A little help

Gregb
Gregb Registered Users Posts: 11 ✭
in Solar Beginners Corner #1
12 Renogy 100 watt mono panelsl 18.9 VMP 22.5 Voc 5.29 amps IMP 5.75 ISC
outback Flex 80 max input volts 150
24 volt battery bank
I read on another forum,that with a MPPT charge controller the best voltage to run out of my panels is 15v to24 volts above the voltage of my battery bank. Is this correct? if not can I run three strings of 4 panels in series using the 22.5 voc the voltage would be 90 volts. Using VMP of 18.9 =75.6 volts . Next with 1200 watts max from panels am i limited to 1200 watts on my pure sine wave 24 volt inverter Now at best my amps from the panels would be 63.48 amps is there a rule for sizing my 24 volt battery bank so I get the best proformance from this system? As I said I can use a little help.
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  • Photowhit
    Photowhit Solar Expert Posts: 6,006 ✭✭✭✭✭
    #2
    Re: A little help
    Gregb wrote: »
    ...with a MPPT charge controller the best voltage to run out of my panels is 15v to24 volts above the voltage of my battery bank. Is this correct?
    Typically MPPT charge controller are most efficient at about double the battery voltage for an input.
    Gregb wrote: »
    if not can I run three strings of 4 panels in series using the 22.5 voc the voltage would be 90 volts.
    You can, the charge controller may not be at it's most efficient, but there are other reasons you might want to run a higher voltage to the charge controller, one of which would be if your panels are a long distance form your charge controller.
    Gregb wrote: »
    Next with 1200 watts max from panels am i limited to 1200 watts on my pure sine wave 24 volt inverter?
    No you can run any size inverter, they essentially run from the batteries.
    Gregb wrote: »
    Now at best my amps from the panels would be 63.48 amps is there a rule for sizing my 24 volt battery bank so I get the best proformance from this system?
    Typically you want to charge flooded lead acid batteries, like golf cart batteries, at 5-13%. I would expect about 80% of your panel rating as the max your array will produce. 1200 watts x .8 / 24v = 40 amps which would be a nice pairing with 4 - 340amp hour L16s or OK with 2 strings of 4 golf cart batteries.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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  • Gregb
    Gregb Registered Users Posts: 11 ✭
    #3
    Re: A little help

    Thank you for your help.
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  • SolarPowered
    SolarPowered Solar Expert Posts: 626 ✭✭✭
    #4
    Re: A little help
    Gregb wrote: »
    12 Renogy 100 watt mono panelsl 18.9 VMP 22.5 Voc 5.29 amps IMP 5.75 ISC
    outback Flex 80 max input volts 150
    24 volt battery bank
    I read on another forum,that with a MPPT charge controller the best voltage to run out of my panels is 15v to24 volts above the voltage of my battery bank. Is this correct? if not can I run three strings of 4 panels in series using the 22.5 voc the voltage would be 90 volts. Using VMP of 18.9 =75.6 volts . Next with 1200 watts max from panels am i limited to 1200 watts on my pure sine wave 24 volt inverter Now at best my amps from the panels would be 63.48 amps is there a rule for sizing my 24 volt battery bank so I get the best proformance from this system? As I said I can use a little help.

    You want (2) 6 panels in parallel string, then connecting the (2) parrallel strings of 6 in series for the best results, for a 24 volt system.
    Each string will produce 12V then once you merge those 2 parrallel strings in a series it will multiply by (2) for 24V
    ISC is not the power factor for your amps to the MPPT your IMP is which I would assume is 5.54IMP based off of 5.75Isc
    6 X 5.54=33.24 amps

    (2) strings in parrallel then connected in series would yield 37.8 Vmp

    You really only need a Outback Power Flex 60Mppt you don't need the 80Mppt
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  • Photowhit
    Photowhit Solar Expert Posts: 6,006 ✭✭✭✭✭
    #5
    Re: A little help

    Greg, I hope you saw my faux pas, the strings of 4 - 12 volt nominal panels would likely be the most efficient for charging a 24 volt battery with a MPPT type charge controller, but as I said there might be other reasons for running higher voltage to the controller, like a long wire run.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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  • SolarPowered
    SolarPowered Solar Expert Posts: 626 ✭✭✭
    #6
    Re: A little help
    Photowhit wrote: »
    Greg, I hope you saw my faux pas, the strings of 4 - 12 volt nominal panels would likely be the most efficient for charging a 24 volt battery with a MPPT type charge controller, but as I said there might be other reasons for running higher voltage to the controller, like a long wire run.

    My bad, amps are to high in (2) parallel strings, increasing voltage drop, (3) parallel strings much better.

    Either way he only needs a 60MPPT not an 80MPPT.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #7
    Re: A little help
    SolarPowered wrote: »
    You want (2) 6 panels in parallel string, then connecting the (2) parrallel strings of 6 in series for the best results, for a 24 volt system.

    Noto bene:

    When constructing strings of panels for an array, they go in series not parallel. The strings of panels in series are then connected in parallel.

    Do not put them in parallel first and then connect them in series.
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  • SolarPowered
    SolarPowered Solar Expert Posts: 626 ✭✭✭
    #8
    Re: A little help
    Cariboocoot wrote: »
    Noto bene:

    When constructing strings of panels for an array, they go in series not parallel. The strings of panels in series are then connected in parallel.

    Do not put them in parallel first and then connect them in series.

    You're right. I didn't think that through.
    That would offer 5.45 IMP per string, then in parallel would make 16.35Imp further reducing conductor size and voltage drop.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #9
    Re: A little help
    SolarPowered wrote: »
    You're right. I didn't think that through.
    That would offer 5.45 IMP per string, then in parallel would make 16.35Imp further reducing conductor size and voltage drop.

    To say nothing of elimination a lot of extra fuses. ;)
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