I would caution PVsyst users modeling in the Northeast or Northwest United States from using the newer NSRDB weather dataset PSMv3 (Physical Solar Model version 3, 1998-2016, 4 km resolution). The PSM data is higher resolution and is derived from the most current weather satellite observations. However, it has been shown to have a large positive bias for locations with above average cloud cover, snowfall, or changing ground albedo. A comparison of weather data from Rochester, NY shows the effect of this bias. Weather Data .................................................Global H.....Diffuse H ..................................................................kWh/M2......kWh/M2 PVGIS api TMY, TMY.............................................1343.5........563.8 Meteonorm 7.2 TMY (1991-2005).............................1349.2........626.8 NREL NSRD : TMY3 (1990-2010, 10 km)......................1349.9........653.5 NREL NSRDB PSMv3 TMY (1998 to 2016, 4 km)..............1390.5........577.4 PSMv3 variance to Meteonorm 7.2............................3.1%.........-7.9% This bias generally leads to a 3.5% higher predicted output in PVsyst compared modeling the same physical PV plant (array tilt angle 25 degrees) using Meteonorm or older NSRDB 10 km data. Until a newer version of the PSM satellite data corrects for these biases and can be confirmed to give reasonable production estimates (when compared to measured plant data), I recommend PVsyst users stick with Meteonorm weather data (with the Hay/Davies transposition model) for modeling plants in the Northern United States.
