Bifacial Performance Ratio

[mmsyther]

How does PVsyst calculate its performance ratio with Bifacial modules?

Is the Irradiance just the front side that it uses for its performance ratio calculation?

Or does it take into account the rear side Irradiance?

I can't seem to find anything useful on this.

[Muthuraj]

As I understand, PVsyst 6.86 uses only front side irradiation for calculating PR.

This is evident when rear side irradiation is significant which results in >100% PR.

Try running bifacial simulation with E-W configuration.

Hope it helps.

[nassar]

How does PVsyst calculate its performance ratio with Bifacial modules?

Is the Irradiance just the front side that it uses for its performance ratio calculation?

Or does it take into account the rear side Irradiance?

I can't seem to find anything useful on this.

 

Hello

No, it doesn't take the rear side irradiance into accounu, 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

[bapossatto]

How does PVsyst calculate its performance ratio with Bifacial modules?

Is the Irradiance just the front side that it uses for its performance ratio calculation?

Or does it take into account the rear side Irradiance?

I can't seem to find anything useful on this.

 

Hello

No, it doesn't take the rear side irradiance into accounu, 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

 

And what about now... IEC 61724-1:2021 is available!

[dtarin]

Manually calculate PR and include the rear-side irradiance with the front-side irradiance.

[Michele Oliosi]

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.

[dtarin]

Are rear IAM losses included when computing the bifacial PR?

[Michele Oliosi]

At the moment IAM losses are automatically included in the irradiance contributions. Therefore measurements (e.g. with a pyranometer) may differ from (GlobBak - BackShd). As you mentioned in another topic, we will think about adding an IAM loss estimate so that we can remove it from the PR normalization.