Battery bank vs. PV input

NZRR
NZRR Registered Users Posts: 28 ✭✭
in Advanced Solar Electric Technical Forum #1
Is there an easy way to determine the balance between the battery bank size and the PV production? As an example, I will shortly have 3720 watts of PV on my roof, and 900 AH of battery capacity. My main concern is being able to completely charge the batteries with a day or two of sun, and not have to use the generator. Any suggestions would be appreciated.
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  • AntronX
    AntronX Solar Expert Posts: 462 ✭✭
    #2
    Re: Battery bank vs. PV input

    Voltage of your system?
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #3
    Re: Battery bank vs. PV input

    Fire ! Ready ! Aim!

    NZRR wrote: »
    Is there an easy way to determine the balance between the battery bank size and the PV production? As an example, I will shortly have 3720 watts of PV on my roof, and 900 AH of battery capacity. My main concern is being able to completely charge the batteries with a day or two of sun, and not have to use the generator. Any suggestions would be appreciated.


    Your charging amps, should be about 10% of your battery amps, so if you have 900A of battery, you need 90A of charging. That keeps current limit below plate warping heat, and still enough amps to stir / bubble electrolyte in the EQ cycle.

    What you haven't told us, is the battery voltage, and the array voltage, if all batteries are in series, or parallel, or series-parallel combo. What is your charge controller, and how cold in winter, and hot in summer . Those all affect the PV voltage and how to set it up with the charge controller.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
    Re: Battery bank vs. PV input

    Basic, "starting point" formula used for off-grid:

    Battery Amp/hrs ('20 hr rate') * 10% = Target Charging Current
    TCC * charge Voltage = effective array Watts needed
    Watts / system efficiency (typically 80%) = total array size

    Without the system Voltage, this is as close as anyone can come to an answer.
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  • NZRR
    NZRR Registered Users Posts: 28 ✭✭
    #5
    Re: Battery bank vs. PV input

    My system voltage is 48. I have an Apollo T80HV and the batteries will be two banks of 8 Rolls S600s connected in parallel (450 Ah for each bank). I am using UniSolar PVL-124s, three in series for 90 volts, with 10 arrays, which should generate up to 40 amps. It gets to around 86 degrees on average in the summer, and to maximum -32 degrees (F) in the winter. Thanks for the input.
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  • dmiller
    dmiller Solar Expert Posts: 68 ✭✭✭✭
    #6
    Re: Battery bank vs. PV input

    This thread had good discussion from the opposite imbalance. If you two were neighbors solar perfection would be within reach. :)
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