Cycling Degradation VS Calendar Aging w/ LiFePO4 Batteries Used for Solar Application

[Skypower]

I’m backing down on the midnight low rate grid assist now that the air conditioning isn’t running. Lowered the Solar Assistant automation for winter time so I’ll be having a lower average SOC. I’ll be having fewer and deeper valleys on my graph again(more like summer).

 

[HRTKD]

Maybe I missed it when my eyes glassed over with all that technical jargon, was cell compression ever mentioned as being a contributing factor in longevity?

It's Will's thread so I'll defer to him, but I recommend you read the many threads here on the forum where cell compression is the topic.

 

[Will Prowse]

Thank you @HRTKD
I cannot even find consistent data points for the cell compression. And that is highly dependent on the cell manufacturer and how the cell walls are designed. And how the layers are folded or stacked inside the cell. No way for me to give recommendations on that. Each manufacturer has different recommendations on compression. @Kornbread

 

[Will Prowse]

Thank you . Will stick to 14.1 slow roll and keep it there , can it stay there for say upto 4 hrs plus before dropping back down after the sun goes out ?

If you have a solid 4 hours at 100% it should be fine at 14.1V, but I am still going to keep my recommendation of 14.5V for most systems. But you should be fine.

 

[Kornbread]

It's Will's thread so I'll defer to him, but I recommend you read the many threads here on the forum where cell compression is the topic.

That's the problem.

According to the hords on this forum, if you don't compress your cells they will die an early death.

I've been arguing the point that in our systems, the cells will age out before they cycle out, and compression isn't really needed, even referencing one of the stickied papers on this forum regarding temperature vs aging. I always get hammered for even suggesting compression is probably wasted, as far as longevity of the cells are concerned. As far as I can tell, nothing that @Will Prowse posted even mentioned compression as a longevity factor. Is compression not important to longevity?

Just to be clear, this is on the topic of this thread about aging/cell degradation and the factors at play.

 

[BarracudaBob]

So it is safe to say in simple terms that Temperature and elevated charge/discharge C rates have the greatest factor on aging/cell degradation?

 

[Sojourner1]

So it is safe to say in simple terms that Temperature and elevated charge/discharge C rates have the greatest factor on aging/cell degradation?

I think it's also safe to say "henpecking" leads to cell degradation.

 

[BarracudaBob]

I think it's also safe to say "henpecking" leads to cell degradation.

Kind of like the:

King Chicken Theorem​

 

[sunsurfer]

Lets throw another parameter in the mix. Time at SOC. Batteries that see say only 20% cycle BUT are kept at the higher end of SOC will have much more capacity loss VS 20% cycle BUT are kept at the lower end of the SOC.

Thread - study shows capacity loss with high average charge state (LFP)

 

[D34DM0053]

IDK bro. This seems fishy.

 

[BarracudaBob]

Lets throw another parameter in the mix. Time at SOC. Batteries that see say only 20% cycle BUT are kept at the higher end of SOC will have much more capacity loss VS 20% cycle BUT are kept at the lower end of the SOC.

"Cycling near the top of charge (75%–100% SOC) is detrimental to LFP/graphite cells"

"The average SOC was found to be the most critical factor influencing capacity fade for LFP cells, over the factors of temperature, depth of discharge, electrolyte salt choice or graphite choice"

So a according to this article less than 75% SOC was best for longevity.

Without the occasional charging to the knee and letting the balancer circuit kick in also causes issues.

I was curious about the programable delayed equalization setting for SLA/FLA being used for LPT to get it to the knee once a week and letting it sit in mid range most of the time.

 

[sunsurfer]

So a according to this article less than 75% SOC was best for longevity.

Basically that and also staying at the lower end did not have a big affect on aging.

 

[BarracudaBob]

Basically that and also staying at the lower end did not have a big affect on aging.

So I can't drive 55V, dam it!

 

[Kornbread]

"Cycling near the top of charge (75%–100% SOC) is detrimental to LFP/graphite cells"

"The average SOC was found to be the most critical factor influencing capacity fade for LFP cells, over the factors of temperature, depth of discharge, electrolyte salt choice or graphite choice"

So a according to this article less than 75% SOC was best for longevity.

