Poor efficiency at high ambient temperatures

[KaiserSoze]

I've collected a small amount of data using teslafi.com and noticed that efficiency tanks as the ambient temperature rises.

TeslaFi.com Tesla Model S X Data Logger

Temperature Efficiency

Temperature Wh/Mile Efficiency % Miles Recorded
60 to 70 F 365.27 87.1 13.79
70 to 80 F 371.25 85.8 46.34
80 to 90 F 449.13 70.9 19.73
90 to 100 F 531.68 59.9 23.43

This data was recorded over one week of random urban/suburban trips of ten miles or less.

Above 90 degrees, I get only 60% of EPA rated mileage. The cooler the weather, the better the efficiency.

I presume this is due to the large amount of glass in the X, resulting in a lot of energy spent cooling. Can anyone else confirm? Is my A/C functioning at correct efficiency? Can we quantity the A/C load so that it can be factored into long trips?

 

[andrewket]

You need to record humidity. Air density has an impact as well.

 

[KaiserSoze]

You need to record humidity. Air density has an impact as well.

I could crunch the humidity numbers, but I'm skeptical that humidity could significantly contribute to an efficiency decline of 31%. What kind of humidity loss have you seen?

 

[Saghost]

With trips of less than ten miles, you're probably still capturing the energy cost of the initial cool down of the car. I've noticed that on these summer days I always use a lot of power in the first five miles, which then falls off as the trip goes on. I'm assuming that's the cost of cooling the car down (as opposed to the cost of keeping the car cool, which is a lot lower.)

 

[eye.surgeon]

in 2 yrs I have noticed my cold weather efficiency is notably worse than hot weather. Here in Fresno where it gets very hot in the summer (100+) and only cool in the winter (40-50), my summers are more efficient than winters.

 

[KaiserSoze]

in 2 yrs I have noticed my cold weather efficiency is notably worse than hot weather. Here in Fresno where it gets very hot in the summer (100+) and only cool in the winter (40-50), my summers are more efficient than winters.

One additional fact worth mentioning is that my X is not garaged and rarely parks in garages. Thus, it is constantly exposed to the sun. This differs from other areas of the country where cars can transit almost exclusively from covered parking to covered parking.

 

[David99]

As saghost said, on trips of 10 miles and less, you are getting the hot of the AC needing to cool the car down. Once it's cool it takes far less energy to keep it cool. I notice the same here living in Los Angeles. Warmer temperatures are actually better for the battery.

 

[CmdrThor]

Although the Model X windshield glass is very large, Model S with a pano roof has a lot of glass as well. I think part of the issue is Model X has a greater volume of air to cool. My efficiency in high temps in stop and go traffic are pretty awful. But I also set the AC to 68-70 and expect to pay the cost for that. Thankfully I charge mostly at work and don't have to pay for my AC preferences

 

[Jdeck]

I added a quick selectable filter on the temperature efficiency page on TeslaFi to only include drives over X miles in the output. Definitely makes the data more useful.

 

[travwill]

All the above seems accurate, short trips in Winter are the worst, Summer they are bad as well but not nearly as bad. Post heating/cooling is caught up things get better.

For the X, unless needed, make sure the rear A/C unit is on Auto (it will say no rear passengers detected) unless you really need it running - both on at first will zap quite a bit.

 

[KaiserSoze]

Quick update: the efficiency in 50-60 degree weather is also a bit low (thank you, physics) but by my rough calculations my short trips each take about 3.5 percent of my battery on the 90D. These trips employ forced air hearing. Thus, it can do twenty short outdoor-to-outdoor trips per day (90% -> 20%). That's plenty. I'll update with estimates for 30-40 and 40-50 degree weather when we get there.