Batteries For Winter Backup and Cottage Use during Spring Through Fall

[BoSho]

I'm a Solar newb but have long awaited Solar's affordability before making any moves. The goal is to power a small cottage with a couple of 24v 280ah eve batteries and Solar panels collecting during the week. I have seen Will talk about batteries lasting virtually forever as far as my life goes based on keeping them running between 20% and 80% SOC. I am also seeing people say that they really need to be kept around 50% for optimal storage when not in use.

From those 2 ideas it makes me think I just need to cycle them 1 or more times every month and they would be fine as a Winter Backup and then use them at the cottage the rest of the time.

Can folks confirm that letting batteries sit from time to time won't make a difference?

 

[MPRanger]

You either need all Lead Acid or you need a battery warming mat and blanket. It is one of two choices

 

[Daddy Tanuki]

Agree with MPRanger above.

chiming in from 1100 meters on the north west flank of Mt. Fuji. I just swapped a few months back to Lithiums from AGM's doing basically what you intend. (I plan on retiring to my cabin in the future, so my build is a bit overkill.) I built a battery warmer myself out of an aluminum plate thats 6mm (.25") thick and big enough for all the batteries to sit on top of it. with 8 of the 25 watt 12 volt 1.5"x1.5" taped to the bottom and wired in series. the total amp load is .7 Amps when they are all wired in series and they distribute the heat nice and evenly across the plate. I use a cheap temp controller (actually two wired in series just in case. I set the values as 10-15°C along with a duty cycle controller tht teurns them on for 60 of for 15 with a third temp sensor close to the bottom to act as emergency shut off if the bottom 1/4 of the pack goes above 20°C. Enclosed the entire pack in the 50mm blue foam insulation board on all sides includieng top and bottom. all sides and bottom are sealed with a thin bead of expanding foam to make it airtight, the top is friction fit with packing tape. the only openings are for the BMS leads as it sits outside the pack, as well as the B+, and B- posts copper bussbars so I bent the end at the packs +, and - up at 90° and out side the pack. all holes were sealed of course. only time will tell but testing so far has been good.

remember having them in series raises the resistance, lowers the amps, so it does not use as much as you would think, but the pads themselves put out less heat when wired this way. this allows you to space the pads out and get a more even distribution of heat.

good luck.

 

[upnorthandpersonal]

Also, if you're only storing them in the cold and not using them, you don't have to keep them warm. Research also shows that storing them colder slows calendar aging.

How to Find Happiness With LiFePO4 (Lithium-Ion) Batteries – Solacity

By: Rob Beckers You have just sold your first-born into slavery, remortgaged the house, and bought yourself a lithium-ion battery! Now you want to know how to take care of your precious new purchase: How to best charge lithium-iron batteries, how to discharge them, and how to get the maximum...

www.solacity.com

"Storing batteries below freezing is fine, even at very low temperatures such as -40 Centigrade (that is the same in Fahrenheit), or even less! The electrolyte in LiFePO4 cells does not contain any water, so even when it freezes (which happens around -40 Centigrade, depending on the particular formulation) it does not expand, and does not damage the cells. Just let the battery warm up a bit before you start discharging it again, which is OK at -20 Centigrade and above. You will see an apparent loss of capacity when discharging at below-freezing temperatures that reverses when the battery gets above freezing, and there is a slightly accelerated effect on aging. Storing them at low temperatures is certainly much better than storage at high temperatures: Calendar aging slows down dramatically at low temperatures. Try to avoid storing them at 45 Centigrade and above, and try to avoid storing them completely full if possible (or nearly empty)."

 

[Hound dog 78]

Greetings! I am brand new to the channel so please forgive any gaffes.

BoSho, I have pretty much the same situation with a cottage in Maine. It sits idle for most of the year; only used in late spring and summer. The system is primarily used to charge laptops, phones, etc. but there are a few 12vdc lights and I want to install a 12vdc ceiling fan.

Only within the last few years have I introduced a small PV system of used parts: 6 Kyocera 51W panels (1993) Blue Sky Solar Boost 50 controller with the following.

Output current rating ..........................50A
System voltage...................................12/24VDC nominal
Max. PV Open circuit voltage.............57VDC
Max. battery voltage...........................57VDC
Output current limit.............................50±2A
Volt meter full scale range..................60.0V
Volt meter accuracy ...........................±0.3% full-scale
Current meter full scale range............±60A
Current meter accuracy......................±0.5% full-scale
Acceptance voltage............................13-16/26-32V typical
Float voltage.......................................0-2/0-4V <Accept.
Equalize voltage.................................1V/2V >Accept.
Power conversion efficiency...............97% typical @ 40A


Maximum wattage for 12vdc is 670W
Maximum wattage for 24vdc is 1340W


At present, I have two 12vdc Lifeline AGM batteries (also used.) The controller can be configured for both 12vdc in and out, 24vdc in and out, or 24vdc in with 12vdc out, which is what I am using now.

Not able to spend a lot, I am looking to upgrade the batteries; probably 2 12vs again.

My question is this. Would there be any significant advantage to switching to 24vdc in and out? I still want to use 12vdc in the cottage but would use a converter to step down.

Any thoughts or suggestions would be greatly appreciated. Thanks