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So by accident I came upon an idea that would test regen efficiency in a controlled way; at first I was just interested in how much energy it takes to lift the I-Pace uphill, with me and my bike and not much else. Which inspired this thread:

### How much battery do you use uphill?

This thread is inspired by Steve's post ONE discharge to 0% causes >5% battery capacity loss Each 1000ft of climbing (roughly 300 meters) uses 1.89 kWh if it's just you. Each additional passenger will be about 1/25 more. You should get back 90% of that on the downhill if you drive at the same...

www.i-paceforum.com

Then it occurred to me that one can measure the regen efficiency by comparing the energy spent going uphill with the energy regenerated while going the same downhill.

I drive to a trailhead several times a week. It's exactly 690 ft above my house, 10.6 miles one way. I go back and forth the same way except for a quarter mile at the end where the way into our neighborhood is different from the way out, but the overall distance is the same and it's flat there anyway.

Distance-wise and regarding all other parameters, the way there and back are identical. On average it takes me 23 minutes to get there and 24 minutes back. Consequently, the average speed going there is slightly higher than coming back (28 mph vs 27 mph, respectively). Not much different, probably reflecting time spent at stoplights which are slightly more forgiving on the way there (and I tend to drive slightly faster on the way downhill.) Anyway, point being that there and back are identical except: the elevation.

Soooo.

I know it takes 1.89 kWh to lift my I-Pace with me and my bike (2270 kg) 304.8 meters (1000 ft). Therefore, it takes 0.69*1.89 = 1.3 kWh to lift my I-Pace 690 feet.

Going there I use 4.7 kWh on average. 1.3 kWh of that is the potential energy required for lifting. Therefore, 4.7 - 1.3 = 3.4 kWh are for the driving.

Going back I use 2.3 kWh on average. Assuming the driving consumption (see above) is the same, I therefore regenerate 3.4 - 2.3 = 1.1 kWh of potential energy. That's 85% (1.1 / 1.3 = 0.85) of what I spent lifting the car. Therefore, by this calculation, the regen efficiency is 85%.

Independently of that calculation, the car also provides the amount of regenerated energy (last column in the spreadsheet). Going there (uphill) I regenerate 1.2 kWh on average. Going back I regenerate 2.4 kWh. The difference should be what I regenerate due to recuperating potential energy going the net downhill of 690 feet: 2.4 - 1.2 = 1.2 kWh. Using this figure, I get back 1.2 / 1.3 = 0.92, implying a regen efficiency of 92%.

Bottom line, there's of course some measurement variance and some minor confounders but it's pretty clear that regen efficiency is very high, somewhere around 80 to 90 percent. 🍺