Model step
Townsend snow
Monthly snow loss from the Townsend model
Inputs used: Monthly snowfall, Monthly snow events, Monthly relative humidity, Lower-edge height (snow), String factor (snow), Angle of repose (snow), Plane tilt, Collector band width, Rotation limit (symmetric), Ambient temperature, Relative humidity
What it is
This step is the Townsend monthly snow model only. Snow lying on the modules blocks the light until it slides off or melts; the model estimates the energy lost to it each month from how much snow falls, how steep and how high the modules are, how much snow piles up on the ground under the lower edge, and how humid, how cold and how sunny the month is. It is off unless a snowfall table is entered. Snow can also be entered as part of the monthly soiling fractions on the Soiling row; use one or the other, not both.
Options
- Townsend monthly: Townsend's monthly snow loss from snowfall, tilt, ground interference, humidity, temperature and insolation
- Do not model: no Townsend snow loss; snow can be entered as part of the monthly soiling
References
- Townsend & Powers 2011, Photovoltaics and snow: An update from two winters of measurements in the SIERRA, IEEE 37th Photovoltaic Specialists Conference
- Townsend & Previtali 2023, A Fresh Dusting: Current Uses of the Townsend Snow Model, Photovoltaic Reliability Workshop 2023, NREL/CP-5900-87918
API
site.snow_model = off | townsend