Building integration of semitransparent perovskite-based solar cells: Energy performance and visual comfort assessment

This study presents a prediction of the yearly energy production and visual comfort benefits deriving from the adoption of building integrated semitransparent photovoltaic windows. Measured electrical and optical properties of neutral-colored solid-state planar heterojunction perovskite cells, characterized by promising transparency and photovoltaic conversion efficiency, were applied to a hypothetic photovoltaic glazing. Such experimental data were used as input to estimate annual energy production and visual comfort effects. The effect of different climate conditions was also investigated. A south-oriented test-room was modelled, assuming two window-to-wall ratios (WWRs) for office buildings, 19% and 32%, respectively. Energy yield was calculated at different locations showing figures between 20 and 30 kWh/m2 per year, with negligible reduction (not exceeding 3% in the hottest climates) when cell temperature was taken into account. Visual comfort assessment was carried out using two typical metrics: Useful Daylight Illuminance (UDI) and Daylight Glare Probability (DGP), comparing the performances of a photovoltaic glass with those of a commercial solar control glass and of a clear glass, acting as a reference. We found that the use of photovoltaic glass, independent of the location latitude, showed a significant increase in UDI values respect to clear glasses and performances comparable to solar control glasses. With reference to DGP, the use of photovoltaic glass allowed the reduction of occurrence of high DGP values (>0.45) of about 12-23%, depending on the location. Finally, we compared the annual energy production of building integrated photovoltaic cells to the annual use of electric energy for artificial lighting, finding that in most of the cases the annual energy production overcomes the amount of electric energy used for artificial lighting.