Battery storage and ventilation

I am trying to design a system for an off grid cabin. The cabin is about 10,000 ft elevation. I have a cellar with inside dimensions of 4 ft by 8 ft that is used for food storage. The cellar is underneath the cabin, constructed of cinder block and concrete and has a 4 inch diameter PVC pipe to vent cold air inward. Average year round temperature is 35 degrees F.
If I used part of this area for my battery bank, would there be sufficient ventilation to prevent build up of gas? Or, would it be better to build a separate area for battery storage?
Any advice would be greatly appreciated.



  • BB.
    BB. Super Moderators, Administrators Posts: 33,479 admin
    Re: Battery storage and ventilation

    That is pretty cool for a battery bank--Batteries will last a long time (cold batteries can last 2+x longer), but you will have reduced AH capacity due to colder temperatures.

    Is this a summer/winter or year round residence... And how much power will you need (amp*hours @ ?? volts or Watt*Hours per day).

    You could put a foam board insulation around the battery bank and probably keep it a bit warmer for insulation. And vent the box directly out the roof (not to mess up your cold air trap). Also, flooded cell batteries do outgas with a bit of electrolyte mist--so you don't want things you care about right next to the batteries or they will get sulfuric acid on them and corrode.

    What type of batteries are you looking at? AGM/Sealed or standard flooded cell storage batteries.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    Re: Battery storage and ventilation

    As Bill points out, the cooler temps will be good for battery life. But they'll heat up when charging so they could raise the temperature of the cellar which may not be ideal for the food you plan on storing there.... which is the other big concern: mixing food storage with corrosive and poisonous substances, I wouldn't do it.

    I'd prefer to have a separate storage for the batteries outside.
  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    Re: Battery storage and ventilation

    ...regarding ventilation, the European standard EN 50 272-2 uses the formula:

    Q=v·q·s·n· lgas·Crt·10^-3[m3/h]

    Q = minimum air flow in m3/h
    v·q·s = 0.05 m3/Ah
    n = number of cells in the battery
    lgas = gas value specific to type of battery mA/Ah
    Crt capacity in C10 in Ah

    lgas during float charge on FLA batteries = 5, and 1 for AGM/Gel
    lgas during absorb/bulk for FLA = 20 and 8 for AGM/Gel

    800Ah FLA battery at C10, and 48V (so 24 cells)
    n = 24
    lgas (during absorb) = 20
    Crt = 800

    So Q = 0.05 * 24 * 20 * 800 * 10^-3 = 19.2m3/h

    Area of opening needed for natural ventilation = A = 28 * Q [cm2]
    So that would be 28 * 19.2 = 537cm2 = 83 square inches.

    Got the above from here (Spanish):
  • TheBackRoads
    TheBackRoads Solar Expert Posts: 274 ✭✭
    Re: Battery storage and ventilation

    I would do what Bill suggested, build an insulated box in the cellar if you are OK with giving up some of that small 4x8 space with a vent to the outdoors.
  • System2
    System2 Posts: 6,290 admin
    Re: Battery storage and ventilation

    All of you have brought up some good points. Certainly, I've thought carefully about various options for battery storage. One logistical problem I failed to mention. I access this cellar from inside the cabin. Cabin floor to cellar floor = 12 feet. Obviously, the weight of the batteries poses logistical considerations with simply trying to get them into the cellar. But, cellar construction was due to wildlife considerations, primarily bear. So, it's like a mini vault.
    As I consider all the options, I think a separate storage area may be the wiser choice. Daily outside temps vary from -20 in Jan. to +75 in Aug.
    The cabin is primarily a weekend place in winter and nearly a full time place in summer. As some of my work can be done from home, I want the ability to run my laptop about 6 hrs/day and lights about 4 hr/night. I have a sizing chart to help estimate AH/day use but my calculations seem unrealistic as far as recommended storage capacity. I also have a 400 watt wind turbine. My thoughts are to start with 800 AH storage capacity. I need a minimum of 400 AH capacity just for the wind turbine. Then, go from there.
    Does anyone have any other suggestions?

  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Battery storage and ventilation

    I would posit that the batteries are not going to heat up enough with charging and discharging to effect heat in the cellar very much. I think the cooler battery space is a real advantge, in spite of te reduced capacity.

  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: Battery storage and ventilation

    Time of use of the laptop etc is important in sizing the system.

    If you use the majority of your power in the daytime ( after bulk charge is over) and when the sun is up, you will essentially be using 'free' or wasted power that the PVs will not be putting into the batteries, once the bank is ~ 90% charged.

    Remember that once Bulk is finished the Charge controller lowers the total input to the batteries when it enters Absorb and further reduces input when in Float. The last 10% is a slow process.

    I recommend you go over to the Midnite Solar BB, and read some of the discussions about runaway turbines, very enlightening and somewhat scarey as to what can happen. A lot more complex than it may seem. Several levels of fail safe protection needed.

    As to the Cellar height, that is a major impediment to installing large batteries, if you have a less onerous option it may be the better choice. A chain hoist comes to mind.

    Lights: at least CFLs or better yet LEDs

    If you list your choice of components we will be able to evaluate it as a whole.

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