Batteries, calculating dollars/month for off grid.

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Volvo Farmer
Volvo Farmer Solar Expert Posts: 209 ✭✭✭✭✭
in Advanced Solar Electric Technical Forum #1
I'm doing this exercise because it's time to replace batteries. Looking for 24 volt 800ahr options.

Known: Surrette S530s lasted 72 months. Cost to replace eight with the same $3000 or $42/month.

Option one: Replace with the same, rinse and repeat in six years.

Option two, Buy sixteen Sams GC2 batteries for $1400. At $42/month I need to get 33 months out of them before I'm ahead. I'm dollars ahead at three years and if I can get four years out of them, my battery costs drop to less than $30/month.

Option three. Buy a HUP Solar one. $5200 for 845 ahr. At $42/month, I need to get over ten years out of it to come out ahead. To get to $30/month, A HuP would have to last 14 years.

I know that four strings of parallel GC2 batteries is not ideal and that a single string of 2V cells like the HUP has is much better. However, batteries are dying every time you cycle them. If my goal is $30/month, it seems easier to get four years out of cheap batteries than 14 years out of expensive ones.

Looking for comments, insights, ideas or experience. Thanks
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  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,746 ✭✭✭✭✭✭
    #2
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    Re: Batteries, calculating dollars/month for off grid.

    The choice that is hardest is to use less energy. It is the number one thing that will make any battery design last longer! The other route is to use a higher capacity battery as you know! Good Luck !
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #3
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    Re: Batteries, calculating dollars/month for off grid.
    Volvo Farmer wrote: »
    Looking for 24 volt 800ahr options.
    <snip>
    it seems easier to get four years out of cheap batteries than 14 years out of expensive ones.
    Looking for comments, insights, ideas or experience. Thanks

    How about considering less than 800 AH? Perhaps its cheaper to get 4 years out of 400 AH than 6 years out of 800 AH. --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • ywhic
    ywhic Solar Expert Posts: 621 ✭✭
    #4
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    Re: Batteries, calculating dollars/month for off grid.

    I myself am going just double my guesstimated AH solar output for the day.. 45 IMP * 5 hours = 200 amps roughly..

    So my bank will be about 400 ah when I set it up.. I want my bank back to full every day.. so no uses over say a 40% mark.. also increases that cycle life by not killin the bank...

    I could safely also do 600 ah bank.. but I'm starting is at 400..
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  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    #5
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    Re: Batteries, calculating dollars/month for off grid.

    The choice depends on how young you are and how strong your back is.

    I too chose cheaper, easily available batteries for my system. As I get older though, the physical hassle of changing out batteries more often is not so appealing.
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