Definition of Bifaciality Factor: PVsyst vs. IEC

[kjs55]

According to IEC 60904-1-2, a PV module's "bifaciality factor" aka bifaciality coefficient is the minimum of the bifaciality coefficients of Isc or Pmax (i.e., whichever is lower). The PVsyst help menu [1] says to use the bifaciality coefficient of Pmax. Please explain why PVsyst is not aligned with IEC 60904-1-2 in this regard. Thank you.

[1] https://www.pvsyst.com/help/bifacial_module.htm

[kjs55]

In addition to my above question, is it the pre- or post-LID bifaciality coefficient?

[André Mermoud]

Sorry, I did not know the existance of this norm.

However, I don't know the effective difference between the bifaciality factor of ISC with respect to the bifaciality factor of Pmpp.

No manufacturer has never mentioned this difference, they only specify the factor for the Pmpp (when they specify it... which is not always the case).

NB: several datasheets mention a table of power increase for the bi-facial yield, but without mentioning the corresponding irradiance conditions. Therefore these data are completely useless. However they usually give a stable Vmpp voltage for all powers, which indicates that the bifaciality of Pmpp is identical than the bifaciality of Isc.

I don't have any information about the LID effect on the bifaciality factor. Please ask the manufacturers.