Storing batteries in a northern Ontario winter

rp3703rp3703 Posts: 101Registered Users ✭✭

So my in-laws have a place in Northern Ontario that we visit for a month or two each Summer and that’s it for the entire year. I will be mounting 6 310 watt panels to the roof and I have built a custom rack that allows them to lay flat on the 2 pitch roof during the summer and tilt to a 45 degree angle when we leave. I have built a plywood panel that includes the combiner, charge controller, and breaker panel, that I would like to hang inside the cabin so I can easily see what’s going on with the CC throughout the day. This means I will need to stick my 12 batteries and inverter close by as well. My plan right now is to store them in a box that lays on the ground underneath the floor. Yes, I realize the batteries must be separated from the ground itself or they will drain to ground. My question is how much protection will they need from the potentially 20 below temperatures they will be exposed to during the winter? I found this article 

http://solarelectricityhandbook.com/Solar-Articles/looking-after-your-solar-batteries.html

which suggests using two layers of foil covered bubble wrap on the bottom and sides, just wondering if that will be enough. Also, I need to have ventilation in this battery box. During the winter, won’t that vent out any built up heat inside the box as well? Is this just a bad idea all together?

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Comments

  • mcgivormcgivor Posts: 1,753Registered Users ✭✭✭✭
    edited May 24 #2
    Whilst the cold may be detrimental to the performance while in use, it is actually benificial for storage, being that it retards self discharge overy time. Batteries by the way will not discharge to ground if placed on the ground,. The best thing to do is fully charge them before storage, this will lower the freeze temperature of the electrolyte well below -20°C. Some say, leaving a small controller and panel is beneficial to provide a daily top up I'm sure there will be varied opinions.  
      1500W, 6× Schutten 250W Poly panels , Schneider 150 60 CC, Schneider SW 2524 inverter, 8×T105 GC 24V nominal 

  • littleharbor2littleharbor2 Posts: 914Solar Expert ✭✭✭✭
    edited May 24 #3
    Unless the snow has somewhere to go it will block your panels and effectively prevent charging. Even a small amount of blockage will affect charging.

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric, 700 ah @24 volt AGM battery bank. Plenty of Baja Sea of Cortez sunshine.

  • rp3703rp3703 Posts: 101Registered Users ✭✭
    That's the next thing I need to figure out. I assumed I could leave them hooked up to my CC(Midnite Classic 150)and panels, shut off all loads and set the CC to some kind of trickle charge setting to keep the bats alive. I would also like to figure out a way to make my set up idiot proof since we share the cabin with lots of relatives.
  • rp3703rp3703 Posts: 101Registered Users ✭✭
    Snow is why I made my roof racking hinged, so it can be tilted up in the winter. The panels are 3x5 and there will be 6 of them. Surely there will be enough exposed panel surface to provide a trickle charge.
  • mcgivormcgivor Posts: 1,753Registered Users ✭✭✭✭
    As it's always good to have information I've attached a pdf which will be helpful in understanding the effects of cold and storage. Unfortunately can't find any information on making a system idiot proof, perhaps because there is no such thing  :D education will be the best route or perhaps an instruction manual, but from personal experience those who don't understand exactly how something functions, are prone to mess things up, your mileage may vary.
      1500W, 6× Schutten 250W Poly panels , Schneider 150 60 CC, Schneider SW 2524 inverter, 8×T105 GC 24V nominal 

  • EstragonEstragon Posts: 2,321Registered Users ✭✭✭✭
    My cabin is in NW Ontario. At a 45° winter angle, I suspect snow will be a problem for you at least some years. In a "normal" year, it gets cold in early Nov, and the keeper snow starts in late Nov/early Dec. The cold snow should mostly slide off, and a little remaining snow will melt off if the panels see full sun even in -35° cold.

    Two problems that have come up for me some years though. First, the sun gets very low in Dec., so you may want to make sure the panels will still get full sun. Most of N.Ontario is hilly and treed and what seems like a great spot for solar in June may not be in Dec. For a few weeks around Xmas, the shadows from trees are long enough to create dappled shading which can prevent snow melt. The other problem can be the nature of the early snow. Some years the early snow is the warm sticky stuff instead of the cold fluffy kind. My panels are steeper (~65°), and if enough sticky stuff covers the panels, the sun can't warm them and they'll stay completely covered until either spring or they're cleared manually. If that happens, the classic will drain the bank and the batteries can freeze and burst when in a low state of charge.

