Experimental system cools PV panels while keeping them clean
Researchers had placed a cotton sheet on the back of a PV module, which was then made wet and cooled. On the front side, water was pumped water from a pipe in a way that kept the panel both cool and clean. Their experimental setup showed superior results compared to reference cooling technologies.
Researchers had placed a cotton sheet on the back of a PV module, which was then made wet and cooled. On the front side, water was pumped water from a pipe in a way that kept the panel both cool and clean. Their experimental setup showed superior results compared to reference cooling technologies.
A group led by scientists from Egypt’s Al-Azhar University has proposed a novel dual-use system for solar PV (SPV) panels, cooling them from both sides while also cleaning bird-dropping from the front side. Developing an experimental setup of the system, the group has also tested it under the conditions in Cairo.
“It is estimated that during operation, 17% of incident solar radiation is absorbed for power while the remaining portion is wasted as heat. Additionally, the heat in the surrounding air degrades the efficiency and power output of solar panels by increasing the temperature of their cells,“ the researchers explained. “Bird droppings also contain digestive fluids that heavy rains can’t cleanse. Bird guano accumulated on the SPV modules decreasing the performance of solar panels by reducing the transmittance of the glass cover on the PV panels.”
To solve both efficiency issues, that of high temperature and that of dropping, the team has utilized water. Taking a solar panel with 360 W, the team has attached a wooden surface to its rear. In between the back of the model and the wood, a 1 mm thick cotton fabric sheet was placed, while on the outer side of the wood, a 6 mm thick acrylic sheet was fixed. A central water pipe allowed water to fall via holes onto the cotton, on which fans pushed air.
“The air is saturated with moisture, so the temperature of the air between the fabric and the surface of the solar panel decreases,” they explained.
On the front side of the panel, the academics placed a pipe with holes, allowing water to flow on the panel for both cleaning and cooling. A submersible pump moved water from a 50 L water reservoir to the pipe, while a water collector was installed on the bottom of the module. “To make up for the water deficit, water is periodically added to the tank,” they highlighted.
Image: Al-Azhar University, Scientific Reports, CC BY 4.0
That system was then tested against a control system of a cleaned 360 W panel with no cooling, and against an uncooled 360 W with four bird droppings. Backside and frontside temperatures, module output current, module voltage, sunlight intensity, ambient temperature, and relative humidity were measured for the three modules from 10 AM to 5 PM on August 10, 2023. All panels were oriented southward and had a tilt of 30°.
“The buildup of bird droppings on photovoltaic solar modules creates ‘hot spots,’ on the panel surfaces, raising their temperature by 5% compared to clean modules,” the researchers said. This temperature increase reduces current output by 36–38% when there are four droppings or more.”
The cooled PV module, according to the results, exhibited an output current increase of 8% and 9% compared to the contaminated and controlled modules, respectively; while the output voltage increased by 7% and 9%, respectively.
A power increase of 12%–33% and 7%–12%, respectively, compared to bird droppings and control modules was reported. The average efficiency of the cooled module was 20%, while the control panel was 18%, and the uncooled module with bird droppings dropped to 15%. The levelized cost of energy (LCOE) was $0.11/kWh for both cooled and controlled systems, while it rose to $0.13/kWh in the system with bird dropping.
“As a result of the current study, the cleaning system shall be operated if the number of birds dropping exceeds four drops. That’s because the power reduction was high in the case of the presence of four bird droppings on the PV panels (33% lower than cooled PV panel) which reduced the module efficiency markedly,” the researchers concluded. “The cooling system should also operate based on the temperature of the PV modules during the day. In the operation, we adjust the system to operate when the temperature exceeds 35 C during daytime.”
The results were presented in “Improving solar PV performance under bird-dropping conditions with a dual-cooling approach,” published in Scientific Reports. Scientists from Egypt’s Al-Azhar University and China’s Huazhong University of Science and Technology have conducted the study.
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