Driving an electric vehicle in the winter

Winter driving generally brings two main factors to mind: traction, and cabin comfort. When

driving a BEV (battery electric vehicle) in the winter, there’s one additional aspect that needs to be discussed - Range.

First, a correction to the previous missive concerning driving a battery electric vehicle (BEV). When I estimated the cost of driving my BEV, after charging it at home, I only accounted for the actual cost per KwH (about 7 cents). When I include the taxes, fees, yadda, yadda, yadda, that National Grid tacks on it is closer to 4 cents per mile vs 2 cents. Still pretty cheap compared to a conventional vehicle.

Winter driving generally brings two main factors to mind: traction, and cabin comfort. When driving a BEV in the winter, there’s one additional aspect that needs to be discussed. I’ll cover that at the end of this particular installment. Internal combustion engine (ICE) vehicles have, over the past decades, made great strides in improving traction control on vehicles which have all wheel or 4 Wheel Drive. I once owned an old F150 pickup truck which had 4 Wheel Dr. It required me to get out and lock the front hubs if I wanted to drive it in four‐wheel mode. This was inconvenient to say the least, but worked OK on snow covered roads. But on dry pavement the truck would sometimes experience what we referred to as hunching. Hunching is when the front and rear tires are not rotating at exactly the same rate and it feels like the vehicle wants to move like an inch worm. We’ve come a long way from that! And modern electromechanical drive trains are capable of directing more torque to wheels with better traction. But the engine transmission and differential combination of an ICE vehicle is no match in terms of response time to that of a computer controlled electric motor. Bottom line, I found during the last two winters, that my Tesla model 3, all‐wheel drive vehicle, dubbed dual motor by Tesla, has every bit as good traction as an internal combustion engine vehicle running on the same set of tires. But the model three is definitely no off‐road vehicle, it is too low slung and does not have the suspension for off‐road travel. The dual motor (one for each axle) version of the model three has one other advantage and that is that if for some reason one motor failed the other is sufficient to get you to your destination.

Moving onto the issue of cabin comfort in the winter time, this is one area where the ICE vehicle and the BEV have some distinct differences. First let me say that having driven the model three through two winters, the heat coming from the climate control system has been more than adequate for all the weather conditions I have encountered. And since, like many modern vehicles, it is in nearly constant contact with my iPhone via an app, I can warm up the car remotely, and without generating any noxious exhaust fumes. There is also the fact that the electric vehicle does not depend on waste heat from a gasoline engine. In other words, one does not have to wait for several hundred pounds of cold iron and gallons of liquid coolant to be heated up by the combustion process before you get heat into the cabin. In the electric vehicle the heat is supplied almost instantaneously by resistance heaters using electricity from the battery. And the windshield starts to defrost almost immediately. This of course will negatively impact the range of the vehicle. And that is the downside of the equation because while driving the ICE car, cabin heat is provided by waste heat produced by the engine. It’s a requirement to cool the engine so no matter what, you have that heat energy that needs to be dissipated. In the winter time this is an advantage for the ICE car because it is basically free heat for the occupants of the vehicle. But, when preheating either vehicle prior to departing, you will be using some of the energy stored on board, gasoline or battery energy, and thus reduce the driving range. One further advantage to the BEV in winter that had never occurred to me was recently reported by several Texas Tesla owners. During the recent bout of unusually cold weather and the resulting electrical power outages in Texas, several families were able to find comfort by sleeping in their previously charged Tesla while parked in their garage. All reported that the battery drain from the heating system was relatively modest.

The final issue I’d like to address with respect to driving a BEV in the winter is the effect of below freezing temperatures on the battery. The battery produces its power through chemical reactions and these typically slow down at lower temperatures and thus the power available in a battery is reduced when the ambient temperature drops significantly. It’s hard to say exactly how much this impact is but the estimates I’ve seen run around 20% reduction in range. Sophisticated BEVs like the Tesla, actually use some of the stored energy to warm the battery and reduce the effects of lower ambient temperatures. At first blush this appears counter intuitive. It does not eliminate the effect of the lower temperature, it just mitigates it. A warm battery is able to release more energy to the motor than a cold one. I have noticed this myself;

when bring the cold car into the garage, where it is significantly warmer than outside, after a period of time the battery range may have ticked up a few miles without me charging it. It should be noted that the ICE vehicle also experiences a reduction in range to low temperatures. The EPA estimates that in city traffic this could be as much as 12%. But again, because of the ubiquity of gas stations, ICE vehicle drivers tend to ignore or not even notice this effect. An additional effect of a chilled battery is a reduction in its ability to accept a charge, so regenerative braking (charging) may be reduced until the act of driving the vehicle warms it up.

So, winter driving is a mixed bag of advantages and disadvantages for the BEV. Traction is at least as good as an ICE car and heat is instantly available. But range and regenerative braking are reduced

Net time I will address convenience, maintenance, performance, and some other fun stuff.

- Frank Fazekas May 5, 2021