Elevation Effect

[Anonymous]

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

 

[user 1034]

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.

 

[redpoint5]

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.

 

[Anonymous]

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]

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]

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

 

[Anonymous]

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.

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]

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.

 

[Anonymous]

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]

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.

 

[Anonymous]

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.

The link you provided, if indeed it was the one you correctly wanted to provide, does not support your contentions.

At the end of the day, the Bolt EV has no "coast" mode and in my experience is so well engineered as to provide excellent regeneration when it is needed at the most subtle of times, such as the example I provided: driving from the San Fernando Valley on US 101 to DTLA.

Trying to manually shift back and forth from a "coast" to "drive" modes during this 12 mile drive would be a total distraction. Better to let the Bolt EV do the engineering for me!

 

[redpoint5]

I'm not sure what the argument is, but a few comments.

Motors are generators, and generators are motors. The difference only being if kinetic energy is being converted to electricity (generator), or electricity is being converted into kinetic energy (motor). Magnetic fields induce electricity, and electricity induce magnetic fields. There is no "licensing" of this property of electromagnetism.

It is more efficient to leave sufficient space in front of a vehicle and slowly lose speed by coasting than to drive bumper to bumper and use regenerative braking. The reason is that there is an energy cost any time you convert energy types. To continue coasting, you preserve the kinetic energy. To capture energy with regen requires the following energy conversions; kinetic > magnetic/electrical > chemical,. To use the stored energy requires reversal of those energy conversions; chemical > magnetic/electrical > kinetic. This is why regenerative braking is only 1/3 efficient, whereas coasting is 100% efficient.

Braking is necessary because it isn't practical to coast to every stop, and some hills are so steep that speed needs to be controlled. This is where regenerative braking is more efficient than friction braking, since you get about 1/3 of the energy back instead of 0%.

Since electrical regeneration involves so many energy conversions, it is less efficient than many other regeneration schemes. A very efficient scheme is flywheel storage, which simply transfers the kinetic energy of the moving vehicle into kinetic energy of a spinning flywheel. Another efficient regeneration method is compressed gas. These are impractical because it costs more, takes up space, and introduces new safety hazards such as explosion of compressed gas or poor handling due to the gyroscopic forces generated by a flywheel.

Electrical regeneration is almost free since motors are already generators, and batteries can both supply energy, and absorb energy.

I don't know why the Grapevine always comes up, but the most efficient way to drive it would be to set the cruise at the speed you want to travel, and let regen absorb the excess energy.

Other manufacturers have deemed coast mode a useful feature and included it in their EV. It would have been nice if the Bolt offered the option as well. It would require no extra effort in the Grapevine example because cruise would still control speed by regen.

...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.

Just the opposite is true. Flat uninterrupted highway travel doesn't matter if you use D or L modes, since braking will never occur. Where a true coast mode really shines is stop and go driving. You drive at the average speed of traffic, allowing a gap to occur when traffic moves faster, and coasting when traffic is slowing down and the gap is closing. It takes way more concentration because you need to be looking way ahead to see what traffic is doing, and anticipate the speedups/slowdowns and react accordingly. Most people can't be bothered to concentrate after a long day of work, so they drive bumper to bumper, which takes almost no concentration or ability.

 

[Anonymous]

I don't know why the Grapevine always comes up, but the most efficient way to drive it would be to set the cruise at the speed you want to travel, and let regen absorb the excess energy.

Other manufacturers have deemed coast mode a useful feature and included it in their EV. It would have been nice if the Bolt offered the option as well. It would require no extra effort in the Grapevine example because cruise would still control speed by regen.

When the truck I drive behind northbound on the Grapevine is traveling 45 MPH, I recapture 1.5 KW using cruise control and L; when it is traveling the speed limit, 35 MPH, I recapture 2.0 KW; an obvious difference that I would prefer to have while only driving about 2 minutes longer on the 5 miles of 6% downgrade!

These extra KWs gives me a nice buffer for my 196 miles trip to Paso Robles for the DCFC; especially if it is out of service and I must drive an additional 30 miles to San Luis Obispo!

 

[LeftieBiker]

Just the opposite is true. Flat uninterrupted highway travel doesn't matter if you use D or L modes, since braking will never occur. Where a true coast mode really shines is stop and go driving. You drive at the average speed of traffic, allowing a gap to occur when traffic moves faster, and coasting when traffic is slowing down and the gap is closing.

See if you can spot the mistake you made above. I've helped you. As for coasting in stop and go traffic, that can work well with stoplights with no traffic, but in actual stop and go traffic it's a nonstarter. Regen does best there. But hey, I tend to forget that this is a Chevy forum, so I'll just leave it at that.

 

[redpoint5]

When the truck I drive behind northbound on the Grapevine is traveling 45 MPH, I recapture 1.5 KW using cruise control and L; when it is traveling the speed limit, 35 MPH, I recapture 2.0 KW; an obvious difference that I would prefer to have while only driving about 2 minutes longer on the 5 miles of 6% downgrade!

