Today was the first time I did a longer road trip at below-freezing temperatures. Some interesting results.
The trip was from Ottawa to Kingston and back to Ottawa again, a total distance of 296.1 km. Except for the occasional small town, all the driving was between 80 and 90 kph. I avoided the faster highways to preserve range because of the lack of charging facilities at my destination. (I actually did pick up a few hours of 110V charging, which was nice because it padded my range margin.)
The total trip time was 4:05 hours, and the energy consumed was 49.31 kWh, for an average of 167 Wh/km.
Since the trip was going to be a good fraction of the car's nominal range, and conditions were not ideal, I took it easy on heating. I used the seat heater throughout because it's power draw is negligible (can't even see it on the power meter). When I needed to clear the windows I used the cabin heater very sparingly and only at its lowest power setting. I'd ballpark average heater usage at 3 Wh/km. (Continuous full power could have consumed 40 Wh/km, but that would have been too much heat anyway!).
The main nuisance of driving with the cabin heater off is that air still blows in via the vents. I closed the vents and put the air on the windshield to keep it clear, and turned on recirculation to reduce the flow rate (usually I avoid that in the winter but the Roadster didn't get humid - it was still sucking in quite a bit of outside air). With the seat heater set to low my back and seat were a little too warm, and with cool air bouncing off the windshield made my hands (no gloves) and face a little too cool. The net result was strange because I felt slightly too warm and slightly too cool at the same time; but overall it was reasonably comfortable and I could have stayed that way indefinitely without getting chilled.
Tesla's efficiency spreadsheet predicted 147 kWh at 90 kph. I've previously found that their estimates are quite accurate - in summer driving conditions, that is. Today's results imply that power consumption was about 14% above nominal. Accounting for heating we're probably looking at 11% in extra losses.
The temperature ranged from 0C to -5C. If we assume that Tesla's data is for 20C (room temperature) then the increased air density would account for most of the difference. The ratio is 1.316/1.204 (see Density - Wikipedia, the free encyclopedia) = 9.3%. Pretty close.
We've had a warm winter, and much of the precipitation has been rain instead of snow. Predictably enough a lot of roads around here are in pretty rough shape due to frost heaving. The secondary highways I was driving on were in really bad shape. I wouldn't be surprised if those thousands of bumps added a bit of extra power consumption.
I'm not sure about the rolling resistance of winter tires versus summer tires, but I don't think that was a big factor.
So the net result is 11% range loss, plus about 3% for heating. In comparison, Nissan Leaf owners say that they see a 1% loss in range for each 1C below 20C, not including any cabin heat. This would have predicted a 22% drop in range, and implies that the Roadster handles the cold quite a bit better.
One note: my battery pack was warm throughout. I have previously found that if your pack is cold-soaked well below freezing, you could lose up to 10 km extra during the warmup period.
Have other people seen similar results?
The trip was from Ottawa to Kingston and back to Ottawa again, a total distance of 296.1 km. Except for the occasional small town, all the driving was between 80 and 90 kph. I avoided the faster highways to preserve range because of the lack of charging facilities at my destination. (I actually did pick up a few hours of 110V charging, which was nice because it padded my range margin.)
The total trip time was 4:05 hours, and the energy consumed was 49.31 kWh, for an average of 167 Wh/km.
Since the trip was going to be a good fraction of the car's nominal range, and conditions were not ideal, I took it easy on heating. I used the seat heater throughout because it's power draw is negligible (can't even see it on the power meter). When I needed to clear the windows I used the cabin heater very sparingly and only at its lowest power setting. I'd ballpark average heater usage at 3 Wh/km. (Continuous full power could have consumed 40 Wh/km, but that would have been too much heat anyway!).
The main nuisance of driving with the cabin heater off is that air still blows in via the vents. I closed the vents and put the air on the windshield to keep it clear, and turned on recirculation to reduce the flow rate (usually I avoid that in the winter but the Roadster didn't get humid - it was still sucking in quite a bit of outside air). With the seat heater set to low my back and seat were a little too warm, and with cool air bouncing off the windshield made my hands (no gloves) and face a little too cool. The net result was strange because I felt slightly too warm and slightly too cool at the same time; but overall it was reasonably comfortable and I could have stayed that way indefinitely without getting chilled.
Tesla's efficiency spreadsheet predicted 147 kWh at 90 kph. I've previously found that their estimates are quite accurate - in summer driving conditions, that is. Today's results imply that power consumption was about 14% above nominal. Accounting for heating we're probably looking at 11% in extra losses.
The temperature ranged from 0C to -5C. If we assume that Tesla's data is for 20C (room temperature) then the increased air density would account for most of the difference. The ratio is 1.316/1.204 (see Density - Wikipedia, the free encyclopedia) = 9.3%. Pretty close.
We've had a warm winter, and much of the precipitation has been rain instead of snow. Predictably enough a lot of roads around here are in pretty rough shape due to frost heaving. The secondary highways I was driving on were in really bad shape. I wouldn't be surprised if those thousands of bumps added a bit of extra power consumption.
I'm not sure about the rolling resistance of winter tires versus summer tires, but I don't think that was a big factor.
So the net result is 11% range loss, plus about 3% for heating. In comparison, Nissan Leaf owners say that they see a 1% loss in range for each 1C below 20C, not including any cabin heat. This would have predicted a 22% drop in range, and implies that the Roadster handles the cold quite a bit better.
One note: my battery pack was warm throughout. I have previously found that if your pack is cold-soaked well below freezing, you could lose up to 10 km extra during the warmup period.
Have other people seen similar results?