Possible error in the Performance Ratio´s help section

[allanfisica]

It seems to be a mistake in sign in the help section of the Performance Ratio https://www.pvsyst.com/help/performance_ratio.htm. In particular the help section shows a weather-corrected PR equation as: 

PR (corr)  =  E_Grid  /  ( PNomPV  * Σ hours   ( GlobInc / GRef  * (1 - muPmpp * (Tarray - TArrayAver) )

While the NREL paper (cited in the help section) https://www.nrel.gov/docs/fy13osti/57991.pdf shows the equation with a diferent sign mainly exchanging  (TArrayAver  - Tarray  ):

PR (corr)  =  E_Grid  /  ( PNomPV  * Σ hours   ( GlobInc / GRef  * (1 - muPmpp * (TArrayAver  - Tarray  ) )

Assuming muPmpp is a negative number. 

I will be happy to receive any feedback on this subject.

 

[Michele Oliosi]

Dear allanfisica,

You are right, there is a mistake in the help, we will update the values. Thank you very much for the feedback.

This also allowed us to find a different bug in the software that alters the value of the temperature corrected PR by a tiny amount (typically ~ 0.001). We will correct this in an upcoming patch.

[allanfisica]

Thank you very much for the feedback. I am happy to read that our comment helped.

Greetings.

[Hossam]

@Michele Oliosi
Hope this message finds you well. 
I have the same issue and Can you please explain to me how the weather-corrected PR is calculated in PVsyst and is it fixed or not yet because I get a fixed difference between PR and weather-corrected PR of 0.003

 

[Michele Oliosi]

PR and weather corrected PR are not the same of course, so they shouldn't be equal in general. Or do you mean you find a difference between your calculation and the PVsyst calculation?
The issue has been fixed and you can follow the help page to see the formula ?

Edit: in fact you are right, there seems to be still a small mistake. the PR and PR corrected for temperature should be the same for the yearly value. We will track down the error.

[Hossam]

@Michele Oliosi

I always get a fixed difference in the simulation results. 
When I change the location to different cities, the difference between PR and WCPR is 0.003

[Michele Oliosi]

Dear Hossam,
I would say this must be a coincidence, (taking the demo projects you can find different examples). Are you using the same weather data ?

[Hossam]

Yes @Michele Oliosi
I can show you the results of one single iteration in four different locations, you will find a constant difference in the annual average values. 
Weather Corrected PR - PR = 0.003
The four attachements shows the results of running the simulations with the same system inputs but the only difference is the weather data.

 

 

Edited June 8, 2023 by Hossam

[Michele Oliosi]

Dear @Hossam you are right and I was mistaken. When looking at yearly values the PR and PRTemp should agree. We need to track down the mistake here.

 

[Hossam]

@Michele Oliosi Do you have any updates regarding this issue?
Thanks in advance.

[Michele Oliosi]

Sorry no updates yet on the issue.