    One solution is to disconnect the fully charged batteries and just leave them (fully charged are good to ~ -75°), but with only a month or two of use and 10-11 months of self-discharge, this may not work well. If going this route, you may want to consider AGM batteries, which have lower self-discharge than flooded.

    Another is to assume the snow will slide off (possibly by tilting more), and the panels will be in full sun to melt what remains. If doing this, you may want to set the Classic "skip days" to 7 or so. This will prevent it from needlessly taking the bank to absorb voltage every day, and reduce the risk of gassing causing water levels dropping too far. Most days, the Classic will just go up to float voltage, and every 7th day will do a full bulk/absorb cycle, which is often enough to get the electrolyte mixing to prevent stratification. It can even be left with that setting for summer by setting rebulk voltage high enough that usage will trigger cycling more often.

    A third solution, which was what I eventually did, is to add pv mounted vertically in a location sure to get winter sun and a small controller. IMHO, this is the most effective and idiot-proof solution.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • jonrjonr Posts: 950Solar Expert ✭✭✭✭
    Is there any evidence that a battery not in use (ie, sitting on float charge) stratifies?   Acid and water don't naturally separate (left alone, they will slowly mix/de-stratify).
  • littleharbor2littleharbor2 Posts: 914Solar Expert ✭✭✭✭
    rp3703 said:
    Snow is why I made my roof racking hinged, so it can be tilted up in the winter. The panels are 3x5 and there will be 6 of them. Surely there will be enough exposed panel surface to provide a trickle charge.

     Depending on panel orientation and wiring configuration , even a little panel coverage can pretty much kill output. 

     The thing I'm visualizing with your array, you mentioned they sit on a relatively flat roof.  When tilting the panels up, where does the snow go?  If it can still sit on the 2 in 12 pitch roof , will it just pile up at the bottom of the panels or fall completely off the roof?

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric, 700 ah @24 volt AGM battery bank. Plenty of Baja Sea of Cortez sunshine.

  • rp3703rp3703 Posts: 101Registered Users ✭✭
    Say the panels do get covered or there is little to no sun for one to three months, is that enough time for them to self-discharge to the point of no return?
  • rp3703rp3703 Posts: 101Registered Users ✭✭
    The roof is metal and yes, it will probably stay piled at the bottom. My inlaws went up there this March and even though they could snow mobile across the lake and there was about a foot of snow in places, there was no snow on the roof. I realize this could have just been a light winter though.
  • Wbuffetjr1Wbuffetjr1 Posts: 78Registered Users ✭✭
    I installed a system last Summer at our cabin at 10,000'. While mounting the panels on the roof would have been simpler, I opted for a ground mounted array on a pole. This was specifically so the snow could slide off.  You guys might only use the cabin for a couple months per year currently, but that could change in the future.  A couple years ago we took our family up for Christmas at the cabin and had an amazing time. Having to deal with the generator over that trip was actually one of the many reasons we finally went ahead and installed solar. To make a long story short, think about all the possibilities that open up if you had power all Winter. Panels on the roof with tons of snow just seems like an avoidable issue to me. 
  • littleharbor2littleharbor2 Posts: 914Solar Expert ✭✭✭✭
    rp3703 said:
    Say the panels do get covered or there is little to no sun for one to three months, is that enough time for them to self-discharge to the point of no return?

    As Estragon suggested, A fully charged set of AGM batteries would be fine.  The fact that you don't need to check electrolyte levels is great for long term unattendance. 

    Again Estragon mentions a single vertical panel and small PWM controller. Great idea for  unattended battery bank maintenance. I do this in the summer in Baja, although the panel is lying flat, and mainly to keep my main CC from running  in the heat.

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric, 700 ah @24 volt AGM battery bank. Plenty of Baja Sea of Cortez sunshine.

  • EstragonEstragon Posts: 2,321Registered Users ✭✭✭✭
    edited May 24 #14
    > @rp3703 said:
    > Say the panels do get covered or there is little to no sun for one to three months, is that enough time for them to self-discharge to the point of no return?

