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Aging black and orange cure and whether we should use them to choose the right Imp and Vmp RMS degradation


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Hi PVsyst team, 

My question will follow these assumptions: 

  1. Pvsyst forum suggests :
  • The orange curve (sum of average degradation factor and mismatch increase due to degradation) should generally stay above the black curve (warranty), to be realistic.

From <https://forum.pvsyst.com/topic/3450-degradation-factor-for-pv-module/#comment-9616>

  • As far as I know, without further documentation, I would suggest using the default values.

From <https://forum.pvsyst.com/topic/3424-imp-vmp-rms/#comment-9500>


  1. Pvsyst help:

Now the warranty should normally apply to any module of the sample. Therefore if we assume that it is applicable to 95% of the modules, the sum  "Degradation factor" + 2 * "RMS dispersion" should in principle not exceed the slope of 0.8% of the warranty. This is not the case in our example.


  1. My module datasheet warranty (highlighted below):





Question :

If I use the warranty numbers provided in the module warranty (shown above) and also use the default Imp and Vmp RMS values, the orange line does not remain above the black line (see picture 1 below). Is it a good practice to adjust the Imp RMS until the orange line stays above the black line? In pictures 2 and 3 below, I have changed the Imp RMS dispersion, and at 0.10% per year, the orange line stays above the black one. Is this a reliable procedure to determine the Imp and Vmp RMS dispersion for my simulation?






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I think that in this case, the expected yearly average degradation of the modules is less than 0.4%/year. I cannot say by how much exactly, but you can try 0.3%/year, which is in the range of what n-type modules have.

You can adapt the mismatch degradation accordingly (also 0.3%/year). We do not have information on how the dispersion of the degradation happens for this module, but a reasonable assumption is that it is less extreme if the modules also age less.

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