It is quite natural for dust to accumulate on solar panels installed anywhere esp. in desert zones. But the problem is that this hampers the effective functioning of the solar panels as energy harvesting potential of the panels get adversely effected.
Dust adhesion on solar panels is a major challenge to energy harvesting through photovoltaic cells and solar thermal collectors. New solutions are necessary to maintain maximum collection efficiency in high dust density areas such as the Negev desert in Israel.
Researchers at Ben-Gurion University of the Negev had been trying to find a solution to this problem. So they turned towards nature and observed the self cleaning properties of lotus leaf and investigated the entire mechanism. Taking a cue from this, they reckoned that there are certain microscopic forces and mechanisms that are at play which if optimized can help in removing dust particles from solar panels, thus mitigating the aforesaid challenges. It was found that the new technique removed 98 percent of dust particles.
The team observed that the lotus leaf remains dust and pathogem free due to its nanotextured surface, and a thin wax, hydrophobic coating that repels water. So the researchers tried to replicate this mechanism on the solar panels.
The researchers made some changes in silicon substrate (Si) – a semiconductor used in photovoltaic cells. They then studied if the effects of these changes helped in replicating the self cleaning behavior of lotus leaves by removing dust as the water rolls down.
It is known that superhydrophobicity reduces the friction between water droplets and the surface, thus allowing water drops to slide clean particles from surfaces. However, the forces that attach and detach particles from surfaces during the self-cleaning mechanism and the effect of nanotextures on these forces are not fully understood.
To shed light on these forces and the effect of nanotexture on them, the researchers prepared four silicon-based samples relevant to solar panels: (1) smooth hydrophillic (2) nanotextured hydrophilic surfaces and (3) smooth hydrophobic (4) nanotextured hydrophobic surfaces. This was achieved by wet-chemically etching the surface to create nanowires on the surface, and additionally applying a hydrophobic coating.
Particle removal increased from 41 percent on hydrophilic smooth Si wafers to 98 percent on superhydrophobic Si-based nanotextured surfaces. The researchers confirmed these results by measuring the adhesion of a micron-sized particle to the flat and nanotextured substrate using an atomic force microscope. They found that the adhesion in water is reduced by a factor of 30.
It was eventually concluded that the real reason for increased dust particle removal is not low friction between the droplets and the superhydrophobic surfaces. But it is the increase in the forces that can detach particles from the surfaces.