Daylighting characteristics and experimental validation of a novel concentrating photovoltaic/daylighting system

Daylight plays an important role on the environmental comfort level for buildings. As for the energy consumption in the building, lighting is one of the main contributors. However, traditional building integrated solar utilization systems such as flat photovoltaic or concentrating photovoltaic systems can only supply the heat or the electricity for buildings. Thus, a novel concentrating photovoltaic/daylighting window is proposed as a strategy to effectively generate the renewable electricity for the domestic use while providing a better daylight performance. The indoor experiment and ray tracing simulation are both conducted to identify the effect of the daylighting window on the optical performance of the concentrator. The annual daylight performance of a typical office building installed with the concentrating photovoltaic/daylighting window at various installation angles, window-to-ceiling ratios and under different climate conditions is investigated through RADIANCE. The accuracy and confidence of the simulation model is validated through the outdoor experiment, and the deviation between the experimental and simulation results is as low as 8.7%, which is indicated by the coefficient of variation of the root mean squared error. The simulation results show that the concentrating photovoltaic/daylighting window provides a good daylight performance on the working plane of the office room: the percentage of the working hours under daylight that lies in the useful range (100-2000 lx) can be up to 92.00%. It also achieves a homogenous distribution of daylight within the internal working space and effectively reduces the possibility of glare. Through the simulation results under different climate conditions, besides of the solar irradiance, the latitude also has an obvious effect on the annual daylight performance. So for the application in different latitudes, it's highly recommended to be installed with the inclination angel near the local latitude for a higher annual electricity output and better annual daylight performance.