Mountain driving energy usage - one trip

[SWUtah]

Here's the energy use breakdown in a recent short trip I made in my M3 AWD.

Santa Clara, UT (my home elevation ~ 2600) to Pine Valley, UT (elevation ~ 6600). One way-mileage is 36 miles, 72 R/T. Used a little bit of cabin heat both ways, the return trip had outside air temperature maybe 10-12 degrees warmer than the outbound. Mild headwind on the outbound, slightly more tailwind on the return.

The car burned 72 energy-miles of range to travel that 36 miles outbound with the ~4000 ft elevation gain. The return trip burned 7 (yes, seven) energy-miles on the return. That's a ratio of about 10 to 1. I'm having difficulty wrapping my head around that ratio.

 

[wwu123]

Here's the energy use breakdown in a recent short trip I made in my M3 AWD.

Santa Clara, UT (my home elevation ~ 2600) to Pine Valley, UT (elevation ~ 6600). One way-mileage is 36 miles, 72 R/T. Used a little bit of cabin heat both ways, the return trip had outside air temperature maybe 10-12 degrees warmer than the outbound. Mild headwind on the outbound, slightly more tailwind on the return.

The car burned 72 energy-miles of range to travel that 36 miles outbound with the ~4000 ft elevation gain. The return trip burned 7 (yes, seven) energy-miles on the return. That's a ratio of about 10 to 1. I'm having difficulty wrapping my head around that ratio.

It is pretty cool, but think of it this way. Imagine your car was stationary at home, but on an elevator working hard to lift it 4000 ft straight up in the air. The amount of work to lift it is about 6.3 kwh, but instead of being lost, it's stored in the car itself as potential energy. So the car itself acts as another "battery" storing equivalent to about 8% of the electric battery, or about 25 energy miles equivalent.

Now let the brakes off the elevator, the car wants to come down hard, but you can resist it falling to push or power up a physical motor, or something else, while it comes down more slowly. You're draining that 6.3 kwh of energy stored in the car itself, rather than using 6.3kwh stored in the electric battery, on the return home.

The conversion from kinetic energy to potential when the car goes up is very efficient, as well as the other direction. So it's as if you lfited your car up 4000 feet and then let it back down, which ends up very efficient, but separately used 79 energy miles to go 72 actual miles on a flat road.

 

[SWUtah]

Adding some calcs into those numbers -

4000 lb car x 4000 ft elevation gain = 16,000,000 ft-lbs of potential energy gained by climbing 4000 ft
16,000,000 ft-lbs = 6.026 KWH
6.026 KWH x 4.1 miles / KWH = ~ 25 miles range. The elevation gain accounts for 25 miles of range!

crossed posts with wwu123 - we said the same thing!

 

[Abstrakt1]

I love the mountain drives because on the way down you can actually watch the regen miles add back on to your range. I am 7 miles from snowbird ski resort it takes 15 to 20 miles of range on the way up and gives me back 9-12 on the way down

 

[more863-also]

I've taken a 30kWh Nissan Leaf to the top of Mount Evans, the highest paved road in North America, with about 9% range remaining. I was able to make it the ~40 miles downhill back to my house in Denver and have about 14% range when I arrived.

Potential energy is crazy, yo.

 

[CaptainJ]

I've taken a 30kWh Nissan Leaf to the top of Mount Evans, the highest paved road in North America, with about 9% range remaining. I was able to make it the ~40 miles downhill back to my house in Denver and have about 14% range when I arrived.

Potential energy is crazy, yo.

I went down Mt Evans in a previous ICE relationship and had to pull over for a heat brake when some person was stopping each car and measuring the temperature at the brakes. Potential energy turned into wasted energy.