RGEV

Elevation Effect

Mon Aug 21, 2017 1:55 am

I live in Denver and I was curious about the impact of elevation change on the range of the Bolt. I drove up to Rocky Mountain National Park and back. Here's what I got.

The temp was 62F in the early morning when I started and 48F at Bear Lake trail head, 67.4 miles away. I started from 5,500 ft elev and parked at 9,450 ft, a climb of 3,950 ft. The Bolt used 18 kWh for an average of 3.7 mi/kWh.

For the return trip, the temp was 71F at the trail head and 85F in Denver. Going down the hill used only 6 kWh over 68 miles for an average 11.3 mi/kWh on the return leg. Overall, the car displayed an average for the trip at 5.6 mi/kWh.

The most interesting part was that I used 0 kWh for the first 40 miles since leaving the trail head! I was in Lyons, CO, at an elevation of 5,400 ft when the energy used went above what it had been at the starting point at the trail head. It took 6 kWh to travel the remaining 28 miles and climb 100 ft. Roughly 1/4 the cost of gas for my ICE car to make that trip. Amazing car!

Rick

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gbobman
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Re: Elevation Effect

Mon Aug 21, 2017 5:23 pm

I think what you wrote is the detailed effect of high altitude. Coasting downhill charges the battery.

If you mean the effect altitude has to ICE vehicles having a correlation to electric-only; there isn't. You don't need oxygen so the lack of it doesn't do anything to the propulsion. The only effect would be a lessening of resistance to air, but you won't see that delta without more sensitive equipment.

So enjoy cheapo trips to Estes and Tinytown.
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redpoint5
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Re: Elevation Effect

Wed Aug 23, 2017 4:46 pm

The decrease in aerodynamic drag can be significant and measurable with elevation.

At 10,000 ft, air density is about 70% of sea level. At highway speeds, aerodynamic drag consumes the most energy, so reducing it by 30% would be huge. I wouldn't be surprised if you could get 15% better range at that elevation compared to sea level.

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RGEV

Re: Elevation Effect

Sat Aug 26, 2017 5:49 pm

Redpoint5, that's interesting about the air density. Speeds were slower, seldom over 50 mph, but I don't think that's the major effect here.

If I calculate the potential energy (m*g*h) difference of raising the 3580# car 3,950 feet, I get
( (3580 + 200 lb) / 2.2lb/kg * 9.8m/s^2 * 3950/3.28 ft/m ) = 20.28x10^6 Joules
= 5.63 kWh

So climbing used 12.4 kWh for movement and 5.6kWh to raise the car and me.
Descending used 11.6 kWh for movement and put 5.6kWh back into the battery.

The change in potential energy due to elevation seems like the major effect.

redpoint5
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Re: Elevation Effect

Sat Aug 26, 2017 6:37 pm

RGEV wrote:Redpoint5, that's interesting about the air density. Speeds were slower, seldom over 50 mph, but I don't think that's the major effect here.

If I calculate the potential energy (m*g*h) difference of raising the 3580# car 3,950 feet, I get
( (3580 + 200 lb) / 2.2lb/kg * 9.8m/s^2 * 3950/3.28 ft/m ) = 20.28x10^6 Joules
= 5.63 kWh

So climbing used 12.4 kWh for movement and 5.6kWh to raise the car and me.
Descending used 11.6 kWh for movement and put 5.6kWh back into the battery.

The change in potential energy due to elevation seems like the major effect.

I have to admit I skimmed your post and went off the thread title. Yes, elevation change will affect range due to the electrical energy required to bring a mass (car) to a higher potential energy (elevation).

In petrol powered vehicles, medium grade hills are more efficient than flat driving because it acts like a prolonged "pulse and glide". Petrol engines are much more fuel efficient (like 2 to 3 times) operating near full throttle than partial throttle, so the hill has the engine operating near peak efficiency, while allowing it to idle down the hill. Obviously, hitting the brakes would be wasted energy, so the hill can't be too steep, or a lot of energy would be wasted.

