RegGuheert wrote:I'm not sure it is worthwhile trying to fit a model to the curves which Nissan gave to TickTock. Frankly, I don't expect to see any LEAFs in Phoenix with 76% capacity left after five years, regardless of miles driven.
As usual, I hope I am wrong about this. OTOH, Nissan's track record for making predicitions in Phoenix is quite poor to date.
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
From another thread:
surfingslovak wrote:It should also not come as a surprise that owners experiencing 15% range loss or more after less than 1 1/2 of ownership feel uneasy about Nissan's projections of 80% original range after five years (76% for Phoenix).
Especially true because the Battery Aging Model built from Nissan's own data predicts 76% remaining capacity for Phoenix owners driving 12500 miles per year at an average 4 miles/kwh efficiency after only 3.3 years
. You can only reach 5 years with 76% remaining capacity if you limit your mileage to 7500 miles per year.
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. Published government studies clearly show annual variation, with steeper decline during Summer and a leveling off during Winter, such as this graph from the NREL paper which has been displayed before:
For what it is worth, an update of my data is below, based upon 160 days of monitoring the Gid count whenever I charged to 80% with no End Time specified.
Mileage: 11K per year steady.
DOC: on days not shown on the graph,
Upper Limit: usually 40-50% based upon current Gids, which should be 45-55% of current capacity.
Lower Limit: typically 25%, never more than 2% below LBW.
Charges to 100%: 3 during this period
Charges to 85-90%: 2-3 per month.
A lot of people on this forum do not trust the Gids. I am aware of your opinions, and I have found them not perfect by any means, but more than adequately reliable. Assessing the SOC of a Li-ion battery pack is clearly not an easy problem, but Nissan has done a fairly good first attempt. While we don't know the details, it is clear to me that the Gid calculation uses both voltage and coulomb-counting. The voltage varies substantially as a function of power level, so coulomb-counting must be used for minute-to-minute readings while driving. During stops Open Circuit Voltage can be used to re-calibrate the Gids. At the outer-most, slowest level of the algorithm, the coulomb-counting is used to adjust the SOC vs voltage table as the battery capacity declines. The algorithm has problems estimating the energy stored at the very bottom of the battery, especially if one never goes that low. We can agree to disagree on how relevant are errors below VLBW.
For modeling capacity loss the big problem is trying to get a good measure of the temperature history of the battery pack, with only ambient temperature and the temperature bars to guide us. Given that the thermal time-constant of the battery seems to be somewhere in the range of 4 to 8 hours, my experience is that the battery history over a 24-hr period is quite significant. In my inland Southern California climate, the battery swings between 5 and 6 Tbars, so I have attempted to monitor the fraction of time the battery spends at each level with a scale that runs from 0 to 1, with the following interpretation:
Temperature Value Interpretation
0 100% "deep" within 5 Tbars (24-hr average temperature below 65 F)
.2 "barely" 100% within 5 Tbars,
.5 50% at 5 Tbars, 50% at 6.
.8 "barely" 100% within 6 Tbars
1.0 100% "deep" within 6 Tbars (24-hr average temperature above 80 F)
As the last of the warm 6 Tbar weather draws to a close, we can see about 4 Gids of rebound, but I am still looking at 10% capacity loss for the season, which has been confirmed by several charges to 100%. My graph represents half of one "wiggle" on the research graph. Next May I expect to begin another downward decline. Hopefully it will be shallower, especially since I will have my garage A/C available for a full summer season.