Wetting Properties of Simulated and Commercial Contaminants on High Transmittance Superhydrophobic Coating

Abstract

The large and necessary diffusion of huge solar plants in extra urban areas implies the adoption of maintenance strategies especially where human intervention would require high costs and logistic problems. Animal dejections like bird droppings and agricultural sprays are environmental agents able to significantly decrease light absorption and, in some cases, cause serious damage to the electric conversion systems in a photovoltaic panel. In this work, the performance of a superhydrophobic (SH) coating in terms of durable self-cleaning properties and transparency has been studied in the presence of commercial and simulated contaminants on glass reference and solar panel surfaces. Wettability studies have been carried out both in static and dynamic conditions in order to compare the compositional effect of commercial liquids used as fertilizers or pesticides and molecules like pancreatin as model substances simulating bird droppings. From these studies, it can be observed that the superhydrophobic coating, independently from the surface where it is applied, is able to repel water and substances used such as fertilizers or pesticides and substances simulating bird droppings, maintaining its properties and transparency. This kind of approach can provide information to design suitable spray formulations without the above-mentioned drawbacks to be used in natural environment areas and agrosolar plants.

Keywords: agrosolar; bird droppings; energy; solar panels; superhydrophobic surface; transmittance; wettability.

Figure 8

Optical transmittance as a function of wavelength (nm) for the different tested liquids.

Figure 1

On the left, 3D image of sample and correlated roughness profile acquired by 3D interferometric and confocal profilometer of SH coating with Sa = 52 ± 4 nm, on the right a photo of coated (A) and uncoated (B) solar panel for field experiments.

Figure 2

Surface tension dynamics of liquid C.

Figure 3

Slow motion sequence acquired by the high-speed camera at 3500 fps (Sprinter HD, Optronis) of liquid A and C droplets impacting with a tilted (3°) SH coating. Scale bar 2.5 mm.

Figure 4

Number of bounces of the five different liquids on the superhydrophobic surface from height of 20 mm (tip to the surface).

Figure 5

Contact time vs. We of the tested liquids.

Figure 6

Spreading factor (β) vs. Weber number (We) of the used liquids in the first two impacts (D₁/D₀, D₂/D₀) and between the two impacts (D₂/D₁).

Figure 7

Restitution coefficient vs. Weber number of the used liquids.