about ageing Vmp and Imp RMS disperion values

[Chen]

Dear PVsyst team：

    For the distribution choice is limited to 2 sigmas (95% of the hits) of ageing parameters setting.

    if there is a clear warranty statement for the annual  degradation rate of photovoltaic modules,  such as maximum degradation rate 0.35%/ year，maximum 1% for the first year. 

    The slope of the warranty is 0.35%.  Can the Im or Vm RMS dispersion be set to 0.35/2 = 0.175 %?  thanks！

 

 

 

[Chen]

The 2 sigmas is approximately 65.26% of the hits？

[Michele Oliosi]

The degradation in PVsyst compounds the average degradation rate, and the fact that there is an RMSD in this degradation rate. The worse possible degradation rate is therefore AVG + 2*RMSD.

A warranty is in principle below the worst case (because manufacturers need to play safe with these numbers). Therefore, you could estimate an upper limit for the degradation model by saying: WARRANTY > AVG + 2*RMSD (PMPP degradation). Note that given the first year degrading differently, this is not entirely correct. I also note that this warranty seems too good.

But in this case, I do not think you should set "Vm RMS dispersion be set to 0.35/2 = 0.175 %".

[Chen]

OK，we assume that the degradation given to the user is achievable, that is, in the first year, each solar panel power degradation will not exceed 1%, and starting from the second year, the maximum degradation per year will be 0.35%（the minimum degradation is 0%）. 

According to the upper limit of warranty.

 "maximum average degradation factor"="1/2 of  yearly warranty"="0.175%",  right？ 

So at the end of the first year, the minimum power of the module is still 99% of the initial level, and at least 98.65% at the end of the second year, can the average degradation rate from the second year be equal to 0.35%? The worse possible annual degradation rate we assumed in the  warranty is 0.35%.

 

 "Average degradation factor"+2*"Imp/Vmp RMS dispersion" ＜ "The worse possible annual degradation rate (the upper limit of warranty is 0.35%) " ；

so that "Imp/Vmp RMS dispersion"="0.0875%" ，( 0.35% - 0.175%)/2= 0.0875%

 

Thanks for your time!

[Chen]

The Average degradation value obtained from the the module warranty interface is 0.38%/ year. Is 0.38% used in the PV module ageing parameters input settings interface？should we change 0.35% to 0.38%？thanks!

 

 

[Michele Oliosi]

On 4/15/2025 at 4:04 AM, Chen said:

 "maximum average degradation factor"="1/2 of  yearly warranty"="0.175%",  right？ 

Why do you divide by two ? I am not sure I am following.

 

On 4/15/2025 at 4:04 AM, Chen said:

"Average degradation factor"+2*"Imp/Vmp RMS dispersion" ＜ "The worse possible annual degradation rate (the upper limit of warranty is 0.35%) " ；

so that "Imp/Vmp RMS dispersion"="0.0875%" ，( 0.35% - 0.175%)/2= 0.0875%

No, Imp RMS dispersion are not comparable to a degradation factor. You should first translate into a degradation of the Pmpp. This is done stochastically by PVsyst.

 

On 4/15/2025 at 4:25 AM, Chen said:

The Average degradation value obtained from the the module warranty interface is 0.38%/ year. Is 0.38% used in the PV module ageing parameters input settings interface？should we change 0.35% to 0.38%？thanks!

The following is really important remark. In PVsyst we consider that the warranty is not equal to the actual degradation ! Therefore what you enter under "Module warranty" has no impact on the simulation.

If you want to model the unrealistic scenario in which modules age according to the warranty, then my advice is the following. Simply enter 0.35% per year as average degradation factor, 0% for both RMS dispersions, and put 1% in LID loss (in the tab "Module quality - LID - Mismatch") (almost the same as you did in the screenshot). The lower warranty on the first year is often times due to the LID.

[Chen]

 "Imp RMS dispersion are not comparable to a degradation factor. You should first translate into a degradation of the Pmpp. This is done stochastically by PVsyst".

sorry, I still feel very confused for this topic.

Can you clearly tell users how to operate and take values of  Imp RMS dispersion ? Should we take 0.4% by default or other values for Topcon or HJT /IBC different solar modules？Or is there any relevant basis to support filling in this data. thanks! 

 

 

 

 

[Michele Oliosi]

Unfortunately, I do not think there are sufficient studies on the aging of these types of modules for us to conclude on new guidelines on the dispersion of the aging.
One way would be to contact manufacturers directly about that.

In general, I would advise taking a conservative approach, and leave the default values when unsure. I personally would go on with the 0.4% by default.