Hi Dan,
For information about the NREL National Solar Radiation Database (NSRDB), please see the following:
nsrdb.nrel.gov/
developer.nrel.gov/docs/solar/nsrdb/
The NREL Solar Resource Best Practices Handbook also has information that might be helpful:
Sengupta, M.; Habte, A.; Gueymard, C.; Wilbert, S.; Renne, D.; Stoffel, T. (2017). "Best Practices Handbook for the Collection and Use of Solar Resource Data for Solar Energy Applications: Second Edition." NREL Report No. TP-5D00-68886. (
PDF 8.1 MB
)
Best regards,
Paul.