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Considerable loss of energy in the solar fields of Concentrating Solar Power (CSP) systems is caused by accumulated dust on the surface of the solar reflectors deployed in dusty arid and semi-arid zones. The monthly dynamics of changes in reflectance of the widely used second-surface silvered mirrors and innovative candidate aluminum materials under different site conditions can be useful for finding out the soiling characteristics of these mirror materials. Knowledge of the cumulative soiling of candidate mirror materials is essential to understanding their behavior at sites where cleaning is unavailable and water is scarce.

The monthly soiling study revealed that glass mirrors are more susceptible to soiling than aluminum mirrors during dry seasons with no rain. However, they recover their reflectance best after a rainfall event. In Agadir and Tantan, Aluminum type I performed differently from other aluminum types in that it recovered reflectance poorly after rain. On the other hand, it showed monthly soiling behavior similar to Aluminum types II and III during the dry summer (July August). In terms of cumulative long-term soiling, exposed mirrors were found to lose up to 73% of their initial cleanliness during the first 12 weeks of exposure. DFA modeling of the long-term.soiling time series found, based on the Akaike information criterion (AIC), that the best model has two shared trend patterns. (C) 2016 Elsevier Ltd. All rights reserved.