A recent article highlighted the steps taken to gain a few percentage points in the efficiency of PV panels. While these small gains can have a large impact on output, the gains can be cancelled out by losses due to soiling. Prediction and control of soiling forms an important part of operations for a solar farm.
All solar PV installations, irrespective of type and installation method, suffer from soiling in some form or the other. Soiling is the deposition of a coating of material, mainly dust, on the surface the panel, which blocks out some of the radiation reaching the PV cells. Soiling is due to airborne particles settling on, and remaining on, the glass surface of the panel.
Fig. 1: Global dust potential (DTF (1).
Soiling is a complex process which occurs as a result of the dust originated from a variety of sources such as windborne pollutants, airborne liquid constituents, particulates from construction, mining and pollen. The dust gets suspended atmospherically in some manner, including wind and diffusion, and gravity causes it to settle on the panel. The rate of soiling will depend on the amount of dust in the air, but can be affected by other factors such as wind speed, etc. Another factor contributing to soiling is the adhesion mechanism, which is affected by the surface texture of the module, tilt angle, humidity/moisture and re-suspension [3].
These materials can be present in the air and on the module in different combinations and forms; such that the type of shading that occurs can be considered either ‘soft’ or ‘hard’ shading; Soft shading takes place when haze particles such as smog or light dust on the module reduces the overall intensity of the solar irradiance which reaches the solar cells. Hard shading occurs when a more solid type of dust or material (such as bird droppings) blocks the sunlight in a definable shape [5]… (Click here for the pdf)
