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Two values of GCR appear in the Report


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In the report of my simulations using bifacial modules, the GCR value that appears in "Backtracking strategy" is different from the one that appears in "Bifacial system". I did the maths, and it appears that it is because they do not take into account the same parameters to calculate the collector width :

- in "Backtracking strategy" : L = length module + module spacing (defined in near shadings)

- in "Bifacial system" : L = length module + module spacing (defined in near shadings) + frame (also defined in near shadings)

In both situation the pitch is equal.

Which GCR should I take into account in the end ?

I would also be glad to hear any other explanation for the difference of GCR.

Thank you for your help !

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  • 2 years later...

Bothersome phenomonon indeed.  Wish I didn't have to work around this and trick clients or claim pvsyst doesn't let us type in the correct values.  Either your GCR will read wrong (not equal to module datasheet length/pitch), or your backtracking limit angle will be wrong, or your sensitive area, or your actual 3d scene module width or length idk which.  It's very inconsistent.

Inactive Band Left Right, Inactive Band Top Bottom, bandwidth

X spacing, Y spacing

Frame L/R T/B

Backtracking Limit angle,

GCR, and

bifacial section's version of above conflicts on report

batch version of above

We have to parameterize all this information and test every revision to understand what pvsyst thinks it's doing, vs what it says it's doing, vs what help file says its supposed to do, vs what is on report, vs what forums answers say, vs orientation tab, vs 3d scene, vs bifacial page. All definitions overlap and change depending on if you are in shading scene or elsewhere in program.

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  • 1 year later...

I agree that the two mentions of GCR and other geometric quantities can be confusing. We will try our best to improve on this situation for PVsyst v8.

The main reason some quantities are duplicate, is that in some situations they will not have the same values. Let me give an example with the GCR:
— the GCR in “Sizes”: it is extracted from the 3D scene directly. This is the main “GCR” you should look at, the one which corresponds to PV area over ground area.
— the GCR in “Bifacial model geometry”: as was correctly pointed out above, this depends on the parameters of the bifacial model to estimate the backside irradiance. In PVsyst the bifacial model neglects the frame around the modules, among other approximations (since the model is a 2D model, the other sizes may also differ somewhat from the 3D scene). This means that the effective GCR of this backside model may be different. It was put in the report for transparency, to acknowledge that the bifacial model is an approximation and does not 100% reflect all details of the front side modeling.
— the GCR in Backtracking strategy was removed in recent versions. It was only a derived parameter based on the (sometimes manually adjusted) backtracking reference values. It was not significant enough to stay in the report.

Similar confusions are present for other size parameters. We are gradually improving the situation in the report by being more explicit. One of these changes that happened rather recently is the Pitch and Width for the backtracking controller, which are now explicitly noted as “Backtracking pitch” and “Backtracking width”. This denotes that they can be different from the actual parameters of the trackers.

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