Winter Range and Charging

[Fredneck]

It is pretty well known that winter temperatures hit EVs pretty hard when it comes to range. It's not clear to me how much it impacts charging. I'm not talking about charging currents since level 2 charging at home never rises to a point that it is limited really. I'm talking about how much charging is needed to drive the same miles in winter temps.

I know regen has some impact, but that should be fairly minimal unless you do a lot of stop and go driving. If the driving is mostly at highway speeds and conditions, 50 to 70 mph and no stop and go, what is the source of the reduced range? Is it that more energy is needed to travel the same miles because of the motor, tires or something else in the driveline? Is it that the battery becomes less efficient in returning the energy that was stored in it? Does the capacity of the battery drop so you can't get as many kWh into it in the first place? Does the battery not receive current as efficiently so it takes more energy to charge it up?

Inquiring minds want to know.

 

[Saghost]

Colder air is more dense, requiring more energy to push it out of the way. Colder fluids are more viscous, requiring more energy to push gears through them.

But mostly the extra energy goes into heating the cabin and the pack.

That's why the range impact on a long road trip of freezing temps is only 10 or 15% - once the cabin and pack are warm.

You may well pay 2x the energy on the first few miles while heating the car, though - and most folks don't often get past the half hour range in most winter trips where the energy usage finally drops.

The additional charge time is directly proportional to the list range as a percentage, with possibly slightly more needed to warm the pack or keep it warm while charging.

 

[ewoodrick]

You are looking at about 30% degradation during the winter. That comes primarily from battery capacity.

Long story short.... Took camera to top of Colorado Ski lift, didn't work, dang it. Skied back to lodge where it worked fine. Crap, I had carried the camera outside my jacket and batteries were not around -20F.
Kept it in my jacket next time on the lift and the camera worked well for the next run.

Batteries do not like cold. Same thing with your cellphone. Turn it off, leave it outside in the really cold and see if it turns back on.

 

[Rocky_H]

what is the source of the reduced range? (1) Is it that more energy is needed to travel the same miles because of the motor, tires or something else in the driveline? (2) Is it that the battery becomes less efficient in returning the energy that was stored in it? (3) Does the capacity of the battery drop so you can't get as many kWh into it in the first place? (4) Does the battery not receive current as efficiently so it takes more energy to charge it up?

Huh--you suggested four possibilities but didn't quite hit on the biggest main reason:

(5) People coming from a gas car take it for granted that there is always tons of heat. Gas engines are pathetically inefficient, and they are constantly trying to dump two thirds of the energy of the gasoline as waste heat out the radiator and tailpipe to prevent themselves from melting down. So you just turn a couple of valves, and you can collect some of that wasted heat into heating up you inside the cabin. Electric motors are so efficient (about 90%) that there isn't much waste heat. So you have to effectively run an electric space heater to keep you warm.

It's the same tank of electricity, though. So people wonder why they aren't getting the amount of "miles" they expected. It's because that same battery is having to provide MILES + HEAT. And that just shows up as much lower efficiency numbers.

There are a couple of lesser factors mentioned, like denser air, but the main one is just sucking extra electricity to heat up the cabin and battery pack. Short trips of a few miles are going to look terrible for this if you car starts out cold.

 

[SSedan]

You are looking at about 30% degradation during the winter. That comes primarily from battery capacity.

Long story short.... Took camera to top of Colorado Ski lift, didn't work, dang it. Skied back to lodge where it worked fine. Crap, I had carried the camera outside my jacket and batteries were not around -20F.
Kept it in my jacket next time on the lift and the camera worked well for the next run.

Batteries do not like cold. Same thing with your cellphone. Turn it off, leave it outside in the really cold and see if it turns back on.

Yes cold has some impact but cabin heating is the big factor.

Takes a lot of power to initially warm everything.
I speak to this as someone who lives in a cold climate, was 9f on my way to work today.

 

[drtimhill]

Glass half-empty: "I lose 20-30% of range in the winter"
Glass half-full: "I gain 20-30% more range in the summer"

Reality: Charging at home (in WA) still costs WAY WAY less than equivalent gas costs, even I winter.

 

[mswlogo]

The bulk of the loss is the heater. And the Model 3 has terrible insulation so it needed continuous heat. I’m hoping X will be a little better at that.

