Will LiFePO4 batteries be damaged by underuse / shallow cycling?

[Norwasian]

My setup was engineered in ignorance of the physical capabilities of the panels, the amount of sunlight that would be received in rainy weather, etc. I had believed that the rainy season would test the battery capacity much more than it has, so I may have overbuilt to compensate. Now, in the actual rainy season, the LiFePO4 powerwall battery is only dropping to around 84% at night, which is replenished within 2-3 hours in the morning, even in cloudy weather. This cycles daily, but is not reaching the 80-20 capacity window at all. Is this a problem?

I searched the forum before posting, and found only one thread that appeared to address a similar scenario...however, the answer given was premised with "it has been said" and "probably...." I would appreciate something more definitive and/or based on actual testing or experience.

 

[Suijkerbuijk]

The battery are new .
So real data is not thare
A lot of people test it in real life.

I do not think its a big problem .
So long the battery is not always 100% full charge and stay on 100%
For the rest the battery type its only make to run about 20 years and than liquid inside its worn out.

What you can do its lower the charge profile to slow.
This way you will slow charge the battery to full.

You can always shutdown the pv from the solar charger
This way you can manuel shutdown the solar panels.
And use more of you battery .
One way to maintain the battery.
If you have set dc breakers between the solar panels and your solar charger.

 

[BentleyJ]

You may be thinking of the "memory" effect of obsolete Nickel-Cadmium batteries. What you are describing is called micro-cycling and its not a problem for LiFePO4 chemistry provided your charging voltage and current are within specifications and float voltage is low enough to just keep the batteries topped up while supplying the load while the sun is up.

 

[Norwasian]

The battery are new .
So real data is not thare
A lot of people test it in real life.

I do not think its a big problem .
So long the battery is not always 100% full charge and stay on 100%
For the rest the battery type its only make to run about 20 years and than liquid inside its worn out.

What you can do its lower the charge profile to slow.
This way you will slow charge the battery to full.

You can always shutdown the pv from the solar charger
This way you can manuel shutdown the solar panels.
And use more of you battery .
One way to maintain the battery.
If you have set dc breakers between the solar panels and your solar charger.

Yes, of course there are breakers which can isolate the solar panels. We could shut down the panels and force the battery usage to go deeper...but I guess that is part of my question: Is this recommended?

 

[wpns]

Are you running closed-loop? If not, maybe set your charge controllers to 55.0V so they won't try to overcharge your battery.

 

[jvierstra]

I have an offgrid home that I only use 3-4 months a year and I leave the system on and (almost) 2.5 years in I can't notice a problem in capacity. I even do limited charging below freezing in winter.

Battery is a homebuilt 16s LiFePO4 48V w/ a REC BMS
Other equipment is Victron.
4kW of solar
Homemade electric hottub heater on diversion direct from panels.

I do top the batteries up once or twice in the winter with a small generator (on remote start via Starlink ;-)) because not enough sun.

House is in Chilean Patagonia (53degrees south).

I used to worry but now it seems that 1500$ for a battery bank is nothing for what you get and prices keep coming down.

 

[DPC]

You may be thinking of the "memory" effect of obsolete Nickel-Cadmium batteries.

Hardly
When you really need emergency back up power or critical loads NiCad is still there.
One day that will change when a better Lithium battery has proven itself.

 

[Norwasian]

Are you running closed-loop? If not, maybe set your charge controllers to 55.0V so they won't try to overcharge your battery.

I'm too ignorant to understand what you might mean by "closed-loop." I have two charge controllers, each with its own string of 4 panels (2s2p), that charge the battery in addition to the inverter with its 2s2p string of panels. So there are technically three chargers in the system. I set the inverter's own charge limits a bit lower than the EPEVERs', to help prevent any strife between them, but I think I have the charge controllers' set to top around 56.

 

[BuffaloTrace]

If you're worried about it and want absolute longevity of the lifepo4 battery pack, one can always lower the charge cutoff voltage to say 90%. Storing batteries at lower state of charge (50%?) has been stated to be better for the health of the battery, as well as storage temperature, at various SOC. Unless you forsee heavy useage, I'd keep them at a lower SOC. Sounds like you could get by at 80% fairly easily and probably never go below 10% ever, which seems ideal for longevity. The batteries should outlast the components in this ideal useage.

 

[lexio]

maybe this study

 

[ThaiTaffy]

My setup was engineered in ignorance of the physical capabilities of the panels, the amount of sunlight that would be received in rainy weather, etc. I had believed that the rainy season would test the battery capacity much more than it has, so I may have overbuilt to compensate. Now, in the actual rainy season, the LiFePO4 powerwall battery is only dropping to around 84% at night, which is replenished within 2-3 hours in the morning, even in cloudy weather. This cycles daily, but is not reaching the 80-20 capacity window at all. Is this a problem?

I searched the forum before posting, and found only one thread that appeared to address a similar scenario...however, the answer given was premised with "it has been said" and "probably...." I would appreciate something more definitive and/or based on actual testing or experience.

It's catch 22 most people would recommend you not use the upper portion of the battery if your only discharging 20% better you only charge to maybe 75% of soc and get more cycles from your battery but then again how many hours will you get from 75% during a power cut which are frequent in our situation.
Rainy season is weird the sun is at its strongest(technically summer)so we have days of very high luminance but we also have overcast days that can get very dark during an afternoon.

So far I've doubled almost tripled any projected kWh forecasts every single day this rainy season but once winter comes it gets dry and all the ignorant farmers burn their fields maybe that will give us a better idea of how much solar we actually produce worst case scenario.

 

[Norwasian]

So far I've doubled almost tripled any projected kWh forecasts every single day this rainy season but once winter comes it gets dry and all the ignorant farmers burn their fields maybe that will give us a better idea of how much solar we actually produce worst case scenario.

I guess that's about what I'm seeing. The system is hardly daunted by the rainy weather, or so it seems. The dust season will test the panels' capacity in a new form, so I'm with you on waiting to see what happens then.

 

[wpns]

I think I have the charge controllers' set to top around 56

So set everything to top out around 55.0V and you should be fine.

 

[wpns]

I'm too ignorant to understand what you might mean by "closed-loop." I have two charge controllers, each with its own string of 4 panels (2s2p), that charge the battery in addition to the inverter with its 2s2p string of panels. So there are technically three chargers in the system. I set the inverter's own charge limits a bit lower than the EPEVERs', to help prevent any strife between them, but I think I have the charge controllers' set to top around 56.

Closed-loop is where your inverter talks to your batteries with RS485 or CAN and gets their actual State Of Charge and recommended voltage, and uses that to modulate it's settings.
Sounds like you have three charge controllers, each of which has a voltage setting, so you are 'open-loop' aka 'voltage sensing'. Since SOC is only loosely related to voltage, and can vary depending on current, and you have lots of overcapacity, you should set your voltages to somethign like 55.0, and even though it may take along time, your batteries will (slowly) charge to 100% and not go over.