Impact of inter-row shading on Voc.

Dear SAM team,

I've been using SAM to quantify the impact of PV tracker inter-row shading and backtracking on module Voc.  Is there a parameter visible to the user which indicates when the module bypass diodes are closed due to inter-row shading?  I'm trying to distinguish between zero array voltage due to zero POA irradiance, and zero array voltage due to module bypass diode operation due to inter-row shading.

Much appreciated,
Ben

Hi Ben,

SAM's self-shading model does not have a physical representation of bypass diodes in the module. The "non-linear" self shading model uses an empirical lookup table to adjust the array DC output of the array, which approximates the effect of the diodes. Unlike the "linear" self-shading option, the "non-linear" option calculate the reduction in direct normal irradiance caused by self-shading. The model is described in these publications see the PV publications page for a full list of PV model references:

MacAlpine, S.; Deline, C. (2015) Simplified Method for Modeling the Impact of Arbitrary Partial Shading Conditions on PV Array Performance. National Renewable Energy Laboratory. 8 pp.; NREL/CP-5J00-64570. ( PDF 699 KB )Deline, C.; MacAlpine, S.; Hanson, A.; Stauth, J.; Sullivan, C. (2015) Partial-Shading Assessment of Photovoltaic Installations via Module-Level Monitoring. National Renewable Energy Laboratory. 7 pp. NREL/CP-5J00-63765. ( PDF 816 KB )

The "Shading and Layout" topic in Help has a high-level description of the model with a list of output variables of interest: samrepo.nrelcloud.org/help/pv_shading.htm .

Because there is always some diffuse POA irradiance, the total POA irradiance does not typically go to zero due to self-shading.

Best regards,
Paul.