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PR calculation with bifacial modules


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I have been running some simulations with bifacial modules and it caughts my attention the fact that the performance ratio calculation does not take into account the global in-plane irradiation on the rear side of the module. Should not it be added to the calculation to comply with the PR definition?

Thank you in advance for the help.


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Hi André,

Is that a good question some years later? Is the Bifacial Performance Ratio still calculated as the monofocial one?

Thank you,



Hello Javier

Yes, until know the biracial performance ratio is calculated as the mono-facial.

"PR for bifacial systems

The definition of the performance ratio should be something like a standard, defined by an official instance, and accepted by everybody.

Now I have not yet seen any reference which would define a performance ratio for bi-facial systems. Therefore PVsyst cannot propose any specific value in the present time.

The value provided presently with the PVsyst results uses the definition of the Monofacial systems, so that the bi-facial gain comes as an increase of this ratio.

NB: The main objective of the PR is to find an indicator for comparing real and simulated data, therefore which may easily be evaluated using simple (and "primary") measured data.

However neither the rear side irradiance, nor the part of the bifacial gain is available in usual measurements."

Source: https://forum.pvsyst.com/viewtopic.php?t=31

Best Regards,

Nedal Nassar

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Since version 7.2.13 you will find a bifacial performance ratio in the results summary window.


This bifacial performance ratio is computed as:

PRbifi = PR / (1 + (GlobBak + BackShd)/(GlobInc))

(see https://www.pvsyst.com/help/performance_ratio.htm)

Note that this may not correspond to notes 1 and 2 of §3.20 in the norm IEC 61724-1:2021, since it does not include the bifaciality factor. It is instead based on a literal interpretation of the IEC 61724-1:2021 §3.20 main paragraph.

Edited by Michele Oliosi
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