Wire Sizing need

Jeromeds
Jeromeds Registered Users Posts: 13 ✭
in PV Installers Forum - NEC, Wiring, Installation #1
my (3) Kyocera 7.63 amp panels are in series and only provide about 50 amps in good sun. My wire is #8 which may be my problem. I have 55' btwn panels and batteries in 12v system. Should I go up to #4 wire or move panels closer to batteries or try to change system to 24v?

(1) 80w panel to mark 15 controller @ #12 wire
(2) kyocera 135w to tri star 45 non mpp controller at #8 wire
sunforce 2500w inverter
backup 5000w generac w/IOTA 45
(4) interstate 220AH batteries
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Wire Sizing need
    Jeromeds wrote: »
    my (3) Kyocera 7.63 amp panels are in series and only provide about 50 amps in good sun. My wire is #8 which may be my problem. I have 55' btwn panels and batteries in 12v system. Should I go up to #4 wire or move panels closer to batteries or try to change system to 24v?

    (1) 80w panel to mark 15 controller @ #12 wire
    (2) kyocera 135w to tri star 45 non mpp controller at #8 wire
    sunforce 2500w inverter
    backup 5000w generac w/IOTA 45
    (4) interstate 220AH batteries

    No.
    If you have three of the panels in series their current is 7.63 Amps; only the Voltage goes up (53.1 Vmp).
    You have a "non MPPT" controller (PWM) so the panels must be in parallel: Imp 3 * 7.63 = 22.89. 50 Amps doesn't come in to it anywhere.
    So for wire sizing you are trying to accommodate 22.89 Amps @ 12 Volts over 55 feet. 8 AWG will use up about 13% of your Voltage, and that's no good. For those specs you need 1 AWG or larger to get the V-drop under 3%.
    If you can move the charge controller & batteries closer to the panels then do so. With an odd number of "12 Volt" panels (3) you can't do a 24 Volt system on a PWM controller; you need two in series to make the right array Voltage, so that's a minimum of four panels. Plus you would have to change the inverter.
    The only other option is to change the controller to an MPPT type and put all three panels in series. That would drop the wire size between array and controller to 10 AWG.
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  • Jeromeds
    Jeromeds Registered Users Posts: 13 ✭
    #3
    Re: Wire Sizing need

    Thanks. What would you do? $200 for wire or $400 for MPPT 45? FYI, I am shooting for 1000 usable watts from sun after line loss and inverter consumption.
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #4
    Re: Wire Sizing need
    Jeromeds wrote: »
    Thanks. What would you do? $200 for wire or $400 for MPPT 45? FYI, I am shooting for 1000 usable watts from sun after line loss and inverter consumption.

    If you are not already doing it, use Aluminum wire (properly sized larger than the equivalent amp copper) and AL rated terminations to cut the wire cost considerably.
    SMA SB 3000, old BP panels.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #5
    Re: Wire Sizing need
    Jeromeds wrote: »
    Thanks. What would you do? $200 for wire or $400 for MPPT 45? FYI, I am shooting for 1000 usable watts from sun after line loss and inverter consumption.

    What exactly do you mean by "1000 usable Watts"? 1kW hour AC per day? With three 135 Watt panels it's barely possible: 405 Watts * 5 hours good sun * 0.52 efficiency = 1053 Watts hours AC

    Your 220 Amp hour batteries arranged for 12 Volts would be 440, and you'd want 44 Amps peak potential. That will not come from three 135 Watt panels. At possibly 22 Amps max your charge rate would be only 5%. With an MPPT controller you might see 26 Amps or 5.9%. Or in other words you've got about half as much panel as you need for that battery bank.
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