The Light Transmittance and Visual Effect of Photovoltaic Modules: Starting from a Project

Recently, I discovered a photovoltaic project with quite an interesting idea. The designer utilized the difference in light transmittance between transparent photovoltaic back sheets and black photovoltaic back sheets to arrange the English word "LOVE" on a sunshade using crystalline silicon photovoltaic modules.

Image: Label Architecture This sunshade is part of the renovation project of the Lafemme de Chateau Sports Center in Belgium, designed by the Belgian firm Label Architecture. From the image, it can be seen that the solar cells inside the photovoltaic modules are densely arranged, similar to conventional photovoltaic modules.

Image: Label Architecture However, from another front view photo of the carport provided by the design firm, there is no visible difference in appearance between the transparent and black photovoltaic modules.

Image: Label Architecture How can this phenomenon be explained? When observing the sunshade from the front, the light reaching the human eye from the photovoltaic modules mainly consists of two parts: the reflected light from the front surface of the module and the ground-reflected light passing through the photovoltaic module. The latter determines the visual difference between transparent and opaque areas of the module. If the latter is very weak, it is difficult for the human eye to distinguish the transparent areas. The ground-reflected light is diffuse reflection, meaning it scatters in all directions, as shown in the figure below. The back of the sunshade receives reflected light from different positions on the ground, and this reflected light accounts for roughly 10-20% of the solar irradiance on the front of the sunshade.

The ground-reflected light hitting the transparent areas of the photovoltaic modules from all directions partly transmits through and continues to scatter in all directions along the original path (as shown in the figure), while another part is secondarily reflected on the surface of the photovoltaic modules in other directions (not shown in the figure). The larger the incident angle of the ground-reflected light on the back of the sunshade, the greater the proportion of this secondary reflection loss. From the front photo of the carport, the observer's viewing angle is very low, so the proportion of ground-reflected light passing through the transparent areas of the photovoltaic modules to reach the camera in this direction is small; most of the ground-reflected light is secondarily reflected to other directions by the modules, making it difficult to identify the transparent areas in the photo. Compared to ground photography, I am more interested in the bird's-eye photos taken by drones. According to the previous analysis, the brightness of the transparent areas in the bird's-eye photos may be higher than in the third image but definitely lower than in the first image, because the first image is taken from the back of the sunshade looking upward at an angle, where the transparent areas can capture strong sky-scattered light. What do you think about whether the "LOVE" pattern in the bird's-eye photos can achieve the expected effect?