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Bypass Diodes

Discussion in 'Photovoltaics' started by Jim Avery, Feb 22, 2004.

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  1. Jim Avery

    Jim Avery Guest

    Is there any advantage to using Germanium or Schottky diodes rather than
    Silicon for bypass diodes ?
    In a gridtie system what reverse Voltage rating do the bypass diodes need to
    be ?

  2. There is a question that should have been asked.

    Q: What is the required current rating for a bypass diode?

    A: As listed below by Duane, but if the diode is in a junction
    box on the rear of the module, it must be derated for the
    highest temperature that can occur, or placed on a heatsink
    outside of the box. Depending on ambient temperature,
    air flow around the modules, etc., the J-box can reach
    90C. This is why most PV modules need 90C rated wiring.

    Most PV manufacturers have specific information on this
    subject and the required data sheets should be packed
    with new modules. This is a UL listing requirement.

    An under-rated diode can cause severe damage to a PV
    module if bypassing is necessary (shading or cracked cells).

    Bill Kaszeta
    Photovoltaic Resources Int'l
    Tempe Arizona USA
  3. CEC

    CEC Guest

    In general, a Schottky diode has less voltage drop across it, so,
    running the same current, over silicon vs. Schottky, will
    give less heat inside the Schottky one (I think, about 25 % less
    power dissipated).

    Schottky diodes are in general rated with lower reverse voltage.
    Schottky diodes are in general more expensive than the silicone ones.

    Germanium diodes are sometimes used as RF rectifiers, with current at
    0.01 A only. Those diodes melt-down very easily.

  4. Our new (to us) Siemens ST40 panel came with a shorted diode in the junction

    I removed the diode and the cell works ok now (after I took it down to
    remove the diode...)

    Question is do we need the diode on a single panel, single battery setup.
    The manual states that the diode is to ensure that multipanel setups don't
    feed back into a shaded cell.

    With only one panel I assume that the diode is not needed. We do have a
    Morningstar charge controller which I think has a diode to prevent the
    battery from back feeding.

    Thanks, Graham

    Memo - Test panel _before_ installing atop large tree.
  5. Then why would the panel not work before he removed it, and work fine
    after it's been removed? How would one even notice a Series
    Protection Diode that was shorted?
  6. Siemens built bypass diodes into the ST40 junction box.
    The problem with this is that a reversed connection to a battery
    can really blow up the diode. I had several customers with
    this problem.

    For 12-volt systems you do not need the bypass diode
    and can remove it.

    Bill Kaszeta
    Photovoltaic Resources Int'l
    Tempe Arizona USA
  7. Thanks Group, for the assurance that a diode is only "a complication" on a
    single panel system

    Don't miss the solar powered "significant findings" being released by NASA
    in the press conference 2pm EST Tuesday. (Salty Brine found in trenches,
    "BB"'s are _____ forms of _____)

  8. Anthoney


    Sep 27, 2010
    I have been reading about installing bypass diodes within a photovoltaic panel ( DIY) to prect the cells from shadowing that may occur.
    cosidering, 36 cells at 1.8w, 3.6 amps, 0.5v would a diode per 18 cells be sufficent? thank you
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