Sure, you get more regenerated range by going slower because less of the energy is being wasted as aerodynamic drag. You would waste less time and have more range by slightly lowering your overall top speed on the flat sections, and increase your speed down the Grapevine. Again, the reason for this is that energy conversions are extremely wasteful. Drafting a truck can significantly reduce aerodynamic drag though, so maybe pick the fastest moving truck to follow.

As an aside, I've done 90 MPH down the grapevine and been passed like I was standing still by a semi. I don't recommend trying to draft that guy.

See if you can spot the mistake you made above. I've helped you. As for coasting in stop and go traffic, that can work well with stoplights with no traffic, but in actual stop and go traffic it's a nonstarter. Regen does best there.

I made no mistakes, except perhaps in failing to adequately explain how stop and go driving is where coasting really shines.

When traffic is speeding ahead, you maintain the same average speed of traffic, allowing them to pull away and a gap to form. When traffic ahead comes to a stop, you begin coasting while the gap that formed decreases. If you time it correctly, traffic begins moving again just as you near the person ahead of you.

As a bonus, everyone else driving bumper to bumper behind you gets way better fuel economy as they aren't constantly hammering the accelerator just to hammer the brakes a second later.

Some people will move into the gap that forms ahead of you, but they are likely to eventually leave the lane resulting in no net loss of position. In an hour of stop and go driving, I counted a net gain of 11 cars that filled the gap, which adds about 20 seconds to my 1hr drive.

 

[LeftieBiker]

The Bolt has strong Regen in L, but you tell me it doesn't matter if D or L is used on the highway, because coasting is best. Then you say that L isn't good for stop and go driving. You say coasting is best. Great. How do you "coast" in L? How do you 'maintain the average speed of traffic' in bumper to bumper stop and go congestion? Are you just a troll, perhaps? I need a break from this forum, I think.

 

[Anonymous]

Drafting a truck can significantly reduce aerodynamic drag though, so maybe pick the fastest moving truck to follow.

As an aside, I've done 90 MPH down the grapevine and been passed like I was standing still by a semi. I don't recommend trying to draft that guy.

I don't "draft" trucks when I drive northbound on the Grapevine, thank you!

I am merely driving in the rightmost lane with the trucks using cruise control to maintain their flow of traffic speed, so that I can maintain the maximum regeneration for the 5 miles 6% downhill grade.

No where did I ever claim to be "drafting' trucks on the Grapevine! This is a discussion of regeneration vs. coasting. Please try to not raise red herring issues that I am not doing, even if they are more easily rebutted by you!

AND, you have certainly never driven 90 MPH in the truck lane!

 

[Anonymous]

I need a break from this forum, I think.

We both need a break from this topic, me thinks!

There is no crying in baseball and no "coast mode" in the 2017 Bolt EV! :lol:

 

[redpoint5]

Drafting a truck can significantly reduce aerodynamic drag though, so maybe pick the fastest moving truck to follow.

No where did I ever claim to be "drafting' trucks on the Grapevine! This is a discussion of regeneration vs. coasting. Please try to not raise red herring issues that I am not doing, even if they are more easily rebutted by you!

...AND, you have certainly never driven 90 MPH in the truck lane!

I hope you can appreciate the irony here when you accuse me of something I didn't do, and then proceed to do exactly the thing you accuse me of (red herring).

Nowhere did I claim you were drafting trucks.

Further, I never rebutted your claim of being able to regenerate down a steep hill.

Now you imply that I said I did 90 MPH in the right lane down the Grapevine, which actually is a red herring. Nowhere did I even hint at what lane I was in, not that it matters.

As it happened, I was in the #1 lane, and it was a double-trailer that passed me in #2. Perhaps his braking system wasn't functioning properly.

I don't "draft" trucks when I drive northbound on the Grapevine, thank you! I am merely driving in the rightmost lane with the trucks using cruise control to maintain their flow of traffic speed, so that I can maintain the maximum regeneration for the 5 miles 6% downhill grade.

If a truck is ahead of you, you are benefiting from a draft. To draft is to benefit aerodynamically from an object ahead of you, moving in the same direction. Regardless of whether you do it consciously or not, the benefit is there and extends hundreds of feet behind the vehicle. If you're more than about 2 seconds following distance from the truck, then the benefit is extremely small, which makes it even more pointless to be in the right lane going 35 MPH down the Grapevine.

As I said, it is more efficient (you'll get more range) and save more time, by slightly reducing your speed on the flat sections of road, and increasing your speed down the Grapevine. The reason is that regen is not very efficient (30% efficient), but adding just 1 MPH to your top speed significantly reduces efficiency (wind resistance increases with the square of speed. These facts are not in controversy.

 

[Anonymous]

Even MORE reason to take a break from this topic... :lol: