Backtracking and Self-shading in SAM 2020

Hello,
In SAM 2020.2.29 detailed PV model, when backtracking is enabled for 1-axis tracking, the self-shading option is now available for selection (in 2018.11.11, this selection was disabled).

In SAM 2020, when running a simulation with backtracking enabled, can you explain the difference between running the simulation with self-shading set to "None" versus set to "Standard Non-Linear"? 

Ultimately, I'm confused why I'm getting self-shading losses when backtracking is enabled. 

Thanks,
Jason

Hi Jason,

This is because as of SAM 2020.2.29, all of the shading options in SAM account for diffuse shading. When you run the detailed PV model with "Standard Non-Linear" self shading, there will be some shading loss due to reduction of incident diffuse irradiance even when backtracking avoids a reduction in beam irradiance.

For more details on this, see this GitHub issue (and follow the links to the related issues): github.com/NREL/SAM/issues/292 .

Best regards,
Paul.