Comparative study of a novel heat pipe photovoltaic/thermal collector and a water thermosiphon photovoltaic/thermal collector

To solve the freezing problems associated with the water thermosiphon photovoltaic/ thermal collector (PV/T) system, and decrease the temperature difference between the photovoltaic cells, a novel heat pipe (PV/T), which uses R600a as a working fluid, is proposed in this article. Comparative performance tests with the water thermosiphon PV/T system are conducted. The temperature difference between the PV cells of the novel heat pipe system is obviously smaller than that in the water thermosiphon. Thus, the photovoltaic conversion efficiency of the novel heat pipe system is improved at 9.5 per cent compared to 8.9 per cent in the water thermosiphon system. However, because of secondary heat transfer and large frictional resistance, the photothermal conversion of the novel heat pipe PV/T system is less efficient than that of the water thermosiphon system. Preliminary results show that the photothermal efficiency of the novel heat pipe PV/T system is 23.8 per cent, while that of the water thermosiphon system is 33.0 per cent. Although the two systems exhibit different photovoltaic efficiency and photothermal efficiency levels, from the perspective of the second law of thermodynamics, both systems possess almost the same exergy efficiency of approximately 10.3 per cent.