effective_irradiance =poa_global

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Joanns Engels

May 10, 2024, 9:09:37 AMMay 10
to pvlib-python

Could you please clarify, why mostly in every example I've seen, that as effective_irradance is taken poa_global value.

pvlib.pvsystem.calcparams_pvsyst(effective_irradiance=poa_global, ...

I thought its not totally the same.
In pvlib, effective irradiance refers to the irradiance reaching a module's cells, i.e., 'poa_global', adjusted for spectrum and reflection.
Is there any point to calculate effective_irradiance more precise, instead of taking poa_global value, and whether it will make a big difference to the PVsystem forecast output?

Thank you in advance!

Mark Campanelli

May 10, 2024, 11:56:38 AMMay 10
to Joanns Engels, pvlib-python
Hi Joanns,

  I think you are correct to have suspicions here. Would you be able to share a specific example where the POA irradiance is used instead of effective POA irradiance, and then I would be more confident providing an analysis of potential shortcomings.


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May 10, 2024, 11:57:22 AMMay 10
to pvlib-python
The two quantities are different, as you describe: poa_global is broadband irradiance on the module's outer surface, prior to reflections; effective_irradiance is the irradiance absorbed by the cells, reduced by reflections and adjusted for spectrum. The reflection adjust requires separating irradiance into direct and diffuse; the spectrum adjustment requires using a model, for which parameters or inputs may not be available in the example. Spectrum adjustment can increase or decrease irradiance typically by a few percent. Unless the angle of incidence is quite large (>50 degrees) reflection loss is typically quite small.


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