Experimental and numerical study of a novel thermochromic bifacial photovoltaic glazing system

The direct penetration of solar irradiation through transparent building envelopes often leads to increased cooling demand and compromised indoor environmental quality. Harnessing and regulating solar irradiation on glazed building surfaces is crucial for the development of advanced glazing technologies. Driven by this goal, this study proposes a thermochromic bifacial photovoltaic (TC-BiPV) glazing system, which enables passive modulation of solar irradiation while capturing irradiation from both indoors and outdoors for electricity generation. To comprehensively evaluate its performance, the TC-BiPV glazing was fabricated and experimentally tested using a small-scale box setup. On a summer test day, compared with conventional TC glazing, the TC-BiPV glazing reduced direct solar heat gain by 30% and lowered the test-box air temperature by up to 4.8°C. In comparison with BiPV glazing, it achieved a 62.6% reduction in direct solar heat gain, a decrease in the test-box air temperature by up to 15.1°C, and a 16.5% increase in electricity generation. Subsequently, an optical-thermal-electrical model was developed and validated against experiments. Using this model, the performance of the TC-BiPV glazing as the skylights and vertical windows across tropical regions worldwide was assessed. The results indicated that the TC-BiPV glazing reduced indoor heat gain by approximately 9.1–27.7% and 38.4–40.1% compared with BiPV and TC glazing, respectively, while enhancing annual electricity generation by about 3.1–9.6% relative to BiPV glazing. This study demonstrates the high performance of TC-BiPV glazing and presents a novel and sustainable approach to the design of energy-efficient building envelopes.