As I said, it’s the interaction of cycling with calendar aging. When you cycle only once a day, you’re cracking the SEI that built up over that time. For an example of a paper on that, maybe see this.
Ok, having examined the paper, I’m going to dismiss it as invalid evidence. It uses NMC cells. No grid scale batteries today use this cell chemistry. Tesla did offer NCA cells for a time, but has switched the LFP.
Do you have any evidence for LFP cells? Note that NMC cells have mayfly like lifespans of a nominal 1000-2000 cycles, depending.
$1000 for 5.12 kWh. Claimed lifespan 6000 cycles. There are many listings like this, a utility scale order would be able to find the higher quality suppliers using better quality cells and order a large number of them. So assuming 5.12 x 0.8 x 3500, that’s 14336 kWh cycled. 6.9 cents a cycle.
That’s for the 1 day storage and assuming good utilization. Price skyrockets for ‘long duration grid storage’, if we assume 1 cycle a year (winter storage), and the battery does fail after 20 years, then 102 kWh cycled, $9.74 a kWh.
What do you propose we use for this once/season duty cycle? Synthetic natural gas looks a lot more attractive when the alternative is $10 a kWh.
See other thread. Your evidence is unconvincing and you shouldn’t be convinced yourself. You essentially have no evidence for an effect that should be trivial to measure. You could plot degradation over about 1 year and support your theory or falsify it. It’s rather damning you cannot find such a plot to cite.
Plot must be for production LFP cells with daily cycling.
You are wrong about that, but here’s a paper testing LFP in realistic conditions over a shorter period of time. In the future, you should start by looking for papers yourself if you think one is unsatisfactory, and I will not be replying to your comments, and I really have no interest in interacting with you at all. Bye.
Do you have empirical evidence? Some grid scale batteries, especially of the “server rack” commodity style that use LFP, should have 5 years of life already and by your model about to fail. I would argue that such failures observed over the tens of thousands of them deployed in various grids would be strong direct evidence of an n cycle field lifespan. I do not see any data in this paper collected from field batteries, merely a model that may simply not be grounded.
Are grid operators assuming they have 15-20 year service lives or 5?
Yes, some people have needed to replace batteries in some large storage systems, and/or augment them with extra capacity to balance degradation. I haven’t seen any good data on this, because most operators have no reason to share it. Also, due to rapid growth, most of the volume of first replacements is still upcoming.
If I read the paper right, it refers to degradation similar to leaving the cells at 100 percent SOC. It should be immediately measurable and catastrophic, leading to complete storage failures. Do you not have any direct measurements?
It’s an extremely falsifiable thing, there should be monthly capacity loss and it should be obvious in 1 year the batteries are doomed.
Someone could buy an off the shelf LFP battery and cycle it daily and just prove this.
As I said, it’s the interaction of cycling with calendar aging. When you cycle only once a day, you’re cracking the SEI that built up over that time. For an example of a paper on that, maybe see this.
Ok, having examined the paper, I’m going to dismiss it as invalid evidence. It uses NMC cells. No grid scale batteries today use this cell chemistry. Tesla did offer NCA cells for a time, but has switched the LFP.
Do you have any evidence for LFP cells? Note that NMC cells have mayfly like lifespans of a nominal 1000-2000 cycles, depending.
Without evidence a rational person would dismiss your claim of ’2000 cycles’ and assume ~3500 (on the low end for LFP). In addition they would assume bulk prices for the batteries such as this. https://www.alibaba.com/product-detail/48V-51-2v-100ah-Lifepo4-Lithium_1600873092214.html?spm=a2700.7735675.0.0.19c0fbFofbFoZR&s=p
$1000 for 5.12 kWh. Claimed lifespan 6000 cycles. There are many listings like this, a utility scale order would be able to find the higher quality suppliers using better quality cells and order a large number of them. So assuming 5.12 x 0.8 x 3500, that’s 14336 kWh cycled. 6.9 cents a cycle.
That’s for the 1 day storage and assuming good utilization. Price skyrockets for ‘long duration grid storage’, if we assume 1 cycle a year (winter storage), and the battery does fail after 20 years, then 102 kWh cycled, $9.74 a kWh.
What do you propose we use for this once/season duty cycle? Synthetic natural gas looks a lot more attractive when the alternative is $10 a kWh.
The main mechanism discussed in that paper is about the anode SEI. And the anode is the same.
See other thread. Your evidence is unconvincing and you shouldn’t be convinced yourself. You essentially have no evidence for an effect that should be trivial to measure. You could plot degradation over about 1 year and support your theory or falsify it. It’s rather damning you cannot find such a plot to cite.
Plot must be for production LFP cells with daily cycling.
You know degradation of capacity and resistance isn’t linear, right? You’d need a 5+ year long test to get the complete data for that.
No I don’t know this and the curves I have seen are linear until below 70-80 percent capacity. Please cite evidence.
You are wrong about that, but here’s a paper testing LFP in realistic conditions over a shorter period of time. In the future, you should start by looking for papers yourself if you think one is unsatisfactory, and I will not be replying to your comments, and I really have no interest in interacting with you at all. Bye.
Do you have empirical evidence? Some grid scale batteries, especially of the “server rack” commodity style that use LFP, should have 5 years of life already and by your model about to fail. I would argue that such failures observed over the tens of thousands of them deployed in various grids would be strong direct evidence of an n cycle field lifespan. I do not see any data in this paper collected from field batteries, merely a model that may simply not be grounded.
Are grid operators assuming they have 15-20 year service lives or 5?
Yes, some people have needed to replace batteries in some large storage systems, and/or augment them with extra capacity to balance degradation. I haven’t seen any good data on this, because most operators have no reason to share it. Also, due to rapid growth, most of the volume of first replacements is still upcoming.
If I read the paper right, it refers to degradation similar to leaving the cells at 100 percent SOC. It should be immediately measurable and catastrophic, leading to complete storage failures. Do you not have any direct measurements?
It’s an extremely falsifiable thing, there should be monthly capacity loss and it should be obvious in 1 year the batteries are doomed.
Someone could buy an off the shelf LFP battery and cycle it daily and just prove this.
That is literally what the linked paper did as a basis for their modelling. But of course they used multiple cells.
Right, the actual batteries you can buy with Chinese EV grade lfp cells is what to test. There are many variables here.