edatoakrun said:
evnow said:
edatoakrun said:
Altitude doesn't "kill" range, though the effect is very significant on roads that require a lot of regen, to reduce your speed to the more efficient lower range required to rack up lots of miles. On mild ascents and descents, those that do not require regen or friction braking, the ascent energy is 100% recovered in the subsequent descent, though there is probably still a small loss of efficiency due to the more variable kW use, than on a otherwise comparable level route.
You are kidding, right ? There is never a 100% recovery - given the number of elements in between, even if each one is 95% efficient, you get to below 80% overall efficiency with regen.
...On mild ascents and descents, those that do not require regen or friction braking, the ascent energy is 100% recovered in the subsequent descent...
I would appreciate it if someone else would make a try at explaining the two different concepts, the recovery of ascent energy in descent, and the efficiency rate of regenerative braking. I've tried, at least a half dozen times, on various threads, and for over a year now, with little success.
The quotes in red are correct, but perhaps a detailed example may make it clearer.
Assume your car has reached the top of a hill and is about to descend the other side. At that point it has acquired some potential energy in addition to the energy currently in its battery. In acquiring that potential energy while climbing the hill, there were small amounts of energy conversion loss from the battery, the inverter, and the motor. To a good approximation the battery loss is proportional to the power level. If the ascent is gradual and the climbing speed is modest, such that the power level is 20 kW, then the battery loss is about 2%. 30 kW would be 3%. This can be seen by watching the battery voltage drop with the Gid meter. I have no way to measure the inverter loss, but 6% might be a good number, comparable to solar inverters. Nissan has published a color chart on the motor loss as a function of rpm and power, showing a loss range of 5-7%. The total loss in conversion from battery to potential energy is thus perhaps 13-16%.
For a given speed, the steeper the ascent, the more the loss. There is additional energy expended on rolling resistance and aerodynamic drag, but since these losses are always present, even on level ground, we can choose to ignore them for this discussion.
Now consider the car's descent. There are 3 cases, depending upon how steep the grade and how fast you go. For a given slope there is some equilibrium speed V* at which the car will coast in neutral, with no power going in or out of the motor. The steeper the slope, the higher V*.
In case 1, gentle slopes, your are driving at speeds of V* or greater, where the acquired potential energy is being expended on rolling resistance and aerodynamic drag with
100% efficiency because no electronics are involved. As usual, the faster you go, the higher the aerodynamic loss, and you may have your foot on the throttle to add more power, but the conversion efficiency of potential energy is still 100%.
In case 2, steeper slopes, V* is a higher speed than you want to go, and but you can achieve your desired safe speed using regeneration with either D or ECO mode. You may have your foot gently on the throttle to achieve the right amount of regeneration, but you don't have it on the brake. During regeneration the electrical system works in reverse. The motor acts like a generator, the power electronics act like a charger, and the battery accepts charge. Each of these 3 elements have losses similar to the losses of ascent that were not present in case 1. I believe the battery loss during charging is usually higher than the discharge loss, and the other losses may be higher also. Also consider that the net energy that does get back into the battery will be subjected to the normal losses when it is subsequently discharged.
Case 3 occurs when regeneration is not sufficient to keep the car at your desired speed, and you have to apply the brake, which imposes an additional frictional loss. On the LEAF applying the brake usually can increase the regeneration, at least temporarily, but the friction goes up in parallel.
The net result for descents is that if it is safe to let the car go a little faster to avoid regeneration, that will usually be the most efficient option, even though the aerodynamic drag increases.