[PodCat]

Just got back from Reno in my 2013 Volt.
553.4 miles and 14.6 gallons to go up there,
511.4 miles and 11.0 gallons to come back.

Aside from the different routing and 42 extra miles in one direction, I went from 0 to 4505 ft elevation on the trip up, which at least partially explains the significant change in gas mileage (35.0 mpg up, 42.6 down).

We all well know that going uphill significantly degrades range and miles per kWh.
But just how much?

I realized I really have no idea. Which means that, likely, most others don’t either.
That doesn’t help one bit getting people to trust BEV’s.
Is there some simple way to quantify the cost of going uphill?
As in, the additional cost to raise the car one mile (5280 feet)?
And does this depend significantly on speed, as it does for level driving?

As you probably know, you can get more than double the Volt’s range by keeping to a level, steady 30 mph.
Does a similar coefficient apply to uphill speed?
Or severity of grade?

 

[saghost]

The nominal energy cost to gain or lose altitude does not vary with speed. However, the speed that you're at and gearing/operating strategy do change the engine/transmission efficiency, so there can be some effect.

Potential energy is calculated as the mass of the object times the distance raised times the gravitational acceleration. (Technically, I think it should be an integral to account for the acceleration decreasing as the altitude increases, but the difference is so small down here at the bottom of the atmosphere that it can be neglected.) Doing it in metric avoids a bunch of unit conversions...

One mile is 1600 meters. A Volt with several people or a bunch of stuff is probably around 2000 kg (4472 pounds.)

So the potential energy for raising a loaded Volt one mile is 1600 * 2000 * 9.81 = 31.4 megajoules. There are 3.6 MJ in a kWh, so that's 8.72 kWh.

Of course, that's the energy applied at the wheels. You have to work upwards from there through the efficiency factors to get the original energy applied. With typical Volt efficiencies it should be somewhere close to a gallon of gas used (which would mean the total swing between a trip up and a trip down world be about two gallons.)

 

[obermd]

Don't forget that what goes up must come down as well. My Gen 2 Volt regains over 80% of the extra energy used going uphill and I can drive around Colorado's mountains easily exceeding the 42 MPG EPA rating when running ICE.

The rest of saghost's example is the downhill where I will regain 80% of 8.72 KWh or 6.986 KWh. If I'm on battery at the start of the descent this records as electric range, otherwise it records as gas miles and can a major impact on the gas fuel economy numbers.

Gas and diesels have a similar equation so while some may try to claim the uphill impact is a negative for EVs, the reality is it's a negative for all cars but that EVs with regenerative braking will actually come out ahead because a large amount of that potential gravitational energy is reclaimed during the descent for later use whereas the traditional ICE engines are unable to recapture that energy.

 

[MikeyCVolt]

Interesting. Given that electric motors aren't 100% efficient, the cost on the battery is probably closer to 10 kWH. Add to that the fact that you have to travel some horizontal distance in order to do it and realistically, climbing a 1 mile high slope at say a 10% grade (travel 10 miles to climb 1 mile high) might cost somewhere around 12.5 kWH if you do it at 50 MPH and you basically deplete your battery going up that hill. But what goes up must come down so you may gain half of what you lost on the way back down. Not so with ICE vehicles: what is used on the way up is used and there's no way to get it back.

Mike

 

[saghost]

Interesting. Given that electric motors aren't 100% efficient, the cost on the battery is probably closer to 10 kWH. Add to that the fact that you have to travel some horizontal distance in order to do it and realistically, climbing a 1 mile high slope at say a 10% grade (travel 10 miles to climb 1 mile high) might cost somewhere around 12.5 kWH if you do it at 50 MPH and you basically deplete your battery going up that hill. But what goes up must come down so you may gain half of what you lost on the way back down. Not so with ICE vehicles: what is used on the way up is used and there's no way to get it back.

Mike

ICE cars do get energy back coming down. They only throw it out the window when they have to hit the brakes and dump it as thermal energy.

 

[BillG]

That doesn’t help one bit getting people to trust BEV’s.

