Cooling of a PVT System Using an Underground Heat Exchanger: An Experimental Study

In the recent decades, the researchers have been focused on the use of photovoltaic thermal (PVT) systems that provide the best performance and cooling for the photovoltaic panels. In this study, a PVT system consisting of a monocrystalline PV panel and a spiral heat exchanger was connected to an underground heat exchanger that is buried at a depth of 4 m below the surface of the earth. The procedure of the current study can be considered the first of its kind in the Middle East and North Africa region (based on the researchers' knowledge). The study was carried out on agricultural land in Baghdad-Iraq during months of July and August-2022, which are considered the harshest weather conditions for this city. The heat exchanger consists of a copper tube with a length of 21 m and formed in the shape of 3U, and it was buried in the earth and connected with a PVT system. The results of the study showed that the site chosen to bury the heat exchanger (4 m deep) has a stable soil temperature at 22.5 °C. From various volumetric flow rates, a flow rate of 0.18 l/s was selected which is considered the highest flow rate that can show vibration in the PVT system which may harm the system. The practical measurements showed that the largest difference in the surface temperatures of standalone PV and PVT was around 20 °C in favor of the latter. The electrical efficiency of the studied PVT system also increased to outperform the standalone PV system by 127.3%. By comparing the results of the current study with studies of water-cooled PVT systems from the literature, it is clear that the proposed system is feasible and has an acceptable efficiency in such harsh weather conditions tested during the experiment.