A comparative study on curved air-based photovoltaic/thermal roofs with and without glazing

Abstract

• The validated novel numerical model could describe the performance of the roof system; • The glazed system would increase thermal efficiency and decline electrical efficiency; • The annual electricity per area of the unglazed system was 86.54 kWh/m 2 ; • The heat gain per area of the glazed system was 220.40 kWh/ m 2 ; • The extinction coefficient and tilt angle can affect the system performance. A curved air-based photovoltaic/thermal roof is proposed to manifest traditional Chinese roof features and achieve electricity generation and air-heating functions. The absorption plate in unglazed systems interacts directly with the atmosphere, which may result in heat loss and decrease the system's thermal performance in heating seasons. It is vital to investigate the glazed system's performance compared with the unglazed one. Therefore, a curved transparent polymethyl methacrylate cover was installed on one test rig and comparative experiments were conducted to investigate the influence of the glazing. Besides, a numerical model was developed and validated by the experimental data. The results showed that during the experimental period, the average electrical efficiency of the glazed and unglazed systems was 5.05% and 5.73%, respectively, and the average thermal efficiency was 70.88% and 39.58%, respectively. The glazed system could enhance thermal performance and provide heated air to the linked room while the electrical output is affected by the cover transmittance. Based on the validated model, the electrical output and heat gain of the systems with and without glazing were predicted using the weather data in the test location of Hefei. In addition, parameters of the extinction coefficient of cover material and the tilt angle of the bottom plate are also analyzed.