Optical Performance of Solar Modules

Encapsulation of a solar cell affects its optical performance, a fact that is often overlooked when the efficiency of different types of solar cells is compared. In this work we have measured the reflectivity of silicon wafers with textures typically applied in the industry, i.e. random pyramids and isotropic texture with conventional silicon nitride anti-reflex coatings, as well as a graded porous silicon anti-reflection coating. We investigate how the reflectivity is affected by angle of incidence for all surfaces both with and without encapsulation. The reflectivity of the random pyramidal structure is compared with a ray-tracing model, and we achieve good correspondence both with and without encapsulation for various angles of incidence. The ray-tracing model allows us to do a complete optical loss analysis of the solar module. We apply this loss analysis methodology to four different configurations, and show that encapsulation does not necessarily imply a large optical loss, particularly when we consider higher angles of incidence.