This issue is not specific to BEVs, so I don't understand your concern about "getting people to trust BEV's".

 

[Barry]

This issue is not specific to BEVs, so I don't understand your concern about "getting people to trust BEV's".

I think it makes sense because range anxiety is more relevant to BEVs than to ICE vehicles. If your destination is higher than your origin, your predicted range will be negatively impacted. It is another factor you have to be aware of.

This is an opportunity for a BEV nav system to add some value by calculating the elevation gain, and to use that, along with other factors like speed limits, traffic and weather along the route, to help make accurate estimates of power requirements for the route.

 

[Tacoma]

ICE cars do get energy back coming down. They only throw it out the window when they have to hit the brakes and dump it as thermal energy.

Say what?
This has to be almost nothing. The engine still will combust, even if the requested fuel level to be supplied (meaning foot off the gas pedal) is equivalent to idle. That is totally different from capturing and storing energy that can be re-used later. The ICE vehicle going downhill is more like running at the lowest power level, not capturing and storing energy.

 

[saghost]

Say what?
This has to be almost nothing. The engine still will combust, even if the requested fuel level to be supplied (meaning foot off the gas pedal) is equivalent to idle. That is totally different from capturing and storing energy that can be re-used later. The ICE vehicle going downhill is more like running at the lowest power level, not capturing and storing energy.

Any modern ICE car has fuel cut during deceleration at above idle rpms.

But that's not really relevant to the point. Going up the hill is a form of energy storage, and rolling down the hill with an idling engine would still consume less fuel the driving along a flat at the same speed will.

The degree to which the ICE car can recover the stored energy from climbing the hill is variable, generally higher on freeway hills than right windy paths because the freeway loads can approach the energy release caused by typical hills while the car going down the winding road often has to dump energy with the brakes.

 

[obermd]

Any modern ICE car has fuel cut during deceleration at above idle rpms.

True

​

But that's not really relevant to the point. Going up the hill is a form of energy storage, and rolling down the hill with an idling engine would still consume less fuel the driving along a flat at the same speed will.

The degree to which the ICE car can recover the stored energy from climbing the hill is variable, generally higher on freeway hills than right windy paths because the freeway loads can approach the energy release caused by typical hills while the car going down the winding road often has to dump energy with the brakes.

The EV will always out perform ICE in this scenario simply because it can store the recovered energy for later use. The best the ICE can do is use zero energy via DFCO (Deceleration Fuel Cut-Off) allowing the wheel spin to keep the engine turning.

 

[Barry]

This is true, but it depends on the conditions. If the grade of the hill is low enough that brakes are not needed (either regular friction brakes or engine braking), then an ICE car will do just about as well as a BEV at using the potential energy from the higher elevation. The difference would be the gas needed to keep the engine running, which would be minimal. However, there are lots of descents that require plenty of braking to control speed, so there would be a bigger difference in those cases.

 

[rhodomel]

Just got back from Reno in my 2013 Volt.
553.4 miles and 14.6 gallons to go up there,
511.4 miles and 11.0 gallons to come back.

Aside from the different routing and 42 extra miles in one direction, I went from 0 to 4505 ft elevation on the trip up, which at least partially explains the significant change in gas mileage (35.0 mpg up, 42.6 down).

We all well know that going uphill significantly degrades range and miles per kWh.
But just how much?

I realized I really have no idea. Which means that, likely, most others don’t either.
That doesn’t help one bit getting people to trust BEV’s.
Is there some simple way to quantify the cost of going uphill?
As in, the additional cost to raise the car one mile (5280 feet)?
And does this depend significantly on speed, as it does for level driving?

As you probably know, you can get more than double the Volt’s range by keeping to a level, steady 30 mph.
Does a similar coefficient apply to uphill speed?
Or severity of grade?

I can tell you that it would cost the entire battery pack charge of 14.1 kWH to go 10,180 ft to counteract gravity component alone.

 

[alfon]

Let all not forget basic science. At higher elevations there is less air density which mean less aerodynamic drag...

