For all projects in the United States we directly integrate PVWatts and SAM into our design software. This means all data is coming from the National Renewable Energy Lab, NREL. The closest local TMY2 or TMY3 data is automatically selected.
For all international projects, weather data is pulled from Meteonorm. Meteonorm provides TMY3 data.
TMY2 weather data sets are modeled from a longer sample of years while TMY3 is the most current data.