Effects of thermophoresis on dust accumulation on solar panels

The dust accumulation on a solar panel may be one of the most serious losses in the energy yield of photovoltaic systems, especially in the desert environment. The transport of airborne dust particles onto solar panels is governed by various physical processes and described by particle dynamics in a fluid. Here we investigate how the temperature gradient between the solar panel and the ambient air affects the dust accumulation. This socalled thermophoresis, which drives particles moving from the hot solar panel to the cold air, is examined using the boundary layer approximation for non-isothermal laminar airflow along the solar panel. We find that a strong thermophoretic force is built up at the entry region of the solar panel. With the velocity and temperature profiles of non-isothermal laminar airflow, we simulate Lagrangian particle trajectories. We demonstrate that for submicrometer-size particles, the thermophoresis builds a region free of the dust accumulation on the solar panel. It is shown that the thermophoretic effect may decrease the accumulation of submicrometer-size particles on the solar panel whose temperature is a few tens of degrees higher than the ambient air in the daytime.