Experimental and simulation analysis of a PV/T system under the pattern of natural circulation

Because of the high resistance caused by photovoltaic-thermal (PV/T) systems, the improved electrical energy due to fluid's cooling is much less than energy consumption of pump. To avoid this problem, in this paper, a natural circulation tube plate PV/T system is designed and built in photovoltaic solar simulation laboratory of Tianjin Chengjian University. The circulation velocities, electrical efficiencies, thermal efficiencies, overall efficiencies, and primary energy economic ratios are tested and analyzed under different radiation intensities. The result shows that the operation of the natural circulation PV/T system has hysteresis, and it requires longer time to keep the system operating with higher and stable performance when radiation intensity is at low levels. A mathematical model of heat transfer for this PV/T system has been established and solved using the MATLAB, and the numerical results have been validated by experimental data. The overall efficiency of the system under the pattern of natural circulation is also calculated when used in hot summer and warm winter areas. The generated electricity is about 1281.5 MJ/year; the heat collection is about 4639.6 MJ; and the annual integrative efficiency is 60%.