Malaysian researchers have tested bio-inspired coconut fiber for cooling solar modules. The cooling system has a moist coconut core encapsulated in a polyurethane sheet. It is placed behind the surface of the PV module and acts as a cooling element.
“Our solution uses bio-inspired coconut fiber to regulate heat,” said researcher Sudhakar Kumarasamy. pv magazine. “It can be used in building-integrated photovoltaic (BIPV) rooftop systems, ground-mounted plants and agricultural power systems.”
The researchers described their findings in the paper, “Thermal and Electrical Performance of an Uncooled, Naturally Cooled, Photovoltaic Thermal Module,” published recently International Journal of Photoenergy. They said the cooling system has a moist coconut core encapsulated in a polyurethane sheet. It is placed behind the surface of the PV module to act as a cooling element.
“Water molecules are in direct contact with the back surface of the PV modules with the coco fiber due to the high water holding capacity of the coco fiber, which lowers the temperature of the back surface of the module,” the researchers said, noting that this helps transfer heat from the front to the back surface through conduction. “After this, the water molecules in the coir absorb the sensible heat. Finally, when the water molecules have absorbed enough heat energy, they act as a heat sink by evaporating through the holes in the polyethylene sheet housing.
The researchers compared the temperature behavior and performance of a PV module equipped with the system to a photovoltaic-thermal (PVT) module with water-based cooling. They found that the passively cooled PV module had a maximum operating temperature of 44.6 C, while the PVT panel and PVT reference panel without cooling recorded higher temperatures of 47.8 C and 57.2 C, respectively.
“By integrating moist coconut, the surface temperature of the PV module decreased by 22.03% and 23.46%, respectively, while the PVT system reduced the surface temperature of the PV module by 16.43%,” the researchers explained. “The maximum power point (MPP) of the passively cooled coco fiber, PVT system, and reference module is 24.21 W, 20.21 W, and 14.65 W, respectively.”
They said that the power of the passively cooled PV module increased by 65.26%.
“However, the PVT system managed to increase power by only 37.95 percent,” said. “Convection, which transports water molecules away from the back of the PV module, increases heat loss from the back surface of the passively cooled PV module and consequently the front cover compared to a PVT system.”
The same research group as well published an extensive review of all passive and cooling techniques used in solar power in October 2021. The study looked at active techniques such as air-based cooling, liquid-based cooling, forced water circulation, liquid immersion cooling, and water atomization. Passive methods such as PCM cooling, heat pipes, heat sink or fins and heat exchangers, microchannel heat exchangers, radiant sky cooling, nanofluid based cooling, thermoelectric cooling, evaporative cooling and spectral filter cooling were also considered.