Energy performance of ETFE cushion roof integrated photovoltaic/thermal system on hot and cold days

Solar energy utilization could be evaluated by electricity and temperature which represent photovoltaic and thermal performance, respectively. It is found that average total and net electricity were 54.5 W h and 42.9 W h, indicating that this integration ensures the CIPVT system to be independent on external electricity. Meanwhile, measured air temperature inside ETFE cushion roof was 31.2-67.8 °C and it was 16.8-31.0 °C higher than ambient air temperature, showing an attractive potential in collecting thermal energy. Moreover, virtual system efficiency in terms of electricity and thermal energy was 25.5% based on average experimental results and an approximate method. This reasonable system efficiency is due to annealing effects of a-Si PV under high temperature conditions. For temperature distribution of ETFE cushion roof, temperatures on top-layer and bottom-layer ETFE foils were significantly lower than that on middle-layer ETFE foil, resulting in less temperature effects on structural behavior of ETFE cushion roof. This study could provide useful observations and explanations for evaluating energy performance of the CIPVT system concerning solar energy utilization.