    The rate of self-discharge depends on the type of battery, its age, and ambient temp. A fairly new AGM in cool winter temps should be fine. An older flooded in hot summer temps may not.

    What will be an issue regardless, is that the Classic will take some power just being on, something like 3-5w. Even 3w is 3 x 24hrs x 90 days is 6.4kwh. A bank of a 2 strings of 6v golf cart batteries (a reasonable small cabin setup) is ~ 450ah, or 450x12=5.4kwh. IIRC, the Classic won't wake back up without a battery voltage of ~10v or so. That leaves the bank sitting dead until summer, and likely unrecoverable.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • rp3703rp3703 Posts: 101Registered Users ✭✭
    Ok. Well I will have a bank of 12 6V 215 AH batteries that will provide 24V at 645 AH. How should I size the small PV stay and PWM?
    This may be all for nothing since I left 8 of my 12 batteries in Ontario, wired in groups of two to make them 12V. I then attached each group to one of those cheap Coleman boat trickle chargers and hung them at the top of a sliding glass door that faces south. For all I know, they could be completely dead by now.
  • EstragonEstragon Posts: 2,321Registered Users ✭✭✭✭
    > @jonr said:
    > Is there any evidence that a battery not in use (ie, sitting on float charge) stratifies?   Acid and water don't naturally separate (left alone, they will slowly mix/de-stratify).

    Fully charged electrolyte (acid) in a FLA battery has a specific gravity of ~1.3 vs fresh water at 1.0 (in other words acid is heavier for a given volume than water). Absent the gassing and mixing that occurs in the latter stages of charging st absorb voltage, the denser, more fully charged acid with higher specific gravity will tend to sink, while the lighter, less well charged will stratify above. Over time, the upper plates can sulfate, reducing overall capacity and also impeding charging of the adjacent electrolyte (which is most in need of charging).

    Tall flooded batteries (eg L16s) are more prone to this, and often have higher recommended absorb voltages to offset. AGMs, with the acid absorbed into a glass mat, don't really have this issue.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • BB.BB. Posts: 27,439Super Moderators admin
    Somewhere around 1-2% rate of charge should be fine... More than enough for batteries that are in subfreezing temperatures.
    • 645 AH * 29 volts * 1/0.77 panel+controller losses * 0.01 rate of charge = 243 Watt array
    Would be a good place to start (mount vertically on (snow free south facing wall--For freestanding near vertical mount)...

    But take what I say with a grain of salt... We get less than an inch of snow every 2 or 3 decades (or a bit of slushy hail a couple of times a decade).

    The big issue is to make sure there are no other loads on the battery bank and as Estragon says--Even an MPPT charge controller can be "too much" of a load if the panels are snow covered/shaded for much of the winter season.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • softdownsoftdown Posts: 1,814Solar Expert ✭✭✭✭
    Installing solar for 1-2 months/year of usage would be hard to defend on a fiscal basis. I'd maybe just use a genset to charge the batteries as needed. Unless you like having a bug out spot like many others of course.

    Since you are already committed, here are a couple thoughts from a solar guy in Colorado's second coldest region:
    1) Cold batteries have a real low self-discharge rate and tend to last much, much longer than warm/hot batteries.
    2) I don't see 45 degrees as being enough to reliably shed snow in that location. I'd use one panel at 90 degrees to maintain the batteries. 
    3) Batteries should be fine unless they drop below ~5.5 volts. I intentionally placed my newest bank in a colder location.
    4) You need to specify C(Canadian) or F(Freedom) when talking to Muricans.
    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
  • EstragonEstragon Posts: 2,321Registered Users ✭✭✭✭
    I oversized mine a bit (300w for a 750ah 12v bank, and 600w for a 350ah 48v bank) because of the weak and short winter sun, and because I chose to leave the Classics running on the main arrays. I like to have the logging the Classics do, and the coin battery will run down faster if I cut them off. I also plan to do some monitoring and security stuff that will take a little bit of power.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • rp3703rp3703 Posts: 101Registered Users ✭✭
    Would an easier solution be to just reconfigure my roof mounts to keep all 6 panels vertical during the winter? I built them out of super strut, so cutting new upright bars should be no big deal. I should mention that this cabin is at the south side of a long narrow island that extends north to south. While there are trees directly south of the cabin on this same island, there is water to the southeast and southwest. I've never been there in the winter so I don't know how wide a path the sun covers.
  • 706jim706jim Posts: 202Solar Expert ✭✭✭
    I have to chime in here. My place is on an island so is unattended for 6 months of the year. I leave the panels connected with no load other than my Trace C40 PWM charge controller. The panels are snow covered for about 3 months every winter.