I'm not so sure what the efficiency curve of an EV looks like. A flat surface is likely most efficient for an EV. Since an EV isn't anywhere near 100% efficient at recapturing kinetic energy (I've heard 1/3 efficient but I don't know for sure), it's still better to have a grade that doesn't require use of regen. That said, being able to recapture some of that energy on steep hills is certainly a strength of EVs over conventional vehicles.

Once I almost got a full charge in my Prius plug-in when I started at the top of Crater Lake with no EV range, and regened down to the highway nearly full. Only 13 miles of EV range, but it's better than wasting the energy as heat and brake dust.

LeftieBiker
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Re: Elevation Effect

Sat Aug 26, 2017 7:06 pm

Regenerative braking is never more than 40% efficient at recovering energy. 1/3 is probably closer to typical.
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MichaelLAX

Re: Elevation Effect

Sat Aug 26, 2017 7:29 pm

redpoint5 wrote:Once I almost got a full charge in my Prius plug-in when I started at the top of Crater Lake with no EV range, and regened down to the highway nearly full. Only 13 miles of EV range, but it's better than wasting the energy as heat and brake dust.

I typically get back 1.5 to 2.0 KW driving in the truck lane in L mode with cruise control set to the speed of the truck ahead of me (35-40 MPH; speed limit is 35 MPH) for the 5 miles 6% grade downhill on the Northbound Grapevine on Interstate-5.

LeftieBiker wrote:Regenerative braking is never more than 40% efficient at recovering energy. 1/3 is probably closer to typical.

Isn't that better than no regenerative braking at all?

Probably, since about every EV manufacturer has licensed the technology to include it!

LeftieBiker
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Re: Elevation Effect

Sat Aug 26, 2017 10:09 pm

Isn't that better than no regenerative braking at all?


You miss the point. Coasting is the most efficient, effective way to save energy, so regen should be used only when effective and necessary, as in steep downhills or slowing to a stop.
2018 Nissan Leaf SL with Pro Pilot

2009 Vectrix VX-1 with 18 Leaf modules.

MichaelLAX

Re: Elevation Effect

Sat Aug 26, 2017 11:15 pm

LeftieBiker wrote:
Isn't that better than no regenerative braking at all?
You miss the point. Coasting is the most efficient, effective way to save energy, so regen should be used only when effective and necessary, as in steep downhills or slowing to a stop.
I reread the thread, but I don't see where your source was for your statement. Could you link me to it please.

So you are saying that there are subtle downhills (between steep downhills and slowing to a stop) where regen is less effective than if it were not present at all?

In Southern California, when I drive from the San Fernando Valley on Hiway 101 to Downtown Los Angeles, it hardly uses any KWh for this 12 mile drive due to the subtle downhill nature of the drive and regeneration.

Your thesis is that I should just use propulsion where necessary and coast and it will use less KWh?

LeftieBiker
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Re: Elevation Effect

Sun Aug 27, 2017 12:13 am

Coasting down grades where excessive speed doesn't become a problem is much, much more efficient than regen, which converts momentum into both electrical energy and heat, because the momentum doesn't have to be converted to electrical power and then back again through the drive system - it just stays momentum. The heat isn't from friction as it is with friction brakes, but the process loads the motor in the same way that acceleration does, and this produces heat from induction, wasting at least half of the available energy. This link claims "as much as 50%" but that's more optimistic than anything I've read over the years, and probably applies to laboratory conditions. The highest I've seen claimed elsewhere is 40%, and that was a maximum.

http://auto.howstuffworks.com/auto-parts/brakes/brake-types/regenerative-braking5.htm

This is why B/L modes aren't the best way to drive efficiently in flat, uninterrupted highway travel. They are best used for stop and go driving and for many hills. Letting the car coast as much as possible will always be the best way to extend range.
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2009 Vectrix VX-1 with 18 Leaf modules.

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