Battery Bank underground in concrete structure, good idea?

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logaholic
logaholic Registered Users Posts: 9 ✭
in Off Grid Solar & Battery Systems #1
I'm considering placing my battery bank in basically a septic tank with no lid. Basically 4 walls and a floor, leaving the walls approximately 12-18 inches above ground, with the rest of the tank being below ground. I would frame up a wooden structure above the tank that would essentially be a hinged lid for the tank where the entire bank would be easily accessible, and allow for venting to be placed on a non-hinged portion. I would vent with a pvc pipe coming in through the "roof" and going to the floor on the intake side, then installing a vent fan on a pipe at the highest point in the structure. I have attached a rough image so you might have a better idea what I am considering.
Attachment not found.

Obviously the pipes coming out of the ground would be capped in a manner to allow flow but prevent water/insects from entering the enclosure.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #2
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    Re: Battery Bank underground in concrete structure, good idea?

    When dealing with possible explosive gases and flammable battery cases--I would suggest to design the structure with a "blow out" panel (weak panel) in the safe direction. If the lid is outdoors, that would be the obvious choice (i.e., don't build a "burglar proof bank vault lid" and leave the weak panel facing the home/garage). Fusing/breakering the battery feed is good too. I do like an emergency power disconnect--But finding ones rated for large battery banks can be difficult to find and expensive.

    And, I would try to ensure that any fire in the battery box would not light the wall on fire (use concrete siding, cement board interior to wooden structure in the box, etc.)...

    Hopefully, you will never have these issues--But creating safe structures and using distance (i.e., generator shed, fuel shed, PV power shed) can reduce the costs/effects if the worse does happen.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • logaholic
    logaholic Registered Users Posts: 9 ✭
    #3
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    Re: Battery Bank underground in concrete structure, good idea?

    Bill,
    Thanks for the response. The lid/roof would be a regular stick framed structure framed up and then covered with plywood/roofing, so in effect it would be a large blowout panel. This box will be about 50-100ft from the nearest structure (shed), and about 200ft from the house. Inverter/Charge Controller/Etc will be in a Nema enclosure close but not attached to this structure. The whole reason in going this route is to:

    1. Regulate battery temperature
    2. More importantly, isolate the system from our house, so in the event of any catastrophic failure the house and occupants would be safe.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #4
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    Re: Battery Bank underground in concrete structure, good idea?

    Sound good... Have you looked at running (120/240 VAC?) power to your home and any remote monitoring (charge controllers, battery bank state of charge, etc.) that far from your home? Will your system be near an "energy hog" (such as yur well head)?

    I can see 10-30 feet away--But that far may be making things more difficult/expensive.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • logaholic
    logaholic Registered Users Posts: 9 ✭
    #5
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    Re: Battery Bank underground in concrete structure, good idea?

    I have considered it, but I will either be running wires from the panels that far, or the AC wires, so the cost is negligible really. Our well is solar with it's own array, so it will not draw any power from the house.
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  • 97TJ
    97TJ Solar Expert Posts: 68 ✭✭
    #6
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    Re: Battery Bank underground in concrete structure, good idea?

    I thought this was an interesting article on venting. http://http://www.bdbatteries.com/hydrogenventing.php
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  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    #7
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    Re: Battery Bank underground in concrete structure, good idea?

    Great idea - I did the same :)http://www.casanogaldelasbrujas.com/blog/2009/05/17/generator-exhaust-expansion-chamber/
    The original idea was for 2 reasons: keep the batteries cool and block the sound of the diesel gen. That was way back in the day when I still planned on relying on diesel... in the meantime I bought more solar, the diesel turned into a doorstop so now it's just a battery/electric bunker.

    It's been very good with temperature, today was 30 degrees C outside, but my batteries were at 19 C max. Might make wine in it next year :)
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #8
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    Re: Battery Bank underground in concrete structure, good idea?

    One rather important thing to consider - - - will the sun be shining on the exposed concrete parts and the lid?
    A little story: When I had my well dug and the concrete "pipes" and concrete lid installed, the lid and about a foot of the top section was above ground and exposed to the sun. Well I found by mid summer, the well water was getting warm, wondered why and went to the well to check things out. Lifted off the lid and lo-and-behold, it was like a solar oven in there! Covered the whole thing with plastic to keep it clean, then covered the works with sawdust and earth. By fall, everything had cooled down, and ever since then, the water has stayed cool, no matter how hot the summer.
    Something to think about. Even an open shed roof to keep the sun off would be a huge help.
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  • logaholic
    logaholic Registered Users Posts: 9 ✭
    #9
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    Re: Battery Bank underground in concrete structure, good idea?

    The box will likely be in the shadow of one of my pole mounts, so that will help, and I had planned on insulating the sides and top to help.

    Thanks for all the ideas, I think this will be a great solution to this problem. I will try to post pictures as we make progress this summer on this.
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  • 2manytoyz
    2manytoyz Solar Expert Posts: 373 ✭✭✭
    #10
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    Re: Battery Bank underground in concrete structure, good idea?

    My concern would be the hassle of performing maintenance. I check the water levels in my batteries every month, and clean the cases and connections as needed. For that reason, my battery bank sits on a 36" tall workbench. If you made it like a shallow mechanic's pit, with a couple of steps down to a working level, might work out great.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #11
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    Re: Battery Bank underground in concrete structure, good idea?

    of concern may be accumulated moisture or cold temps conducted from the bottom. the batteries would benefit from being slightly elevated off of the bottom. no they won't self discharge, but i am one that agrees that water and electricity often don't mix well. besides the added space could allow for a cracked case and contain the acid spill without contaminating the others.
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