PV: Re: Peter's PV Battery Box

[Ed <thefuhrmanns@cswebmail.com>]

Peter, 

     I'm presuming that the cabin will be unoccupied the majority of the time... but how periodic will your visits be? Will you be there every weekend, for instance, or only during certain hunting seasons for instance? You said you're looking for "optimum" temps... do you NEED optimum, or will acceptable/nominal do?

     I ask because part of how I manage my L-16HC temps includes re-discovering the moderating effects of "Thermal Mass". It takes several days for my 4-battery bank to decrease temp from 55 to 40 degrees (this in a (winter-average) 38-degree unheated garage.) The insulated battery-box is not THAT insulated: 3/4-inch plywood with 1" styro insulation, plywood lid is not-yet insulated (compound angles I haven't gotten around to yet). 

     If you use a super-insulated battery-box, kept in the cabin, your bank can be happy for quite a while (batteries can take cold temps OK if they're charged). Someone mentioned an earth-tempered box... that's really a good idea, especially since you're in the design phase. 

     I don't know the full-time residency potential of your cabin, or the intent of a potential buyer in the future, but you can design in  a small power-shed to house the (buried) bank, with a slab for generator mounting in the future, bury the lines to the cabin, keep everything neat now, and ready to expand with minimum add'l work if req'd. If the tree-line permits, the roof of the shed could be your PV-array mount. (What's the vandalism potential in that area?)  

     The alternative I would consider (since I have no qualms about sharing a house with my batteries) is to sink a battery "pit" similar to a floor safe in whatever corner of the cabin has the PV equipment (inverter, etc.) and combine the moderating effects of the earth with the sheltering potential of the cabin. 

     FWIW: when I DO have to juice up the temps, I use a 40-watt incandescent which is built into the box. From Radio Shack, I bought an indoor/outdoor digital thermometer which has a dual display so I can quickly see garage temp and battery temp. During the colder months, I keep the batteries between 40-50 degrees. Since your cabin is intended to be PV powered, this probably wouldn't work for you. 

     I'd over-design in insulation, however/wherever you place the bank; insulation is cheap. Anything involving moving parts (i.e.: hydronic pump to circulate water) is "asking for it" in a mostly unoccupied building. 

     Good luck, and post pictures when you're done!

Ed / N. IL

> -------------------------------------------------------------
> 
> Date: Tue, 16 Jan 2001 12:16:11 -0600
> From: Peter Hoyt <hoytp01@satx.rr.com>
> Subject: PV: Battery Box?
> 
> Hello,
> 
> I am designing a PV power system for my cabin. Currently, I'm concerned about battery housing. My present design, on paper only at this point, uses 8 Trojan L-16 batteries configured for 24 volts.
> 
> I would like to know if anyone has come up with a good way to provide optimum temperature conditions for their battery bank that doesn't involve a lot of energy just to maintain the temperature inside the battery container.
> 
> It gets very hot here in South Texas in the summer and often reaches a low in the 20s in the winter. Obviously I need to do something to moderate those conditions if I expect the batteries to last more than a year.
 
> Besides a well insulated container, what else can I do?
> I've thought about providing heat with a thermostatically controlled solar hot water system for the winter. That should be fairly practical. For the summer I've thought about doing the same sort of thing with well water to reduce the temperature of the batteries.
> 
> Does anyone have any advice or experience on the subject?
> 
> Thanks,
> Peter Hoyt
> San Antonio, Texas
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