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    • batteries in cold climate

    Posts: 2,511 admin
    in Solar Beginners Corner #1
    i am building a cabin in Maine, may not be there every winter to top off batteries with generator when not enough sun to charge battaries.
    how can i prevent batteries from frozen, are the batteries freeze in the winter?. the battaries are deep cycle RV type from Walmart.
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    • Solar Expert Posts: 5,436 ✭✭✭✭
      #2
      Re: batteries in cold climate

      I suggest that you read the following links: http://www.batteryfaq.org/ http://www.windsun.com/Batteries/Battery_FAQ.htm#Lifespan%20of%20Batteries

      A fully charged battery will not freeze until -40f. Also if your batteries are in a insulated battery box, they will generate a fair bit of heat as they charge. My bank is often 10-20f warmer than the surrounding air during the day. Since they have such mass, they are slow to cool, and slow to heat, so keeping the heat in is quite easy. (Protect the batteries from the wind however.)

      We have battery banks that sit through the winter at -40 routinely, with only a small solar panel keeping them on a float charge. We have never had a problem since we have had them on a solar panel. Remember, the panel will put out more power in the winter due to cooler temps, as well as significant gain from reflection from the snow. So even if the batteries have to several days of no sun they shouldn't suffer.

      Tony

      This was supposed to be a chart, but it didn't translate properly, but you get the idea. 75% soc = -35f freeze point!

      Electrolyte Freeze Points
      at Various States-of-Charge
      for a Wet Lead-Acid Battery Table

      Approximate
      State-of-Charge
      (SoC)
      Approximate
      Depth-of-Discharge
      (DoD)
      Approximate Electrolyte Freeze Point
      100%
      0%
      -77°F
      (-67°C)
      75%
      25%
      -35°F
      (-37°C)
      50%
      50%
      -10°F
      (-23°C)
      25%
      75%
      5°F
      (-15°C)
      0%
      (DISCHARGED)
      100%
      (DISCHARGED)
      20°F
      (-6.7°C)
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    • Solar Expert Posts: 9,583 ✭✭✭✭✭
      #3
      Re: batteries in cold climate

      Depending on the quantity of batteries, a modest size (10-20watt) solar panel can maintain the charge thru the winter, even on the roof, under snow, sunlight will reach the panel, and it will charge the battery, keeping it full.
      If you have loads (porch lights etc.) that will drain the battery, you will need much larger panels to recharge and maintain the battery.
      Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
      || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
      || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

      solar: http://tinyurl.com/LMR-Solar
      gen: http://tinyurl.com/LMR-Lister ,

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    • Posts: 6,290 admin
      #4
      Re: batteries in cold climate

      Also, if you have a south facing outside wall, and a smaller panel easily mounted on that wall, mount it vertically there. The snow will fall off, keeping it clear and since it's winter, the sun is low in the southern sky anyway, so this works great. I find that works VERY well with my 1000 watt pv system here in Nova Scotia, All PVs mounted on a big rack, hinged at the top, tipped up for summer and hung down vertical for winter. When they are up even 15 degrees the snow would collect on them and if I needed serious power, had to go clean them off, even 1/4 inch of white snow reflected most of the solar energy. Huge difference. Once I hung them vertical, I could walk away and forget them.
      Just something to think about.
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    • Solar Expert Posts: 10,300 ✭✭✭✭
      #5
      Re: batteries in cold climate

      they don't have to be vertical as in 90 degrees straight up and down. about 70 degrees should do it well and be better at solar collection. of course they must face south.
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    • Solar Expert Posts: 5,436 ✭✭✭✭
      #6
      Re: batteries in cold climate

      I think what Wayne is saying and I can confirm, if they are not almost vertical they won't shed snow. 70 degrees, (20 off vertical) will still hold a fair bit of snow depending on temp. My all season panels are on the wall, under the overhand so that they never get snow and seldom get freezing rain. Summers I hinge them up as needed.

      Tony
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    • Solar Expert Posts: 10,300 ✭✭✭✭
      #7
      Re: batteries in cold climate

      tony,
      not quite true as my pvs shed the snow quite well and mine in the winter months sit at 63 degrees. also, note that just because the surface is vertical doesn't mean snow can't or won't stick to it as the telephone poles and trees have snows sticking to their sides often that i can attest to. that also blows your thinking i am south of you guys so i can't know of snows. we see it here though not as much or as often as you guys do. the 1st frost already occured here on oct 18 with a frost also on the 19th and maybe tonight too. snow is a possibility tonight just north of me by a county or 2 or roughly 20-50km though it won't stick long if at all.:p
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    • Solar Expert Posts: 5,436 ✭✭✭✭
      #8
      Re: batteries in cold climate

      Neil,

      Your right, I've even seen snow stick to the underside of things under weird conditions. Having said that, IMHO there is advantage of hanging panels on the wall in unattended locations that don't need maximum charging. In this configuration they don't get ice, branches etc falling on them. Also on a sunny day the reflection off the snow will (mostly) make up for proper angle.

