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 Post subject: PR value greater than 1
PostPosted: Tue Aug 03, 2021 3:43 pm 

Joined: Tue Jun 29, 2021 11:58 am
Posts: 14
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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PostPosted: Fri Aug 06, 2021 12:08 pm 

Joined: Sat Jul 24, 2021 1:45 pm
Posts: 4
will you please share project file?, if possible


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PostPosted: Mon Aug 09, 2021 10:16 am 

Joined: Tue Jun 29, 2021 11:58 am
Posts: 14
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:


Attachments:
Image3.jpg
Image3.jpg [ 40.99 KiB | Viewed 772 times ]
Image2.jpg
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File comment: This is my file:
Image1.jpg
Image1.jpg [ 108.02 KiB | Viewed 772 times ]
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PostPosted: Wed Aug 11, 2021 4:36 am 
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Joined: Tue Oct 18, 2016 3:31 am
Posts: 401
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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PostPosted: Wed Aug 11, 2021 9:14 am 

Joined: Tue Jun 29, 2021 11:58 am
Posts: 14
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?


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PostPosted: Wed Aug 11, 2021 9:39 am 
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Joined: Tue Oct 18, 2016 3:31 am
Posts: 401
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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PostPosted: Wed Aug 11, 2021 11:07 am 

Joined: Tue Jun 29, 2021 11:58 am
Posts: 14
I understand. :)

How can I calculate the correct PR-value?


Thank you very much!


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PostPosted: Wed Aug 11, 2021 5:29 pm 
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Joined: Tue Oct 18, 2016 3:31 am
Posts: 401
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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PostPosted: Thu Aug 12, 2021 8:47 am 

Joined: Tue Jun 29, 2021 11:58 am
Posts: 14
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?


Attachments:
Knipsel2.JPG
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Knipsel1.JPG
Knipsel1.JPG [ 84.23 KiB | Viewed 666 times ]
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PostPosted: Thu Aug 12, 2021 11:12 pm 
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Joined: Tue Oct 18, 2016 3:31 am
Posts: 401
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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