Last winter I was eager to see how efficient the car (Model 3 AWD) would be in summer. I have a fairly short commute so it was not a big deal to leave HVAC off. So I stopped using heat in Feb. I got close to the same range in Feb right through July. I had very limited regen and a snow flake on the battery. I got like 240 wh/mi in winter (no heat) and 230 wh/mi summer. 280+ wh/mi winter with heat. The killer was keep windows clear. Sometimes I had to open the windows

 

[Fredneck]

Huh--you suggested four possibilities but didn't quite hit on the biggest main reason:

(5) People coming from a gas car take it for granted that there is always tons of heat. Gas engines are pathetically inefficient, and they are constantly trying to dump two thirds of the energy of the gasoline as waste heat out the radiator and tailpipe to prevent themselves from melting down. So you just turn a couple of valves, and you can collect some of that wasted heat into heating up you inside the cabin. Electric motors are so efficient (about 90%) that there isn't much waste heat. So you have to effectively run an electric space heater to keep you warm.

It's the same tank of electricity, though. So people wonder why they aren't getting the amount of "miles" they expected. It's because that same battery is having to provide MILES + HEAT. And that just shows up as much lower efficiency numbers.

There are a couple of lesser factors mentioned, like denser air, but the main one is just sucking extra electricity to heat up the cabin and battery pack. Short trips of a few miles are going to look terrible for this if you car starts out cold.

Yes, but you only need the heater when it is cold enough at drive time that the cabin gets cold. Much of my reduced range experience is when the temps are only slightly low, not at freezing. Even if it is cold enough to need cabin heat, the element is only 5 kW I'm told and it doesn't run all the time. Propulsion takes about 20 kW at highway speed in my X. So worst case the heater would add 25% consumption. Most of what I experience is far from worst case.

 

[Fredneck]

Glass half-empty: "I lose 20-30% of range in the winter"
Glass half-full: "I gain 20-30% more range in the summer"

Reality: Charging at home (in WA) still costs WAY WAY less than equivalent gas costs, even I winter.

Supercharging for me is totally free, so I don't really care about the cost. The problem is getting far enough that I'm not stopping to charge every couple hours of driving. Partly the problem is the paucity of chargers. Rather than being able to use the range available, charging can only be done where there are chargers, so sometimes around half a tank of electrons since the other half tank won't get you to the next charger with enough cushion to spare.

 

[SSedan]

Do you understand the HVAC is constantly pulling in fresh cold air that needs heating.

If the pack falls into the high 40s we can see reduced regen, but that doesn't mean the pack is heated, still affects consumption since we aren't recapturing that energy.

How long have you been driving a Tesla?
Winter consumption for my car will show in the 500s with some preheating, have had the 5 mile average spike over 800 if I forget to preheat, my commute is little under 7 miles each way. Based on that you would think I have no chance to make the Way Claire supercharger 180miles away with my P85 that only charges to 242 miles when cold. Reality is that once the cabin is warm consumption falls back much closer to normal and in low single digits the 180miles is no problem.
Tires also require a fall top up as pressure falls due to temp.

 

[Rocky_H]

The problem is getting far enough that I'm not stopping to charge every couple hours of driving. Partly the problem is the paucity of chargers.

You have to stop too frequently at the abundance of Superchargers, but then you say there aren't enough Superchargers. Which is it? I'm still working on the couple of 250+ mile gaps on routes near me. I would be glad to be able to stop every couple of hours to make it across these areas.

 

[ajdelange]

Everyone likes to blame the heater for reduced winter range. Let's say it is a 2 kW heater running 50% duty cycle. In an hour it would require 1 kWhr of energy. If you are going 60 mph then that's 1000/60 = 17 Wh/mi extra burden on the battery. My nominal 300 wH/mi consumption would go up to 317 which is an increase of about 6%. My nominal range of 300 mi would drop to 282. That's not really that much of a loss but it isn't 0 either.

Stats accumulates efficiency data from the fleet. It shows about 86% efficiency in the winter months increasing to about 93% in the warmer weather - a change of about 7%.

It's been mentioned that colder air is denser and that drag, therefore, goes up. That is a factor for sure but not a great one. The one I have found to be the biggie is wet road surface and it doesn't have to be soaking wet either. A good rain will cost 33% efficiency and there appears to be a penalty unless the road is visibly dry. The point being that it rains more (around here, at least) in the winter than in the summer. Snow on the roadway is, I expect, even worse.

Another factor that might come into play more in winter than summer is stronger winds. Before arguing that winds are as likely to be tail winds as head winds keep in mind that drag is proportional to the square of velocity. Thus in traveling at 60 mph you would use energy proportional to 3600 units to overcome drag whereas with a 10 mpH headwind you would require 4900 i.e. 1300 more. OTOH with a 10 mph tail wind your drag requirement would be proportional to 2500 or 1100 units less than 60. Thus a head wind hurts you more than a tailwind of the same magnitude helps.

