Using rotation to remove dust

Dust can collect on photovoltaic modules, particularly in desert environments, severely impacting solar energy production. Although surface materials that reduce accumulation of dust particles are being considered, reliable methods to test them are needed.

Ilse et al. propose a technique known as the rotational force test method (RFT) and report theoretical and experimental validations of it. Three types of dust were used: spherical polymer beads, calcite particles and a substance known as Middle East Test Dust.

The RFT technique involves spinning a flat, dusty glass surface around its center point. Centrifugal forces acting parallel to the surface roll or slide the dust particles to the glass perimeter. The technique uses optical microscopy to observe and analyze the surface before and after spinning.

To enable the determination of dust adhesion forces from RFTs, the investigators also developed simple models for the system. For this, they considered only van der Waals forces. Both gravitational and electrostatic forces are orders of magnitude lower and can be neglected.

“The model includes considerations of distributed particle adhesion forces to account for rough surfaces and arbitrary shapes of natural dust particles,” said author Klemens Ilse. In addition, the model describes both sliding and rolling as mechanisms by which the dust particles are removed. Experimentally determined values of adhesion forces for natural dust particles agree well with these theoretical calculations.

To account for changes the investigators observed when the humidity varied, future work will include additional forces. “Capillary forces are neglected in the present approach reflecting dry desert conditions, but they should be included in future work,” said Ilse

The RFT methodology should have wide applicability since only a spin coater and optical microscope are needed.

Source: “Rotational force test method for determination of particle adhesion—from a simplified model to realistic dusts,” by Klemens Ilse, Muhammad Zahid Khan, Katja Lange, Harish Nagari Gurumoorthy, Volker Naumann, Christian Hagendorf, and Jörg Bagdahn, Journal of Renewable and Sustainable Energy (2020) The article can be accessed at https://doi.org/10.1063/5.0015122 .