Scientists from the University of New South Wales (UNSW) in Australia have used rectangular vortex generators (VGs) as a passive cooling technique for photovoltaic panels and have found they can reduce the modules' operating temperature by between 1.5 C and 2.5 C.
VGs are commonly used to delay flow separation and are often placed on the external surfaces of vehicles and wind turbine blades. These devices have also been applied for cooling in photovoltaic-thermal (PVT) modules at the research level, but they were not yet used for PV modules only, due to “entirely unpredictable” flow conditions, according to the research team.
“Our previous indoor experiments have demonstrated that the rectangular wing VG can achieve up to 3 C of cooling under free convection conditions,” the scientists explained, referring to a previous attempt they made to use VGs for PV panel cooling. “By introducing longitudinal vortices close to the module's rear surface, an array of VGs enhances the convective heat flux, consequently reducing the module's operating temperature. In this study, the same VG design was applied to an outdoor open-rack PV system setup.”
The scientists utilized VGs with a size of 2 cm x 3 cm and with a rectangular wing shape bent at a 30-degree angle. They built 400 pieces based on aluminum and 400 pieces relying on a conductive 3D printable polymer. They were then attached to the back side of two different 285 W polycrystalline panels provided by Taiwanese manufacturer Winaico. The academics also used thermal conductive tape to create a thermal contact between the VG and the module.
“Except for the very bottom and the top row of silicon cells, where the junction box is situated, the VGs covered the majority of the 1 m × 1.65 m module area,” they explained. “The vertical pitch is 8 cm, which allows for two rows of VGs on one M2 format cell and 16 rows of VGs to be installed on each module. Hence, the VGs effectively cover 12.5 % of the module's rear surface, leading to significantly less material usage compared to other heatsink approaches.”
The proposed technology was tested at an experimental setting deployed on the rooftop of a building in Sydney, with the panels having a tilt angle of 30 degrees. Temperature sensors were placed on the panels' rear surface and weather and radiation data were collected via a weather station, while a thermal camera was used to visualize the temperature distribution on the rear surface of the modules.
The tests showed that the VGs based on the 3D printable polymer were able to reduce the modules' temperature by up to 1.5 C under high irradiance and low wind conditions, or with southerly wind. The VGs based on aluminum were found to reduce the modules' temperature by around 2 C under high irradiance conditions or 2.5 C in a high temperature and high wind speed scenario.
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“Both VGs exhibit equivalent performance with south and west winds, indicating the dominance of the vortex generation mechanism,” the group stated. “The module equipped with VGs exhibited an increase in convective heat transfer coefficient as evaluated by the thermal balance model.”
The group presented the new cooling technology in the study “Long-term outdoor testing of vortex generators for passive PV module cooling,” which was recently published in Solar Energy. “In future studies, the correlation between the near-surface flow and the free stream wind direction needs to be verified for a specific type of PV system,” the academics concluded. “Then it will be possible to optimize a VG for a given site with a predominant wind direction.”
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