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 building-integrated 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.