Hello,
SAM reports the module efficiency to give you an indication of how well the module performs. SAM calculates this output by dividing the module power by the solar irradiance incident on the module surface. It does not use the module efficiency to calculate the module power.
For monofacial modules, you can replicate the calculation of module efficiency using simulation results:
Subarray 1 Module Efficiency (%) = Subarray DC Power Gross (kW) * 1000 W/kW / [ Module Area (m2) * Number of Modules * Subarray 1 POA Front Total Irradiance after Shading and Soiling (W/m2) ] * 100%
For bifacial models, SAM does not report the rear-side incident irradiance value required to replicate the calculation.
We will address this issue in the Fall 2023 version of SAM. See
github.com/NREL/SAM/issues/1418 to track our progress.
Thank you for reporting this problem and for your patience while we researched its cause.
Best regards,
Paul.