An active self-cleaning surface system for photovoltaic modules using anisotropic ratchet conveyors and mechanical vibration

The purpose of this work is to develop an active self-cleaning system that removes contaminants from a solar module surface by means of an automatic, water-saving, and labor-free process. The output efficiency of a solar module can be degraded over time by dust accumulation on top of the cover glass, which is often referred to as “soiling”. This paper focuses on creating an active self-cleaning surface system using a combination of microsized features and mechanical vibration. The features, which are termed anisotropic ratchet conveyors (ARCs), consist of hydrophilic curved rungs on a hydrophobic background. Two different ARC systems have been designed and fabricated with self-assembled monolayer (SAM) silane and fluoropolymer thin film (Cytop). Fabrication processes were established to fabricate these two systems, including patterning Cytop without degrading the original Cytop hydrophobicity. Water droplet transport characteristics, including anisotropic driving force, droplet resonance mode, cleaning mechanisms, and system power consumption, were studied with the help of a high-speed camera and custom-made test benches. The droplet can be transported on the ARC surface at a speed of 27 mm/s and can clean a variety of dust particles, either water-soluble or insoluble. Optical transmission was measured to show that Cytop can improve transmittance by 2.5~3.5% across the entire visible wavelength range. Real-time demonstrations of droplet transport and surface cleaning were performed, in which the solar modules achieved a 23 percentage-point gain after cleaning. Micro-patterned, self-cleaning solar panels can maintain their efficiency with little resources or human intervention. The efficiency of solar panels, often built on arid landscapes, can be reduced by up to 40% as dust accumulates on the panels. Di Sun and Karl F. Bohringer, from the United States’ University of Washington, created a micro-patterned solar panel glass that incorporates hydrophilic, curved ‘rungs’ on a hydrophobic surface. When mechanical vibration is applied to the panel surface, water droplets are directionally conveyed along tracks of rungs at speeds of up to 27 mm per second, collecting and removing surface contaminants as they go. The system is simply and inexpensively fabricated and uses minimal amounts of water. In one test, a solar module achieved a 23% gain in power output after cleaning with the system.