Wesley's Tool-Box

I keep a detailed log of my Bolt EV drives to gain insights to the questions I wanted answers to. One of them was this feeling that the drivable range was getting lower on a cold day despite the fact that I drive without having the heater on. Since my EV driving habits became consistent after driving for about half a year, I decided to analyze one full year's of driving from February 2019 to January 2020 to spot a trend between the ambient temperature and the car's efficiency ("fuel economy").

The results above speak for themselves. Even if you don't use a heater, the car's efficiency will certainly drop as the outside air gets colder. This is largely because the air itself becomes more dense, increasing resistance. Using a heater will impact efficiency on top of this. Meanwhile, driving at an average trip speed of about 50 km/h (30 mph) yielded about 1 to 1.5 km/kWh better efficiency than at about 80 km/h (50 mph). Again, less air drag meant better outcome.

If you want to know how the data points were chosen, please read on.

My two most common driving patterns happen on expressways and intercity roads. The former are usually for the long distance family trips. The latter are used in the routine errands between Naju and Gwangju for groceries or movie-going. Downtown driving is done mostly by my wife and there are no records of time or temperature, so they were not analyzed.

As all trips start and end within cities, the most significant and fastest road type used must take up at least 75% of the entire distance for a sample to be representative of a type. And to minimize impacts of traffic jams, average speed of a trip had to be at least 70 km/h for expressway and 40 km/h for intercity. Driving under rain or snow were also out in order to avoid other weather factors. Additionally, expressway trips had to be at least 100 km long and the intercity trips had to have no significant deviations from the most common 22 km-long route I take. Use of heater was completely avoided, while air conditioning was used very sparingly if needed and took up less than 1% of the battery consumption.

In the end, 108 samples spanning a total distance of more than 10,600 km were chosen out of the 27,000 km total distance covered during the period. The real life driving conditions did still create some variability, but the trends were clearly present. I can now use this analysis to better plan for future trips.