 

[Saghost]

Everyone likes to blame the heater for reduced winter range. Let's say it is a 2 kW heater running 50% duty cycle. In an hour it would require 1 kWhr of energy. If you are going 60 mph then that's 1000/60 = 17 Wh/mi extra burden on the battery. My nominal 300 wH/mi consumption would go up to 317 which is an increase of about 6%. My nominal range of 300 mi would drop to 282. That's not really that much of a loss but it isn't 0 either.

Stats accumulates efficiency data from the fleet. It shows about 86% efficiency in the winter months increasing to about 93% in the warmer weather - a change of about 7%.

It's been mentioned that colder air is denser and that drag, therefore, goes up. That is a factor for sure but not a great one. The one I have found to be the biggie is wet road surface and it doesn't have to be soaking wet either. A good rain will cost 33% efficiency and there appears to be a penalty unless the road is visibly dry. The point being that it rains more (around here, at least) in the winter than in the summer. Snow on the roadway is, I expect, even worse.

Another factor that might come into play more in winter than summer is stronger winds. Before arguing that winds are as likely to be tail winds as head winds keep in mind that drag is proportional to the square of velocity. Thus in traveling at 60 mph you would use energy proportional to 3600 units to overcome drag whereas with a 10 mpH headwind you would require 4900 i.e. 1300 more. OTOH with a 10 mph tail wind your drag requirement would be proportional to 2500 or 1100 units less than 60. Thus a head wind hurts you more than a tailwind of the same magnitude helps.

Tesla uses a 6 kW PTC air heater in the S/X, and also a 6 kW coolant heater for the pack.

They certainly aren’t on at full power the entire time you’re driving the car, but they are at the start. 12 kW of draw while parked...

Using your example, that’s an extra 200 Wh/mile at 60 mph, or an extra 400 Wh per mile at the 30 mph that’s more likely for short commutes.

But once the cabin and pack warm up, your scenario is close to realistic on long distance drives.

Which is why it really depends on the situation.

 

[ajdelange]

I sort of thought it went without saying that if you want to achieve best mileage you prewarm the cabin and battery on shore power (if that is possible). I have no idea what the max capacity of either of the heaters is but the biggest draw I have seen from them is 2.5 kW, I'm sure it's PID control and maybe in Yellowknife at midnight in January the draw would be higher.

But supposing you set out with it drawing 6 kW. Your usage would be 2 kW hr if it took 15 min to get the cabin to temp and then 3/4 kw hr for the remaining 45 min for a total of 2750/60 = 46 Wh/mi higher for that first 60 mi and lower for the rest of the trip.

The point I am really trying to make is that I think the heater gets more blame than it deserves. Were I to spend a winter in Yellowknife I might change my view.

 

[Rocky_H]

I have no idea what the max capacity of either of the heaters is but the biggest draw I have seen from them is 2.5 kW,

6kW + 6kW = 12kW. The cabin heater and battery heater in the S and X each draw 6kW at full rate. It's not forever, but it can be pretty outrageous for the first 10-15 minutes.

 

[IdaX]

The battery pack itself has significantly higher internal resistance at low temps, and so you lose some power to resistive heating until it warms up. Not sure how to quantify this with the information available to us drivers tho!

 

[ajdelange]

You can WAG it by estimating observing that the charging capacity of the X 100 battery is about 98 kWhr and the discharging capacity about 93 kWh so that evidently about 2.5% of energy withdrawn (or stored) is dissipated as heat. Thus if you are drawing 30 kW from the battery about 750W are being dissipated in the battery. This is awfully rough, though.

 

[Saghost]

I sort of thought it went without saying that if you want to achieve best mileage you prewarm the cabin and battery on shore power (if that is possible). I have no idea what the max capacity of either of the heaters is but the biggest draw I have seen from them is 2.5 kW, I'm sure it's PID control and maybe in Yellowknife at midnight in January the draw would be higher.

But supposing you set out with it drawing 6 kW. Your usage would be 2 kW hr if it took 15 min to get the cabin to temp and then 3/4 kw hr for the remaining 45 min for a total of 2750/60 = 46 Wh/mi higher for that first 60 mi and lower for the rest of the trip.

The point I am really trying to make is that I think the heater gets more blame than it deserves. Were I to spend a winter in Yellowknife I might change my view.

Without getting in to precise math, you’re still focused on averaging the load over the first hour of a longer trip.

The folks who complain about high winter consumption are usually driving ten or fifteen miles at a time, like most people do most days.

You’re both right - a cold soaked cabin and pack on a typical commute might double consumption on a cold day, but on a multiple hour drive the impact is fairly small.

 

[ajdelange]

No argument there. I used to talk about a "departure tax" and at one time posted plots showing that Wh/mi were worse for shorter trips. Plus short trips are usually in town with lots of stop and go and done when regen is limited in cold weather.

 

[jboy210]

We find using the seat heat more and keeping cabin temp lower reduces the drain.