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

Abstract

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.

AFM Force Measurements to Explore Grain Contacts with Relevance for Planetary Materials

“…There are several alternative approaches that may be used in studies of the adhesion forces of small particles and powders. One such alternative is the use of centrifugal techniques to measure detachment forces for a bulk distribution of grains from a surface (e.g., Mizes et al 2000;Dove et al 2011;Nagaashi et al 2021;Varga & Wiesner 2022). This technique determines the force at which distributions of particles detach from a surface to set a limit on grain adhesion forces, based on percentages of particles removed from the surface as a function of rotation speed.…”

“…This technique determines the force at which distributions of particles detach from a surface to set a limit on grain adhesion forces, based on percentages of particles removed from the surface as a function of rotation speed. Recent work by Varga & Wiesner (2022) directly compares results from AFM and centrifugal forces studies, finding that the adhesion forces measured directly from AFM were comparable to those determined from centrifugal forces techniques; however, a larger range of possible forces were determined in the centrifugal techniques. Measurement results from both techniques are dependent on similar variables, including surface composition, size, shape, and experimental conditions.…”

Observing Real-Time Adhesion of Microparticles on Glass Surfaces

“…Here, mechanical vibrations were utilized to remove dust particles in the presence of water as they trickled down the surface . Vagra and Wiesner utilized a centrifugal force of ∼65.9 nN to dislodge silica particles in the size range of ∼15 to 30 μm from a glass surface . Recently, Kawamoto and co-workers installed parallel electrodes on the surface of PV panels connected to a high-voltage AC supply.…”

“…23 Vagra and Wiesner utilized a centrifugal force of ∼65.9 nN to dislodge silica particles in the size range of ∼15 to 30 μm from a glass surface. 24 Recently, Kawamoto and co-workers installed parallel electrodes on the surface of PV panels connected to a high-voltage AC supply. When the panel was tilted and the electrodes were switched between positive and negative potentials alternatively at regular intervals, the resulting electrostatic forces made the dust particles fall, cleaning the surface without water.…”