Wire size?

I have 3 sets of 4 sharp 208w panels wired in series for a 48v system and plan to add 1 more set of panels for 16 total. These are about 100 feet from my area where the battery bank, inverter and other equipment will be. I used a wire size calculator formula and came up with 2/0 awg wire for each set of 4 (100' x 2). This will make it a total of 800' of wire for the system. 800' x $3.00 foot for the wire = $2,400. This seems a little expensive to me. Does this seem to be the correct wire size? I might have to build a shed for the equipment and run AC to the house.
Also it does get a little confusing about the voltage. The no load voltage across the 4 panels is about 130 volts not 48. Any help would be greatly appreciated. Ken


  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Wire size?

    maybe your batteries are a 48v system, but your pvs as stated are not at 48v. each pv is rated for operational volts at 28.5v. now x4 is 114v. open circuit voltage is 36.1v per pv and x4 is 144.4v. i say this just to clarify what you have. now at 7.3amps i find that for your 100ft run(200ft of wire) #10 (1.51%) or even #12 (2.4%) could be used per string of 4 sharp 208s. now if you wish to combine all 4 strings into one run i get almost 2.4% using #6. it works because of the very high voltages you are working with when there are 4 of them in series.
    if you were to cut each string down to 2 in series then the wire resistance needs to be cut in half and that would mean a difference of 3 wire gauges so that the effective wire is physically larger now and that would be like going for example from #12 wire to #9 for the same current passing, but that would double the current too so do another 3 gauge numbers.
    btw, i should have run it as 96v on the pvs and not 114v and this ups the wire requirement slightly, but not enough to change the gauges i've mentioned. what i see here for you is 200ft of #6 and if you'd like to you can make it even better with #4 with a loss percentage of about 1.8% based on 96v per string and 4 strings at 7.3amps. that isn't for each string, but all of them together to be very clear.
    if it was the calculator here on naws that you had tried, i'd say you did something wrong.

    edit to add:

    having a short dc run to an inverter in a shed and then to the house with 120vac is a good option too, but you won't gain much in reduction of wire because you are using a high voltage in the first place.
    now about that high dc voltage, i do hope you are using a good downconverting mppt controller that can take that high of an input voltage as a standard pwm will not downconvert that voltage and most likely will not handle that high of an input voltage either.
  • System2System2 Posts: 6,290 admin
    Re: Wire size?

    (2) (distance) (amps) (k-value)
    _________________________________ =CM (cir. Mills)

    (% voltage drop) (voltage)

    I will use the calc. on this forum. Equipment I have purchased:
    Xantrex SW4048 Inverter
    Outback MX-60 Chg controller
    Xantrex 250A DC disconnect
    Outback pspv combiner box
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