Optics for smart building-integrated photovoltaic systems

The tendency to integrate photovoltaic or photovoltaic/thermal modules into building envelope is changing due to the utilisation of optical elements for sunlight management. However, the viability of these systems mainly depends on two factors: 1) to offer cost-efficient solutions comparing to traditional building-integrated photovoltaic or photovoltaic/thermal systems, 2) to create designs, without being extremely difficult to manufacture and operate them on a large scale. In light of the issues mentioned above, this article presents a comparative analysis of the most relevant and recent smart building-integrated designs, including different optics. The designs have been categorised by the type of technology used to manage sunlight, placing emphasis on buildingintegrated applications. The results show that, in the case of reflective systems, the most usual designs are based on compound-parabolic-concentrators (usually: static; low concentration ratios). On the other hand, there are numerous configurations using total internal reflection to guide rays to photovoltaic cells. There are also hybrid systems (reflective/refractive) and different types of holograms, luminescent systems, etc., offering smart glazing elements and building-integrated solar panels. Key factors such as effective cooling devices and system functionality are discussed. Gaps in the literature on optical elements for building-integrated photovoltaics are identified. Future research directions are proposed.