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Accuracy of Performance Ratio calculation


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Performance Ratio calculation of PVsyst for grid connected large-scale PV systems is clear to me, since it depends on the following formula " PR = E_Grid / (GlobInc * Pnom) ". This PR value is also shown in the report at the "Main Simulation Results".

I thought that,if I want to create the same PR value from the "Loss diagram over the whole year (Arrow diagram)", I should multiply the loss percentages. However it seems like the PR value created by multiplying the loss percentages from Loss Diagram is around 0,7% (not for every project) lower than the PR value shown at the "Main Simulation Results".

Does this difference come from rounding the involving values? How should this difference be explained?

Best Regards,


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The deviations you observe can be due to rounding errors, since the percentages in the loss diagram are displayed with a precision of one decimal.

Your reasoning is correct, the losses reported in the loss diagram should match the result summary.

If, for crosschecking, you would like to repeat the whole calculation, you can export all the intermediate results of a simulation by selecting 'Output file' in the Simulation Dialog. Here you can make a choice of the variables you would like to look at and have them written into an ASCII file. In this way you should get less rounding errors.

Best regards,

Bruno Wittmer

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