BEV mass and Regeneration efficiency

[freebeard]

As an experiment, I let vBulletin handle the enumeration:

1. The aerodynamics hasn't changed.
2. Between all three driving cycles, aerodynamics plays a subservient role.
3. Overall efficiency is weighted towards urban driving. It's biased.
4. The BSFC-e of the BEV is 311% more efficient than the ICE stablemate. The inertia loss associated with accelerating the increased mass is meaningless with this 311% advantage compared to the ICE variant. The electric motor just laughs at it.
5. 81.1% of braking energy is recovered by regeneration. There is no energy lost to braking. Mass is your friend.
6. A 10% increase in mass costs only a 1-2 % penalty in rolling resistance.
7. Even with a 20% mass increase, the energy gain from regen is 14.6% net overall, after allowing for the increase in inertia and R-R losses.
8. Again, aerodynamics remains the same.
9. It's a net OVERALL efficiency gain for the small Volvo.
10. Your zero-mass analogy is not germane to the Thesis.
11. I agree
    completely with your premise about reduced drag and R-R, however they're not germane to the Thesis.
12. Electric motors with powertrain are typically rated at 95% efficiency, with no stipulation as to 'curves.'
13. 'Power' to weight is not germane with BEVs, as 100% torque is always available from zero-to- full rpm.

That said it looks like you're going for an evidentiary chain, but premises and rebuttal have equal weight.

That makes it harder to follow.

[Isaac Zachary]

Originally Posted by aerohead

1) The aerodynamics hasn't changed.
2) Between all three driving cycles, aerodynamics plays a subservient role.
3) Overall efficiency is weighted towards urban driving. It's biased.
4) The BSFC-e of the BEV is 311% more efficient than the ICE stablemate. The inertia loss associated with accelerating the increased mass is meaningless with this 311% advantage compared to the ICE variant. The electric motor just laughs at it.
5) 81.1% of braking energy is recovered by regeneration. There is no energy lost to braking. Mass is your friend.
6) A 10% increase in mass costs only a 1-2 % penalty in rolling resistance.
7) Even with a 20% mass increase, the energy gain from regen is 14.6% net overall, after allowing for the increase in inertia and R-R losses.
8) Again, aerodynamics remains the same.
9) It's a net OVERALL efficiency gain for the small Volvo.
10) Your zero-mass analogy is not germane to the Thesis.
11) I agree completely with your premise about reduced drag and R-R, however they're not germane to the Thesis.
12) Electric motors with powertrain are typically rated at 95% efficiency, with no stipulation as to 'curves.'
13) 'Power' to weight is not germane with BEVs, as 100% torque is always available from zero-to- full rpm.
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The 2021 VOLVO XC40 P8 AWD Recharge ( R-Design ) is still ' such a small vehicle.' ( Mark Rechtin, MOTOR TREND ), but now has ' Strong regenerative braking.' ( Duncan Brady, MOTOR TREND ).
Volvo increased it's weight from, 1572-kg, to 2165-kg.
It out-accelerates the ICE version. It's faster in the quarter-mile. It's 'fuel economy' is 311% higher. I has 1,109 miles range on the ICE's 'tank', compared to 355-miles, 93.4-mpg-e, to 25-mpg.

In my post I also was comparing effects of mass with vehicles that had the same aerodynamic drag.

If losses are irrelevant to efficiency, then why a thread on EV efficiency?

It seems to me you're not taking into account energy needed to accelerate back up to speed.

Say it takes 100Wh to accelerate one vehicle up to speed and the other it takes 200Wh because it's twice as heavy. But they are 95% efficient, so it takes about 105.26 and 210.52Wh to accelerate respectively. We'll pretend they have the same rolling resistance for sake of comparison. We could add aerodynamics into the equation here if we want. Say we lose 25Wh to aerodynamic drag during the acceleration phase of these two vehicles since both are identical in shape and size. The lighter would use 130.26Wh and the heavier would use 235.52Wh, which is seemingly 76.8% and 84.9% efficient respectively: the heavier vehicle seeming more efficient due to its greater mass in comparison to the aerodynamic drag.

Once on the road both lose the same amount of energy because they are neither accelerating nor decelerating, both have the same aerodynamic drag and we've made them have the same rolling resistance for comparison.

Then as they both decelerate both lose the same amount of energy to aerodynamic drag too since they are the same shape. Say aerodynamic drag takes off 25Wh off of each vehicle. So we have 75Wh and 175Wh to recuperate respectively. At 80% regen efficiency the total recuperated is 60Wh and 140Wh respectively. The lighter vehicle recuperated only 60% of its inertial energy whereas the heavier one recuperated 70%. But the total energy lost to acceleration that couldn't be recuperated by regen braking is 35.52Wh in the heavier vehicle, whereas the lighter vehicle only losses 30.26Wh.