Without the occasional charging to the knee and letting the balancer circuit kick in also causes issues.

I was curious about the programable delayed equalization setting for SLA/FLA being used for LPT to get it to the knee once a week and letting it sit in mid range most of the time.

Didn't Will's posted material say keeping the cells at a high state of charge slowed their aging process?

 

[gyrex]

That temperature graph isn't good news for Australians. My batteries are stored in a garage where temperatures in summer hover between 30-35C. A lot of that heat is generated by a 15kW Fronius inverter and 3x Victron 5000kVA Multiplus inverters which are also located in the garage. Based on that graph, I should only expect to get 4-5 years out of my cells?

 

[AntronX]

Didn't Will's posted material say keeping the cells at a high state of charge slowed their aging process?

That's likely false. See my post.

 

[BarracudaBob]

Didn't Will's posted material say keeping the cells at a high state of charge slowed their aging process?

I was just reviewing new material. It gets the conversation going makes the thread longer and I found it interesting

 

[sunsurfer]

That temperature graph isn't good news for Australians. My batteries are stored in a garage where temperatures in summer hover between 30-35C. A lot of that heat is generated by a 15kW Fronius inverter and 3x Victron 5000kVA Multiplus inverters which are also located in the garage. Based on that graph, I should only expect to get 4-5 years out of my cells?

combined with lots of time at full charge, I would think they would age faster. That temp is hard on your other gear too, why not build an insulated closet and put a small AC unit to keep it all cooler?

 

[mvonw]

So, if I’m 60 years old, what battery do I buy and how do I charge it so we both die a peaceful death together?

 

[OffGridForGood]

None of the studies consider temperatures lower than 25-degrees C,
In my shop, the highest temp in the ESS room is 20C all year, and the low can be 15C for months during the winter.
temperature inside the battery pack - as reported by the BMS's can be 3-5 degrees higher due to cycling/load/charge.
Extrapolation outside of the test data is a big no-no but I wonder if the lower than 25C temps are "good" or "bad" or unlikely to be significant to the ESS aging.
I can heat the room up, but this comes at a cost, does the lower temp actually benefit the ESS, I wonder.

 

[AntronX]

I wonder if the lower than 25C temps are "good" or "bad" or unlikely to be significant to the ESS aging.

Most likely it's good for longevity as long as you don't get lithium plating from charging too fast at temps too low. But at solar fractions of C rates you are probably safe. You really don't want to charge beyond 3.5v/cell near freezing or below at any C rate. Big damage happens. Here is LFP charging at -10°C. Source

 

[BarracudaBob]

So, if I’m 60 years old, what battery do I buy and how do I charge it so we both die a peaceful death together?

If you had the COVID vaccine then LFP 6000 cycles should be just fine.

 

[J.H.]

My goodness… what ever happened to KISS…?

This is stressful …it not that hard to run your system , have it work good , and have fun doing it.

Jim.

 

[gyrex]

why not build an insulated closet

Because it's a garage and its primary function is to store cars and there's no room to build a closet.

I could probably look at A/C but it seems like overkill. I've already insulated the steel garage door to try and keep ambient temps down in the summer but it's a hard task in a location which is renowned for higher temperatures. My Tesla (LFP) is also stored in the garage and I don't hear the cooling system come on when the car is idle so if the ambient temperature in the garage is good enough for my Tesla then I guess it's good enough for my home battery I guess.

On the topic of the Tesla and EVs with LFP cells, where I live there's tonnes of other Teslas and EVs, many of which would be parked outside, exposed to much higher ambient temps so what do these results mean for EVs which are subject to higher temps and their cooling systems aren't running when parked? How much weight can we really attribute to this study? How many samples did they use? I've got to say I'm somewhat skeptical of the temperature results.

 

[BarracudaBob]

Maintain operating

My goodness… what ever happened to KISS…?

temperatures between 68F to 86F, charge/discharge at 0.5 C rate. Balance cells every 2 months by bringing up the voltage and holding it. Run between 75% to 20%. Buy more batteries if you need more. Put a shrimp on the BBQ, open your favorite refreshment. Live long and prosper.

Even if you are ignoring unused capacity what you have will last longer. Your battery provider will love you for buying a couple extra batteries