PV module soiling measurement uncertainty analysis

The accumulation of dust and other environmental contaminants on PV modules, also known as PV module soiling, is a significant source of lost potential power generation for PV installations. Designers and operators of utility-scale solar power plants are increasingly seeking methods to quantify soiling-related losses, in order to improve performance modeling and verification or to optimize washing schedules. Recently, soiling measurement equipment has been introduced based on the measurement of two co-planar PV modules, one of which is regularly cleaned, and the other of which naturally accumulates environmental contaminants. These measurements are used to determine a soiling ratio (SR), which may be applied as a derate factor in analysis of the PV system performance. In this work, we have performed an analytical calculation of the uncertainty in soiling ratio measurements. We find that soiling ratio measurements can be performed with uncertainties on the order of ~±1% or better on an absolute basis, depending on calibration conditions, operating temperatures, angular alignments, and other factors we discuss.