Characterization of Bifacial Silicon Solar Cells and Modules: A New Step

Being interested in the characterization of bifacial solar cells and the maximizing of their potential, we studied how the sample holders add an external current mainly due to the reflectance properties of their surface. We found that this influence can be higher than one percent relative with respect to current. Using the same type of cells, mini modules were encapsulated using different back sheets. An increase of up to 8% in power output is visible before and after encapsulation if the back sheet is highly reflecting. Larger modules were laminated using transparent back foils with 16 of these cells and outdoor measurements performed. We changed the reflectance of the underlying surface and so the bifacial performance of the module varied, in a proportional manner. We have observed a relative increase in relation to monofacial averaged value of 7.9% of current if the reflectance of the surface is high, with major peaks up to 20%. The underlying area must be optimized to reveal the real potential of these devices. We have found a difference of about 30% relative comparing a small underlying area vs. a bigger area. There is also a saturation point when the underlying area is six times the area of the module. For this size or larger areas, the surface can be considered as infinite because its contribution will not change the performance of the module.