Comparison of Glass/Glass and Glass/Backsheet PV Modules Using Bifacial Silicon Solar Cells

Bifacial solar cells can be encapsulated in modules with either a glass/glass or a glass/backsheet structure. A glass/backsheet structure provides additional module current under standard test conditions (STC), due to the backsheet scattering effects, whereas a glass/glass structure has the potential to generate additional energy under outdoor conditions. In this study, we quantify the current contributions due to various mechanisms in both module structures under STC. The current contributions due to different mechanisms are calculated by measuring the reflectance and transmittance of mini-modules with both structures, together with a MATLAB-based simulation. Our results show that under STC, glass/backsheet modules provide approximately 2.2% more power, as compared with glass/glass modules using the same bifacial solar cells with a standard cell gap of 2.0 mm. Using module optimization, we demonstrate that the maximum possible cost reduction benefit in $/W_P of glass/backsheet modules over glass/glass modules under STC is limited to 3.3%. Due to the potential outdoor energy yield advantages of glass/glass modules reported in the literature, we recommend a glass/glass module structure for bifacial solar cells. Furthermore, in order to compensate for the lower performance of glass/glass modules under STC, we propose a methodology to measure and fairly rate bifacial glass/glass photovoltaic (PV) modules.