allanfisica Posted March 17, 2022 Share Posted March 17, 2022 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. Link to comment Share on other sites More sharing options...
Michele Oliosi Posted March 17, 2022 Share Posted March 17, 2022 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. Link to comment Share on other sites More sharing options...
allanfisica Posted March 25, 2022 Author Share Posted March 25, 2022 Thank you very much for the feedback. I am happy to read that our comment helped. Greetings. Link to comment Share on other sites More sharing options...
Hossam Posted May 30 Share Posted May 30 @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 Link to comment Share on other sites More sharing options...
Michele Oliosi Posted May 30 Share Posted May 30 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. Link to comment Share on other sites More sharing options...
Hossam Posted May 30 Share Posted May 30 @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 Link to comment Share on other sites More sharing options...
Michele Oliosi Posted June 1 Share Posted June 1 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 ? Link to comment Share on other sites More sharing options...
Hossam Posted June 8 Share Posted June 8 (edited) 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 by Hossam Link to comment Share on other sites More sharing options...
Michele Oliosi Posted June 12 Share Posted June 12 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. Link to comment Share on other sites More sharing options...
Hossam Posted July 5 Share Posted July 5 @Michele Oliosi Do you have any updates regarding this issue? Thanks in advance. Link to comment Share on other sites More sharing options...
Michele Oliosi Posted July 6 Share Posted July 6 Sorry no updates yet on the issue. Link to comment Share on other sites More sharing options...
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