Spanish scientists have built a cooling system with solar panel heat exchangers and U-shaped heat exchangers installed in a well at a depth of 15 meters. The researchers claim that this reduces the temperature of the panels by up to 17% while improving performance by about 11%.
Researchers at the University of Alcalá in Spain have developed a cooling technique for solar modules that uses an underground single-phase closed-loop heat exchanger circuit that acts as a natural heat sink.
“Our analyses, carried out for different types of residential and commercial installations, show that the system is economically viable with investment amortization periods ranging from five to ten years,” researcher Ignacio Valiente Blanco told pv magazine.
The cooling technology involves the use of a heat exchanger on the back of the solar panel to remove excess heat. This heat is transferred underground by a coolant that is cooled by another U-shaped heat exchanger inserted into a 15-meter-deep borehole filled with natural water from an underground aquifer.
“The cooling system needs additional energy to activate the coolant pump,” the researchers explained. “Since it is a closed loop, the difference in potential energy between the well bottom and the solar panel does not affect the energy consumption of the cooling system.”
The scientists tested the cooling system on a stand-alone photovoltaic installation, which they described as a typical solar farm with a single-axis tracking system. The array consists of two 270 W modules supplied by the Spanish company Atersa. They have a temperature coefficient of 0.43% per degree Celsius.
The heat exchanger of the solar panel mainly consists of a set of six plastically deformed, flattened U-shaped copper tubes, each with a diameter of 15 mm. All the tubes are thermally insulated with polyethylene foam and connected to common inlet and outlet collectors with a diameter of 18 mm. The research team used a constant coolant flow rate of 3 l/min or 1.8 l/min per square meter of solar panel.
The experiment showed that the cooling technology can reduce the operating temperature of a solar module by 13-17 C. It also improved the module’s performance by about 11%, which means that throughout the day, the cooled panel will provide 152 Wh more than its uncooled counterpart, according to the study.
The scientists presented the cooling system in “Improving the efficiency of photovoltaic solar modules by cooling using an underground heat exchanger,” which was recently published in the Journal of Solar Energy Engineering.
“With the necessary investment, the system can be used in conventional installations,” said Valiente Blanco.