10C). That is the temperature that is required before the battery can be charged, some regenerative braking is available. The second temperature threshold is 68F (20C) that is the temperature when the Model Y has warmed the battery for general driving; excess heat is used to warm the passenger cabin. The third temperature threshold is used when navigating to a Supercharger. The Tesla's battery management system will pre-warm the battery pack while on route to a Supercharger; the optimal temperature is right around ~114F to 115F for the fastest and most efficient Supercharger session. In cold weather the battery may not be able to be fully warmed to this temperature but the vehicle will still be able to be charged using the Supercharger just not at the maximum charging rate.
As for the Energy screen, this only displays energy used while driving so any energy used for preconditioning using the Tesla phone app or using the Scheduled Departure setting located on the Charging screen inside the Tesla vehicle will not be factored/displayed on the Energy Screen.
You can observe how much energy is being used while preconditioning if the vehicle is plugged in and the battery has already completing charging to the maximum charging level that you have set. For example, yesterday I charged my Model Y to 80%, charging completed after 1 hour. I turned on the Climate Control using the Tesla app and when I opened up the Model Y the Charging screen indicated that the Model Y was charging at 1kW (normally when charging at this particular public charging station the charging rate is 6kW.) So only ~1kW was being used to precondition the Model Y (in this case the HVAC was set to Auto and cooling the passenger cabin from 83F to 70F.)
In general the HVAC system will use much less energy than when the motor stators are being used to warm up the battery, the passenger cabin. I don't have an exact figure but probably no more than about 50% so somewhere around 4kW maximum. To be more precise would require installing a tool such as Scan My Tesla or TeslaFi or observing the Energy Screen while parked out doors in 95F temperatures and letting the vehicle warm up. (Note if Cabin Overheat Protection is turned on the Tesla vehicle will automatically turn on the HVAC fan and also the AC compressor (depending on the settings you select for Cabin Overheat Protection.) With the Cabin Overheat Protection turned on, able to run the AC, the cabin temperature should not exceed ~105F. When you do enter the vehicle or use the Tesla app to turn on the Climate Control to precondition the cabin it will be faster and use less energy to cool the cabin from 105F to your preferred cabin temperature (~70F) than if Cabin Overheat Protection was not active and the temperature inside the passenger cabin was allowed to reach 140F or higher.
In winter temperatures when you precondition the Tesla Mode Y, assume that the vehicle uses ~6kW (for illustration purposes) while preconditioning. If you precondition for one hour this will use 6kWh. If you precondition for 10 minutes this would use ~1kWh, for 30 minutes 3kWh. When you consider that charging from a 120V/15A circuit is limited to 12A and 120V X 12A = 1.4kW you can see how topping up the battery while plugged into a 120V receptacle is not very practical. You would need to charge for more than 40 minutes to top up the battery after preconditioning for just 10 minutes, by then the vehicle's passenger cabin would have cooled down. (Even though the battery is charging at 1.4kW you are using 6kW to precondition the Tesla vehicle so the net energy drain on the battery is ~4.5kW. Instead of taking 40 minutes to finish topping off the battery after preconditioning maybe only 35 minutes additional would be required.)
In summer, again for illustrative purposes, assume the HVAC uses 3kW and you precondition for 10 minutes. This would be 0.5kWh used over the 10 minutes, 1.5kWh for 30 minutes of preconditioning. Using 120V/12A charging to top up the battery after 10 minutes of preconditioning in warm weather would take ~20 minutes. This assumes you stopped preconditioning so the cabin would start heating up again over the 20 minutes as the outside air temperature would still be ~95F. (Since the Tesla vehicle is plugged into a 120V receptacle. charging at 1.4kW rate the net energy drain o the battery would be ~1.5kW. Instead of taking 20 minutes to finish topping off the battery after preconditioning maybe only 15 minutes additional would be required.)
Just as with cooling down the cabin in warm weather the energy needed to warm the battery pack and the passenger cabin in cold weather will vary with the temperature and conditions. If snow and sleet has been falling during the day and the vehicle is parked outside then you will want to turn on the maximum defrost function using the Tesla app before you drive to help to melt the snow and ice from the windshield, other windows. When you double tap on the windshield defroster icon on the Climate Control screen within the Tesla app this will activate maximum defrost function (the icon changes from blue (for defogging) to red (for maximum defrosting.) You may need to precondition the vehicle for more than 10 minutes depending on the conditions, especially if defrosting the windows.
