Experimental energy performance assessment of a bifacial photovoltaic system and effect of cool roof coating

Abstract

In the quest for high albedo materials that boost the energy production of bifacial photovoltaic systems, a range of material already exists for reducing building roof surface temperatures, called cool roof materials. However, there is a noticeable absence of scientific literature addressing the combination of cool roofs and bifacial photovoltaic systems. This study investigates the photovoltaic performance of a bifacial photovoltaic system with cool roof coating on the underside and its impact on floor temperature. For this purpose, four ∼1kWp prototypes were installed on the terrace of the GAIA building of the UPC near Barcelona, Spain: (1) bifacial panels above a cool roof, (2) bifacial panels above normal floor, (3) bifacial panels above a normal floor with n-type solar cells encapsulated in TPO, and (4) monofacial panels. The results reveal 8.6 % higher PV yield for bifacial with cool roof compared to monofacial, and 4–4.5 % higher for bifacial (normal floor) compared to monofacial. Additionally, the cool roof coating contributes to reducing the floor temperatures, particularly in the unshaded (exposed) areas during summer (−3.8 °C). The presence of photovoltaic panels has also demonstrated a positive impact on floor temperatures during both winter and summer. Thus, the cool roof coating offers two benefits: increased photovoltaic yield and reduced building cooling requirements, both of which are associated with economic advantages. The cool roof coating can be integrated into existing or new bifacial roof systems.