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  • Solar Wiring

    Here is some background information about my project. My solar project is 45kW DC with three SE11400H, and one SE5000H SolarEdge inverters with 400-watt optimizers for 39.2kW on the AC side. I have 120 Mission Solar panels at 375 watts. My racking is an iron ridge ground mount and going to be 5 modules high in one row of approx 160ft.

    My question is about the proper wire size for this project. My distance to the meter and service panel is about 400ft. According to my research I have done, the optimizers essentially condition to power by changing the voltage and match the current from the panels to hit the operating voltage of the inverters. The SE11400H is 400 volts, and SE5000H is 380 volts. My thinking is to have 3 separate strings of 12 panels for the SE11400H and 1 string of 12 panels for the SE5000H. Now I'm told to take the wattage of the string which is 12 panels x 375 watts = 4,500 watts and divide that by normal operating voltage of the inverter which is 400 or 380. Doing that by 380, I get 11.84 amps and 400, I get 11.25 amps. I'm rounding both of those numbers up to 12 and using a voltage drop calculator I get a 4.74% drop with 12awg and 2.98% with 10awg.

    A. Am I doing the correct calculation for the wire size? B. Do I need to take anything else into consideration besides the cost of wire? C. If I went with 10AWG wire stranded, can I use that for all the wire hookups? For example; wiring from panels to the inverter and the wiring from the inverter to the main service panel?

    Sorry for the long possibly confusing post, but any help would be greatly appreciated.

  • #2
    I am assuming your grid tie inverters are near the meter, so that most of the distance is run
    by the higher 400VDC wiring. My preference would be to keep DC voltage drop near 1%
    using larger gauge wire. Convention for multiple strings to an inverter is use a combiner box
    at the array to combine strings to an inverter, then use a heavier pair (probably in conduit) to
    cover the long run. Dual ckt combiners such as mine are available for 2 inverters.

    Can not tell what your snow situation is, but there are things you can do with a panel ground
    mount to lessen snow impact. If clearing them is anticipated, multiple array rows 2 or 3 panels
    high would work better, and spaces between landscape panels along with adequate ground
    clearance will really help. Some more stuff here on [B]Snow Tolerant PV Mounting[/B]

    good luck, Bruce Roe
    Last edited by bcroe; 05-01-2019, 09:57 AM.

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    • #3
      Originally posted by bcroe View Post
      I am assuming your grid tie inverters are near the meter, so that most of the distance is run
      by the higher 400VDC wiring. My preference would be to keep DC voltage drop near 1%
      using larger gauge wire. Convention for multiple strings to an inverter is use a combiner box
      at the array to combine strings to an inverter, then use a heavier pair (probably in conduit) to
      cover the long run. Dual ckt combiners such as mine are available for 2 inverters.

      Can not tell what your snow situation is, but there are things you can do with a panel ground
      mount to lessen snow impact. If clearing them is anticipated, multiple array rows 2 or 3 panels
      high would work better, and spaces between landscape panels along with adequate ground
      clearance will really help. Some more stuff here on [B]Snow Tolerant PV Mounting[/B]

      good luck, Bruce Roe
      I'm not super familiar with a combiner box, but for example it takes the 3 strings of DC for one inverter and combines them into 1 coming out into the inverter? If that is the case what happens to the voltage and amps when you combine all three into one? Do you have to add those together?

      Comment


      • #4
        Originally posted by Hunter View Post

        I'm not super familiar with a combiner box, but for example it takes the 3 strings of DC for one inverter and combines them into 1 coming out into the inverter? If that is the case what happens to the voltage and amps when you combine all three into one? Do you have to add those together?
        What is your snow situation?

        Same voltages tied in parallel, amps add up. Once you transition to conduit, you will not be using
        PV outdoor rated wire. You need to bring in someone with more experience on this project, which
        certainly has fatal level hazards. Bruce Roe

        Comment


        • #5
          Originally posted by bcroe View Post

          What is your snow situation?

          Same voltages tied in parallel, amps add up. Once you transition to conduit, you will not be using
          PV outdoor rated wire. You need to bring in someone with more experience on this project, which
          certainly has fatal level hazards. Bruce Roe
          SE Minnesota, so snow is definitely a concern. I've have an electrician who will be here and a structural engineer for the racking. I'm just trying to lay out the plan exactly so I know what to expect.

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          • #6
            I am in northern IL, not far from you at 42 deg Lat., with similar array and distances. If
            you build the simplest possible array arrangement as you described, it will be very
            vulnerable to snow accumulation, and will join so many northern installations which lose
            most of their snow season production. That may not be so much, given the winter clouds.

            If you add spacing around and under panels as I have shown, it will be much easier for
            panels to clear themselves on sunny days. If you use my summer/snow season tilt
            positions, the potential production will increase, and the panels will collect far less snow.

            Building lower arrays (not 5 high) will not use more ground space after you include the
            space in front that must be clear of shadows. That would allow cleaning them by hand
            after a storm, with FAR LESS time and effort as happens here.

            Your electrical design needs standard safety devices, as an installer would know and
            your local regs and PoCo net metering permit would require. good luck, Bruce Roe

            Comment

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