winter recommendations

System · November 2008

well, It has been a while since I have posted any cries for help, and in fact things ran smoothly for the duration of the summer for my first solar installation on my Travel trailer. now we have parked the trailer for the season, and I am wondering how my batteries will fair over the winter. the modules aren't in the best location for full power production, but I'd say they get at least 3-4hrs of direct sunlight a day, which seems to be keeping the battery bank state of charge around 12.8v. does anyone have any suggestions for maintaining batteries in the off season?

BB. · November 2008

Re: winter recommendations

Keep them fully charged and check the water once a month or so until you figure out how often you need to check.

Monitor the float voltage--if your controller has a float setting.

If you are not using any power, and your controller does not have a float setting or adjustment--you can probably just turn on the solar charger one day per week to keep the batteries topped off and avoid overcharging (which may be your bigger problem at this time).

Without searching your previous posts--knowing the battery type, total AH/voltage rating, and controller brand/model would probably get you a more exact answer.... i.e., if these are flooded cell batteries, you still want to equalize them once per month or so to keep the electrolyte well mixed, if your area freezes--how cold does it get--flooded cell batteries that are near dead freeze very easily--AGM's are not susceptible to freeze damage at all--but you need dto avoid charging while any battery type is frozen, etc.).

-Bill

System2 · November 2008

Re: winter recommendations

these are sound recommendations thank you. I guess at this point I should avoid leaving the charger on full time like I have been. What I have are two AGM 220 AH deka batteries, and the charge controller is a mppt bluesky
3024di. As for the climate here in Montana, things will definately be dropping below zero through out the winter, so If it has been wicked cold out, I should hold off on charging until things warm up a bit?

-and I am hoping to use some power probably just by running an extension cord from the inverter to our cabin, twould be a shame to use all coal power, when I have free juice from the sun...

icarus · November 2008

Re: winter recommendations

Assume you have a good charge controller, and you have no phantom loads, you will be fine. I have one system that sits alone for 7 months, through the winter. The batteries just sit there fully charged, and even thought they get to -40 once in a while, they are fine after 10 years.

As Bill says, check the water if you can, and if you can check the cells with a hydrometer every month or so. A Dead cell can kill the whole string, depending on how long it is left on the string,

Tony

crewzer · November 2008

Re: winter recommendations

...two AGM 220 AH deka batteries, and the charge controller is a mppt bluesky 3024di.

The batteries are sealed AGM models, so the electrolyte level can't be checked, nor should they be equalized in the conventional sense. If they're just going to sit and be maintained by the PV array and controller, then I recommend you set the target absorption- and float voltages (ref 77 F) at the lower end of the ranges suggested by East Penn (Deka and MK).

See: http://www.eastpenn-deka.com/assets/base/0139.pdf

All of this assumes that the controller has a remote batetry temp sensor attached to the battery bank.

HTH,
Jim / crewzer

niel · November 2008

Re: winter recommendations

as crewzer said and once everything is right with proper voltages set and a bts it is fine to leave it on all of the time as the controller won't let anything bad happen to the batteries assuming there's no loads on the batteries. if no sun for awhile, it will be ok as agms will hold their own longer than standard lead acid batteries as their self-discharge rates are lower and being more efficient they charge up slightly faster too. only problem may be snow on the pvs longer than you'd like, but as said the batteries have a lower self-discharge rate.

mike95490 · November 2008

Re: winter recommendations

solsauce wrote: »

well, It has been a while since I have posted any cries for help, and in fact things ran smoothly for the duration of the summer for my first solar installation on my Travel trailer. now we have parked the trailer for the season, and I am wondering how my batteries will fair over the winter. the modules aren't in the best location for full power production, but I'd say they get at least 3-4hrs of direct sunlight a day, which seems to be keeping the battery bank state of charge around 12.8v. does anyone have any suggestions for maintaining batteries in the off season?

IF you have no loads on the batteries, you should be fine, as long as your charger does not overcharge the batteries. Fully charged flooded cells (and AGM I suppose) won't freeze till they are about - 77F, I think thats when tires break off the rims.
http://jgdarden.com/batteryfaq/carfaq4.htm#freeze_points
If they are true AGM's 3-4 hours of sun, per week, should be enough, if there are no loads.

dbuckles · September 23

New to this forum. While this is an old chain, I am still posting here, hoping for discussion. I have a pair of Trojan SPRE 06 255, 6 Volt deep-cycle, 229Ah / 20h, solar series, group GC2, with a 1x Longi LR4-60HPB-350M, 350 Watt, 60-cell (120 split-cell) mono PV module, black-on-black and 1x EPSolar – EPEver XTRA2210N-XDS2, 20 Amp MPPT charge controller, 12/24 Volt, 100 Volt DC input, with display. For three winters I have successfully put the system into winter mode by disconnecting the inverter and leaving the panel, controller and a battery capacity metre connected. Location is cold, minus 15 C at night, in North Bay, Ontario. This year I left the system the same but one of the cells on each of the batteries had a specific gravity of 1.217 (indicating a 70:percent charge) with rest at 90 percent. Are the batteries at risk of freezing or other damage? I’m also unclear how an overcharging situation could arise in this set up.

