Amorphous silicon (a-Si) have a lower thermal coefficient, but the electrical performance is undermined by the fact of Staebler-Wronski (S-W) effect. Study on the effects of temperature on a-Si cells shows that a-Si cells can obtain higher electrical output at higher operating temperatures. This property makes a-Si cells more suitable for photovoltaic/thermal (PV/T) system where the operating temperature can easily reach higher level. At present, a-Si cells have attracted less attention in the PV/T application, but are promising photovoltaic (PV) materials for PV/T system. Research on the effects of temperature on a solo a-Si cell is already available, but the long-term impact on the a-Si PV/T system is still lacking. In a PV/T system, the operating temperature not only affects the electrical and thermal performance, but also the technical and thermodynamic reliability. To investigate the effect of temperature on the performance of a-Si PV/T system, long-term outdoor experiments of two identical a-Si PV/T systems operating at medium temperature (60°C) and low temperature (30°C) have been conducted from December 2017 to June 2019. At the initial phase of the long-test test, the electrical efficiency of the a-Si PV/T system operating at 30°C is 6.14%, which is much higher than that at 60°C (5.69%). During the long-term operation, both the electrical performances at 30°C and 60°C show an obvious download trend owing to the S-W effect. The initial difference in the electrical efficiency between 30°C and 60°C is 0.47%, while the gap eventually narrows to only 0.13%. In the past year and a half, the two a-Si PV/T systems operated stably without significant degradation in thermal and electrical performance. Through the long-term performance monitoring at different operation temperatures, it is demonstrated that a-Si cells are suitable for the PV/T application.
Keywords Photovoltaic/thermal, amorphous silicon cells, operating temperature, long-term experiments