It seems that PVWatts uses dew point in its calculation. However I couldn't find dew point data in the data file. I only see Tdry and Twet in the weather file I am using. Also, it mentions in Help that there is a way to specify the albedo in the user interface, but I can't see how to do that.
PVWatts only uses the dry bulb temperature data from the weather file. It does not use the wet-bulb or dew-point temperature data. You can see a table showing the data elements used by each of SAM's performance models in Help, under Weather Data, Weather Data Elements.
PVWatts either assumes a fixed albedo of 0.2 or reads albedo values if they are included in the weather file (SAM CSV, TMY3, and EPW files may have albedo data).
The detailed photovoltaic model allows you to either choose use albedo values from the weather file if they are available or specify 12 monthly values. The default monthly values are 0.2, so if you run the model with a weather file that does not have albedo data, it will use 0.2. You can change the albedo options for the detailed photovoltaic model on the Location and Resource page, under PV Albedo and Radiation by clicking the blue plus sign to make those inputs visible.
Best regards,
Paul.
