Quote:
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.
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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.