A group of scientists from the Chiang Mai University in Thailand has used sparked titanium films to develop an anti-reflective, super hydrophilic, and photocatalytic coating for commercial solar modules.
The coating has photocatalytic properties that make the organic compounds adsorbed on the solar module surface decompose, thus preparing them to be easily washed off by rainwater. The films were prepared by the sparking process and resulted in fluffy morphology due to the irregular stacking of primary nanoparticles, which is the key factor ensuring the coating's superhydrophilic properties
The researchers used titanium wires with a size of 0.25 mm and purity of 99.5% supplied by UK-based high purity metals provider Advent Research Materials Ltd. “To form sparking tips, the wires were cut and aligned with a gap of 1 mm between the anode and cathode,” they explained. “The titanium wires were sparked off with a high DC voltage of around 3 kV discharged from a 24-nF capacitor.”
The design of the sparking system, according to them, enables the rapid deposition of nanoparticle films over large-area stationary substrates such as those of photovoltaic modules. “During sparking, electrons and ions produced from the neutral air molecules migrate toward the anode and cathode, respectively,” they further explained. “The bombardment of high-energy electrons and ions melt the metal tips. Hence, the nanodroplets are nucleated, which move toward the substrate and oxidized in atmospheric air.”
The scientists measured the surface morphology and film thickness through scanning electron microscopy, the water contact angles (WCA) through a custom-made tensiometer, and its optical transmittance via a UV–Vis spectrophotometer. “Due to the limitation of PV cover glass thickness and transparency, the experiments were performed on both the cover and slide glass substrates,” they specified.
The coating was tested on four south-oriented solar panels with a tilt angle of 19°. The panels have a power output of 5 W and were provided by Sun Solar Ecotech. Their performance was compared to that of another four panels of the same type provided by the same manufacturer. The surface topography of the uncoated and coated glasses was examined using atomic force microscopy (AFM). The static contact angles of a water droplet on the uncoated and coated PV cover glass were evaluated to determine their hydrophilicity
The data collected during the outdoor experiment showed that the coated solar modules achieved a higher power yield of 6.62% during the entire study period, which spans from December 2018 to March 2019. “The long-term outdoor experiment demonstrated that the power difference per day (ΔP) increased significantly owing to the reduction of dust accumulation on the panel surface,” the scientist concluded. “ΔP reached the highest value of 14.22% in scattered light (cloudy day), which may be attributed to the antireflective properties of the coating.”
All the details on the coating technology can be found in the study “Antireflective, photocatalytic, and superhydrophilic coating prepared by facile sparking process for photovoltaic panels,” published in scientific reports.
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