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High volt panel vs lower volt

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  • High volt panel vs lower volt

    I see newer 325 watt panels for the same dollar cost as 200 something watt panels.

    The high watt panels typically state for grid tie.

    I want a battery system only.

    If they are the same cost. And exterior dimensions don't matter.

    Why would you buy lower watt panel for the same money?

  • #2
    Use a MPPT controller for GTI panels.
    MSEE, PE

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    • #3
      Originally posted by Douglas View Post
      I see newer 325 watt panels for the same dollar cost as 200 something watt panels.
      The high watt panels typically state for grid tie. I want a battery system only.

      If they are the same cost. And exterior dimensions don't matter.
      Why would you buy lower watt panel for the same money?
      The "battery" panels may be closely matched to the battery voltage, so that a pulse width charge controller
      can be reasonably efficient. Once you go for a MPPT controller, you can get maximum efficiency without
      critical voltage matching; then go for the cheaper panels. Bruce Roe

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      • #4
        Because the higher voltage may be a poor fit for system design.

        Lets take my situation in Wyoming. State code requires us to derate the input voltage of charge controllers by 1/3 because of cold temps. So a charge controller normally rated at 150V input means we can only have a string voltage of 100 VOC.

        A 325W panel with a VOC of 60 would only allow us 1 panel in a string or an array voltage of 60. Where as a 200W panel with a VOC of 33 would allow me to run 3 in a string. Running an array voltage of 99 would allow for smaller wiring and possible better effiecency through the MPPT charge controller.

        WWW

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        • #5
          Originally posted by Wy_White_Wolf View Post
          Because the higher voltage may be a poor fit for system design.

          Lets take my situation in Wyoming. State code requires us to derate the input voltage of charge controllers by 1/3 because of cold temps. So a charge controller normally rated at 150V input means we can only have a string voltage of 100 VOC.

          A 325W panel with a VOC of 60 would only allow us 1 panel in a string or an array voltage of 60. Where as a 200W panel with a VOC of 33 would allow me to run 3 in a string. Running an array voltage of 99 would allow for smaller wiring and possible better effiecency through the MPPT charge controller. WWW
          It sounds like that is a situation somewhat unique to states like Wyoming. Those areas
          may need a higher voltage rated MPPT to maintain wiring efficiency. However, most
          panels don't run 60 Voc. The grid tie panels in use here run 36 Voc or 42 Voc. With some
          choice of panels and controllers, an efficient solution using cheaper panels can be
          worked out. Bruce Roe

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          • #6
            Yes. I was just using those numbers as an example to answer the OP's question. Even 36 to 42 VOC panels would still only let me run 2 in series.

            I do like the higher voltage midnight controllers, but trying to sell them to someone that reads all the rants and raves about Outback or Xantrax can be a little hard. If not impossible.

            WWW

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            • #7
              NEC Table 690.7 shows the derate required for cold temps. Keep in mind that's record cold, not average cold. Midnite has a nice writeup about over voltage behaviors of charge controllers, and includes the table here, http://www.midnitesolar.com/pdfs/whyHyperVOC.pdf

              What is the VOC of the 315W panel you are looking at? Multiply it by the derate factor that matches your temp in the table. Let's use 44Voc x 1.25 for -40F = 55Voc temp derated. Most MPPT charge controllers can handle 150Voc temp derated. 150V / 55V = 2.7, so up to 2 in series can be used. If you use a typical ~38V panel, which will probably be under 300W, 38Voc x 1.25 = 47.5, 150V / 47.5V = 3.15, up to 3 in series.

              The higher voltage charge controllers are lower amperage, so while you may be able to do more in series, the overall number of panels it can handle may be smaller.

              Schneider and Morningstar also make 600V charge controller, for much more money. But if you have a long distance to run, it may be worth it.
              Solar Queen
              altE Store

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              • #8
                Originally posted by Wy_White_Wolf View Post
                Yes. I was just using those numbers as an example to answer the OP's question. Even 36 to 42 VOC panels would still only let me run 2 in series.

                I do like the higher voltage midnight controllers, but trying to sell them to someone that reads all the rants and raves about Outback or Xantrax can be a little hard. If not impossible.

                WWW
                Oh, they sell, they sell a lot.
                Solar Queen
                altE Store

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