Battery Aging Model

I'm not sure that's the appropriate direction to take, since it makes the heat-induced degradation rate in Honolulu very close to the rate in Phoenix.

I'd be more inclined to steepen the heat-induced curve by doubling every 5 or 8 degrees but assume "normal" is a lower percentage of the total loss per year. The cycling losses would, then, represent a larger percentage of the total loss and the sum total loss rate would be more linear.

Stoaty said:

Based on the Prius study of solar loading, parking in the sun full-time can cause a 10% (low solar load) to 24% (high solar load like Phoenix) increase in battery aging compared to avoiding parking in the sun completely. The solar loading depends on geographic location. Of course, the Leaf may be designed in such a way that the solar loading factor would be less.

Click to expand...

I would expect the LEAF's battery temperature to be somewhat less dependent on solar loading than the Prius battery. The Prius vents its battery pack via the passenger cabin, which in full sun can be far hotter than the outside ambient temperature. The LEAF's battery, under the car, would more closely track the temperature of the pavement below, which might not be too much higher than ambient if it is parked in the same spot all day, particularly with other cars around.

I would agree that solar loading doesn't seem to be a big issue with the LEAF battery (something Nissan got right in the design?). Over the past summer, even with the heatshield in the windshield, cabin temps in my car got up around 110F and held that high most of the day. But, with outside air temps in the lower to mid 90s, I never saw seven bars on my battery's temperature gauge.

Weatherman said:

I'm not sure that's the appropriate direction to take, since it makes the heat-induced degradation rate in Honolulu very close to the rate in Phoenix.

I'd be more inclined to steepen the heat-induced curve by doubling every 5 or 8 degrees but assume "normal" is a lower percentage of the total loss per year. The cycling losses would, then, represent a larger percentage of the total loss and the sum total loss rate would be more linear.

Click to expand...

I agree that it isn't really the right direction, but that is what I found. I don't think steepening the curve will help, because I couldn't make the numbers work even with the original factors--I had to make the battery aging factors somewhat lower in order to get the numbers to work properly. The ratios weren't too far off, since normalizing on "Normal" produced:

Phoenix - 1.5
Normal - 1.0
Boston - 0.83

That number is really kind of a side alley, since the model currently works quite well with numbers that are at least fairly reasonable.

As I said before, if anyone wants to play with the spreadsheet, just PM me. I have an almost perfect fit to Nissan's data (including TickTock). I am going to try adding a few other factors I think may be important (solar loading, percent of time spent at high SOC, perhaps DOD), then need data to calibrate it (and test it). Unfortunately, I no longer trust the Gid meter as a proxy for usable range. Only a range test will suffice, although going to VLBW and then extrapolating would certainly be acceptable. My next task is to set up the spreadsheet so I can just plug in some number and the predicted range will pop out for comparison with the measured range.

I found this study which looked at parking lot temperatures in Phoenix at various times of the year. They measured temperatures in June of 149 deg F (figure 2a). BTW, measurements are taken at 8 feet above the surface.

Weatherman said:

I'm not sure that's the appropriate direction to take, since it makes the heat-induced degradation rate in Honolulu very close to the rate in Phoenix.

Click to expand...

Hopefully, we will learn more about the state of Hawaii Leafs soon. It's been surprisingly quiet on the islands. The low average annual mileage could be an ameliorating factor:

Hawai'i drivers ranked near the bottom in per capita miles driven, averaging 7,907 miles per person per year, according to data from the Bureau of Transportation Statistics.

Click to expand...

abasile said:

I would expect the LEAF's battery temperature to be somewhat less dependent on solar loading than the Prius battery. The Prius vents its battery pack via the passenger cabin, which in full sun can be far hotter than the outside ambient temperature. The LEAF's battery, under the car, would more closely track the temperature of the pavement below, which might not be too much higher than ambient if it is parked in the same spot all day, particularly with other cars around.

Click to expand...

I left my Leaf out in the sun on a hot day once. The sheet metal on the roof was at about 130 F. The battery container was a few degrees warmer compared to what I would see when the Leaf was parked in a shade. Additionally, the battery was about two degrees warmer on side facing the sun.

Weatherman said:

I would agree that solar loading doesn't seem to be a big issue with the LEAF battery (something Nissan got right in the design?). Over the past summer, even with the heatshield in the windshield, cabin temps in my car got up around 110F and held that high most of the day. But, with outside air temps in the lower to mid 90s, I never saw seven bars on my battery's temperature gauge.

Click to expand...

However, the real difference between a high 6 TB and a low 7 TB is slight. I found that with the windows up at 100*+ air temp this summer the battery would hit 7 bars. This even happened when I parked in an abandoned bank drive thru that was in the shade all day. With the windows down so the cabin was the same temp as the air, the battery would stay at 6 TB even when the outside air temp was 110* with a 115*F heat index (i know that doesn't apply to the battery only the poor miserable humans).

