Every discussion of ascent energy recovery always seems to lead to anecdotal testimonies, leading to lack of resolution, which has led to many believe that the incorrect range of estimates on the range chart, has some validity.
As posted yesterday:
If we're talking about how much potential energy you can recover on the way down a hill after going up and comparing efficiency to driving the same distance on flat ground - the answer is a big "it depends".
What does it depend on? Mostly, it depends on the slope of the hill and how fast you are going.
I will tell you that rolling resistance, air resistance and climate control have nothing to do with it.
Say you're cruising at 60 mph on flat ground and pulling 15 kW out of the battery to maintain speed.
Now say you encounter a slight hill which increases power requirements to 20 kW going up. Coming back down the hill of the same slope and at the same speed will only require 10 kW.
Your average power requirements will be the same 15 kW as if you kept on flat ground - IF (and it's a fairly significant IF) one assumes that the efficiency curve of the motor is flat and that any increase in resistive losses between the motor and battery are minimal (which it should be at such a modest change in power)
So for a situation like that - you do get all your potential energy back.
But if the hill is steep enough that power requirements go negative and regen is required to maintain speed - now you end up having to add in the inefficiency of regen - which is probably around 70% efficient.
So for a case where power requirements go from 15 kW to 40 kW to climb the hill at 60 mph, coming back down you need 10 kW regen to maintain 60 mph, only about 7 kW of that 10 kW will be of use.
To get actual numbers, assume that you drive for an hour. Flat ground: 15 kW * 1h = 15 kWh. Hill: 40 kW * 0.5h - 7 kW * 0.5h = 16.5 kWh. So in this case the hill will take about 10% more energy.
NOTE: Number purely back-of-the-envelope but should be in the right ballpark!
Thank you for this explenation.
Does anyone dispute: this part of "drees" comment, can we try to resolve that issue, before moving on to the next question?
What amounts of regen are actually required in descents, and so, how much additional energy is required, and how much is the driving range of the LEAF reduced, due to ascents and descents, in real-world conditions?
I can't tell, from several of the comments since yesterday, whether there are objections to ...you do get all your potential energy back...
in drees statement, or if you are just objecting to his assumption:
...IF (and it's a fairly significant IF) one assumes...
If that assumption was the only part of "drees'" comment above, that anyone actually objected to. Can we all please now discuss the same question, the validity of this assumption in "drees'" statement?