How does PVsyst take the spectral effect into account ?

[André Mermoud]

The model implemented in PVsyst includes a spectral correction for amorphous modules, but not for crystalline nor other technologies.

The correction for amorphous modules is based on a parametrization as a function of air mass and Kt proposed by Betts and al "SPECTRAL IRRADIANCE CORRECTION FOR PV SYSTEM YIELD CALCULATIONS", 19th European Photovoltaic Solar Energy Conference, 7-11 June 2004, Paris, France.

According to my own experiments, when putting amorphous modules (tandem or tripple juction) at sun, recording one I/V curve every 10 minutes, and applying the one-diode model to each measurement, the errors Pmpp (measure-model) have RMSD of the order of 2.3% of Pnom over a full year (i.e. under any irradiance and temperature conditions). Without applying the spectral correction, this RMSD increases by about 0.6%, which is therefore the order of magnitude of the spectral effect over a full year for this amorphous module.

(see my article "Performance assessment of a simulation model for PV modules of any available technology", Mermoud, A. & Lejeune, T., 2010,

25-th European Photovoltaic Solar Energy Conference and Exhibition (EU PVSEC), Valencia, Spain, 6-10 september 2010)

For crystalline modules, the sensitivity to the spectral variations according to weather are rather small (see the conclusions of the article of Betts).

My measurements show errors Pmpp (measure-model) with a RMSD of the order of 1.2% of Pnom over a full year, in any irradiance and temperatures conditions. And still less for CIS (RMSD = 1% over 6 years!).

Therefore if a spectral corrections has to be applied, it would be within this 1% to 1.2 % dispersion.

Now the one-diode model is based on the STC performances, which are specified for an AM1.5 spectrum. The eventual variations of spectrum along the year would be around this STC Pmpp value. But who knows exactly the spectral contents of the irradiance for any weather (and especially the covered conditions), except through Air mass and Kt correlations ?

NB: The Sandia model does indeed define a spectral correction for crystalline modules, as a correlation by respect to the Air mass (therefore valid for clear sky conditions). Applied to simulations in middle-Europe, this induces a spectral gain of the order of 0.4 to 0.5% over the year. However this correlation is probably over-estimated during the simulation, because it is not related to the clearness index Kt, so that it is applied identically to cloudy conditions.