lukati
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Re: Lost Battery Capacity and Range / Autonomy, Page 2

Mon Aug 13, 2012 1:30 pm

I did a back-of-the-envelope calculation of how much capacity degradation can be expected in different climates based on simple chemistry. The approach is very simple. I assume that the chemical processes that degrade the battery follow a simple Arrhenius equation with a temperature dependence of the rate of 2-fold per 10C. I then estimate the relative time a battery would sit at a given temperature given the location and then multiply this temperature-time with the temperature specific rate. I did this for four locations: Chicago, Phoenix, Los Angeles, and Seattle. The ambient temperature information is from

http://fs.weatherspark.com.s3.amazonaws ... nt_pct.png" onclick="window.open(this.href);return false;

The temperature resolution is quite poor. The temperature bands are frigid (<15F), freezing (15F-32F), cold (32F-50F), cool (50F-65F), comfortable (65F-75F), warm (75F-85F), hot (85F-100F), and sweltering (>100F). For all bands I took the average temperature in the band and I assumed 10F for frigid and 105F for sweltering. The rate was set to 1 for 20C (room temperature).

These are the total annual rates for the different locations (constant exposure to 20C would equal 1): Chicago (0.69). Phoenix (1.61), Los Angeles (0.81), and Seattle (0.58). The relative rates compared to Chicago are: Phoenix (2.35), Los Angeles (1.18), and Seattle (0.84).

So it would seem that a substantial difference in battery degradation is expected for different locations in the US based on first order chemical assumptions. There is almost a factor of 3 between Phoenix and Seattle.

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GeekEV
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Re: Lost Battery Capacity and Range / Autonomy, Page 2

Mon Aug 13, 2012 1:34 pm

TonyWilliams wrote:I hope the above summary helps, and provides a launching point for a concise discussion about these issues.
Awesome, Tony. This is exactly the sort of summary I was looking for...

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TonyWilliams
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Re: Lost Battery Capacity and Range / Autonomy, Page 2

Mon Aug 13, 2012 1:41 pm

lukati wrote:I did a back-of-the-envelope calculation of how much capacity degradation can be expected in different climates based on simple chemistry. The approach is very simple. I assume that the chemical processes that degrade the battery follow a simple Arrhenius equation.... There is almost a factor of 3 between Phoenix and Seattle.
Please read all the well informed comments to the announcement of the LEAF at the following website, almost one year before the first LEAF was delivered:

Is the Nissan LEAF Battery Pack Under-Engineered?

There is an abundance of data BEFORE THEY PRODUCED A SINGLE LEAF to suggest Nissan seriously made a mistake. I don't know what they thought would happen once the crap-hit-the-fan. The only suggestion that makes any sense so far is that Nissan would blame battery issues on Quick Charging, but the network of chargers never developed.

Naturally, the Nissan legal department made clear the battery capacity wasn't warranteed, but as we know, consumers can't be hoodwinked by being sold a car in a place like Phoenix that the manufacturer knew would NOT survive the heat and then NOT tell the consumer.

I predict Nissan losing virtually every well crafted legal attack concerning these issues.
Last edited by TonyWilliams on Mon Aug 13, 2012 1:51 pm, edited 3 times in total.

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surfingslovak
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Re: Lost Battery Capacity and Range / Autonomy, Page 2

Mon Aug 13, 2012 1:44 pm

lukati wrote:I did a back-of-the-envelope calculation of how much capacity degradation can be expected in different climates based on simple chemistry.

These are the total annual rates for the different locations (constant exposure to 20C would equal 1): Chicago (0.69). Phoenix (1.61), Los Angeles (0.81), and Seattle (0.58). The relative rates compared to Chicago are: Phoenix (2.35), Los Angeles (1.18), and Seattle (0.84).
Great thinking! It's funny, I did something similar in the wake of our discussion last week. My results are still preliminary, but they seem to agree with your findings. Moreover, I'm getting effective temperatures for Phoenix, Minneapolis and Houston comparable to what NREL determined empirically with their NCA/graphite cells. I would love to refine this dataset, but I've been very busy at work, which left me with little time to spare.

Image
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DaveinOlyWA
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Re: Lost Battery Capacity and Range / Autonomy, Page 2

Mon Aug 13, 2012 1:55 pm

interesting chart but i see a glaring issue with Minneapolis being warmer than Seattle. they are significantly colder making them significantly hotter in Summer and i think an analysis of sustained average temperature ranges is going to provide more accurate results.

i look for how often do you average X temp at least 3 days in a row, radiant heat, environmental heat, etc.

i think a lot of the degradation is the inability to cool off between heating events. i think its worse to see temps sustained in the 90's for 4 days than it is to have a single day at 110 but until we can gather much more data, we will never know what Nissan knows and is not telling us.
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shrink
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Re: Lost Battery Capacity and Range / Autonomy, Page 2

Mon Aug 13, 2012 2:09 pm

DaveinOlyWA wrote:ii think an analysis of sustained average temperature ranges is going to provide more accurate results...

i think a lot of the degradation is the inability to cool off between heating events. i think its worse to see temps sustained in the 90's for 4 days than it is to have a single day at 110.
Yeah, it's been crazy hot here in Phoenix lately. See below from today's paper. I don't think historical averages have much meaning in the attempted analyses being conducted. The LEAF has been in the Phoenix area for only about 1-1/2 years and I think (I don't have time to look up the data) the temps over that period have been significantly warmer than historical averages. It certainly feels that way from living here.

http://www.azcentral.com/members/Blog/S ... non/169204" onclick="window.open(this.href);return false;
The heat goes on

This is how hot it is in Phoenix: The temperature hasn't dropped below 90 degrees at the official reporting station, day or night, since Aug. 6, a full week ago.

