Vmp and Imp RMS disperion values (Ageing tool)

[mag]

Hello,
I am currently researching the topic of ageing photovoltaic parks. In doing so, I came across a problem in PVSyst that concerns the ageing parameters of PV modules. To be more precise, the Imp and Vmp RMS disperion values. Does anyone in this forum have any experience or reference values? Thank you for your answer!

Kind regards,
Markus

[Lazare Fesnien]

Hi,

You can account for the aging of the PV modules in ‘Detailed losses -> Aging’. This allows you to make a simulation for one specific year of operation. You can also make multi-year simulations in ‘Advanced simul. -> Aging tool’.

PVsyst will not change the nominal power of the PV modules, but simulate with a model of degraded PV modules. This means that the performance ratio PR will decrease with time, since nominal power stays the same, but effective generated power will decrease.

The aging of inverters is not modeled in PVsyst.

For more explanations on how to use the aging tools of PVsyst, please see the corresponding help page : https://www.pvsyst.com/help/ageing_tool.htm

[mag]

Hello Lazare,

thank you for your quick reply. I am still struggling to find any empirical data for the Imp and Vmp RMS dispersion values. I have been reading in the PVSyst Help that you don't have much references about the average module degradation. Nevertheless, do you have any recommendations what values to choose for PV parks with a size over 25 MWp. 

Best regards

Markus

[Ali Raza]

On 11/25/2022 at 8:21 PM, Lazare Fesnien said:

Hi,

You can account for the aging of the PV modules in ‘Detailed losses -> Aging’. This allows you to make a simulation for one specific year of operation. You can also make multi-year simulations in ‘Advanced simul. -> Aging tool’.

PVsyst will not change the nominal power of the PV modules, but simulate with a model of degraded PV modules. This means that the performance ratio PR will decrease with time, since nominal power stays the same, but effective generated power will decrease.

The aging of inverters is not modeled in PVsyst.

For more explanations on how to use the aging tools of PVsyst, please see the corresponding help page : https://www.pvsyst.com/help/ageing_tool.htm

What do these values (Vmp and Imp RMS dispersion)  represent, and what is the process for determining them? Is it possible to optimize these values, and if so, how can they be improved?

[Agnes Bridel]

In PVsyst, there are 2 effects that contribute to the losses due to PV module aging, i.e.,

1. Average degradation of the module, and,
2. increasing mismatch caused by different aging of the individual PV modules.

The increasing mismatch is hard to access due to lack of literature. PVsyst assumes that the distribution of Impp and Vmpp will broaden by time and this broadening is described by the 2 factors: "Imp RMS dispersion" &  "Vmp RMS dispersion". Very few studies are published on this topic and no general values or models exists yet. The default value in PVsyst is 0.4% and is meant to be compatible with typical warranties given by the PV module manufacturer. PVsyst uses a Monte Carlo approach to randomly generate many PV modules according to the distributions. It will then combine them to strings and calculate the mismatch losses to estimate the "Mismatch degradation factor".  With the Monte Carlo method available in PVsyst, you can put the values that you think is suitable.

Best regards,