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I've had the Bolt for a little over 1,000 mi. now and wanted to get a sense of what happens going up and down long, steep hills, so took a 71.5-mile-round-trip ride from Santa Fe to Los Alamos, NM, with a total elevation change of about 5,000 feet (that's up and down both, RT). I started with a near-full battery and zeroed the trip counter. The temp was somewhat less than ideal, about 60 degrees. Used no auxiliary power other than screen and radio.

I recorded the high range prediction after the long downhill out of Santa Fe (see photo): 461 miles. I drove up to Los Alamos, a long climb, then recorded the high range estimate about 20 miles later after coming back down to the low point (the Rio Grande): 420 miles. So adding the 20 miles traveled it dropped from 461 to 440, and that included the very severe climb up to Los Alamos.

I remember reading somewhere that the regen efficiency is about 40 percent, but my sense from this trip is that it is considerably better than that. Has anyone else tried this kind of experiment or does anyone know what the alleged regen efficiency is, meaning from the kinetic energy of the rolling car to the kWh actually absorbed by the battery?

I have also included a photo showing the odometer back in the driveway after the 71.5-mile trip with a 5,000-foot elevation change: 5.6 miles/kWh, which is not much worse than the 6.2 miles/kWh I average around town. I drove 50-55 on the highway, slower up the hill where there is a 45 mph limit. I never take the car out of "L", haven't touched the foot brake while rolling forward since the car had 9 miles on it, and have real air pressure in my tires, but not so real the ride is impossibly harsh, if you know what I'm saying between the lines.

I will add that in my former 1st gen 2000 Honda Insight hybrid I found that it got some of its best mileage in exactly this kind of extreme hill-climb/downhill-regen situation, although its battery was full before I got to the bottom of the Los Alamos hill--small capacity--so that regen potential was wasted. On the same trip it averaged between 90 and 100 mpg RT. Yet shallow hills, ups and then downs in series with few flats, as in the Midwest terrain, are the worst. That would be 75-80 mpg. Flat highways, 85 mpg. Between Santa Fe and Taos, NM, 7000 feet to 5000 feet and back up to 7000 feet I would average about 100 mpg. Empirically, regen seems to like long, steep ups and downs. I wonder if physics bears this out. Physicists? Momentum men? Want to weigh in? Are my empirical observations borne out? If you know how to drive one of these for range, are long, steep hills better than flats? It's certainly counter-intuitive.
 

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I remember reading somewhere that the regen efficiency is about 40 percent, but my sense from this trip is that it is considerably better than that.
It's very misleading to use the range meter to do this kind of evaluation because it takes recent driving conditions into account. So if you spend 20 miles driving downhill the car thinks "gee, this guy is driving really efficiently!" and ups the range estimate.

For a better estimate of how effective regeneration is you should base it on the kilowatts consumed going uphill vs. downhill.
 

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The REG (Range Estimate Gauge) is not a true reading and as stated, it's very optimistic with regen VS mileage estimation.
It adds more range than a true battery gauge because it's adding your current driving conditions to the readout data.

I like to push the range meter up (green indicator on the left) to add range mileage :nerd:
 

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Sean and Doc, I included the whole-trip photo showing 5.6 miles/kWh realizing that range estimates are a loose science. At the same average speed on a flat highway I suspect I would get fewer than that. (We don't have flat highways here!) On the other hand, perhaps the estimator is not quite as spontaneous and mercurial a science as you suggest because it is my sense--I could be wrong--that the estimate of 460 miles is based not only on my downhill driving of the past five minutes as you note, but on long memory of the previous 1,100 miles driven and the real performance there, where I am averaging about 375 miles per full charge (85 percent city/15 percent hwy). Or said otherwise, if a diver is getting a real 200 miles per charge instead of 375, then after driving the same downhill I did his upper range prediction might have been 260, not 460. It seems to be relative and the estimating algorithm perhaps smarter than we give the Chevy geeks credit for. At least in my case I have found the middle number to be remarkably accurate, adjusting quickly to a change in driving conditions.

The photo showing the 71.5 miles traveled on this steep trip supports what the range estimator says, namely, that miles traveled per unit energy are perhaps counter-intuitively good given the relatively extreme up/down terrain and the question is, does this kind of terrain support efficiency more than intuition might say, and possibly because regeneration is more efficient than we might assume. Or said more simply, do regen vehicles like extremes of terrain? If I had been driving 50 mph on flat highway, I don't know that I would have gotten all of 5.6 mi/kWh. I don't know the answer, which is why I ask if there are any physics teachers out there who might explain why steep hills might actually be friends--or enemies--of regenerating vehicles. As I said, I noticed the same pattern in my 2000 Insight.
 

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Yes, the center readout has been pretty accurate on my driving experience too, but it can be difficult to follow without an actual round trip on the same road. I noticed it's good at gaining range in city traffic where a true battery SOC wouldn't be so optimistic :eek:
 

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The energy screen that shows the % battery used for driving, climate control and battery conditioning also shows the amount of kWh used during trip. I've found that this number is (mostly) the net amount of battery used up, meaning that when you regen the number actually decreases.

