The most important parameter of a PV plant is the soiling rate. Therefore, it needs to be as accurate as possible.

Several methodologies can be used to assess the degradation, due to soiling on panels.

For greenfield projects, if the location and the design are standard, it is recommended to consider a soling rate between 1% and 2% per year.
It is then highly recommended to re-assess this rate after at least 1 year of operation, to check the soiling seasonality (heavy rain, snow, sandstorm, pollen etc). Several research papers [2][3] discuss the methodologies to calculate this rate and to evaluate the losses. For example, the bird dropping’s impact on the Yield can be three times higher than dust [3]).

For the first approach, an evaluation of the historical PR can be carried out by identifying periods with sudden drops. As part of the O&M contract scope, monthly I-V curve measures can be undertaken on a module’s sample (which is more adapted for ground-mounted plants). This rate can also be assessed using a specific sensor [4], which can monitor in real time the soiling on modules.

By David Roisse, Asset Manager

[2] M. Deceglie, L. Micheli, and M. Muller, “Quantifying soiling loss directly from PV yield,” IEEE Journal of Photovoltaics” ; January 2018.
[3] Dounia Dahlioui, Bouchra Laarabi, Moulay Abdelmjid Sebbar and Abdelfettah Barhdadi (Semiconductors Physics and Solar Energy Research Team High Education School, Mohammed V University in Rabat Morocco) ; Gauthier Dambrine, Etienne Menard, Jay Boardman (HELIOSLITE, Savoie Technolac) ; “Soiling Effect on Photovoltaic Modules Performance” ; October 2017.