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Japanese scientists have designed a cooling system that reduces the operating temperature of the solar panel and the modules air inlet. It consists of a dew point evaporative cooler that supplies nearly saturated air to humid air channels that adhere to the back of a photovoltaic panel.
A group of scientists led by Japans Kyushu University has developed a new technique based on dew point evaporative cooling (DPEC) to reduce the operating temperatures of photovoltaic panels.
DPEC is a heat and mass transfer technique that has been widely used to date for energy saving in various industrial sectors. This technique is one of the most effective and energy efficient ways to cool hot air. It has higher cooling efficiency than traditional evaporative cooling and can reach the dew point temperature, which is the temperature point at which the air can no longer contain water vapor and is always less than or equal to the air temperature. .
DPEC systems are typically designed to supply air to a wet channel as working air. This improves the heat and mass transfer process in the wet channel, due to the lower temperature of the incoming working air. “The exhaust air from the DPEC system can reach saturation, while the supply air in the dry channel can reach its dew point temperature,” the researchers explain. “The proposed system consists of an independent dew point evaporative cooler that supplies near-saturation air to humid air channels that are fixed to the back of the photovoltaic panels.”
The proposed system consists of two wet channels, one located in the DPEC system itself and another placed on the back of the photovoltaic panel. The DPEC system supplies near-saturation cooled air to the wet channel fixed at the back of the PV panel, where additional evaporative cooling occurs to ensure maximum cooling effect.
Academics claim that the DPEC system is capable of considerably reducing the operating temperature of the solar panel, especially at the panels air inlet. “A large temperature difference is observed between the layers at the entrance of the panel, due to the cold air supplied from the DPEC unit,” they state. “As air flows along the channel, the temperature difference between each layer is reduced through heat transfer.”
They also explained that the water evaporation process triggered by continuous heat transfer from the dry channel to the wet channel embedded in the DPEC system and to the wet channel placed in the panel caused an increase in air humidity.
The system was tested for 10 hours a day and the group found that the DPEC system consumes 0.0736 kg of water, while the second wet channel located at the back of the PV panel consumes 0.7157 kg, the total consumption being water of about 0.7893 kg.
The team also found that the height of the channel has a significant impact on system performance. “Increasing the height of the channel allows a greater amount of unsaturated air to enter the photovoltaic panel, which favors the heat and mass transfer process to control the panel at a lower operating temperature and, therefore, improves the efficiency of the solar cell,” he stressed.
The researchers compared the performance of a solar module cooled by the novel technique with that of an uncooled panel and that of panels cooled by direct evaporative cooling and sensitive cooling systems based on DPEC. They verified that, in all cases, the proposed system achieved better cooling performance and maintained higher module efficiency.
“A shorter channel length and higher channel height improve cooling performance and increase the efficiency of the photovoltaic panel,” they stressed. “On the other hand, a higher inlet air velocity and a higher proportion of working air are favorable.”
They presented the system in the study “ Dew-point evaporative cooling of PV panels for improved performance ,” published in Applied Thermal Engineering . |