Using this screen may be a better gauge of your travel. You can record what the kWh used is at the bottom of the hill, record at top, then again at the other side. Then you can measure the net amount of kWh that you used to make it to the top, then measure how much of that you gained back as you get to the bottom again.

I think the GOM will fluctuate too much as your efficiency goes up and down to be a good measure of things.
 

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For a better estimate of how effective regeneration is you should base it on the kilowatts consumed going uphill vs. downhill.
Good to know as the range estimate seems way over optimistic after a long downhill run as you say. I just tried driving up from LA to a spot in the mountains at just over 7100ft.

Home to destination: 48 miles driven, range meter went from 216 to 123 miles, kWh consumed: 19.4kWh.

Return trip: 48 miles driven, range meter went from 123 miles to 176 miles, now kWh consumed reads 21.3kWh.

In reality based on what's left in the battery this should be more like about 140 miles I'd guess.
 

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I need to do a series of round trips up to Alta Ski Resort and back. Did that back in the day with my VW TDI to prove that the engine cuts off while in gear (long story). Would be great to go up and down about 10 times and get the total kW numbers. On the "to do" list!
 

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regen should be at least 60% if not 80% efficient - it's way above 40% - you do lose about 5% on AC/DC/AC conversions - and regen physically only captures 80% of the kinetic energy…

but think about it this way - there are two factors going uphill

X kwh to go the "distance"
Y kwh to go "up"

you will always spend "X" - you can recovery some of "Y" on the trip back down - but will spend another "X" for the distance

if you spend 2 kWh to go 8 miles distance + 2 kWh because it's uphill (4 kWh total) - you can recover some significant percentage of the 2 uphill kWh going back down hill…

in both my bolt/Tesla you can basically go downhill for 'free' and stay either at the same battery %'age or gain a little bit - basically making the downhill portion free even though you still covered some distance - I've rarely seen a significant "gain" in battery percentage as a result of downhill recovery - but I often get the downhill portion for "free" - i.e. I have the same percentage of battery at the bottom of the hill as that top - which is free because I still drove the car some distance.
 

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I remember reading somewhere that the regen efficiency is about 40 percent, but my sense from this trip is that it is considerably better than that. Has anyone else tried this kind of experiment or does anyone know what the alleged regen efficiency is, meaning from the kinetic energy of the rolling car to the kWh actually absorbed by the battery?
It's very misleading to use the range meter to do this kind of evaluation because it takes recent driving conditions into account. So if you spend 20 miles driving downhill the car thinks "gee, this guy is driving really efficiently!" and ups the range estimate.

For a better estimate of how effective regeneration is you should base it on the kilowatts consumed going uphill vs. downhill.
Have been curious and had the day off today so went up the local pass to get some numbers! After much trial and error I settled on a 2.7 mile run where I could regen all the way to a complete stop barring traffic. It was steep enough that in "D", I didn't need to lighten up the regen, but did need to add some extra regen at a couple of curves and the very end of the run. It would run up to about 63 mph top speed on the run. Started each run up by gradually accelerating up the hill to a cruise-controlled 55mph (later tried some at other speeds). I then assessed kWh used as I passed a sign post near the top at that speed. Then stopped down the road, turned around and got the car up to the same speed (55mph) and started recording kWh used from that same point until the complete stop at the bottom, at the starting location (well, other side of the road of the starting location, but negligible diff).

I did 6 55 mph runs, one of which was confounded in an interesting way. They were very reproducible, in fact, on the last run I predicted what the kWh would say at each leg including the stop and start at the top, and it was right on. Each of the 6 55 mph run used 2.0 kWh on the way up, and the 5 unconfounded runs all regenerated 0.8kWh on the way down. You could tell that if you were able to measure in hundredths some of the runs were a bit different, but not over a tenth, so pretty reproducible. Using the 5 unconfounded runs gave, interestingly, 40% efficiency (talking broad strokes here, 1 tenth diff either way gives 5% difference!).

The confounded run occurred when, on the way down, I got behind a slow poke, therefore had to regen more to keep speed lower (around 40-45 all the way down) to not run into him. This run regenerated 1.0 kWh, which would give you 50% (broad strokes, people!). I'm pretty sure this difference is real, and likely related to wind resistance stealing energy from the regen at the higher speeds. I did another run where I went 55 up, then mimicked the slow way down by using more regen to keep speeds at 40-45 and it came out the same (2.0 up, 1.0 regen on way down).

Did a few other runs to "heighten the contrasts" as they say.

Three runs with 45 mph up, and letting it go but from 45 mph on the way down. Each gave 1.8kWh up, two regenerated 0.9 kWh down, the other 0.8kWh down. So that would give you 48% if you average the runs. Makes sense for slower up being more efficient due to same factors (i.e. drag) as matter on level ground. Going down was kind of in between the 55mph starts and the really slow downhill runs above, also fits that the loss from drag might matter.

