Wiring 2 panels in series......not next to each other?

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porch13
porch13 Registered Users Posts: 68 ✭✭✭
in Off Grid Solar & Battery Systems #1
Hello solar gurus!

I'm getting ready to add a second panel to my RV setup which will be wired in series. With the roof layout, the only way to do it without potentially damaging to roof is to mount it at the other end of the trailer. THis would put the two panels connections 19 feet apart. Will this setup be okay if I'm using 10 ga. wire w/ MC4 connectors and the closest panel is roughly 10 feet from the charge controller?
Northern Arizona...4050 Watt off-grid system - Outback FP1 - Rolls 605 in a 48V bank
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
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    Re: Wiring 2 panels in series......not next to each other?

    The distance is not daunting. You can check for Voltage drop using your nominal panel Voltage and Isc across the wire. It would be something like 2X Voltage (48 ) and 1X Isc (7?) for those 210 Watt panels. I think the V-drop will be <1%.

    Of bigger concern is the difference in shading potential: a shadow at one end or the other will 'knock out' the whole string. Why would it not be possible to wire them in parallel? Changing the numbers for V-drop around it still looks like <3%, and the connections could be made with MC4 'Y' adapters perhaps.
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  • porch13
    porch13 Registered Users Posts: 68 ✭✭✭
    #3
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    Re: Wiring 2 panels in series......not next to each other?

    Thank you for the reply! Both panels will get full sun all day. The two panels in series should give 53.2V (Vmpp) and 8A (Impp). Since I have no shading worries, is there any benefit to running in parallel over series?
    Northern Arizona...4050 Watt off-grid system - Outback FP1 - Rolls 605 in a 48V bank
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,447 admin
    #4
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    Re: Wiring 2 panels in series......not next to each other?

    If you wiring can handle the parallel current and the MPPT charge controller can handle Voc-cold (open circuit voltage in cold weather)--It is almost a draw.

    A MPPT controller is slightly less efficient at higher voltages (maybe a percent or two?). But you have lower wiring losses which may save you a percent or two there--For a near "wash" overall...

    -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 ✭✭✭
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    Re: Wiring 2 panels in series......not next to each other?
    porch13 wrote: »
    Thank you for the reply! Both panels will get full sun all day. The two panels in series should give 53.2V (Vmpp) and 8A (Impp). Since I have no shading worries, is there any benefit to running in parallel over series?

    Yes: the Voc on these is about 33. Times two is 66. One cold morning it could exceed the maximum input Voltage for the Sunsaver which is 75. Along those lines the array Vmp at 50+ would be pretty far from the system nominal and as such efficiency will suffer a little as well.

    I'm not saying it won't work, just pointing out any little potential pitfalls in advance so you can consider them.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #6
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    Re: Wiring 2 panels in series......not next to each other?

    Wait a minute. This is a 12 Volt system on an MPPT 15 controller? You've already got 210 Watts on the controller. Adding another 210 Watts will be a waste as the controller can't handle that much. Basically 15 Amps * 14.8 Volts = 222 Watts, factor in derating and you've got 288 Watts maximum.

    Morningstar specifically recommends 200 +/- Watts on 12 Volts, 400 +/- on 24.
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  • porch13
    porch13 Registered Users Posts: 68 ✭✭✭
    #7
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    Re: Wiring 2 panels in series......not next to each other?

    Sorry for the confusion! When I add the second panel, I am upgrading to the Morningstar TriStar 45A MPPT controller.
    Northern Arizona...4050 Watt off-grid system - Outback FP1 - Rolls 605 in a 48V bank
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
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    Re: Wiring 2 panels in series......not next to each other?
    porch13 wrote: »
    Sorry for the confusion! When I add the second panel, I am upgrading to the Morningstar TriStar 45A MPPT controller.

    Then there's no problem at all. :D
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