A group of scientists from the University of Bristol and Egypt's Benha University have used saltwater to cool PV modules. They tested a passive cooling technique based on saturated activated alumina, with saline water as a cooling agent, after initially using freshwater.
In their tests, they replaced the PV panels with blue coated plates with equivalent optical characteristics of commercial polycrystalline products. “Sample boxes, containing activated alumina tablets, with improved fins configuration, were manufactured from 6 mm acrylic plates and assembled,” the researchers said.
A solar simulator consisting of six 1,000 W halogen lamps was used for testing, with ambient temperatures ranging from 30 C to – 3 C, and relative humidity levels of 40% to 50%. Wind speeds were kept close to zero. The panel efficiency was assumed to be 17.1%.
Three horizontal layers of aluminum wire mesh were assembled under the simulated panel to enhance the heat transfer throughout the system.
The academics said aluminum wire mesh is preferable to aluminum plates because it's cheaper and weighs less. They also noted that sheets are more feasible than small mesh cuts.
They tested saltwater with five different salinity levels – five, 10, 35, 80, and 377 parts per thousand (ppt) mixed through a salinity meter. The mixed solution was kept in a closed container to settle.
“Boxes were fitted with the new internal configuration, simulated plates, activated alumina tablets and dipped in saline water container for three hours then released and kept under the pre-measured radiation for six hours,” the scientists said.
They also added perforations to rectangular containers to increase the heat and facilitate mass transfer between the saturated materials and the surrounding air.
The seawater system configuration offers better thermal performance than freshwater systems. This is due to the higher uniformity of heat transfer in both vertical and horizontal directions, due to the vertical solid aluminum fins and the horizontally aligned wire mesh.
The cooling system can reduce a plant's operating temperature by 12 C to 14 C at different tested radiation intensities, compared to projects with no cooling systems.
“The results showed that the saline water can be used as an alternative for the pure water as it gives the same performance,” the group said. “Despite having the same performance, it is preferable to use the saline water due to its availability and the high potential to use this system for desalination purposes.”
They recommended solutions with lower salinity, as higher levels have shown a higher deterioration rate.
“The group is currently investigating the economic and environmental aspects of their system and proposing a complete system that provides higher energy efficiency, deploying nanotechnologies and distilled water,” researcher Saber Abdo told pv magazine.
The group presented its findings in “Cooling solar panels using saturated activated alumina with saline water: Experimental study,” which was recently published in Solar Energy.
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