Relationship between Atomic Force Microscopy and Centrifugation Measurements for Dust Fractions Implicated in Solar Panel Soiling.

This work tests the reliability of a simple, rapid centrifugal technique to estimate the removal force necessary to detach common airborne particles from the surface of a photovoltaic panel. Previously, we have used atomic force microscopy (AFM) to obtain the surface-particle adhesion force for different pollutant types that generally contribute to panel soiling. To overcome the limitations of AFM, the same particles were studied as a population using an ultracentrifuge. Detachment was quantified at speeds between 1000 and 10,000 rpm, both as individual particle counts and as projected surface area coverage. The force of centrifugal detachment for each particle type followed a similar trend as the adhesion force given by AFM. Organic and carbon-based materials needed higher centrifugal speeds to be removed, suggesting a stronger attachment to the surface. However, the technique also highlighted the importance of particle diameter, aggregates, and individual particle characteristics, which should be considered when predicting the probability of detachment. We have identified the relationship between AFM-derived adhesion and centrifugal detachment forces using model particle fractions of materials commonly found to soil solar panels, demonstrating the utility in using the more easily applied to centrifugal method to obtain information that can be calibrated to direct measurements of the force of particle attachment. This technique could be applied effectively in further studies on the influence of dust composition on long-term soiling and its reversibility.

Effect of Dust Composition on the Reversibility of Photovoltaic Panel Soiling.

Eight types of common airborne particles were used to investigate whether the composition of dust influences its soiling potential on photovoltaic panels. Chosen model particles were roughly spherical, 10-30 µm in diameter to minimize the differences in size and shape. While the predicted van der Waals forces were lower than the adhesion forces measured with an atomic force microscope (AFM), the adhesion potential as a function of surface energy did follow the theoretical pattern. The organic and carbon-based materials, namely the pollen grains and spherical graphite, exhibited a significantly larger adhesion force to the glass surface, indicating high attachment efficiency. The developed generalized linear model confirmed that the type of material should be included in soiling models as a variable, as it provides information on the likelihood of particles sticking to and remaining on the surface. The adhesion force between soiled particles and the surface can be estimated based on the local ambient dust composition to predict the short-term fate of the depositing particles and develop cleaning schedules and techniques accordingly. The results also highlight the need to study dust composition to understand long-term soiling, where chemical characteristics and changing environmental conditions may lead to cementation.