Electric Cars’ Heat Problem

If the world is going to slash greenhouse emissions from transportation, then we need a vast number of drivers to switch from fossil fuel engines to electric cars powered by renewable energy. Yet the EVs we need to mitigate further climate damage might, in one way, be ill-suited to the warmer and more extreme climate we’ve already created.

You may have heard that frigid temps are no friend of the electric vehicle. That is true, since extreme cold is a two-pronged problem. First, physical processes in the battery happen more slowly if it’s chilly out. When the mercury drops, my Tesla Model 3 displays a little snowflake icon to warn me the battery unit is too cold to actually use all the range that should be in there. The second problem is maintaining a comfortable cabin. The battery expends a lot of energy generating enough heat to keep the interior warm for its occupants when the temperatures fall to freezing or below.

When it comes to hot days, that second problem is the big one. The agency Recurrent completed a study this month that demonstrated just how much range is lost on sweltering days like those of this month’s nationwide heat wave.

As long as the afternoon high temperature doesn’t get too high, an EV’s range loss is manageable. With an outside temp of 80 degrees Fahrenheit, they found the car loses only 2.8% of its range to keep the cabin at 70 degrees. Even at 90 degrees, the loss reaches just 5%. That amounts to just 10 miles lost from a 200-mile EV. You might not even notice it — it’s probably not that far off from what’s lost by driving 80 miles per hour down the freeway instead of the posted speed limit of 65.

When it’s dangerously hot out, though, the story changes quickly. At 95 degrees outside, the average EV loses 15% of its potential range. At 100 degrees outside, the car suffers a staggering 31% range loss to maintain 70 degrees inside the car. The bigger the difference between the outside temperature and the desired inside temperature, the more of your juice is lost to climate control rather than moving the vehicle. This is why range loss is typically worse in winter — a 10-degree day in Duluth means you’re 60 degrees away from the desired 70 Fahrenheit, while a 110-degree day in Phoenix is “only” 40 degrees from the target.

I’ve seen this phenomenon first-hand during scorching trips across the desert from Los Angeles to Las Vegas or up the interstate toward the San Francisco Bay Area, where the drive passed through areas that exceeded 110 degrees. The car offers an estimate for how much will be left on the battery upon arrival at the next charging stop — then that estimate slowly dips lower and lower as more energy is expended just on air conditioning. After a few anxious drives, I learned to hoard a bit more charge than the car thinks it needs to make it comfortably to the next station.

There is also the possibility that lots of high-temperature driving will cause long-term damage to the battery’s electrolyte or other components. There isn’t too much to do about this one other than limiting how often you drive on extreme days, if you can, and hope that future battery materials that are more resistant to heat become a reality sooner rather than later.

However, there are ways to mitigate the EV heat problem during your drive time. It takes more energy to air-condition the cabin down to the proper temperature than it does to maintain the temperature. So, if you’re plugged in to charge at home or at a public charger, have your vehicle reach the desired temp before you unplug and leave.

Also, the figures in Recurrent’s study are based on setting the climate control to 70 degrees. If you and your passengers can cope with a higher cabin temperature, say 75 degrees, then you’re shortening the difference by 5 degrees and giving your battery a break. (Plenty of EV adopters have gone through a moment of panic where they thought they might need to turn off the climate control entirely to ensure they reached their next plug-in.)

Should the planet’s new normal of extreme heat deter you from going electric? First, remember the manta that experts repeat as a rebuttal to range anxiety: Most people do the vast majority of their driving close to home. Running the A/C on max to survive an August trip to Trader Joe’s isn’t going to make your EV battery hit zero unless you were too low to begin with.

If you’re really worried about the extreme temperatures of your home region, then splurge for range. I’ve recommended this before regardless of where you live and drive. But if you live in the middle of the desert and can afford the longer-range version of a particular EV, then buy it and save yourself the mental strain of wondering whether the summer sun will limit how far you can really drive your car.