Hi Robert,
You can download weather files with clear sky data from the NREL National Solar Radiation Database (NSRDB). SAM does not include that data when you download files from the Location and Resource input page, but if you download files direclty from the NSRDB Data Viewer at
maps.nrel.gov/nsrdb-viewer/, you can include the clear sky data in your request.
If you use that approach, you will have to use a text editor or spreadsheet software to edit the column headings and trick SAM into using the clear sky data instead of the regular DNI and DHI data: Rename the "Clearsky DNI" column heading to "DNI" and "Clearsky DHI" to "DHI" and also rename the original DNI and DHI column headings to something like "DNI original" and "DHI original" to prevent SAM from reading those columns. SAM ignores any columns of data in the file that it doesn't recognize so you don't need to remove the data itself.
Best regards,
Paul.