Lithium battery storage temperatures

Estragon · June 22

It's time to replace my 48v flooded bank, and I'm strongly considering something like Midnite Solar Powerflo. One thing giving me pause is the cold winters at the cabin.

I know charging is a Bad Thing below freezing, so I'd build an insulated box with some sort of heating if/when required. The PF16 has heating built in, but it's pretty heavy to get to the cabin and installed (and out of stock at NAZ). The 5kw rackmount isn't heated, but easier to move. I'd likely use a Midnite AIO for closed-loop charging.

The cabin isn't used much in the winter, so I'd turn the system (including the batteries) off when not there. Midnite's specs for both batteries is:
Charging Temperature   32°F to 122°F(0°C to 50°C)
Operating Temperature -4°F to 122°F (-20°C to 50°C)
Storage Temperature 14°F to 113°F (-10°C to 45°C)

It seems odd that the storage temp window is narrower than the operating. Anyway, it gets to -40F at times in winter and even in an insulated box the batteries will likely end up cold-soaked to something approaching that while everything is turned off.

Does anyone know if this is going to be a deal-breaker?

BB. · June 23

I would certainly contact the battery supplier, if not the mfg., regarding minimum storage temperatures and warranty support...

If you can dig (or have) a small cellar, something like 4 feet or more below ground level, there is a good chance that (in most areas of the world), the ground temperature will not drop much below freezing.

Some charts for Toronto Canada areas that suggest the frost line:

Soil seasonal variations vs soil depth:

https://www.builditsolar.com/Projects/Cooling/EarthTemperatures.htm

Construction "Frost Line" example for Toronto:

https://www.thepostholediggers.ca/frost-line-facts-post-hole-digging-and-frost-lines-in-toronto/

You can probably check with your local building department for more information on Frost Line levels for your area...

Of course, other issues may arise--Can you did a cellar (stone/rocks?), will it remain dry during winter?

Design of cellar? Need an insulated lid/door/walls to prevent heat flow from "over cooling" the cellar air (hear rising, cold settling).

Some examples of electric battery heating pads (if you will be going in winter and have a genset to "preheat" the batteries for winter stays (as well as insulated boxes/storage area):

https://www.batteryskills.com/how-to-keep-lithium-batteries-warm-in-cold-weather/

Or use RV tank heating pads (12 volt example):

https://www.amazon.com/Heater-Fresh-Water-Holding-Gallons/dp/B07ZJMW636/ref=sr_1_5?th=1

-Bill

BB. · June 23

I was just thinking... "Heat Pipes" have been used to take heat from the ground and bring it "up" (for example, used to keep ground frozen around Alaska oil pipeline supports).

Another would be using ground heat with small fan/or elevation change to bring "relatively warm/non-freezing" air to the battery storage area using plastic pipe of some sort:

https://milligansganderhillfarm.wordpress.com/2013/12/01/earth-tubes-how-to-build-a-low-cost-systemto-passivly-heat-and-cool-your-home/

-Bill

Dave Angelini · June 23

I would spec compare the midnite bat with the Discover rack mount. They both will close loop but the Discover rack may be easier to move. I think the powerflow also is available in a rack? Look at Rosie also!

Lot's of things changing out there! Good Luck! Stay Safe !

JRHill · June 23

I have pondered this dilemma as I have the same issue but we are here year around. And it sure doesn't hit -40f. An insulated pit with a heavily insulated lid and a cheap wireless thermometer is about the only thing I can see to do. At least you don't have to do any maintenance to the batteries. Hurray!

With self heating batteries I can't get by the problem of the blocks becoming discharged because the panels are under snow - if we had to leave. But the bigger problem is what to do with three Catahoula farm dogs here by themselves.... They and livestock are the reason we can never both be gone at the same time.

Dave Angelini · June 23

Drop the dogs at the vet and try and hire someone to go out and take care of livestock.
That is what a few I know do. If the reason to leave is compelling, you might have to bite the big one.

You can buy a whole battery/inverter with solar inputs for chicken feed theses days.

Horsefly · June 24

I built two insulated & heated battery boxes for my two DIY 24V LiFePO4 batteries. They are in use in our cabin in Colorado at around 9,000 ft elevation, so the temps get pretty cold in the winter. One of the two has been there for 3 winters now, and the other has been there 2 winters. They stay on and connected to the SCC all winter.

The heating elements in both batteries are (if I recall correctly) 24W output, so they heat very slowly. My experiments before the build convinced me that low and slow heating is critical, so that the cells don't get too hot near the heating elements before the other side even gets warm. My math (mostly confirmed by my testing) indicated that even with no solar for over two weeks, the batteries would be able to continue keeping the cells warm. The heat is set to turn on when the battery gets below 40°F, and turns off when it gets above 50°F.

I think I probably posted about the system here somewhere, but I'm not sure.

Having said all this, there are lots evidence that if the battery is truly in storage (no power in or out) they can do fine completely frozen. At least this appears to be true for LiFePO4, but I'm not sure about other chemistries. Fact is, calendar aging of the cells - which is much more likely to kill them before you have used them up - essentially stops when they are kept cold.

Lithium battery storage temperatures

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