spooka said:
Got the following graph from The U.S. Dept of energy at this link:
http://search.nrel.gov/cs.html?url=http%3A//www1.eere.energy.gov/vehiclesandfuels/pdfs/merit_review_2011/electrochemical_storage/es110_smith_2011_p.pdf&charset=utf-8&qt=life+trade+off+analysis&col=eren&n=1&la=en" onclick="window.open(this.href);return false;
I added the Casa Grande test line to the graph below. Normal, expected capacity loss??? I'll let you be the judge.
I am posting the image url here in case the photos does not load in my post.
http://www.flickr.com/photos/38343689@N02/7927151004/
There are quite a few reasons you would not expect the the Casa Grande test cars to match the NREL study results.
First, the C. G. test cars were selected for study
precisely because they were outliers from what most Phoenix LEAFs were experiencing, at least as indicated by those cars accelerated capacity bar losses.
It is possible that their unusual rate of capacity loss, up to "15%", is what is often reported, IIRC, is due in part to factors unrelated to battery use by the LEAF's drivers, such as reduced battery capacity at delivery, due to poor quality control at the factory, or poor battery care prior to delivery, such as long periods of 100% charge at high temperatures.
This accelerated degradation of the CS test group may also be accounted for largely or in part, by LEAF use habits of the five test vehicles outside of the controlled study, a few of which may have been:
Miles driven per day in the NREL study is 33 miles, in two trips. Obviously, many or all of the CS LEAFs frequently exceeded this range, with increased battery cycling required to drive up to twice the ~12,000 miles per year of the study, and using a higher percentage (far higher for the C.G. drivers with long commutes) of the total battery capacity on each day of driving.
Ambient temperatures for the NREL study apparently did not take into account the "garage heating effect", the propensity for EV drivers to maintain higher battery temperatures, by parking their cars overnight in garages, at higher-than-ambient temperatures. Of course, this would be expected to accelerate heat-related capacity loss in batteries, relative to those EVs that cooled their battery packs at night, with either ATM use, or space cooling.
The study apparently did not account for the heating effects (and possibly other degradation effects) of fast charging, which at least some of the C. S. test LEAFs, may have used frequently.
A big question I still have about the NREL study, is the capacity level and charging habits assumed.
If I understand correctly, it looks to me like the study reports use of 54% of battery capacity, to drive that 33 daily miles?
So, basically, they tested a Volt sized battery pack, with the daily driving range limited to the optimum Volt-range commute?
Obviously, if the C.G. LEAF drivers had limited their daily driving range to 33 miles, limited their their battery packs' charge to ~ten bars, and only discharged them to to ~four bars, and then only recharged them back up to ~ten bars, immediately before driving again, on every day of their ownership, we might expect them now to have very different capacity bar loss reports.
