Snow stow effects

Hello SAM team:

I have a few questions regarding snow loss with 1-axis trackers: 

Page 10 of the "Integration, Validation, and Application of a PV Snow Coverage Model in SAM" paper indicates the Authors were able to implement overnight snow stow angle to increase snow shedding::  " By instructing the simulation of the Mesa Top systemto set the nighttime tilt angle to 20° instead of 5°, we found that the energy predictions for the
simulated system could potentially increase on the order of 1-2% as a direct result of snow
sliding during the night"

• Is it possible to set a nighttime tilt angle in SAM (or Pysam)? 
• If an an angle can be set, does SAM allow sliding overnight to occur, such that I would see an effect in %coverage? Marrion's paper refers to "daytime" hours and based on the runs I've done sliding only seems to occur with irradiance >0. 
• Assuming nighttime sliding is not allowed, is there a way to override?  

Thank you,
Brian

Hi Brian,

SAM's Detailed PV model (pvsamv1) sets the tilt angle at night to zero.

From my tests, it looks like the snow cover may increase at night based on the snow depth data in the weather file, but it does not decrease at night, suggesting that the model does not allow snow to slide at night.

I will check with the model authors to confirm this.

It is not possible to manually set the subarray surface angle in PySAM to override the model's surface angle calculations.

Thanks,
Paul.

Hi again,

The night-time stow angle analysis described in the validation paper was done by modifying the surface angle values in the model's C++ source code as an experiment. A night-time stow angle input was not implemented as part of that work.

I have created a GitHub issue for this. If we get funding to do more work on the snow model or if someone wants to make a code contribution ,  we can implement this for a future version of SAM:

github.com/NREL/SAM/issues/477

Best regards,
Paul.