Scientists from the United Kingdom’s University of Nottingham and China’s Southwest Jiaotong University have developed a novel hydronic closed-loop PV cooling system for hot and arid regions. “We believe this proposed system will demonstrate good economic performance. We plan to conduct a detailed economic analysis of this system for specific application scenarios in the future,” corresponding author Dr. Qiliang Wang, told PV magazine.
The closed-loop system consists of a 15%-efficient PV module with several layers, a water tank with a capacity of 150 L, water pipes, and a circulation pump. An absorber plate is placed at the backside of the panel and copper water tubes are welded to the rear of the absorber plate. The water tank forms a complete closed loop with the pump and PV module connected via water pipes.
According to the researchers, the system can operate in a 24-hour continuous water circulation mode. Firstly, during the daytime, the water circulates through the rear surface of the PV panel, effectively cooling it down. At nighttime, the continuous water circulation releases the accumulated heat back to the PV panel, thereby improving its temperature during the night. This thermal energy spot utilization reduces the PV temperature fluctuation between day and night and is said to improve the lifespan of the PV panel.
The proposed set-up was modeled through Comsol software, based on the conditions of the Iraqi city of Basra. Two copper manifolds were affixed to the panel, and eight water tubes for water flowing inside to cool down and heat the PV panel.
“The proposed design intentionally excludes an insulation layer for the water tank and water tubes on the rear surface of the PV panel,” highlighted the academics. “By omitting the insulation layer, the system allows for the release of thermal energy to the environment, preventing the water from reaching excessively high temperatures and generating an adverse impact on PV efficiency. Additionally, the absence of insulation in the water tank and water tubes facilitates enhanced heat dissipation during nighttime discharge, ensuring that the water coolant is sufficiently cooled.”
The proposed system was then tested against a reference PV system without cooling and the test showed that the cooled PV system's lifespan may increase from 18 years to 24 years, as its operating temperature was lower by 10 C on average. Furthermore, generated 6.7% more output power than the benchmark system in December and 2.5% more in June.
Following this testing, the proposed system was tested with different configurations. Among the factors that were checked were the effect of the tank size, shape, and level of insulation, as well as the different number of tubes cooling the system and the rate of water flow in them.
“It has been observed that performance gains begin to level off once the tank volume exceeds 150 L for a 0.988 m2 PV panel. The proposed system, with 150 L and 250 L, can generate 1.28% and 1.36% more power, respectively, compared to the conventional PV module,” the scientists said. “Different tank shapes were found to have minimal impact.”
Furthermore, they found that changing the number of tubes from 5 to 12 improved power output by 1.17% and 1.36%, respectively, compared to the reference PV system. In addition, they ascertained that increased mass flow rates resulted in lower PV panel temperatures and enhanced electrical power efficiency.
The system was described in the paper “A hydronic closed-loop photovoltaic cooling system designed for hot and arid regions: Performance evaluation and degradation rate/ lifetime analysis,” published in Applied Energy.
“Overall, this suggested closed-loop PV cooling system provides a sustainable and cost-effective solution for enhancing PV panel performance,” the researchers concluded.
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