Thin film bypass diode

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  • h_1985
    Junior Member
    • Sep 2015
    • 23
    #1

    Thin film bypass diode

    Hi,

    while i'm exploring some datasheets of thin film manufacturers i found that company like First Solar don't have bypass diode on their panels, but another manufacturer like Hanergy flexible panels i found that panel with 108 cells each cell have one diode and one diode in junction box!!

    my question about why not all thin film panels have bypass diodes ??
    Tags: bypass, diode, thin film
    • SunEagle
      Super Moderator
      • Oct 2012
      • 15126
      #2
      My guess is how those cells are wired together to create the desired voltage and current needed for the rating of the panel.

      If the cells are very low voltage you need a lot of them in series (which is maybe what First Solar is doing). But to get more current you have to wire those cells in parallel. That is when the diodes become important to keep from backfeeding the dc voltage into a parallel circuit..

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        • loobosh
          Member
          • Mar 2015
          • 40
          #3
          I just bought 16 Sanyo Hip 190 watt used, one was dead. Opened the junction box took out all four diodes, now works fine, panel will be in parallel should be ok.

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            • inetdog
              Super Moderator
              • May 2012
              • 9909
              #4
              Originally posted by SunEagle
              ... But to get more current you have to wire those cells in parallel. That is when the diodes become important to keep from backfeeding the dc voltage into a parallel circuit..
              You are talking there about the role of blocking diodes, not bypass diodes.
              SunnyBoy 3000 US, 18 BP Solar 175B panels.

                Comment

                • inetdog
                  Super Moderator
                  • May 2012
                  • 9909
                  #5
                  Originally posted by loobosh
                  I just bought 16 Sanyo Hip 190 watt used, one was dead. Opened the junction box took out all four diodes, now works fine, panel will be in parallel should be ok.
                  If one or more of the diodes were shorted, it would reduce the panel output, possibly to zero volts,, and removing it would make the panel appear functional.
                  But if one or more cells in the panel were damaged you could read full Voc and full isc from the panel and still get only a fraction of its rated power. The simple test will be to measure its output current while it is in parallel with other cells and driving a load such as a CC.
                  SunnyBoy 3000 US, 18 BP Solar 175B panels.

                    Comment

                    • loobosh
                      Member
                      • Mar 2015
                      • 40
                      #6
                      Still putting them up, will have 4 strings of 4 panels in parallel so I can compare this suspect string to the other 3.

                        Comment

                        • PNjunction
                          Solar Fanatic
                          • Jul 2012
                          • 2179
                          #7
                          Originally posted by h_1985
                          my question about why not all thin film panels have bypass diodes ??
                          Because unlike a mono/polycrystalline cell, where shading can force the output of the entire panel though those now reverse-biased cells, (hence the usual practice of dividing the panel into at least two parts electrically with bypass diodes, cutting the reverse bias in half or more) destroying them with heat, a thin-film distributes the reverse-bias all along the shadow surface edge where it can be safely dissipated.

                          Still, thin films should not be subject to very repetitive shadows that don't move rapidly across the surface - it will hurt their longevity.

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