Meteo data selection

[wgs]

I'm a new user, in the U.S. midwest. I have found that the simulation results are significantly different (ie. 13%) between Lat/Long generated NASA-SSE (synthetic) and TMY3, which i believe uses NREL data. Two questions: is this kind of variance to be expected between simulations using these different data sets? And is there a generally accepted viewpoint of which of these sets of data are considered to be more accurate?

[André Mermoud]

I have done a comparison between the different sources of data imported in PVsyst, and available for Europe: we can observe a discrepancy of the order of +/- 10 % (yearly sums) between all these sources, and this is of course the first uncertainty of the PV production forecast.

Please see the FAQ What is the accuracy of the different meteo data ?

And I agree with Marvin: nobody knows where is the truth (if truth exists) ...