That's a lousy streak for early August, when mornings can typically start to provide a little bit of relief, especially if there's rain nearby. But once more this morning, the nighttime "cool-down" reversed course when it reached 90 degrees.

Our last sub-90 reading was just before 7 a.m. Aug. 6, after an overnight low of 88. That's seven toasty days with barely a break in the heat, not unheard-of, according to Ken Waters at the National Weather Service, but notable all the same.

The normal overnight low at Sky Harbor International Airport this time of year is 83 degrees, but the average low for the past week is a little over 91, according to weather service records. It surely helps that daytimes have been equally hot, with an average high over the past seven days of 113 degrees, also eight degrees above normal for this time of year.

During those seven days, the heat has broken six records, five for daytime highs and one for a record high minimum temperature (93 degrees on Aug. 9).

A stubborn high pressure system has kept conditions hot and helped prevent afternoon thunderstorms from developing into something with actual rain. The airport has recorded only a trace of rain so far in August, although monsoon moisture has produced storms elsewhere in the region.

The forecast is calling for temperatures to moderate this week as storms push back into metro Phoenix and lows are predicted to settle into the 80s by midweek.
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surfingslovak
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Re: Lost Battery Capacity and Range / Autonomy, Page 2

Mon Aug 13, 2012 2:11 pm

DaveinOlyWA wrote:interesting chart but i see a glaring issue with Minneapolis being warmer than Seattle. they are significantly colder making them significantly hotter in Summer and i think an analysis of sustained average temperature ranges is going to provide more accurate results.
Thanks for your comment, Dave. If you've read lukati's post above, you would see that this is exactly how it was done. There is not a lot of publicly available data out there, and we ended up sourcing temperature profiles from the same website. See further below to get an idea of how the profiles for Minneapolis and Seattle look like.

While we certainly can debate the validity of this data, I'm confident about the value I calculated for Minneapolis. It's within a degree or two of an empirically measured effective isothermal temperature published in a recent NREL study. It's so close that it can't be a coincidence.

As I said earlier, while I enjoy reading all comments on this board, I don't always agree with them. Especially if they are not based on hard data and models we can all compare against field data. Aside from Minneapolis and Seattle, this model predicts that both Hawaii and Florida are pretty hard on batteries. It should be interesting to see if and when we will get the first reports of lost capacity from there.

I don't mean to criticize, since you have a lot of EV experience, but I believe that we need to move away from a gut-feel approach to something more material and comprehensible to new EV owners. Tony demonstrated how it's done with his range chart. It's easily understood and very valuable. I wish Nissan came up with that, instead of their weasel response that "there is an infinite number of range scenarios".

Although there definitely is a nearly infinite number of temperature profiles and microclimates, I believe that it's important to come up with an easily understood chart that will give new owners an idea of the severity of the climate they live in. It would be good to have an assessment how well EV batteries will do in your climate before making a purchase.


Seattle Temperature Profile

Image


Minneapolis Temperature Profile

Image
Last edited by surfingslovak on Mon Aug 13, 2012 2:14 pm, edited 1 time in total.

DaveinOlyWA
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Re: Lost Battery Capacity and Range / Autonomy, Page 2

Mon Aug 13, 2012 2:12 pm

wow, you are getting it from both ends. its to the point now that many products, not just LEAFs are going to require a "Phoenix" model. my cellphone would be destroyed in that weather outdoors in less than an hour
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surfingslovak
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Re: Lost Battery Capacity and Range / Autonomy, Page 2

Mon Aug 13, 2012 2:18 pm

shrink wrote:I don't think historical averages have much meaning in the attempted analyses being conducted. The LEAF has been in the Phoenix area for only about 1-1/2 years and I think (I don't have time to look up the data) the temps over that period have been significantly warmer than historical averages. It certainly feels that way from living here.
Sorry to hear that! I certainly wish it wasn't so. Last weekend, I had to drive to Central Valley, and the temps were in the 100s. I saw seven battery temp bars all the way. Crazy.

That said, the beauty of models is that you can update them with new data. If we believe that it makes sense to use 2012 temperatures, one of the hottest, if not the hottest year on record, that can be done. We just need to get a good reliable source of meteorological data.

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TonyWilliams
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Re: Lost Battery Capacity and Range / Autonomy, Page 2

Mon Aug 13, 2012 2:21 pm

surfingslovak wrote:
shrink wrote:I don't think historical averages have much meaning in the attempted analyses being conducted. The LEAF has been in the Phoenix area for only about 1-1/2 years and I think (I don't have time to look up the data) the temps over that period have been significantly warmer than historical averages. It certainly feels that way from living here.
..... 2012 temperatures, one of the hottest, if not the hottest year on record, that can be done. We just need to get a good reliable source of meteorological data.
If I were the Nissan legal team, I'd start polishing my defense based on this !!!!

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