I did my first out of town road trip today. It was a one day turn-around trip from Arrowhead (northern Phoenix) to Flagstaff AZ. This is not a typical road trip for the Model S in that in the 125 miles in the trip there about 5000 feet of elevation change as you go up I-17 to Flagstaff. The plan was to travel to Flagstaff to a second home we own there, do a few hours of work there and then drive back to Phoenix. Near the end of the summer, my son and I had installed a NEMA 14-50 outlet in our garage in Flagstaff and this would be my first time testing it out.
I started off at 745AM with a range-mode charge on my P85. The temperature in Phoenix in the morning was about 40 and by the time I got to Flagstaff, it was 15. I didn't use any range mode setting and had the cruise control set for 78 - definitely was not trying to save any energy. The car performed flawlessly. The roads by the time I got to Flagstaff were slushy, but I had no traction problems even with the 21 inch wheels. I was defintely blowing through the electrons though. By the time I reached Flagstaff, I had driven 127.4 miles and used a total of 61.3 kWh for an average of 481 Wh/mi and had 31 miles projected range left. At this point, I couldn't really tell if this increased rate of consumption was mainly due to the cold, the speed, or the elevation change. I immediately plugged in to the 14-50 which thankfully worked without a hitch. I was getting 240v at 40a but the maximum rate of charge I got to was 18 mph.
After getting some work done and charging for 6 hours at which time I had 225 miles rated range, I started back on the return trip to Phoenix. The weather was about 10 degrees warmer than the morning, I set the cruise control on the same 78 as on the way up. The return was a huge difference in energy usage despite going at the same speed and not much of a difference in temperature. On the return, I used only 37.2 kWh (vs 61.3) and had an average of 293 Wh/mi. This is about a 40% drop in energy consumption which at this point can only be due to the elevation change. This elevation change of about a mile in height over 125 miles in length works out to slightly less than a 1% grade on average the whole way.
So the take away is that changes in elevation have a huge impact on range which seems obvious, but I did't think it would be so dramatic. In an ICE car, you would certainly use less gas going downhill instead of uphill, but I don't think that you would see a 40% drop in gas usage. This is because of inefficiency of the ICE, 60% of the energy is going to be lost anyway and uphill/downhill only affects the remaining 40%.
For those in Phoenix wanting to take this trip, please remember that I started from Arrowhead and even with the increased consumption on the way up, I didn't have any range difficulty with an 85 kW battery. If you are leaving from Chandler or Mesa, I think you would be cutting it close. As far as trying it with a 60 kW battery, it is probably possible if driving at slower speeds and leaving from northern Phoenix. But remember, I only had one passenger in the car and if you have more, your range will be less.
On the way up - just after Camp Verde. The big regen area you see is on the hill going down to the Verde Valley - regen the whole way down.
Some slush and ice on the road in Flagstaff.
Energy usage to Flagstaff
Charging up in Flagstaff
On the drive back. One of the rare places in the US you can have the cruise control set for 78 and still be using 158 Wh/mi over a 30 mile range.
Energy usage back to Phoenix
Dirty but home.
I started off at 745AM with a range-mode charge on my P85. The temperature in Phoenix in the morning was about 40 and by the time I got to Flagstaff, it was 15. I didn't use any range mode setting and had the cruise control set for 78 - definitely was not trying to save any energy. The car performed flawlessly. The roads by the time I got to Flagstaff were slushy, but I had no traction problems even with the 21 inch wheels. I was defintely blowing through the electrons though. By the time I reached Flagstaff, I had driven 127.4 miles and used a total of 61.3 kWh for an average of 481 Wh/mi and had 31 miles projected range left. At this point, I couldn't really tell if this increased rate of consumption was mainly due to the cold, the speed, or the elevation change. I immediately plugged in to the 14-50 which thankfully worked without a hitch. I was getting 240v at 40a but the maximum rate of charge I got to was 18 mph.
After getting some work done and charging for 6 hours at which time I had 225 miles rated range, I started back on the return trip to Phoenix. The weather was about 10 degrees warmer than the morning, I set the cruise control on the same 78 as on the way up. The return was a huge difference in energy usage despite going at the same speed and not much of a difference in temperature. On the return, I used only 37.2 kWh (vs 61.3) and had an average of 293 Wh/mi. This is about a 40% drop in energy consumption which at this point can only be due to the elevation change. This elevation change of about a mile in height over 125 miles in length works out to slightly less than a 1% grade on average the whole way.
So the take away is that changes in elevation have a huge impact on range which seems obvious, but I did't think it would be so dramatic. In an ICE car, you would certainly use less gas going downhill instead of uphill, but I don't think that you would see a 40% drop in gas usage. This is because of inefficiency of the ICE, 60% of the energy is going to be lost anyway and uphill/downhill only affects the remaining 40%.
For those in Phoenix wanting to take this trip, please remember that I started from Arrowhead and even with the increased consumption on the way up, I didn't have any range difficulty with an 85 kW battery. If you are leaving from Chandler or Mesa, I think you would be cutting it close. As far as trying it with a 60 kW battery, it is probably possible if driving at slower speeds and leaving from northern Phoenix. But remember, I only had one passenger in the car and if you have more, your range will be less.
On the way up - just after Camp Verde. The big regen area you see is on the hill going down to the Verde Valley - regen the whole way down.
Some slush and ice on the road in Flagstaff.
Energy usage to Flagstaff
Charging up in Flagstaff
On the drive back. One of the rare places in the US you can have the cruise control set for 78 and still be using 158 Wh/mi over a 30 mile range.
Energy usage back to Phoenix
Dirty but home.
But it does look grey in the last picture!
