Hi Paul,
None of SAM's performance account for the effect of dew or other moisture evaporating from the solar collector. The solar radiation data in the weather file should account for the reduction in solar radiation due to fog.
As for which data source is best for use in SAM, the answer depends on the purpose of your analysis. For techno-economic analysis, I would recommend using a weather file that represents the solar resource over a period of many years because SAM's cash flow model uses hourly performance data for a single year to represent the system's performance over the project life, which is typically 25 or 30 years. If you are ignoring the financial model, and modeling the system's performance for a single year, then the pyranometer data may be more useful than satellite-derived data if the pyranometer is at the project site. If you have more than one source of data, you can run SAM using different weather files: For example you could run SAM using both satellite data and pyranometer data to gain insight into your system's design.
A useful resource for evaluating weather data from different sources is the solar resource data best practices manual (
PDF 7.3 MB
).
Best regards,
Paul.
