what kind of wire to extend from Solar Panel to Controller?

hmong2017
hmong2017 Registered Users Posts: 39 ✭✭
edited March 2018 in Solar Beginners Corner #1
I have 6 of 260W 24V Solar Panels. 
They are Parallel because I am using a 24V System.

Each module put out 8.37AMP 
I have a total of 50.22 AMPS 

As my previous question, I now have a Combine Box with appropriate Breakers. 

So next question is, what kind of PV wire to use from the Combine box to the Charge Controller? 
My extension is 90FT at least.
I was thinking to go with 8 AWG PV wires. Will this do?
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  • MichaelK
    MichaelK Registered Users Posts: 236 ✭✭✭
    #2
    What kind of charge controller do you have?  If you have a MPPT type controller, you can wire three panels in series (two arrays).  With the higher voltage of series wiring, you can use smaller gauge wire.
    System 1) 15 Renogy 300w + 4 250W Astronergy panels,  Midnight 200 CC, 8 Trojan L16 bat., Schneider XW6848 NA inverter, AC-Delco 6000w gen.
    System 2) 8 YingLi 250W panels, Midnight 200CC, three 8V Rolls batteries, Schneider Conext 4024 inverter (workshop)
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    edited March 2018 #3
    what is the Vmp of your panels ? 

    I think you are making a poor move running panels in parallel.   Getting a name brand 60A MPPT controller will cost less than the expense of buying 200' of heavy  2ga copper wire for your DC run

    Going in series, 3SpP array, you could use 200'  #10 or #8 wire
    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

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  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    #4
    The Vmp is important because from the sounds of it they are 60 cell panels which cannot be used with a 24V PWM controller, which the parrallel arrangement would suggest, getting a MPPT controller is more a requirement rather than an option, that being said I have seen 60 cell panels with a Vmp of 37V which seemed odd.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
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  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,109 ✭✭✭✭✭
    #5
    mcgivor said:
    The Vmp is important because from the sounds of it they are 60 cell panels which cannot be used with a 24V PWM controller, which the parrallel arrangement would suggest, getting a MPPT controller is more a requirement rather than an option, that being said I have seen 60 cell panels with a Vmp of 37V which seemed odd.

    Some of the higher powered (300+ watts) 60 cell panels have higher voltage than older, lower watt panels. So it seems the lines have blurred as to whether a 60 cell panel is appropriate for 24 volt charging. The 260 watt panels in question are, well, questionable.

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric,  460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.

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  • MichaelK
    MichaelK Registered Users Posts: 236 ✭✭✭
    #6
    If these 260W panels are putting out 8.37A, then we can assume their Vmp is ~31.06V.  That's marginally adequate for charging a 24V battery bank, but not in really hot weather, and not enough to properly equalize.  You will get better results wiring the panels at least 2 in series, but you have to use an MPPT controller for that.

    Getting back to the original question, here is a link to a ampacity table.
    https://xtronics.com/wiki/Wire-Gauge_Ampacity.html
    If the wire is enclosed, 8 gauge only has a max capacity of 46amps, so no, it isn't adequate.  Getting back to running your panels in series, if using a 3S2P configuration, you'd be producing <17amps at 93V, so 8 gauge would be more than adequate.  In the real world, you might never actually see full amperage, but you are working around the ragged upper edge, which is never advised.

    System 1) 15 Renogy 300w + 4 250W Astronergy panels,  Midnight 200 CC, 8 Trojan L16 bat., Schneider XW6848 NA inverter, AC-Delco 6000w gen.
    System 2) 8 YingLi 250W panels, Midnight 200CC, three 8V Rolls batteries, Schneider Conext 4024 inverter (workshop)
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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #7
    Just to clarify, it isn't just a problem of wire ampacity, the voltage drop in a parallel config may be too high to get charging voltage unless using really heavy wire.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
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  • MichaelK
    MichaelK Registered Users Posts: 236 ✭✭✭
    #8
    Oh, 90 feet.
    Using this voltage drop calculator on the distance mentioned
    http://www.calculator.net/voltage-drop-calculator.htm
    you loose 5.65 volts.  That drops the end voltage down to 25.35, which will NOT adequately charge your 24 volt bank.

    Using the same calculator, it shows you don't get above 29.5V till you use 2 gauge wire


    Like everyone is saying, you need to go serial and MPPT.

    System 1) 15 Renogy 300w + 4 250W Astronergy panels,  Midnight 200 CC, 8 Trojan L16 bat., Schneider XW6848 NA inverter, AC-Delco 6000w gen.
    System 2) 8 YingLi 250W panels, Midnight 200CC, three 8V Rolls batteries, Schneider Conext 4024 inverter (workshop)
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,623 admin
    #9
    Also remember that warm to hot solar panels (pretty much all solar panels except in sub freezing weather are "hot" under mid-day sun) run around 0.9 to 0.82x Vmp(stc) standard test conditions. So, before you even have wiring voltage drop, the Vmp-array-hot is something like:
    • 31 volts * 0.90 warmish panel derate = 27.9 volts (Vmp-array can be ~5-10% higher and a bit less current)
    • 31 volts * 0.82 hot panel derate = 25,42 volts (can be upwards of +5-10% because of "soft" IV cure peak)

    You really need an STC rated Vmp-array~17.5-20 volts (12 volt battery bank) or ~35-40 volts (24 volt battery bank) for a PWM charge controller.

    When you add long wire runs and/or an MPPT charge controller, then you are looking at 45-50+ volts Vmp-array-stc (standard test conditions) minimum.. It is pretty common practice to run a MPPT controller Vmp-array input at ~2x nominal battery operating voltage (i.e. 24-30 volts (nominal-charging) volt battery bank ~48 to 60 volts).

    -Bill

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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