Assessment of dust adhesion forces on the hydrophilic/hydrophobic glasses at two representative CSP sites in Morocco

Abstract

Many sites with high solar radiation like MENA regions face high dust loads that reduce the efficiency generation of solar plants. In this context, this paper provides an overview of dust adhesion mechanism on the surfaces of concentrated solar power (CSP) mirrors. The assessment of dust adhesion was performed on the hydrophilic/hydrophobic glasses at two representative CSP locations in Morocco (Ouarzazate and Midelt). Two types of reflecting mirrors are examined. The first one is based on superhydrophilic TiO₂ protective coating, and the second one is the reflector mirror based on hydrophobic Al₂O₃ protective coating. The research shows that for particle radius of 2 µm, the Van der Waals force dominates for hydrophobic coating for Midelt with high humidity. In contrast, the capillary forces are prominent on the superhydrophilic TiO₂ coating for Ouarzazate with low humidity. The results show good agreement with the X-ray diffraction results. However, as compared to Midelt dust, the dust particles from Midelt are formed of Smectites for the clay fractions. Smectite is highly swelling clay in water compared with Illite, Kaolinite, and Vermiculites types of clay minerals (low swelling clay in water). This work provided a facile method for the calculus of adhesion forces on the surfaces of CSP mirrors and as result helps us to select the best types of anti-soiling coating for reflector mirrors.