Model step
Rear-side geometry
Slope length, clearance, transmission and structure shade of the rear model
Inputs used: Rear-side geometry, Collector band width, Height above ground, Transparent fraction of the module plane, Structure shading factor, Technology
What it is
The rear model needs the slope length of a row, the height of the row above the ground, the share of the sunlight that passes through the module plane and the share of the rear light the structure blocks. This step sets where they come from: the racking and bifacial sections, or the fixed values PVWatts version 8 uses whatever the system.
Options
- Racking and bifacial sections: the collector width and the bifacial section's clearance, transmission and structure shade
- PVWatts 8 fixed layout: PVWatts 8's fixed rear geometry: 300 W modules, 1 m clearance, transmission 0.013, no structure shade
References
- NREL SAM Simulation Core (SSC) source code, release 2026.7.3, github.com/NatLabRockies/ssc: ssc/cmod_pvwattsv8.cpp, the representative module's geometry and the rear irradiance in exec() (calc_rear_side(0.013, 1, module.length · nmody), passed to the module model without a mismatch)
API
bifacial.geometry = racking | pvwatts_layout, array.collector_width_m, bifacial.ground_clearance_m, bifacial.transmission_factor, bifacial.structure_shade_factor