      (This assumes an unattended location, where you can't shovel them off, and you don't need maximum charging).

      T
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    • Solar Expert Posts: 10,300 ✭✭✭✭
      #9
      Re: batteries in cold climate

      believe me, mine catch the reflected light too. maybe you should try a side-by-side experiment as to which provides you with more if you have 2 meters that will totalize the outputs for each identical pv at differing angles. i'd put money on the one that's slightly angled.
      btw, mine are above my porch roof mounted against the wall, but angled.
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    • Posts: 6,290 admin
      #10
      Re: batteries in cold climate

      thanks every one for the the advised, i feel better that don't have to carry those heavy batteries back to VA when the cabin close down for the winter.
      i will start with very small system, 4 batteries to minimize the lost until i learn how to manage the system better.

      tony, thanks.
      A fully charged battery will not freeze until -40f. Also if your batteries are in a insulated battery box, they will generate a fair bit of heat as they charge. My bank is often 10-20f warmer than the surrounding air during the day. Since they have such mass, they are slow to cool, and slow to heat, so keeping the heat in is quite easy. (Protect the batteries from the wind however.)

      We have battery banks that sit through the winter at -40 routinely, with only a small solar panel keeping them on a float charge. We have never had a problem since we have had them on a solar panel. Remember, the panel will put out more power in the winter due to cooler temps, as well as significant gain from reflection from the snow. So even if the batteries have to several days of no sun they shouldn't suffer.

      Tony

      This was supposed to be a chart, but it didn't translate properly, but you get the idea. 75% soc = -35f freeze point!

      thanks Mike,
      Depending on the quantity of batteries, a modest size (10-20watt) solar panel can maintain the charge thru the winter, even on the roof, under snow, sunlight will reach the panel, and it will charge the battery, keeping it full.
      If you have loads (porch lights etc.) that will drain the battery, you will need much larger panels to recharge and maintain the battery.

      thanks Wayne,
      Also, if you have a south facing outside wall, and a smaller panel easily mounted on that wall, mount it vertically there. The snow will fall off, keeping it clear and since it's winter, the sun is low in the southern sky anyway, so this works great. I find that works VERY well with my 1000 watt pv system here in Nova Scotia, All PVs mounted on a big rack, hinged at the top, tipped up for summer and hung down vertical for winter. When they are up even 15 degrees the snow would collect on them and if I needed serious power, had to go clean them off, even 1/4 inch of white snow reflected most of the solar energy. Huge difference. Once I hung them vertical, I could walk away and forget them.
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    • Solar Expert Posts: 5,436 ✭✭✭✭
      #11
      Re: batteries in cold climate
      niel wrote: »
      believe me, mine catch the reflected light too. maybe you should try a side-by-side experiment as to which provides you with more if you have 2 meters that will totalize the outputs for each identical pv at differing angles. i'd put money on the one that's slightly angled.
      btw, mine are above my porch roof mounted against the wall, but angled.

      Neil,

      We are arguing about nothing. I agree that you will get more gain with panels properly aimed. My only point is that if your system is unattended for months on end in winter climes, (and you don't NEED 100% output) then there can be an advantage to hanging them.

      Tony

      PS In spite out ourselves, I think we have answered the original question!
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    • Solar Expert Posts: 10,300 ✭✭✭✭
      #12
      Re: batteries in cold climate

      ok. i also wasn't aware that we were arguing.:confused:
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    • Posts: 6,290 admin
      #13
      Re: batteries in cold climate

      By the way Boonwsun, one thing I forgot to mention, I've found much better results during times when snow may collect and slide to the bottom of the panel, if the panel is mounted on it's side. Reason is, many panels have 2 series strings of cells that run lengthwise. If mounted "normally" and the snow slides down to cover the bottom cells, it basically kills the output. If however you mount the panel on it's side and the snow slides down, it only covers the cells on one of the two strings, leaving the other string to produce.
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    • Posts: 6,290 admin
      #14
      Re: batteries in cold climate

      thanks Wayne,
      boon.
      Wayne from NS Cana wrote: »
      By the way Boonwsun, one thing I forgot to mention, I've found much better results during times when snow may collect and slide to the bottom of the panel, if the panel is mounted on it's side. Reason is, many panels have 2 series strings of cells that run lengthwise. If mounted "normally" and the snow slides down to cover the bottom cells, it basically kills the output. If however you mount the panel on it's side and the snow slides down, it only covers the cells on one of the two strings, leaving the other string to produce.
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    • Solar Expert Posts: 10,300 ✭✭✭✭
      #15
      Re: batteries in cold climate

      for the record-- today was our first snowfall here and it stuck for awhile too.:grr to my southeast and some northern counties it has been labled a storm as some areas already have more than 6 inches of snowfall from this system.
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