Recent developments in climate change have increased the frequency of dust storms in the Middle East. Dust storms significantly influence the performances of solar energy harvesting systems, particularly (photovoltaic) PV systems. The characteristics of the dust and the mud formed from this dust are examined using various analytical tools, including optical, scanning electron and atomic force microscopies, X-ray diffraction, energy spectroscopy and Fourier transform infrared spectroscopy. The adhesion, cohesion and frictional forces present during the removal of dry mud from the glass surface are determined using a microtribometer. Alkali and alkaline earth metal compounds in the dust dissolve in water to form a chemically active solution at the glass surface. This solution modifies the texture of the glass surface, thereby increasing the microhardness and decreasing the transmittance of the incident optical radiation. The force required to remove the dry mud from the glass surface is high due to the cohesive forces that result from the dried mud solution at the interface between the mud and the glass. The ability altering the characteristics of the glass surface could address the dust/mud-related limitations of protective surfaces and has implications for efficiency enhancements in solar energy systems.

An understanding of the dynamic motion of a water droplet is critical to reduce the effort required to remove dust particles from such surfaces.

A water droplet behavior on a hydrophobic surface is examined relevant to the dust particles removal from the surface. Surface crystallization of polycarbonate is realized in acetone bath and the resulting surface is coated by the functionalized nano-size silica particles towards reducing contact angle hysteresis. This arrangement provides droplet rolling/sliding on the hydrophobic surface. Droplet translational velocity is formulated and predictions are compared with those resulted from the high speed recorded data. Influence of surface inclination angle on droplet dynamics is investigated and the dust removal mechanism on the inclined surface is analyzed. It is found that predictions of droplet translational velocity agree well with those obtained from the experiment. Droplet rolling dominates over sliding on the inclined surface and droplet sliding velocity remains almost 10% of the droplet translational velocity. The main mechanism for the dust particles removal is associated with the droplet fluid cloaking of the dust particles during its transition on the hydrophobic surface. Droplet acceleration, due to increased surface inclination angle, has effect on the rate of dust particles removal from the surface, which is more apparent for large droplet volumes. Increasing droplet acceleration improves the coverage area of the clean surface.

The dynamic motion of a water droplet on an inclined hydrophobic surface is analyzed with and without environmental dust particles on the surface. Solution crystallization of a polycarbonate surface is carried out to generate a hydrophobic surface with hierarchical texture composed of micro/nanosize spheroids and fibrils. Functionalized nanosize silica particles are deposited on the textured surface to reduce contact angle hysteresis. Environmental dust particles are collected and characterized using analytical tools prior to the experiments. The droplet motion on the hydrophobic surface is assessed using high-speed camera data, and then, the motion characteristics are compared with the corresponding analytical results. The influence of dust particles on the water droplet motion and the amount of dust particles picked up from the hydrophobic surface by the moving droplet is evaluated experimentally. A 40 μL droplet was observed to roll on the hydrophobic surface with and without dust particles, and the droplet slip velocity was lower than the rotational velocity. The rolling droplet removes almost all dust particles from the surface, and the mechanism for the removal of dust particles from the surface was determined to be water cloaking of the dust particles.