Analysis and quantification of effects of the diffuse solar irradiance on the daylighting performance of the concentrating photovoltaic/daylighting system

The hybrid photovoltaic-daylighting window system has aroused more and more attention in recent years, because of its higher solar energy utilization ratio and better adaptability to building's energy consumption. In this area, the concentrator-PV type glazing technology is an important branch that smartly adopts the optical concentrators to realize the efficient use of solar energy for renewable electricity generation and daylighting at the same time. A novel transmitting lens-walled compound parabolic concentrator (TLWCPC) is designed, which is able to achieve the function of daylighting without decreasing its optical efficiency. Based on the TLWCPC, the TLWCPC-Photovoltaic/Daylighting (TLWCPC-PV/D) system is designed. Considering that the sun rays for daylighting will experience complex optical transmission processes in the concentrator, the proportion and amount of the diffuse solar irradiance have significant impacts on the overall daylighting performance of the concentrator-type PV glazing systems in both daylighting energy level and distribution uniformity. In order to address this issue, in this research, the ray-tracing simulation model for the TLWCPC-PV/D system installed on the roof of a typical office room is developed and the experimental results under sunny and overcast weather conditions are used to validate the accuracy and confidence of it. The validated ray-tracing model is then used to evaluate the effects of the proportion of the diffuse solar irradiance with the total solar irradiance set at a constant value on the overall daylighting performance of the TLWCPC-PV/D system at different incidence angles. It is found through the simulation results that at different incidence angles, the daylighting energy levels on the analysis grid show obvious decreasing trends with the increase of the proportion of the diffuse solar irradiance via different rates but the distribution uniformity of them is enhanced significantly. Finally, two actual tested weather profiles on either date with different proportions of the diffuse solar irradiance are selected to make the daily energy performance analysis for the TLWCPC-PV/D system, which further emphasizes the effects of the diffuse solar irradiance on the concentrating solar systems.