    There has been no problem to date with leaving fully charged batteries in the cold and my place will reach -20F at times. No attempt at insulating the battery box.

    And my last set of 12 GC's lasted NINETEEN seasons.
    Island cottage solar system with 1400 watts of panels, Trace DR1524 MSW inverter, Trace C40 PWM controller 8 Trojan L16's. My 25th year.
  • EstragonEstragon Posts: 2,321Registered Users ✭✭✭✭
    Being able to set vertical would certainly help.

    In my part of NW Ontario, solstace sun is roughly 20° above the horizon near solar noon. Usable sun from maybe 9:30-3:00 covering about a 90° swath of the southern horizon.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • rp3703rp3703 Posts: 101Registered Users ✭✭
    Here is the best shot I could find of the southern view from the roof where the panels will be mounted.
  • rp3703rp3703 Posts: 101Registered Users ✭✭
    Nineteen seasons, way to go! I hope I am that successful. 
  • littleharbor2littleharbor2 Posts: 914Solar Expert ✭✭✭✭
    Sure are a lot of shadows on that roof. What time of the year was this pic taken?

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric, 700 ah @24 volt AGM battery bank. Plenty of Baja Sea of Cortez sunshine.

  • rp3703rp3703 Posts: 101Registered Users ✭✭
    That's probably about 4-5 in the afternoon towards the end of July. The Panels will be going in the sunny spot towards the right. Sun will be shining there all day long. The island is covered in trees. I just don't see a better location for the panels anywhere else that is a readable distance from the cabin except for on the roof. 
  • jonrjonr Posts: 950Solar Expert ✭✭✭✭
    Estragon:  once mixed and left alone, acid and water don't separate.     You only get stratification in a battery when the battery is being charged and discharged.    This pretty much doesn't happen when batteries are being stored on a float charge.   Don't add wear to your stored batteries with weekly absorb cycles.

    See page 3 here:
    http://www.eastpennmanufacturing.com/wp-content/uploads/Guide-to-VRLA-Batteries-1927.pdf

    "Stratification occurs during discharge and recharge..."
    http://usbattery.com/how-to-equalize-charge-and-prevent-stratification/
  • EstragonEstragon Posts: 2,321Registered Users ✭✭✭✭
    @jonr - you may be right that I don't need a weekly absorb - maybe a 14 or 28 skip days setting would work. I have flooded L16s, so stratification is a concern.

    The banks are being charged and discharged (self-discharge & CC load) with float cycles. They aren't sitting at float voltage on a grid float, they get an hour or two (maybe) daily at float.

    @706jim - 19yrs/seasons is outstanding for a set of GCs!

    For 6 winter months, I'd agree. In OP's case though, it's maybe 11 months, including some when the bank could be pretty warm with higher self-discharge. I leave my boat batteries (fuĺly charged) over the winter and they're fine. If I let them sit from August though, they might not be.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • softdownsoftdown Posts: 1,814Solar Expert ✭✭✭✭
    Just want to reiterate that almost any shade on the panels is simply not acceptable. May have to break out the chainsaw...
    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
  • EstragonEstragon Posts: 2,321Registered Users ✭✭✭✭
    Hard to tell from the pic, but it looks like the roof might get some early morning & late afternoon winter sun. Almost certainly in shade much of the day though.

    I'd be inclined to get the chainsaw out, not just for winter shade, but also to let a south breeze through. Helps keep the bugs away on a hot summer day.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • 706jim706jim Posts: 202Solar Expert ✭✭✭
    And trees close to your cabin have a nasty way of falling onto the roof at the most inopportune times.
    Island cottage solar system with 1400 watts of panels, Trace DR1524 MSW inverter, Trace C40 PWM controller 8 Trojan L16's. My 25th year.
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