5.25Wh lost due to heavier vehicle.

Mass is NOT a friend in an EV. You only break even in the end if regen and motoring efficiencies are 100%. The supposed increase in efficiency due to larger mass is simply a result of weight vs aerodynamic drag but is not the whole story and is not an increase of overall efficiency, but rather a decrease. If you take these two vehicles that are identical in every aspect except mass and drive them around, especially in a city environment the heavier one will use more energy and have less range. And that would be true even if you matched the rolling resistance on both vehicles by using slightly worse tires on the lighter vehicle.

[aerohead]

Originally Posted by Isaac Zachary

In my post I also was comparing effects of mass with vehicles that had the same aerodynamic drag.

If losses are irrelevant to efficiency, then why a thread on EV efficiency?

It seems to me you're not taking into account energy needed to accelerate back up to speed.

Say it takes 100Wh to accelerate one vehicle up to speed and the other it takes 200Wh because it's twice as heavy. But they are 95% efficient, so it takes about 105.26 and 210.52Wh to accelerate respectively. We'll pretend they have the same rolling resistance for sake of comparison. We could add aerodynamics into the equation here if we want. Say we lose 25Wh to aerodynamic drag during the acceleration phase of these two vehicles since both are identical in shape and size. The lighter would use 130.26Wh and the heavier would use 235.52Wh, which is seemingly 76.8% and 84.9% efficient respectively: the heavier vehicle seeming more efficient due to its greater mass in comparison to the aerodynamic drag.

Once on the road both lose the same amount of energy because they are neither accelerating nor decelerating, both have the same aerodynamic drag and we've made them have the same rolling resistance for comparison.

Then as they both decelerate both lose the same amount of energy to aerodynamic drag too since they are the same shape. Say aerodynamic drag takes off 25Wh off of each vehicle. So we have 75Wh and 175Wh to recuperate respectively. At 80% regen efficiency the total recuperated is 60Wh and 140Wh respectively. The lighter vehicle recuperated only 60% of its inertial energy whereas the heavier one recuperated 70%. But the total energy lost to acceleration that couldn't be recuperated by regen braking is 35.52Wh in the heavier vehicle, whereas the lighter vehicle only losses 30.26Wh.

5.25Wh lost due to heavier vehicle.

Mass is NOT a friend in an EV. You only break even in the end if regen and motoring efficiencies are 100%. The supposed increase in efficiency due to larger mass is simply a result of weight vs aerodynamic drag but is not the whole story and is not an increase of overall efficiency, but rather a decrease. If you take these two vehicles that are identical in every aspect except mass and drive them around, especially in a city environment the heavier one will use more energy and have less range. And that would be true even if you matched the rolling resistance on both vehicles by using slightly worse tires on the lighter vehicle.

Please read the thesis. There's no point discussing it until you have. This place where I use the computer is closing. I'll be back Thursday.

[Isaac Zachary]

Originally Posted by aerohead

Please read the thesis. There's no point discussing it until you have. This place where I use the computer is closing. I'll be back Thursday.

This is physics. Not magic. I don't second guess physics. Nothing in the thesis proves that a heavier BEV is more efficient overall.

In fact it states in figure 4.1 that the small BEV uses the least amount of energy per distance.

It also states on page 26 that

The small BEV’s efficiency is noticeably lower in the city cycle than the medium sized but responds predictable in the other two cycles in line with the larger cars. This rather strange behaviour is connected to the regenerative braking which is dependent on available wheel power and mass. Larger mass results in both a higher accelerating kinetic energy and thus carries more energy which is available during braking.

This is exactly what I am getting at. The small BEV uses less energy overall. But it seems less efficient in urban driving due to a smaller mass that results in a lower accelerating kinetic energy.

[freebeard]

Logic would suggest any difference would lie at the extreme edge cases, not some hiccup a the crossover point, like ice expanding or something.

[aerohead]

Originally Posted by Isaac Zachary

This is physics. Not magic. I don't second guess physics. Nothing in the thesis proves that a heavier BEV is more efficient overall.

In fact it states in figure 4.1 that the small BEV uses the least amount of energy per distance.

It also states on page 26 that

This is exactly what I am getting at. The small BEV uses less energy overall. But it seems less efficient in urban driving due to a smaller mass that results in a lower accelerating kinetic energy.

