yovandeer Posted August 3, 2021 Share Posted August 3, 2021 Hello everyone! When i'm analysing my results of my simulation, I get an PR value greater than 1. But in practice that's not possible.Can someone explain how it is possible that I get an PR value greater than 1?Kind regards Yoline Link to comment Share on other sites More sharing options...
shubham Posted August 6, 2021 Share Posted August 6, 2021 will you please share project file?, if possible Link to comment Share on other sites More sharing options...
yovandeer Posted August 9, 2021 Author Share Posted August 9, 2021 Hi, Sorry for my late respons. Didn't receive an notification of your answer. I'm not able to upload my report files ( I don't know why?), so here are images of my project report:This is my file: Link to comment Share on other sites More sharing options...
dtarin Posted August 11, 2021 Share Posted August 11, 2021 Is this a vertical bifacial system? I believe the PR calculation you see does not take into account rear-side irradiance in the PR calculation, and only the front-side POA irradiation. Since your bifacial gain is so high and your POA (GlobInc) is negative, this would lead to a PR greater than one. Try manually calculating PR to include the rear-side irradiance, and see what your results are. Link to comment Share on other sites More sharing options...
yovandeer Posted August 11, 2021 Author Share Posted August 11, 2021 Thank you for your answer. Yes, it is a vertical bifacial system. I was wondering, how is it possible that the global inc is negative? Link to comment Share on other sites More sharing options...
dtarin Posted August 11, 2021 Share Posted August 11, 2021 It is due to the orientation. PVsyst calculates POA as if it is a monofacial module first. A monofacial module oriented vertically 90 degrees in the EW direction would not receive direct light when the sun is behind the module, which is essentially for half the day. A module flat on the ground at 0 tilt receives no transposition gain, POA = GHI (roughly speaking). When you tilt that module vertically to 90 degrees in the EW direction, it's halved. In your waterfall diagram, GlobInc is -51%. Link to comment Share on other sites More sharing options...
yovandeer Posted August 11, 2021 Author Share Posted August 11, 2021 I understand. :) How can I calculate the correct PR-value?Thank you very much! Link to comment Share on other sites More sharing options...
dtarin Posted August 11, 2021 Share Posted August 11, 2021 https://www.pvsyst.com/help/performance_ratio.htmIn your case, GlobInc should be replaced with (GlobInc + GlobBak * ϕ), where ϕ = bifaciality factor of module Link to comment Share on other sites More sharing options...
yovandeer Posted August 12, 2021 Author Share Posted August 12, 2021 Now I ran a simulation with my own data data for the months of July and August.Now I do come up with a PR value that is smaller than 1.How is this possible? Link to comment Share on other sites More sharing options...
dtarin Posted August 12, 2021 Share Posted August 12, 2021 I think more information is needed to understand. What does your meteorological instrument set-up look like, where are the sensors and what are they measuring? What data was imported into PVsyst? Also, unrelated to you PR question, I noticed you are modeling degradation at year 20 which I am not sure you want to be doing, but I could use some more information to better understand. Feel free to shoot me a pm if you'd like to discuss. Link to comment Share on other sites More sharing options...
yovandeer Posted August 16, 2021 Author Share Posted August 16, 2021 Hi I'm sorry for my late answer. I was waiting for a respond of my collegue (who measured all the data) to give you some more info about the measurements setup. I hope to receive the info soon. Thank you for noticing but why is it not smart to module degradation at year 20? Link to comment Share on other sites More sharing options...
dtarin Posted August 16, 2021 Share Posted August 16, 2021 Unless your site is 20 years old, you want the model assumptions to match the conditions of the site you are testing. You're including degradation and mismatch losses which may not exist for your site. Link to comment Share on other sites More sharing options...
yovandeer Posted August 16, 2021 Author Share Posted August 16, 2021 oh okay thank you! And to answer your question about the measurement setup: we measure the air temperature, wind speed, GHI, POA from both sides of the solar panel and the module temperature. The POA instrument is directly in the plane of the panels and the temperature sensors are glued to the panels. Temperature , wind and GHI are simply measured in the field. GHI and POA are given in W/m². Link to comment Share on other sites More sharing options...
dtarin Posted August 16, 2021 Share Posted August 16, 2021 Since this is a vertical bifacial module, you probably need to import GHI into your custom weather file and not POA, and let PVsyst calculate front/rear POA. Link to comment Share on other sites More sharing options...
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