Stoaty said:

Weatherman said:

I'm not sure that's the appropriate direction to take, since it makes the heat-induced degradation rate in Honolulu very close to the rate in Phoenix.

I'd be more inclined to steepen the heat-induced curve by doubling every 5 or 8 degrees but assume "normal" is a lower percentage of the total loss per year. The cycling losses would, then, represent a larger percentage of the total loss and the sum total loss rate would be more linear.

Click to expand...

I agree that it isn't really the right direction, but that is what I found. I don't think steepening the curve will help, because I couldn't make the numbers work even with the original factors--I had to make the battery aging factors somewhat lower in order to get the numbers to work properly. The ratios weren't too far off, since normalizing on "Normal" produced:

Phoenix - 1.5
Normal - 1.0
Boston - 0.83

That number is really kind of a side alley, since the model currently works quite well with numbers that are at least fairly reasonable.

As I said before, if anyone wants to play with the spreadsheet, just PM me. I have an almost perfect fit to Nissan's data (including TickTock). I am going to try adding a few other factors I think may be important (solar loading, percent of time spent at high SOC, perhaps DOD), then need data to calibrate it (and test it). Unfortunately, I no longer trust the Gid meter as a proxy for usable range. Only a range test will suffice, although going to VLBW and then extrapolating would certainly be acceptable. My next task is to set up the spreadsheet so I can just plug in some number and the predicted range will pop out for comparison with the measured range.someones measured range.

Click to expand...

i think temp loading should be formulated as a delta from a "normalized" point creating an exponential degradation formula from that point.

also something to consider is that in situations where higher rates of degradation are present, i think we need to also consider that it might affect cycling degradation as well, changing it from a near linear loss to one where the loss also accelerates based on mileage driven AND heat. iow; a double heat penalty.

this might account for small changes in temperature from FL and HA having less degradation than AZ. we all know that AZ may average out to only be slightly warmer than HA, but in reality its much more uncomfortable which is key since batteries react to heat very much the same way we do. they get sluggish when cold, they overheat (and may die) in extreme heat just like we do

ENIAC said:

They measured temperatures in June of 149 deg F (figure 2a).

Click to expand...

That's certainly enough to cook a battery. The body repair manual states that 140F is the max temp in a paint booth for any period of time. 149 is enough to do damage for sure.

Update on progress on Battery Aging Model:

--cleaned up spreadsheets, added some color to make it clearer what goes together
--merged spreadsheets into one "Battery Aging Model" by moving "Leaf Climate Data" to its own tab in the Battery Aging Model. I don't want to deal with 2 spreadsheets, plus will need to access Battery Aging Factors
--scaled Battery Aging Factors to correspond with empirically derived aging factors from the model; this will allow predictions for any of the cities for which we have calculated aging factors

More work planned as time allows.

Currently, the spreadsheet is only available in .ods (Opendocument) format. Spreadsheets were created in OpenOffice (a free download). For some reason, one of the pre-merged spreadsheets would not save in Excel Format (says there are too many rows???). If someone wants to take a look at the spreadsheet and try to figure out what the problem is, you are welcome. Perhaps I formatted an entire column so the Excel format thinks there are a lot more rows than there are (there are about 135)?

Sloaty; the row requirement for Excel "used" to be in the neighborhood of 255 columns and 65,000 rows or so, but both those parameters were increased for Excel XP i believe so i doubt that changing the rows will alleviate the issue. i use open office also because its free and works just as well as MS Office.

i have also had random issues trying to convert but others were still able to open the document in Excel anyway. there would always be a popup starting "possible" formatting errors but all the data was still ok.

JPWhite said:

ENIAC said:

They measured temperatures in June of 149 deg F (figure 2a).

Click to expand...

That's certainly enough to cook a battery. The body repair manual states that 140F is the max temp in a paint booth for any period of time. 149 is enough to do damage for sure.

Click to expand...

I did some more poking around and found this article where Mark Perry was interviewed. He describes "120F-140F" as the temperature range to be concerned over. Clearly 149F is well above the "concerned" range! Also, for a large part of the year parking lot temperatures in Phoenix (and likely many other areas) will exceed 120F. This, in my opinion, feels like the "smoking gun" for the issues we're seeing in the southwest.

So with regard to EVs and hybrids that have battery pack temperature management systems. If the vehicle is turned off and parked on extremely hot asphalt, is the temperature management system still operational? I assume so and then have to wonder how much energy would be used to keep the pack cooled.

City Temp Profile spreadsheet http://bit.ly/citytemprofiles does not agree with the graphic at http://bit.ly/QI714Y

Should I update my spreadsheet to utilize the numbers from the city temp profiles sheet, or adjust those numbers by another factor?