Returning to the beginning:
1) When Oil Pan 4 mentioned weight reduction of the Tesla Model 3, my 'little gray cells' flashed to the 2015 thesis.
2) Gustafsson & Johansson had said that the 'small' Volvo V40 SUV BEV demonstrated 'strange' behavior with respect to European test cycle constraints and proportionally-weighted urban performance, having to do with regenerative braking, and mass.
3) The Tesla Model 3 is the 'small' Tesla. I threw a caution flag out on the field.
4) And we're having a conversation about it.
5) The physics is quite clear to me.
6) The thesis authors provide the caveats, conditions, constraints, and boundaries for their argument.
7) I'm limiting my participation to only the operational parameters, as laid out by the original authors.
8) Those parameters are specifically limited to a 'small', Volvo V40 SUV BEV, in a CITY cycle segment of the New European Driving Cycle ( NEDC ).
9) It is a fact, that since 2015, Not only did Volvo increase the mass of the V40 to that of the 'mid-sized' S80, they exceeded the mass of the 'full-sized' XC90 by another 28-kg, arriving at a 593-kg ( 1,307- LB ) mass increase. Delta- 37.7%.
10) The ' such a small' ( Mark Rechtin, MOTOR TREND ) Volvo outruns it's ICE stablemate, and has 316% higher 'fuel' economy.
11) It has ' Strong regenerative braking' ( Duncan Brady, MOTOR TREND ).
12) All automakers are held to official testing protocols, and internationally, combined testing results are proportionately-weighted towards 'CITY/Urban' performance.
13) Everyone is free to run all the calculations and compare the differences.
14) Everyone is free to explore ULRR tire technology and ponder what options Volvo might have with respect to any RR increase to additional mass, over all the testing cycles.
15) Everyone is free to calculate the delta-Inertia Resistance.
16) Everyone is free to calculate the delta-energy recovery to the Volvo, via regenerative braking.
17) I should have my math finished by tomorrow. Storm weather is predicted for the time I'd be walking here in the morning, so I elected to come today, losing a day for calculations.

[aerohead]

Originally Posted by Isaac Zachary

This is physics. Not magic. I don't second guess physics. Nothing in the thesis proves that a heavier BEV is more efficient overall.

In fact it states in figure 4.1 that the small BEV uses the least amount of energy per distance.

It also states on page 26 that

This is exactly what I am getting at. The small BEV uses less energy overall. But it seems less efficient in urban driving due to a smaller mass that results in a lower accelerating kinetic energy.

1) Please read #66 ( permalink )
2) Please do all the mathematics, then we'll discuss the results.
3) We'll do the hypotheticals after we have a clear numerical representation of the 2015 thesis quanta.
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4) Less energy overall is what most impacts the life-cycle-cost to the consumer and planet.
5) After you have the BSFC-e for the Volvo, you'll be able to numericalize any delta- urban/ ' extra urban' cycle efficiency.
6) Your analysis of the 'penalty' of Inertia Resistance sets the stage for regenerative-braking energy capture contrast. Which I believe you'll find most interesting.

[aerohead]

Originally Posted by oil pan 4

I do stuff like haul bags of coal, wood pellets with my leaf. Heavier does not appear to be more efficient at all.

So, after looking at this for weeks now, all I can offer is that, without operating the LEAF on a dyno, under a prescribed test regimen like the NEDC City segment, we'd be challenged to reliably quantify any changes in performance.
Accelerations, decelerations, stops, starts, 'idling', etc., would have to be exactly identical, before and after a weight change.

[aerohead]

Originally Posted by redpoint5

Some fraction of x is always less than x, even if that fraction is very high. It would always be more efficient to avoid spending energy than attempting to recover it.

When you run the numbers for Inertia Resistance you'll see some values which puts a face on 'strange.'
Also, Volvo has the option of specifying a ULRR tire which can compensate for what would otherwise be additional rolling resistance, just as GM did with it's patented tires for Impact/ EV1, and Ultralite.
Aerodynamics never changes.
And average cycle velocities are weighted towards 'City' driving, where R-R dominates, and can be erased with tires.
The NEDC cycles have to be respected. That's not negotiable.
The authors of the thesis were just trying to work within the NEDC constraints.
And when you see the actual BSFC-e of the Volvo, you'll realize how the SUV can just shrug off the extra mass during acceleration.
There are no 'braking' losses.
It's not 'strange' but it is significantly different compared to 'legacy' dynamics.

[aerohead]

Originally Posted by redpoint5

I've heard great things about central planning. A few geniuses making all the decisions in an infinitely complex and interconnected system is sure to go smoothly.

One Richard Feynman would suffice.