Driving Smart in the Cold with an Electric Vehicle

While my fellow Tesla Model S owners in Manitoba and Alberta will likely have further thoughts on cold weather driving I found the premise behind John Broder’s recent article in the New York Times disturbing. In his follow-up post he mentions:

Virtually everyone says that I should have plugged in the car overnight in Connecticut, particularly given the cold temperature. But the test that Tesla offered was of the Supercharger, not of the Model S, which we already know is a much-praised car. This evaluation was intended to demonstrate its practicality as a “normal use,” no-compromise car, as Tesla markets it. Now that Tesla is striving to be a mass-market automaker, it cannot realistically expect all 20,000 buyers a year (the Model S sales goal) to be electric-car acolytes who will plug in at every Walmart stop. – Broder, John M. “The Charges Are Flying Over a Test of Tesla’s Charging Network,” New York Times, February 15, 2013.

Taking the position that an electric vehicle (EV) should behave exactly the same as an internal combustion engine (ICE) car, especially in sub-zero temperatures was a big mistake on his part. You do not need to be a chemist to know that the differences in fuel source will mean that the car will respond differently in certain conditions and that it is wise to take the appropriate measures to learn how it behaves before you push its limits.

Before my wife and I took our Model S on the longest sub-zero temperature trip I took note of the impacts of cold weather during my 110km daily commute. During an eight hour period of being unplugged in sub-zero temperatures, for example, I would notice a drop off in range of between 25-50km when I started out. What I have not watched closely for is how much I gain back during the initial few minutes of driving when the battery warmed up. While driving I do, however, pay attention to the average Watt Hours per Kilometer so I would be aware of when the car was drawing more energy so I could adjust my range expectations accordingly. Factors that affected the draw included excessive use of cabin heat (when my wife was in the car especially ;)), driving up hill and sub-zero temperatures as the car worked a bit harder to keep the battery warm. When we set out our coldest weather trip yet to a winter driving course in -15C to -20C conditions we planned accordingly:

  • Spend the night at a hotel within 100km of the course that had a 70A charging station
  • Charge the car overnight at the hotal with a maximum range charge
  • Expect a signicant draw as the car sat while we were in the classroom between driving sessions
  • Use a 110V/12A outlet at the community centre where classes were being held to allow the car to draw a charge to keep the battery as warm as possible

We monitored the range throughout the day to ensure we had enough remaining to return to the hotel for the evening. When we wrapped up we left with 110km of rated range for an 88km drive. We decided to play it safe by using the heated seats to minimize the use of cabin heat while driving at a steady 65 km/hr. We arrived at the hotel with 20km of rated range remaining. Neither of us paniced about the range instead focused on practical choices based on what we had learned from my daily commute and the energy usage throughout the day at our course. We also had discussed that if we had come within 10km of the rated range being exhausted that we would find a safe place to pull over and call for a tow back to the hotel. This is type of planning would have been the same if we had a limited amount of fuel left in an ICE car and were driving a route where we did not know whether we would come across any gas stations.

When you get a new vehicle, especially one that is powered by a different fuel source, it is the responsibility of the driver to learn how their vehicle responds under various conditions. This applies not only to the drive systems but also safety and handling of the vehicle. The way that you choose to drive an EV cannot be the same as ICE car. We are still learning collectively about the considerations that one must take when driving an EV. I am encouraged that Tesla is building upon the Roadster and Model S experiences using real data to refine the technology and develop more specific guidance of EV behaviour under various conditions. If Tesla and other EV manufacturers can learn from each other, and drivers can learn from each other, then we can identify the limits of this technology then collectively seek to innovate to push those limits to the next level.