Comprehensive evaluation of windows integrated semi-transparent PV for building daylight performance

Abstract Building-Integrated Semi-transparent Photovoltaics Window (PV window) has been considered as one of the potential candidates to replace conventional windows to improve buildings’ energy efficiency hence reducing their carbon emission. With the integration of PV windows, the indoor luminous-environment may be significantly affected. The presence of solar cells may cause undesirable shading, low illuminance level and affect colour quality of the transmitted daylight. Therefore, it is important to comprehensively assess daylight performance of PV windows to ensure a comfort luminous environment. In this study, the daylight performance of CdTe PV window with four different transparencies (i.e. 20%, 30%, 40% and 50%) applied to a typical office have been assessed in terms of daylight quantity and daylight quality. RADIANCE was selected to predict the annual daylight performance through advanced dynamic metrics including Useful Daylight Illuminance (UDI), Daylight Glare Probability (DGPs) and Illuminance Uniformity (Uo). Correlated Colour Temperature (CCT) and Colour Rendering Index (CRI), which are two attributes to characterise colour quality of transmitted daylight specified in CIE standard, were used to evaluate performance of the selected PV windows. CCT and CRI were calculated under three CIE standard daylight scenarios (CCT of 4000 K, 6500K and 25000K respectively). It is found that CdTe PV window can significantly improve the homogeneity of daylight distribution on the task area and reduce risks of daylight glare when compared to these of a conventional double glazing. Moreover, recommended CCT (i.e. 3300-5000K) can be achieved with the employment of CdTe PV window under the 4000 K and 6500 K daylight scenarios. All types of CdTe PV windows can maintain a CRI at a comfortable level i.e. above 90 under the three tested daylight scenarios.