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Scientists in the United States have developed a new photovoltaic-thermal system design that uses parallel water pipes as a cooling system to reduce the operating temperature of photovoltaic panels. The waste heat generated by this process is then used to generate domestic hot water.
Researchers at the Multiphysics Interaction Lab (MiLab) in the United States have developed a new photovoltaic-thermal (PVT) system design that uses waste heat from photovoltaic panels to generate residential hot water systems.
The system is based on parallel water pipes that attach to the back of the solar panels and reduce their operating temperature. “Our study presents a simple and practical cooling method that improves the electrical efficiency of photovoltaic panels and, at the same time, offers a sustainable solution to the hot water needs of homes,” the scientists say.
The experimental system is based on a 250 W polycrystalline photovoltaic panel facing south with a temperature coefficient of -0.45%/ºC and an inclination angle of 30 degrees. The copper cooling tubes are connected through upstream and downstream manifolds and covered with an aluminum cap to secure them to the back of the PV panel.
The experimental setup includes a hot water storage tank and an 11 W centrifugal pump that maintains a constant flow rate of 3 L/min.
“The water flow is controlled with a flow meter,” the scientists explain. “To collect accurate data, a set of thermocouples are strategically placed to simultaneously measure multiple temperatures, including the inlet and outlet water temperatures of the PV/T system, the surface temperature of the PV panel, and the ambient air temperature.”
The system also uses a multimeter to measure the output power of the photovoltaic module and a pyranometer to evaluate solar radiation.
The academics compared the performance of the cooled photovoltaic panel with that of an uncooled reference panel during the month of May on the campus of Notre Dame-Louaize University, located in Zouk Mosbeh, Lebanon.
Their analysis showed that the PVT panel can generate 4% more energy than the photovoltaic module, thanks to the cooling effect of the copper tubes. However, they also warned that a saturation effect related to the fact that the hot water stored in the tank is not used effectively can limit the ability to optimally cool the photovoltaic modules in a given phase.
“This reduction is likely due to the absence of residential water demand in the waste heat recovery system,” the researchers further explained. “This absence causes the temperature of the cooling water in the hot water tank to gradually increase, thereby reducing the heat removal rate of the PVT system.”
The tests also showed that the PVT panel achieved an average electrical efficiency of 11.5%, while the uncooled PV panel achieved an average efficiency of 10%. The scientists also revealed that the total efficiency of the PVT system reached around 75% and that of the reference PV system was only 10%.
“The average thermal efficiency, which represents the ratio between the recovered waste heat and the solar energy absorbed by the PV panel, was approximately 60% in the cooled PV/T system,” they also stated. “The cooled PV/T system not only generated a higher fraction of electrical energy, but also showed an approximately 40% higher rate of heat loss through the back face of the PV module, indicating the effectiveness of heat recovery.” residual".
The system was presented in the article “ An experimental analysis of a hybrid photovoltaic thermal system through parallel water pipe integration ,” published in the International Journal. of Thermofluids . |
