# PR value greater than 1

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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

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will you please share project file?, if possible
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Hi,

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:

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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.
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Yes, it is a vertical bifacial system.

I was wondering, how is it possible that the global inc is negative?

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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%.
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I understand. :)

How can I calculate the correct PR-value?

Thank you very much!

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https://www.pvsyst.com/help/performance_ratio.htm

In your case, GlobInc should be replaced with (GlobInc + GlobBak * ϕ), where ϕ = bifaciality factor of module

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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?

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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.

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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?

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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.
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oh okay thank you!

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.

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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.

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