 

[MikeyCVolt]

ICE cars do get energy back coming down. They only throw it out the window when they have to hit the brakes and dump it as thermal energy.

ICE cars don't get any energy back when going down the hill. Even if you turn the ICE engine completely off, you are not getting anything "back". It may not use as much energy (or may not even use any at all), but that's not the same as actually getting some back that you can use later.

Mike

 

[saghost]

True

The EV will always out perform ICE in this scenario simply because it can store the recovered energy for later use. The best the ICE can do is use zero energy via DFCO (Deceleration Fuel Cut-Off) allowing the wheel spin to keep the engine turning.​

Mostly agree. (I dislike absolutes, and there exist cases where the ICE does equally well because the slope is a perfect match. I don't think there's ever a case where the ICE does better, and the vast majority of cases the EV does better.)

I was replying to a post that said ICEs don't get energy back going down, which is why I attempted to clarify. On reflection, it may be a communication failure; they might have been talking about getting energy into the battery rather than out of the mountain. The ICE does the second, but obviously can't do the first unless it's some form of hybrid.​

 

[saghost]

ICE cars don't get any energy back when going down the hill. Even if you turn the ICE engine completely off, you are not getting anything "back". It may not use as much energy (or may not even use any at all), but that's not the same as actually getting some back that you can use later.

Mike

Of course they are. Energy spent going up the hill is turning into distance going down, getting the energy back. They don't gain gas in the tank, of course, but they do gain distance covered that they wouldn't have if they didn't come down the hill.

 

[PodCat]

I think it makes sense because range anxiety is more relevant to BEVs than to ICE vehicles. If your destination is higher than your origin, your predicted range will be negatively impacted. It is another factor you have to be aware of.

This is an opportunity for a BEV nav system to add some value by calculating the elevation gain, and to use that, along with other factors like speed limits, traffic and weather along the route, to help make accurate estimates of power requirements for the route.

Agreed. I’ve owned a Volt for years and still really have no feel for how much extra range will get sucked up by a big climb.
Really could add to range anxiety ... if I had a Leaf.

Good point on adding gained altitude to the formula for the GuessOmeter®️™️ 2.0.

ICE cars do get energy back coming down. They only throw it out the window when they have to hit the brakes and dump it as thermal energy.

If only.
Actually that energy is put to work tearing the car apart (brake wear, engine braking).

 

[MikeyCVolt]

If only.
Actually that energy is put to work tearing the car apart (brake wear, engine braking).

Right. You get exactly 0% back in an ICE car: 100% is wasted heating up your brake pads/rotors or heating up the engine via compression. Not using energy isn't the same as actually getting it back. The EV is doing the equivalent of using say 2 gallons going up the hill and then synthesizing a gallon and putting it back in the tank when you go down the hill.

Mike

 

[obermd]

ICE cars don't get any energy back when going down the hill. Even if you turn the ICE engine completely off, you are not getting anything "back". It may not use as much energy (or may not even use any at all), but that's not the same as actually getting some back that you can use later.

Mike

ICE cars do get energy back in the form of more velocity. If you let the ICE accelerate downhill on gravity alone you're converting some of that gravitational potential energy to kinectic energy. However, you can't do too much of this as you'll either leave the road (mountains) or be pulled over for speeding (more likely). Any energy not captured this way does indeed end up as waste heat.

 

[saghost]

Right. You get exactly 0% back in an ICE car: 100% is wasted heating up your brake pads/rotors or heating up the engine via compression. Not using energy isn't the same as actually getting it back. The EV is doing the equivalent of using say 2 gallons going up the hill and then synthesizing a gallon and putting it back in the tank when you go down the hill.

Mike

So in your experience, ICE cars don't roll down hills?

That's horizontal distance gained by transferring potential energy into kinetic, moving the car along. If you don't start at the top of the hill, it's energy you put in to pushing the car up the hill coming back as you roll down the hill.

It's only when the hill exceeds a certain steepness and you want to go down slower than the slope would provide that the ICE starts throwing energy away...