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Re: Battery Aging Model

Posted: Tue Oct 30, 2012 6:09 pm
by Stoaty
tbleakne wrote:I commend all the detailed work that has been reported on this thread, using solid analysis to apply corrections, but I still agree with this comment posted on pg 1. The curves Nissan gave to TickTock are not data, but rather their model. We should suspect that this model has been massaged to fit with the optimistic projections that Nissan is still standing behind. I am concerned that folks might put more faith in your results than is warranted to the extent that they are based upon their model.
Actually, I believe that at least the Phoenix curve is their model, slightly refined from data they got from Carwings. Correct me if I am wrong, but Nissan stated that Phoenix Leafs are on track for 76% capacity remaining after 5 years at 7500 miles per year using the Carwings data they have since the Leaf started selling in Arizona. Of course, this was a real revelation to all of us, because it meant that 12500 miles a year was "high mileage" in Phoenix, and that the predicted EOL (70%) was more like 4.5 years if you drive 12500 miles a year, not 10 years.
One clue that Nissan's curves might not be based upon solid science is that they show no seasonal variation, contrary to what we know will happen from the Arrenhius factor.
You have to remember that Nissan's curves were to show the overall trend, and are likely a rough summary of their findings. They most likely know about annual variation, but they are looking at the big picture.

Re: Battery Aging Model

Posted: Thu Nov 01, 2012 3:27 pm
by tbleakne
A question about your model: the Wiki seems to imply that you are estimating temperature dependence for the calendar-loss component of battery degradation, but assuming no temperature dependence for the cycle component of battery degradation. I have not seen any claims or research that cycle loss is temperature-dependent. However, in the LEAF's case, on the one hand we have Nissan claiming that "excessive" mileage, now defined as over 7.5K mi/year, is a major component of loss in AZ, and on the other hand we have lots of folks in cool climates claiming negligible loss to date, irrespective of their mileage. My impression is that this group includes folks with mileage greater than perhaps 15K miles per year, comparable to folks in AZ with excessive loss.

This suggests that it would be hard to fit a model with no temperature dependence of its cycle component to both sets of data. Do you see this in your results? If not, it would seem the only other likely possibility is that the higher mileage folks in cool climates are not accurately reporting their loss.

Re: Battery Aging Model

Posted: Thu Nov 01, 2012 5:03 pm
by Stoaty
tbleakne wrote:A question about your model: the Wiki seems to imply that you are estimating temperature dependence for the calendar-loss component of battery degradation, but assuming no temperature dependence for the cycle component of battery degradation. I have not seen any claims or research that cycle loss is temperature-dependent. However, in the LEAF's case, on the one hand we have Nissan claiming that "excessive" mileage, now defined as over 7.5K mi/year, is a major component of loss in AZ, and on the other hand we have lots of folks in cool climates claiming negligible loss to date, irrespective of their mileage. My impression is that this group includes folks with mileage greater than perhaps 15K miles per year, comparable to folks in AZ with excessive loss.
I really need to flesh out the description of the Battery Aging Model in the Wiki. I am probably going to give it a separate section under Battery Capacity Loss. In my model, cycling loss is also temperature dependent, using the same aging factor as calendar loss. Also, the aging factor that was calculated using the 10 degree C. increase causes doubling of rate of loss was adjusted to fit Nissan's model the graph from TickTock. The adjustment required the high aging factors like Phoenix to be scaled back (roughly 1.8 -> 1.5 for Phoenix on the scale we were using, although the model has the values adjusted to a slightly different baseline of 0.9 for "normal", so the actual value for Phoenix is 1.35 (still 50% greater than basline as the 1.5 factor). The adjustments were all made empirically so that the model reproduced the "known" values from TickTock's graph. All of that definitely needs to be made clear for those who don't want to read through long threads to figure it out.

Re: Battery Aging Model

Posted: Fri Nov 02, 2012 1:57 pm
by Stoaty
I put the Battery Aging Model in its own section of the Battery Capacity Loss portion of the Wiki, and rewrote that section to describe the model in more detail:

http://www.mynissanleaf.com/wiki/index. ... ging_Model" onclick="window.open(this.href);return false;

As always, comments, criticisms, suggestions, etc. are welcome.

