Researchers in Iran have investigated how twisted tape in water-cooled channels can improve heat transfer in solar panels. They used a computer simulation to analyze the new approach with different parameters and found that the electrical efficiency of the panels increased by as much as 11.84%.
Researchers from Iran’s University of Tabriz have developed a new cooling method for PV modules that uses twisted tape in water-cooled channels to improve heat transfer.
“The use of twisted tape in the channel creates an eddy current that disrupts the velocity and temperature boundary layers in the channel, directly increasing the heat transfer coefficient,” the academics explained. “A three-dimensional geometry of a PV panel model was created using SolidWorks 2020 software.”
The group tested different variants and parameters for the latest cooling device using a computational study.
The software created a PV panel consisting of five layers, namely glass, the top layer of ethylene vinyl acetate (EVA), polysilicon cells, the bottom EVA layer and a single layer of Tedlar. Thermal paste was used to attach the cooling channels, made of rectangular or circular aluminum metal, to the bottom surface of the PV module. The length, width and height of the PV panel were 1,000 mm, 600 mm and 4.6 mm, respectively.
The rectangular housing has a height, width and length of 30 mm, 37.5 mm and 1,000 mm respectively, of which 16 are attached to the back of the PV panel. On the other hand, the circular housing has a diameter of 33.334 mm and a length of 1,000 mm, with 18 channels used in the numerical tests. A twisted tape with a pitch of 31.25 mm, 62.5 mm or 125 mm is placed in both types of channels. A pitch represents the distance required for the tape to make a complete 360° turn.
In addition, the tape has been tested with single and double V-cuts of 7.5 mm. Further variables, including changing solar radiation levels of 500 W/m², 800 W/m² or 1,000 W/m², at a constant ambient temperature of 20 C. Reynolds numbers, which represent how smoothly water flows, were set at 50, 100, 150, 200 and 300. The model was validated against previous work, with a standard deviation error of 0.33%–3.71%.
“It was found that using the twisted tape reduced the cell temperature from 31.70 C to 27.83 C, and the electrical efficiency increased from 11.68% to 11.84%. The optimized design reduced the cell temperature by 4.823 C compared to the smooth channel,” the scientists pointed out. “As the distance of the twisted tape decreased, the average cell temperature decreased by 1.14 C and the electrical efficiency of PV modules improved by 0.5%.”
The researchers also said that no apparent effect was observed when using a single or double V cut on the twisted tape. Furthermore, as the Reynolds number increased, the average cell temperature decreased and the electrical efficiency of the PV modules improved. “Using a smooth circular channel is better than a smooth rectangular channel. Using twisted tape inserts in the smooth rectangular channel leads to better results than using them for the smooth circular channel,” the scientists concluded.
The new cooling technology was presented in “Numerical study of the effect of a new cooling method using twisted tape with water on photovoltaic energy performance”, published in Ain Shams Engineering Journal.
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