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Reducing PV module temperature with twisted tape

Source：pv magazine

Researchers from Iran’s University of Tabriz have developed a novel PV module cooling method that uses twisted tape in water-cooled channels to enhance heat transfer.

“Using twisted tape inside the channel creates a swirl flow that disturbs the speed and temperature border layers inside the channel, thereby 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 has tested several variations and parameters for the latest cooling device, using a computational study.

In the software, a PV panel consisting of five layers was created, namely glass, upper ethylene vinyl acetate (EVA) layer, polysilicon cells, lower EVA layer, and a single layer of Tedlar. Thermal paste was used to affix the cooling channels, constructed with either rectangular or circular-shaped aluminum metal, to the bottom surface of the PV module. The PV panel’s length, width, and height were 1,000 mm, 600 mm, and 4.6 mm, respectively.

The rectangular casing has a height, width, and length of 30 mm, 37.5 mm, and 1,000 mm, respectively, and 16 of them were attached to the back of the PV panel. On the other hand, the circular casing has a diameter of 33.334 mm and a length of 1,000 mm, using 18 channels in the numerical testing. Inside both types of channels, a twisted tape is placed, with a pitch of 31.25 mm, 62.5 mm, or 125 mm. A pitch represents the distance required for the tape to complete one whole 360° twist.

Additionally, the tape was 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, with 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 a previous work, with a standard deviation error of 0.33%–3.71%.

“It was found that the use of the twisted tape reduced the cell temperature from 31.70 C to 27.83 C, and electrical efficiency increased from 11.68% to 11.84%. The optimized design reduced the cell’s temperature by 4.823 C compared to the smooth channel,” the scientists stressed. “As the twisted tape pitch 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. In addition, 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 inside the smooth rectangular channel leads to better results than using it 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 the performance of photovoltaic,” published in Ain Shams Engineering Journal.