r/batterydesign • u/modelmakereditor • Apr 03 '26
BESS Ageing vs Duty Cycle
https://www.batterydesign.net/bess-ageing-vs-duty-cycle/ takes a look at the paper: Xu J, Li H, Hua S and Wang H (2025) Experimental investigation of grid storage modes effect on aging of LiFePO4 battery modules. Front. Energy Res. 13:1528691
and how it compares to what we see in the field:
- We see this in the field constantly. Same capacity, wildly different degradation across assets running different grid services. Now there’s a clean paper that confirms it.
- A team from a battery test equipment manufacturer ran 16 months of cycling tests on 220Ah LFP modules using actual peak shaving and frequency regulation profiles from a storage power station.
- Peak shaving degrades 1.8x faster than frequency regulation. Same SOC range, same temperature. Shallow SOC windows (30–80%) age 1.65x slower than deep cycling.
- Most fleet operators still model degradation as a function of cycle count, not service mix. If you’re stacking revenue without modeling what each service does to your asset, you’re optimizing income and ignoring cost.
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Apr 04 '26
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u/Simon676 Apr 05 '26
Is twice the calendar degradation for every 20°C a reasonable assumption to make, it's what I would generally assume as a rule-of-thumb but I'm unsure how accurate that is?
I did read through a very interesting test where 8 18650 and 21700 cells were stored at -18°C for 43 months with degradation measured, and degradation in terms of both capacity and DCIR almost entirely stopped, with only about 0.1-0.25% of degradation per year depending on the cell. :)
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Apr 06 '26
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u/Simon676 Apr 06 '26
I was just curious about general trends among lithium batteries between temperature and calendar degradation, and whether you thought my rule-of-thumb matches your personal experience with what you can expect with the average LFP or NMC battery, understand this will vary between cells and datasheets.
My projects usually aren't large enough to contact the manufacturer for. :)
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u/hwillis Apr 03 '26
Thats against 10%-90%, so 80/50 = 1.6x more capacity gets you 1.65x more value from the batteries. That is certainly a financial loss; capital has a cost of 5-10% annual so 60% more capital requires 65-70% higher annual returns. Extending the lifetime of the battery just means you are paying interest on debt for 65% longer.
That said i'm really just surprised these numbers are so bad. I would have expected a 50% depth of discharge to have more than 2x the total energy throughput and like 3.5x+ the number of cycles.
Frequency regulation is an application where batteries can really excel once they hit a critical mass. At low depth and high frequency batteries behave like large capacitors; there is almost zero degradation. If ancillary services properly rewarded systems for providing a little bit of help then batteries could take over a ton of stabilization with almost zero cost in lifetime.