[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.