Battery Box insulation

New here and new to off grid living.

My wife and I have some "get away property" at 6K ft and have placed a small trailer as a"beachhead" to get away from it all. As we have gotten older, pure camping has lost its appeal. Having a fridge for ice and a small bathroom sure make up for a lot.:p

We have a small solar set up that works well for what we need. There are two 105AH batteries that do a fine job during most of the year but I worry a bit about winter. The batteries are outside and the drain by the heater fan makes me wonder a bit about battery insulation. The nights will get down into the teens and even single digit F on occasion. I'm thinking of adding to more batteries and building a battery box but wonder how much good insulating it would be. Also if insulation would be any problem during the summer when temp gets into the 90's.

Any info as to the positives and negatives of insulation and spacing of batteries would be appreciated.

Thanks

Comments

  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Batery Box insulation

    hi ron.
    i think the batteries will be fine as long as they are kept up with a float charge from the solar. it's when the batteries drain off some power, even if it's only the idle losses of storage without a float charge, that's when there's more water content in the batteries and more of a possibility of freezing and cracking the case. if you want to you can loosely place styrofoam or some other rigid foam type insulation around them, but leave room on the top of the batteries to breathe and it need not be totally air tight to the outside. if the insulation has a metal foil facing, be sure to peel that off or add an electrically insulative covering to be sure no shorts are possible.
    if adding new batteries to old ones you will find the new ones will be pulled back to the level the old ones are at. if the ones you have are run of the mill and 5 years old there's no question in my mind it would be better to change them out or place a switch between the old and new batteries. the switch would place problems in trickle charging all of the batteries while you aren't there in the winter.
    also be sure your pv system has enough capacity to handle more batteries as the charge rate should be at least 5%.
  • System2
    System2 Posts: 6,290 admin
    Re: Batery Box insulation

    Thanks Niel for the quick reply.

    Right now the batteries (they are just run of the mil type) are only one year old so if I want to do this I shouldn't wait too much longer. The batteries are now sitting in an old cooler with the top off. I have about 400 watts of peak solar output so I'm sure that would be enough to handle the extra batteries. On a clear day (during the summer at least) the existing system is back to float (trickle) charge by 10 AM. During the winter last year, that took to 1 or 2 in the afternoon. That includes our normal usage on the system for 12 volt lighting and control circuits for the gas fridge as well as 120 volt inverter use for computers and power tools for building our expanding universe.

    When we are gone, I cannot imagine any time when after a day of recharging that the system would not reach float by noon or three in the afternoon on overcast days. Perhaps snow on the collectors could be a problem but with their winter angle I would imagine melt off fairly quickly.

    Actually that is something I've never thought about before. When your around to brush the snow off, no problem. When your away, how thick of a snowfall before the collectors stop collecting?:confused:
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Battery Box insulation

    Batteries will be just fine down to -40 as long as they are kept on charge. Even partially charged (50%) won't freeze at 0f. Counterintuitively, battery CAPACITY goes down with colder temperatures, and goes UP higher temps. Battery LIFE EXPECTANCY, on the other hand, goes down with higher temps and up with lower temps.

    A simple sytro-foam cooler makes a pretty good, cheap battery box. The battery itself will generate a fair bit of heat on it's own so there is really no reason to worry about freezing.
    Unless it never cools at 90f the same styro-foam box will keep the batteries cooler in really hot weather.

    On another note, a battery monitor, like a Tri-metric to figure out how much power you put in/take out on any given day. Also, if you are away from you site for long periods in the winter, consider mounting one or two panels on the wall, so that they won't accumulate snow. They won't run at peak efficiency, but in the real world, who cares?

    To answer your question, any snow fall will cut production, and fully covered will drop it to near zero. (The advantage of hanging one or more vertically!) The plus side, is that Pv steeper than ~45 degrees will shed snow quite quickly, assuming they have a clear area below to shed. As soon as the sun comes out after a snow, the panels, unless they are buried really deeply, will begin to heat up and begin to melt themselves.


    As for adding new batteries to an older string, it is not really suggested, but I suggest that you read the following links: http://www.batteryfaq.org/
    http://www.windsun.com/Batteries/Battery_FAQ.htm#Lifespan%20of%20Batteries
    Tony
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Battery Box insulation

    tony's point of at least one pv vertical or nearly so is a good one and will keep something going to the batteries during those times of heavy snowfall. just be sure the ground accumulations won't sneak up and start covering the bottom edge of the pv.
    as to your batteries, if you feel these 1 year old batteries are still in great shape, then by all means add to it, but be sure they are the same batteries as you don't want to mix different types or capacities for this could lead to problems.
    of course in the summer or any of the warmer times, you don't want the batteries to be hotter than they normally would be without the insulation for as tony pointed out you don't want them too hot in the summer taking away battery life. shade from any sun adding to the batteries' already warm temperature is good though.
  • System2
    System2 Posts: 6,290 admin
    Re: Battery Box insulation

    Thank you all and especially Tony's links. (I now know more about batteries then I ever wanted.:D)

    From what everyone has said, I think I'll just leave things as they are (insulation wise). The batteries are in an old cooler under the trailer. They are thus out of the Sun and have a constant air flow over the top to remove any gases.

    During the spring, summer, and fall we are at our outpost two or three times a month for two or three days at a time. Winter is more of a problem but we still try and get there once a month.

    Snow is not that big of a problem and I have never heard of it lasting (except on the north side of rocks) for more then three or four days.

    As for the existing batteries, they were installed new a year ago May and have always been on the system, controlled by a Blue Sky solar boost 2512i(X) unit. The trailer has a rather useless indicator for battery level with led's for: full, 2/3, 1/3, empty. During the warmer months the indicator never drops below the 2/3 indicator. Last winter, with the load of the heater fan, it did drop down to the 1/3 third line which made me wonder if I was overtaxing the system. I should put a voltmeter on the system as the led indicators are fairly useless, or perhaps I should get one of the remote display units. I'm thinking doubling the capacity should get me through winter visits with no dent in electrical activities.

    I've had good luck with batteries. Take my work van which only goes out two or three days a month. I bought it in 2000 and immediately put a small 5 watt solar panel on the dash board to keep the battery up. Believe it or not, I'm still on the original battery.