Experimental, study and design sensitivity analysis of a heat pipe photovoltaic/thermal system

Gravity-assisted heat pipe (HP) is usually introduced to overcome the freezing and corrosion problems associated with the traditional water-based photovoltaic/thermal (PV/T) solar collector. This study presents the design, construction and experimental study of a HP-PV/T system. A transient model for the proposed system is also developed and validated on a sunny day and a cloudy day, respectively. Based on the validated model, a design sensitivity analysis, including the effects of mass flow rate, dimensions of the heat pipe evaporator and condenser sections, the width of header pipe and the types of heat pipe working fluid, is conducted. The results indicate that the mean deviation between the simulation results and the experimental data is no more than 4.5%. The photothermal and photovoltaic efficiencies increase with increasing the water mass flow rate, the diameter of heat pipe condenser section and the number of heat pipes; however, the growth gradients become smaller when these three variables are respectively bigger than their respective specific values. Photothermal efficiency increases first and then decreases with increasing the length of heat pipe condenser section, suggesting an optimal length of 12 mm. Increasing the width of header pipe decreases both the photothermal and photovoltaic efficiencies. For the working fluid of heat pipe, H2O is suggested for mild climatic regions while R134a is suggested for cold climatic regions.