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Integrating photovoltaics into windows provides the possibility of including an additional function of energy production to a conventional building fenestration component. There is no doubt that electrical power can be generated on-site. However, the effect of PV windows on the indoor luminous environment of the space served by them has not been comprehensively researched. This paper investigated the daylight performance of integrating four types of photovoltaics (semi-transparent thin film Cadmium telluride (CdTe) solar cells with 10% and 50% transparency, crystalline silicon solar cells with and without crossed compound parabolic concentrators (CCPC)) to a window of a typical south-facing office under different Window-to-Wall Ratios (WWRs). Annual useful daylight illuminance (UDI), daylight uniformity ratio (UR) and daylight glare probability (DGP) have been analysed based on dynamic simulation using RADIANCE. The simulation results show that windows integrated with crystalline silicon cells and CCPC optics have the potential to provide best daylight availability when compared with standard double glazed windows and other tested PV window prototypes, if it is applied to rooms with large WWRs (e.g. 60% or 75% WWR) at high latitudes (e.g. city of Harbin). Its application also improves the uniformity of daylight spatial distribution and eliminates the risk of glare. Semi-transparent CdTe PV window with 10% transparency can also improve the percentage of working hours that fall into UDI 500–2000lux range, however, it will result in the most sharp illuminance contrasts within the room. Applying all of these tested PV windows can effectively reduce the possibility of glare. • Window integrated PV provides daylight control in addition to energy generation. • Comprehensive daylight analysis was undertaken for four different PV windows. • Dynamic daylight metrics UDI, UR and DGP have been investigated using RADIANCE. • The effect of different WWRs on PV windows' daylight performance was explored. • PV windows can reduce the possibility of glare and maximise use the daylight. [ABSTRACT FROM AUTHOR]

Building-integrated semi-transparent photovoltaic windows (PV windows) have been considered as a potential candidate to replace conventional windows to improve building energy efficiency and hence reduce carbon emissions. 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 levels and affect colour quality of the transmitted daylight. Therefore, it is important to comprehensively assess daylight performance of PV windows to ensure a comfortable luminous environment. In this study, the daylight performance of Cadmium telluride (CdTe) PV window with four different transparencies (i.e. 20%, 30%, 40% and 50%) applied to a cellular office space has 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), simplified Daylight Glare Probability (DGPs) and Illuminance Uniformity (Uo). Correlated Colour Temperature (CCT) and Colour Rendering Index (CRI), which are two attributes to characterise the colour quality of transmitted daylight 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, 6500 K and 25000 K respectively). It is found that CdTe PV windows can significantly improve the homogeneity of daylight distribution on a task area located close to the window and reduce the risk of daylight glare when compared with the performance of a conventional double glazing. Moreover, the recommended CCT (i.e. 3000–7500 K) can be achieved with the employment of CdTe PV windows under 4000 K and 6500 K daylight scenarios. All of the CdTe PV windows examined were able to maintain CRI at a comfortable level i.e. above 90 under the three daylight scenarios. • To evaluate the indoor luminous environment with semi-transparent CdTe window installed. • To assess the UDI, DGPs and U O using RADIANCE with CdTe windows installed. • To evaluate CCT and CRI influenced by CdTe windows using CIE standard. • The semi-transparent CdTe window offers good daylight quality and quantity. [ABSTRACT FROM AUTHOR]

Abstract Building-Integrated Photovoltaic Window can potentially improve building energy efficiency. However, with the integration of solar cells, the colour properties of daylight passing through PV windows may be affected. It is important to explore the colour properties of the transmitted daylight to ensure a comfort luminous environment for its occupants. In this study, the spectral transmittances of four types CdTe PV window have been measured, subsequently the colour properties of the tested windows are examined and evaluated by Correlated Colour Temperature (CCT) and Colour Rendering Index (CRI). It was found that CdTe PV windows can achieve recommended CCT (i.e. 3300-5000K) when the daylight source is in the range of 4000K and 6500K. The general CRI of all the CdTe PV windows can be maintained in a comfort range, which is higher than 90, under different daylight scenarios. [ABSTRACT FROM AUTHOR]