Quantifying effect of cooling, cleaning in PV systems operating under desert conditions

A group of researchers from Oman's International College of Engineering and Management and Malaysia's Universiti Teknologi Petronas investigated the effects of cooling and cleaning on PV systems operating under desert conditions and found that water injections may provide significant increases in power yield.

The tests took place in Muscat, the capital of Oman, which experiences hot summer temperatures of up to 43 C, considerable humidity, and little rain. “Though there have been efforts made to improve PV performance through cleaning and cooling, not much research has been done to fully understand the role that cleaning and water injection play in improving PV performance,” the scientists said. “The study aimed to provide insights into the influence of cooling PV panels and interval cleaning in improving the performance of photovoltaic cells.”

The academics placed a few monocrystalline modules in the same area, each with three thermal sensors at different points. In addition, they installed devices to measure solar irradiance, open circuit voltage, and short circuit current, and their readings were logged into a computer every minute.

All panels, with unmentioned capacity, were set at a height of 1.2 m facing south, and their performance was measured for two weeks. One panel was kept as a reference, with no cleaning or water injection for cooling. Another one was cleaned every three days with towels.

A third panel had water injected through nine nozzles arranged in parallel. In the first week, water was only injected once, on the first day, for half a minute. In the second week, water cooling took place daily, for two minutes each time.

“The results show that the highest power generated was 85.6 W with an efficiency of 23.6%, and the lowest values were 73.4 W, 18% efficiency, for the PV panel cleaned after three days,” the results showed. “In contrast, the uncleaned panel had the maximum power and efficiency of 75.7 W and 17.1%, respectively. The lowest power and efficiency were 67.5 W and 15.4%, respectively. The amount of dust measured after exposure to weather conditions at 20 C was 0.9 g.”

The panel that was only cleaned once for 30 seconds had maximum power and efficiency of 67.13 W and 15.8%. Its lowest power value was 20.6 W with 7.1% efficiency.

“Through the results, it was noticed that the uncleaned panel, in some instances, performed marginally higher than the water injection panel, and this is mainly due to a minimal duration of water injection with a potential of forming mud-like dust accumulation on the surface of the solar panel,” the researchers emphasized. “Another reason is that the water injection nozzles may cast a shadow on the panel, reducing the output power.”

Improved power and efficiency were observed in panels with 120 seconds of daily water injection. In that case, the highest power and efficiency reached 76.68 W and 18.68%, respectively. The lowest measurements were 11.8 W power and 14.4% efficiency.

“The introduction of water for cooling led to a 23.9% increase in energy output,” the scientists concluded. “These findings highlight the importance of regular cleaning and cooling techniques in maximizing the efficiency and output power of photovoltaic modules.”

Their findings were presented in the paper “Effects of cooling and interval cleaning on the performance of soiled photovoltaic panels in Muscat, Oman,” published in Results in Engineering.