Bifacial Notes

Infinite Sheds Model

This 2D model was developed at DNV by Jeff Newmiller originally for the front side, but was adapted to the rear side for SolarFarmer, which was presented at PVSC-46 in 2019 [1].

Reflected GHI considering row-to-row shading

Split the ground into shaded and unshaded sections with f_gnd_beam, the shaded sections, only see DHI, while unshaded see GHI = DNI*cos(ze) + DHI, the view factor vf_gnd_sky only applies to the shaded sections see Eqn (2) "Practical Irradiance Model for Bifacial PV" Marion, et al. [2].

(GHI/GHI)*unshaded  + (DHI/GHI)*shaded            <-- unshaded gets all GHI but unshaded only gets DHI
          unshaded  + (DHI/GHI)*shaded
         f_gnd_beam + (DHI/GHI)*(1 - f_gnd_beam)
         f_gnd_beam + df       *(1 - f_gnd_beam)
         f_gnd_beam + df - df*f_gnd_beam
         f_gnd_beam - f_gnd_beam*df + df
         f_gnd_beam*(1 - df)          + df        <-- (1-df) is the non-diffuse component or DNI*cos(ze)
          unshaded *(DNI*cos(ze)/GHI) + DHI/GHI

Only apply diffuse sky view factor, vf_gnd_sky, to diffuse component (df) incident on ground between rows, not the direct component of the unshaded ground:

reflected = albedo * GHI * (f_gnd_beam*(1 - df) + df*vf_gnd_sky)

References

1. Bifacial Performance Modeling in Large Arrays, Mikofski, et al., IEEE PVSC 2018
2. A Practical Irradiance Model for Bifacial PV Modules, Bill Marion, et al., IEEE PVSC 2017