BB. · September 23

Welcome to the forum db.

From the Rolls manual:

https://www.rollsbattery.com/wp-content/uploads/2018/01/Rolls_Battery_Manual.pdf

So, a 1.217 SG cells will freeze below -30C ... So by itself, not an issue with freezing.

In theory, you should recharge a flooded cell lead acid battery to >75% State of Charge. Below that, a non-cycling battery (discharging/recharging) will begin to sulfate faster.

Normally, for a battery stored at 25C, a flooded cell lead acid battery should be recharged back to >90% State of charge once a month because of self discharge.

HOWEVER, the rate of self discharge is temperature dependent. For every 10C drop in temperature (from 25C), the rate of self discharge is cut by 1/2... I.e., at ( 25C-10C= ) 15C, the battery will only need recharging every 2 months. 20C drop, every 4 months, etc.

Given that you have left the panels+charge controller connected, hopefully you have enough sun to bring up the battery State of Charge over days/week or so (no shade from trees, no snow over panels, etc.).

The last quick question, what are the loads on your battery bank during winter (if you kill all of your DC loads -- You still have the load of the solar charge controller)... Not usually an issue, but if you have months of drifting snow on the solar panels, the charge controller can discharge the battery bank somewhat (I.e., snow on panels, no charging power). One option is to have a smaller/single panel mounted vertically, or on a vertical wall as a winter backup.

For example, the EPEver seems to have around 0.015 amps (15 mAmps) of self consumption:

https://www.epever.com/product/xtra-10-40a-mppt-solar-charge-controller/

0.015 Amps * 24 hours per day * 30 days = 10.8 Amp per "dark month" of self discharge

Does not look like an "excessive" winter load on a 229 AH @ 12 volt battery bank (less than 5% discharge per month). Only "issue" would be a 4-5 month of "drifted snow on panels" to get you near to the below 75% SoC / sulfating issue.

Only question is the battery capacity meter's discharge current (same "math" as the charge controller sleep question).

As long as your charge controller is properly programmed and not 'over charging' your battery bank and/or "boil your cells dry" (if plates are exposed to air, really harmful to battery life)--Over charging should not be an issue (as long as your plates are 'not exposed to air/low electrolyte levels' when you come back in spring).

Most of the FLA battery in cold climate issues I can think of (from a guy in California).

-Bill

dbuckles · September 23

Thank you Bill for your thoughtful and detailed analysis. It has helped me think through the situation and conclude that freezing is very low risk in my situation. The panel is south facing and at a 50 degree angle, sitting at the lake shore well above the level of the water and any accumulating snow. There could be snow accumulation on the panel some times but I am confident that it would melt in the sun on warmer days and that there would be little likelihood of packed drifting snow impeding exposure of the panel to sun.

I hadn’t mentioned that the batteries are in a ridged foam insulated box inside a tool shed, which should help from a freezing perspective. The box is not air tight yet provides protection from wind and some R value. In retrospect, I wish I had given the batteries a little more room inside the box, and not placed any insulation on top of the batteries (a light ridged foam resting on top). Given that there is minimal but some air flow out of the box, does the box and foam greatly increase the risk of concentrating combustible gases?

The location is a small island on a very remote part of a lake (Lake Temagami), with no access in winter due to water currents nearby that limit ice formation at safe levels. The cabin remains unused and virtually inaccessible for 6-7 months. So hard for me to get there to change anything after November, unless it was really necessary to manage fire risk. Risk seems very low, but I’m a neophyte. DB

dbuckles · September 23

While I’m at it, I have another question. When I first noticed the drop in specific gravity of several cells, I topped up all cells with distilled water. I didn’t measure the volume added, but rather just eyeballed to go for cover of about a half inch above the plates. Might be slightly more than half inch in some cells. This action seemed to even out the specific gravity across all cells after a few days. Any error here on my part? Is the specific gravity likely to improve while the batteries sit in non-discharging mode? I will read more about how the chemistry works, but I have not found anything that would suggest adding electrolytes to the solution as a matter of course. Given the remote off grid location, and weight of the batteries, I have not yet considered bringing them out for a charge top up, but could in future if a good idea.

winter recommendations

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