Did one last run at 70 mph up, and going even slower on the way down like 35-40 (without traffic of course!). Used 2.3 kWh going up, regenerated 1.1 kWh on the way down for about 48% again. I think these numbers are pretty good estimates of regen efficiency on a hill steep enough to require regen. But it does make you wish for hundredths of kWh on the gauge. Also, as the uphill and downhill runs are largely separate events except for the starting speed, it makes you realize this isn't a perfect test of the actual regen efficiency. This is due to how much the different speeds you use driving up the hill affects the regenerative % numbers, even though it's regenerating just the same on the way down. For example, if you took the most efficient way I tested on the way up at 45 mph, and used 1.8 kWh, then regenerated the most efficient way I tested on the way down (35-40), regenerating 1.1kWh, it would suggest 61% regenerative efficiency. If you took the least efficient way up and used 2.3kWh, and the faster, less efficient way down as well, getting 0.8 kWh regenerated, it would suggest 35% efficiency. Makes you wonder how you would do with slower traffic, gentler pedal pressure than you have to use on the hill, etc... My guess is it actually would be closer to the 60% or more in that setting, based on what we've seen with the slower runs here.

I'm sure someone will tell me where my math was wrong in here somewhere :D
 

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When going downhill some of your potential energy can recovered by regenerative braking and some is used to overcome aerodynamic drag, rolling resistance, ... The portion that is used to overcome aerodynamic forces, ... is 100% efficiently used. So regenerating while going downhill will result in an efficiency that exceeds that of the regen efficiency.
 

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I'm sure someone will tell me where my math was wrong in here somewhere
I think the missing piece is to factor in how many kWh it takes to cover the same distance at 55mph on level ground. For sake of argument, let's say that it takes 0.3kWh. If you're consuming 2kWh going uphill at 55mph, then we can infer that 1.7kWh of it is due to the grade. If you're generating 0.8kWh going downhill at a constant 55mph, then we can infer that you must also be using (and therefore generating) an additional 0.3kWh to overcome things like air and rolling resistances - and therefore regen must be giving you a total of 1.1kWh. If those assumptions are correct, it would mean that regen efficiency is actually around 65% (1.1kWh divided by 1.7kWh).
 

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To know for sure really someone would need to hook something up to the car that would log all the needed details. Power used (and for what it was used) incline, decline, time, distance, power regenerated, etc. If you wanted to get real fancy also have some equipment to measure air pressure, humidity, wind speed, etc.

Doing it through the cars interface can give us a rough idea but we won't know for sure until someone gets fancy with the right gear. :)
 

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I too had some question about the Bolt's ability to "climb a mountain" and how much would be lost in regen. In Tucson, we have a mountain nearby, called Mt Lemmon, where a good test can be performed. On that climb, we gain 6,200 feet in 27.8 miles on a pretty steady grade, at modest (35-40 mph) speed, with no stop/starts, no wind and no friction braking in either direction. I think, near perfect conditions for such a test, which I ran on April 21, 2019.

Here are the basic numbers of my test:
Distance, one way: 27.8 mi., 56.1 mi. round trip,
Total kWh to make the climb: 14.2 kWh or about 2 mi/kWh
Net energy required for the round trip: 14.2 kWh on the climb, 4.2 recovered on the return, net 10 kWh for the round trip of 56 mi. or 5.6 mi/kWh.
Total net kWh recovered on the return of 4.2 kWh, plus the 4.8 friction loss for the return trip calculated below, accounts for almost all the 9.4 kWh spent in elevation gain.
Average mi/kWh: 5.7 reported by the Bolt, for the round trip
Calculations: By dividing the climbing mileage of 27.8 mi by my trip average 5.7 miles/kWh, I concluded that the flat land kWh for the trip up should have been about 4.8 kWh. The actual energy for the climb was 14.2 kWh, so I attributed the difference of 9.4 kWh to the elevation gain of 6,200 feet. That meant that the energy cost of elevation gain was about 1.5 kWh per thousand feet gained.
Conclusions: From the forgoing, it appears that the Bolt is very, very efficient at recovering energy spent for elevation gain and that trips planned with big elevation changes need not include allowances for climbing losses, as long as the net elevation change is minor. In the event of net gains in elevation, the trip planning calculations should include an allowance of 1.5 kWh for each thousand feet gained and not recovered.
Comment: The average mi/kWh of 5.7 for this trip was considerably above my around town mileage, which I attribute to the ideal test conditions described above.
 

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Most excellent post Loring!

I would also attribute your better than typical efficiency to the slow uphill speed. 35-40 MPH is quite efficient compared to 55+

Your 1.5 kWh per 1000 ft is reasonable given mathematical calculations on potential energy. Assuming a total weight of 3,650 pounds, and 1000 ft of elevation gain, the potential energy is ~1.37 kWh. So, a little extra needed to run computers and other accessories, plus a little bit of waste converting chemical energy into electric, then to mechanical. Plus drag from rolling resistance and aero.

BTW- That climb averages 4.2% grade.
 
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