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Possible error in the Performance Ratio´s help section


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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.


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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.

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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.

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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 by Hossam
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