This post answers a question emailed to the SAM support email address.
"How was the insolation data used by SAM affected by snow cover? Did the data come from a pyranometer that might have been heated or cleaned? I have done a rough derate estimate for snow cover for various tilts based on the PVWatts Minnesota illustration, but I would like to make sure that there isn't already a snow cover effect in the basic PVWatts data."
If you are modeling a solar energy system in SAM using one of the TMY files from the National Solar Radiation Database (NSRDB), you can assume that SAM models the system assuming that the modules or collectors are kept clear of snow.
SAM can use weather data from a variety of sources, so the answer to this question depends on the source of the solar radiation data in a particular weather file. For the TMY3 and TMY2 files from the NSRDB, any gaps in the solar radiation data were filled using a synthetic algorithm described in the data sets' user manuals. If any data gaps were caused by a pyranometer at a given site being covered with snow, the data in the final TMY weather file would not include the gaps.
Best regards,
Paul.
