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  • Solar panel expected degradation

    Will the degradation expected on solar panels, affect both the voltage and wattage?

  • #2
    Originally posted by Brian53713 View Post
    Will the degradation expected on solar panels, affect both the voltage and wattage?
    More likely it will affect amperage and wattage only.
    The voltage is pretty well fixed by the choice of semiconductor material.
    SunnyBoy 3000 US, 18 BP Solar 175B panels.

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    • #3
      The way it was explained to me was that the I-V curve tends to lose definition in its "knee" and tend to flattening out a bit as the cells degrade and generally time goes on, with the MPP shifting downward and to the left, but more downward than leftward, meaning current will probably be affected more than voltage. But, there are several mechanisms at work, and it may be pretty hard to make blanket statements or generalizations about all types of cells, materials and mfg. processes.

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      • #4
        If the main effect were voltage, it would be possible to check temperature and measure the degradation pretty
        accurately. If its the current (as I expect), much harder since sun intensity is so variable. And who has a lab
        flash tester? Something to do in a decade... Bruce Roe

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        • #5
          Originally posted by bcroe View Post
          If the main effect were voltage, it would be possible to check temperature and measure the degradation pretty
          accurately. If its the current (as I expect), much harder since sun intensity is so variable. And who has a lab
          flash tester? Something to do in a decade... Bruce Roe
          Because the current in a solar cell or an array is pretty linear with respect to irradiance, using a silicon cell pyranometer like a Li-Corr that's kept in reasonable calibration and put in the same plane as the array might serve as a comparison to array current. Just ratio the array current to the pyranometer output and keep an eye on how that ratio changes over time. Been at it for 3+ years now. Finally convinced myself that the current output from the array is itself a pretty decent pyranometer, just not for measuring horizontal irradiance (except for horizontal arrays) - long, boring story - also hard to send back for calibration checks.

          Also, as it turns out, the array voltage is a fairly accurate way to measure an array's temperature, provided the voltage is measured at reasonably consistent plane of array irradiance levels - and one tool to estimate array fouling - more long boring stories.

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          • #6
            I am going to guess, that the current degradation is pretty much tied to the total amount of sun a panel has received. So
            if the panel is kept tied to an MPPT load, the total amp hours, or the total KWH delivered to date, would track degradation.
            Bruce Roe

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