I need help on solar panels connection

lockwood
lockwood Registered Users Posts: 4
in General Solar Power Topics #1
My question is, can I charge a bank of four 12v batteries in parallel with these solar panels ;

Pm 230 Watt
Vamp 30.0v
Imp 7.66 Amp
Voc 37.0 Volt

These panels are connected in parallel.

Anybody please help.
Thanks
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: I need help on solar panels connection

    Well yes, but then again no. :p

    The Vmp of the panels is 30, which is well above 12 Volts and therefor capable of charging them. The problem is it is too well above, so with a conventional charge controller much of the panels' power will be lost. Instead of realizing 230 Watts from them you will get something like 7.66 Amps * 14.4 (charging) Volts or 110 Watts. Now that isn't a problem unless you need that extra Wattage.

    The solution here is to use an MPPT type charge controller which can down-convert the higher-than-necessary Vmp and turn it into extra charge Amps if needed.

    The other question would be how many 12 Volt batteries and of what capacity? That will determine the amount of power needed for recharging and whether or not there would be any current-sharing difficulties caused by multiple batteries.
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #3
    Re: I need help on solar panels connection

    Here's a thread to read which explains why 4 batteries in parallel is a bad idea:
    http://forum.solar-electric.com/showthread.php?14674

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • GreenPowerManiac
    GreenPowerManiac Solar Expert Posts: 453 ✭✭✭
    #4
    Re: I need help on solar panels connection

    Why not hookup both pairs in series to achieve 24v nominal, then both sets in parallel with a 24v charge controller ?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #5
    Re: I need help on solar panels connection
    GreenPowerManiac wrote: »
    Why not hookup both pairs in series to achieve 24v nominal, then both sets in parallel with a 24v charge controller ?

    Same problem; different scale.

    For a 24 Volt system the panel Vmp of 30 is too low. Put two in series and it's too high (and too low for a 48 Volt system). With these "grid tie" panels you either use an MPPT controller for battery charging or you throw away much of the power.

    But yes, if you've got a lot of 12 Volt batteries in parallel going up in system Voltage is a good idea if at all possible: http://forum.solar-electric.com/showthread.php?15989-Battery-System-Voltages-and-equivalent-power
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  • GreenPowerManiac
    GreenPowerManiac Solar Expert Posts: 453 ✭✭✭
    #6
    Re: I need help on solar panels connection

    Coot, where is Lockwood getting these specs from ? Number of panels looks like one, yet says, "Panels", more than one. Every panel I've seen either works for a 12v,24v, or 48v system and the rest was the appropriate sized charge controller and battery setup. 37 volts open circuit sounds about right with no load.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #7
    Re: I need help on solar panels connection

    37 Voc is a bit too low... You want ~30 volts to charge the battery bank, and on a not day, Voc will fall about ~20% (or 6-7 volts) which starts to reduce your voltage for battery charging--and forgetting voltage drop for wiring/charge controller. If you have "cold batteries" on a hot day--The battery charging voltage will be higher than the ~14.5 volts nominal too.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #8
    Re: I need help on solar panels connection

    When charging it's the Vmp that matters.
    Curiously Voc tends to be about 7 to 9 Volts higher than Vmp. My Sharp's have a Vmp of 35 and a Voc of 44. They are fine on a 24 Volt system (especially wired for nominal 48 through the MX60 :D ).

    The specs on the OP's panels look like KD230's to me.
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