My runs of PVsyst indicate that, for exactly the same system design inputs, a percent decrease in GHI levels causes about the same percent decrease in energy generation. So far I have tested 5%, 10%, 11%, 12%, 15%, and 17% GHI decreases by editing my hourly GHI data in PVsyst standard format. In each case, these decreases produce a PVsyst-predicted decrease in solar plant energy generation of about 1% less than GHI was decreased (i.e. a 10% decrease in GHI results in a 9% decrease in energy generation). Is this conclusion largely accepted by the community of solar energy plant analysts? If so, and given the mathematical relationship between GHI and insolation, can I presume that the same conclusion can be stated for an insolation decrease by the same above percentages? Thank you for any insights!
