A group of researchers from China’s Shandong University and Xi’an Jiaotong University has developed a radiative cooling (RC) cover for PV panels that can reportedly reduce their operating temperature by up to 3.72%.
Radiative cooling occurs when the surface of an object absorbs less radiation from the atmosphere and emits more. As a result, the surface loses heat and a cooling effect can be achieved without the need for power.
“Our study is based on numerical simulations, of which the simulation reliability was guaranteed by cross-validations with existing studies including experimental results,” corresponding author Dr. Maoquan Huang told PV magazine. “We are also planning experiments to test prototype RC covers on photovoltaic panels under different weather and environmental conditions.”
The new cover is made of polydimethylsiloxane (PDMS) films doped with soda glass (PDMS-SG) and is intended to replace conventional glass covers. “On the foundation of previous studies, this study presents a transparent RC cover with a randomly doped particle structure in a PDMS substrate,” said the researchers. “The study further explores the efficiency and potential of RC-PV systems across China’s varied meteorological using hourly weather data.”
Using numerical analysis, the group has compared several doping materials, including titanium dioxide (TiO2), tantalum pentoxide (Ta2O5), soda glass, silicon dioxide (SiO2), polyvinyl chloride (PVC), and polystyrene (PS). “Soda glass emerged as the superior choice, offering an optimal mix of solar transmittance and long-wave infrared (LWIR) emissivity,” the academics said.
Following this analysis, and also using numerical studies, the group calculated the structural parameters of PDMS-SG that would yield the best radiative results. They found the ideal results when the PDMS-SG film was simulated at a particle diameter of 4μm, a volume fraction of 1.5%, and a film thickness of 100 μm. That led to solar transmittance of 94.8% and sky window emissivity of 95.3%, resulting in 147.6 W/m2 peak power.
Following the design optimization, the group simulated its performance in different regions in China. For that, the cell was assumed to be a 200-μm-thick crystalline Si layer positioned above an aluminum (Al) back-reflector. It was compared to a reference cell with a 5 mm thick silica glass cover in the different regions of China.
“In the pursuit of understanding the application potential for RC-PV systems across China, we have delineated four distinct zones based on the annual efficiency increase rates 𝜂,” the group explained. “These zones are named as follows: the Optimal Application Zone (𝜂 ≥ 3.50%), the High Potential Zone (3.26% ≤ 𝜂 < 3.50%), the Moderate Potential Zone (3.02% ≤ 𝜂 < 3.26%), and the Limited Potential Zone (2.78% ≤ 𝜂 < 3.02%).”
According to their findings, the novel RC was able to increase the annual electricity output by 2.78%- 3.72%. The optimal application zone was found to be Tibet, as it benefits from a severe cold climate zone, the most abundant solar radiation, and clear skies. Provinces like Xinjiang were found to be in the high potential zone, while inner Mongolia was placed in the moderate potential zone. Provinces like Hunan and Sichuan fell under the limited potential zone of this research.
“The performance of RC-PV systems decreased from west to east in China, with the highest increase in regions characterized by dry, cool climates and predominantly sunny days,” concluded the academics. “These results highlighted the advantages of RC-PV covers under real weather and environmental conditions. This study contributes to the application of RC films to PV systems and provides valuable insights into the utilization of solar energy in future energy infrastructures.”
Their findings were presented in “The potential of radiative cooling enhanced photovoltaic systems in China,” published in Advances in Applied Energy.
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