Sandia has coded a view factor model that estimates back-side irradiance across a row of bifacial modules, accounting for the row’s shadow on the ground and assuming an isotropic model for sky diffuse irradiance. Figure 1 and Figure 2 show the modeled variation in back-side irradiance by cell at noon and 3 PM, respectively, for the left 4 modules in a single row of 8 modules at a tilt of 35° on a September clear day in Albuquerque, NM. As the array shadow extends to the east (right), the cells on the west (left) edge of the array receive increasing back-side irradiance from the greater sunlit area on the ground behind those cells.

Sandia’s Matlab code is here: Sandia_Bifacial-PV_View-Factor-code_0.2-1.zip (2968 downloads)

Figure 1. Figure shows back side irradiance on the left half of an array of 8 modules at noon.  Model represents edge effects.  Gray area represents shadow of the array on the ground.

 

Figure 2. Figure shows back side irradiance on the left half of an array of 8 modules at 3PM.  Model represents edge effects.  Gray area represents shadow of the array on the ground.

 

Reference: Yusufoglu, U.A., et al., Simulation of Energy Production by Bifacial Modules with Revision of Ground Reflection. Energy Procedia, 2014. 55: p. 389-395.