## 4 Conclusions  
This paper proposes a methodology to understand the influence of local geology on soiling deposition and to support decision-making in cleaning PV plants. The methodology is based on geologic analysis using pits and the physicochemical characterization of materials deposited on PV modules. Data to make recommendations regarding cleaning methodologies to be used in a desert zone with soluble salts were obtained. This methodology can be used in any place around the world, in so far as there is interest in developing a PV project, considering that some necessary and mandatory work must be done, e.g., making pits, from which invaluable data can be obtained.  
As a whole, the results show that soils with soluble salts (gypsum) have a positive influence on crust formation, thus avoiding high soiling levels. However, the influence of soluble salts on the PV module is negative since it fosters the cementation process. These data suggest that cemented crust formation must be avoided by daily cleaning. If this cannot be done, solvents that are able to dissolve the soluble salt crust should be used.  
Additionally, this study shows the impact of local geology on PV glass soiling deposition, using one of the most common configurations (fixed slope) on a worldwide basis. The results show a connection among the deposited material chemistry, the installation configuration, and the local geology. Crust formation is favored on the lower part of the PV glass, where a greater amount of cemented material is generated. This is also the place where more energy is needed to eliminate the soiling crust. Electric measurements of IV curves show that the greatest concentration of crusted material occurs where electric losses are greater.  
In general, the methodology used is suitable for studying soiling in different places around the world. One of the advantages is that data are obtained during the PV plant construction process, during which soil studies (pits) are needed. This process is neccessary for all PV projects. Hence, this stage can be used to obtain data on local geology and its possible influence on soiling. This must be complemented with the morphological and chemical analysis of the material deposited on PV modules to improve decision-making regarding mitigation and cleaning techniques. These simple methodological characteristics have become highly important due to the great development of solar projects, seeking PV plant profitability on a worldwide basis.  
Conceptualization, D.O. and A.T.; Formal analysis, D.O. and D.E.; Investigation, D.O. and A.T.; Methodology, P.F. and A.M.; Project administration, M.H.; Supervision, J.L. and E.F.; Writing--original draft, D.O., A.T. and P.F.; Writing--review & editing, P.F. All authors have read and agreed to the published version of the manuscript.  
The authors thank ANID/FONDAP/15110019 \"Solar Energy Research Center\" SERC-Chile; Chilean Economic Development Agency (CORFO), contract No17 PTECES-75830 for project \"AtaMoS Tec\"; GORE-Antofagasta, Chile, FIC-R Antofagasta Project 2017 BIP code 30488824-0; Unidad de equipamiento cientifico \"MAIN\" at Universidad Catolica del Norte for supporting sample preparation and data analysis and generation through the SEM and AFM team; ANID/FONDECYT Project N\({}^{c}\)11190289 (APC funding project); and FONDECYT Project 1181302 for IPCE use.  
Not applicable.  
The authors declare no conflict of interest.