JPWhite said:

City Temp Profile spreadsheet http://bit.ly/citytemprofiles does not agree with the graphic at http://bit.ly/QI714Y

Should I update my spreadsheet to utilize the numbers from the city temp profiles sheet, or adjust those numbers by another factor?

Click to expand...

JP, the graphic is based on older, less accurate data. The Google spreadsheet should have new information, which is now reflected on the Wiki as well. I did not have the time to enter all the new locations into the spreadsheet, and that data is only available offline from Stoaty for the time being. Sorry for the inconvenience.

JPWhite said:

City Temp Profile spreadsheet http://bit.ly/citytemprofiles does not agree with the graphic at http://bit.ly/QI714Y

Should I update my spreadsheet to utilize the numbers from the city temp profiles sheet, or adjust those numbers by another factor?

Click to expand...

As Surfingslovak stated, numbers have been updated with more accurate readings from the Weatherspark data (and generally confirmed with hourly data from Weatherman). Those numbers are listed in the Wiki near the end of this section:

http://www.mynissanleaf.com/wiki/index.php?title=Battery_Capacity_Loss#Factors_Affecting_Battery_Capacity_Loss" onclick="window.open(this.href);return false;

However, those numbers could not be made to work in my battery aging model, so I searched for the numbers that would work for Phoenix, "Normal" and Boston. Once I arrived at those numbers and got a very close fit, I went back and scaled the Weatherspark numbers so that they were on the same scale as the numbers I arrived at in the spreadsheet. That is to say, I interpolated between Phoenix and LA Civic Center, and between LA Civic Center and Boston. For cities with lower aging factors than Boston, I extrapolated (best I could do). I plan to use the numbers on the new scale for my prediction model (TM) coming shortly. If you want a copy of the current spreadsheet to look at or play with, just PM me. When I feel it is ready I hope to get some help from Surfingslovak to put it on googledocs (which I know nothing about) so that anyone can access it from a link in the Wiki.

surfingslovak said:

JPWhite said:

City Temp Profile spreadsheet http://bit.ly/citytemprofiles does not agree with the graphic at http://bit.ly/QI714Y

Should I update my spreadsheet to utilize the numbers from the city temp profiles sheet, or adjust those numbers by another factor?

Click to expand...

JP, the graphic is based on older, less accurate data. The Google spreadsheet should have new information, which is now reflected on the Wiki as well. I did not have the time to enter all the new locations into the spreadsheet, and that data is only available offline from Stoaty for the time being. Sorry for the inconvenience.

Click to expand...

No inconvenience. If I get time I'll update the google docs with the right factors. I have an excel version I've extended to 30 years Norway is good for 30 years if the model is accurate at the extremes. Once complete ill share the excel spreadsheet.

JPWhite said:

No inconvenience. If I get time I'll update the google docs with the right factors. I have an excel version I've extended to 30 years Norway is good for 30 years if the model is accurate at the extremes. Once complete ill share the excel spreadsheet.

Click to expand...

While I haven't plugged any numbers in yet, I would strongly doubt that the battery will be good for 30 years until EOL, unless perhaps the Leaf is kept in a location that has freezing temperatures most of the year and is never driven. Certainly the battery will fare a lot better in Norway, I just don't think 30 years is possible.

TaylorSF has over 54,000 miles and has lost around 10-13% by his reckoning so its looking like he will hit EOL around 120-150,000 miles. a bit less than i had expected. i was thinking under better circumstances something near 200,000 miles might be possible. so that might get you half that 30 years

Stoaty said:

JPWhite said:

No inconvenience. If I get time I'll update the google docs with the right factors. I have an excel version I've extended to 30 years Norway is good for 30 years if the model is accurate at the extremes. Once complete ill share the excel spreadsheet.

Click to expand...

While I haven't plugged any numbers in yet, I would strongly doubt that the battery will be good for 30 years until EOL, unless perhaps the Leaf is kept in a location that has freezing temperatures most of the year and is never driven. Certainly the battery will fare a lot better in Norway, I just don't think 30 years is possible.

Click to expand...

Granted.

I updated the sheet on Google Docs using weather spark data points. A second set of eyes to make sure I didn't munge anything up?

I did put the locations in alphabetical order. Just an OCD thing

Put an Excel spreadsheet here
http://dl.dropbox.com/u/2881567/Degradation Model Pub.xlsx

ENIAC said:

I found this study which looked at parking lot temperatures in Phoenix at various times of the year. They measured temperatures in June of 149 deg F (figure 2a). BTW, measurements are taken at 8 feet above the surface.

Click to expand...

Remember, a lot of us almost always park in shaded parking spots so those temps are only valid for those that usually park in unshaded ones.