Experimental study and performance enhancement of a novel micro heat pipe photovoltaic/thermal system in a cold region

Abstract

The photovoltaic/thermal (PV/T) system, which utilizes solar energy to generate electricity and thermal energy, has significant potential in the northwest region of China, an area with abundant solar irradiation. To improve the performance of the micro heat pipe PV/T system, the study analyzed the system's thermal collection efficiency and power conversion efficiency using numerical simulation of the PV/T panel. The model incorporated double-layer glass and replaces water with nanofluid as the working medium inside the airfoil heat exchanger. The average relative error of the model was 0.9 %. In experiments conducted in Lanzhou, located in the northwest region of China, the power conversion efficiency reached its peak of 12.64 % during winter, while the thermal collection efficiency reached its maximum of 39.45 % during summer. Moreover, utilizing R141b as the working fluid in the micro heat pipe resulted in an average increase of 7.14 % in thermal collection efficiency and an average increase of 4.46 % in power conversion efficiency compared to acetone. This indicated that R141b outperforms acetone in terms of system performance. The study observed that the highest overall efficiency is achieved when the air layer thickness of the double-layer glass is 11 mm. The thermal resistance between the inner wall of the airfoil heat exchanger and the water in the PV/T components was the highest, reaching 48.85 %. Therefore, it was necessary to use nanofluids instead of water to reduce the thermal resistance of PV/T modules. The system performance remained relatively stable when the volume fraction reaches 8 %. At this volume fraction, the Al2O3-water nanofluid, Cu-water nanofluid, and Ag-water nanofluid increased the power conversion efficiency by 0.34 %, 0.72 %, and 0.77 % respectively. Moreover, they improved the thermal collection efficiency by 1.16 %, 2.69 %, and 2.78 % respectively. The micro heat pipe PV/T system was utilized for winter heating of farmers in Lanzhou and Jinchang cities. It maintained an indoor temperature of over 16 ℃ throughout the day, thus meeting the indoor heating standards.