Re: Battery Aging Model

Posted: Fri Nov 02, 2012 6:40 pm
by Stoaty
The table of battery aging factors in the Wiki has now been expanded to show predicted remaining battery capacity at 1 year, 2 years, 3 years, 5 years, 10 years and the number of years to end of life (70%). Table was created assuming 12500 miles per year and 4 miles per kwh efficiency, but does not include possible losses from solar loading (if you park in the sun).

http://www.mynissanleaf.com/wiki/index. ... ging_Model" onclick="window.open(this.href);return false;

Of course, if you want an individualized prediction for your annual mileage, driving efficiency and amount of time parked in the sun you can download the Battery Aging Model spreadsheet and enter your own numbers.

Re: Battery Aging Model

Posted: Fri Nov 02, 2012 9:58 pm
by TonyWilliams
Stoaty wrote: http://www.mynissanleaf.com/wiki/index. ... ging_Model" onclick="window.open(this.href);return false;
This following quote from the wiki is missing an important piece of the puzzle; the heater or air conditioner use will lower the "useable battery capacity" available for range autonomy. 4 miles/kWh multiplied by 21 = 84 miles, however with the climate control on, the same 4 miles/kWh could equal 76 miles of range autonomy (76 / 4 = 19kWh), or any range between 76 and 84 miles, as suggested in the quoted Nissan bulletin.

"One deduction from this table is that Nissan expects a range of usable battery capacity of 19-21 kwh when the car is new. It would be surprising if manufacturing tolerances are that large, so it may be due to variations in the time between manufacture and when the buyer takes delivery, or more likely to give some leeway for some dealers who store unsold Leafs at 100% SOC in the hot sun. Another possibility is that up to 1 kwh may be due to pack imbalance. A fourth possible explanation for the range in the chart is variability in the economy meter due to instrumentation accuracies (i.e. Gids). "

Re: Battery Aging Model

Posted: Sat Nov 03, 2012 6:43 am
by Stoaty
TonyWilliams wrote:
Stoaty wrote: http://www.mynissanleaf.com/wiki/index. ... ging_Model" onclick="window.open(this.href);return false;
This following quote from the wiki is missing an important piece of the puzzle; the heater or air conditioner use will lower the "useable battery capacity" available for range autonomy. 4 miles/kWh multiplied by 21 = 84 miles, however with the climate control on, the same 4 miles/kWh could equal 76 miles of range autonomy (76 / 4 = 19kWh), or any range between 76 and 84 miles, as suggested in the quoted Nissan bulletin.

"One deduction from this table is that Nissan expects a range of usable battery capacity of 19-21 kwh when the car is new. It would be surprising if manufacturing tolerances are that large, so it may be due to variations in the time between manufacture and when the buyer takes delivery, or more likely to give some leeway for some dealers who store unsold Leafs at 100% SOC in the hot sun. Another possibility is that up to 1 kwh may be due to pack imbalance. A fourth possible explanation for the range in the chart is variability in the economy meter due to instrumentation accuracies (i.e. Gids). "
Thanks Tony, I will add that to the Wiki later this weekend.

Re: Battery Aging Model

Posted: Wed Nov 07, 2012 8:12 pm
by DaveinOlyWA
TaylorSF used my SOC meter for a bit to record his commute. i put it on a google doc

https://docs.google.com/spreadsheet/ccc ... 2s3NGViSnc" onclick="window.open(this.href);return false;

this should give us a bit of help in long term range degradation. also HAVE to mention; he is still on his OEM :o tires still has plenty of tread left! :shock:

Re: Battery Aging Model

Posted: Thu Nov 08, 2012 5:31 am
by SmilingWhenSailing
Interesting model... I really hope it is accurate on the low temperature environments. Living in Tromsø/Northern-Norway, with probably a similar temperature profile as Juneau in Alaska, according to the model I should see the Leaf battery aging more slowly than I have ever dreamed of. Good for Tromsø Leaf owners. For the time being there are at least 6 Leafs up here in Tromsø (probably more, since I only can tell them apart by the colors and they are all present plus at least one with the same color as mine ;-) ). Unfortunately I don't know anybody with a Gid-meter, so I really don't know in what kind of state the battery was last March when I bought the car new or in what kind of state it is now. Anyhow I haven't seen any range reduction yet, but I would hardly be able to identify reduction below 10 % anyway. There are a lot of Northern lights here in the winter... I hope they don't affect the battery chemistry negatively...

Re: Battery Aging Model

Posted: Thu Nov 08, 2012 7:17 am
by RegGuheert
DaveinOlyWA wrote:this should give us a bit of help in long term range degradation. also HAVE to mention; he is still on his OEM :o tires still has plenty of tread left! :shock:
That's an interesting data point! Can you please tell us what tire pressure he uses? TIA!