## 2 Methodology  
This study was conducted at the Solar Platform of Atacama Desert (PSDA, for its acronym in Spanish). This site constitutes a natural lab for studying and testing different types of solar technologies because the quality and availability of its solar resource (8 kWh/m\({}^{2}\) global radiation) and 3% cloudiness is appealing [15; 16]. It is located at 1000 m.a.s.l. in the Atacama Desert (24.09\({}^{\circ}\) S, 69.93\({}^{\circ}\) E), with a BNK-type Koppen climatic classification, corresponding to a cold arid desert zone [17]. This platform is operated by the Antofagasta Energy Development Center (CDEA, for its acronym in Spanish), Chile.  
For the geological study of the soil, seven pits were made around PSDA (Figure 1). Each of them was excavated at 3-3.7 m deep, including underground material sampling and a stratigraphic description. In addition, natural soil densities were measured to evaluate and classify them according to natural compactness, along with solubility tests according to norm NLT-1 1 4/99.  
To study material deposition on PV modules, four 6.5 cm \(\times\) 4.5 cm standard PV glasses were installed and were oriented northwards, with a 20\({}^{\circ}\) slope (fixed structure). These glasses were subjected to soiling in open air for one year (September 2020-2021) to observe the effect of the four seasons on the material deposition. Special attention was paid to the significant physical and chemical changes of the material deposition, as compared to other years of study on the site [18]. To evaluate the physical and chemical changes of the deposited material, morphological and elemental characterization tests were conducted with scanning electron microscopy (SEM-EDX), using a Joel SEMjSM-6360 LV equipment. To study PV glass soiling topography, a Witec Raman-AFM Alpha 300 atomic force microscope was used and operated in ambient temperature.  
To study soiling effects, four pieces of glass were left on a reference cell in the open air. Each PV piece of glass was divided into three sectors (low, middle, and high). Each sector was divided into three subsectors, thereby obtaining nine quadrants, and their middle and low parts (six spaces) were measured. To observe the soiling effect, the soiled glass measures were compared to the values of clean PV glass with the same characteristics as the reference cell. For a better representativity, measurements were taken in triplicate. To do this, a Photo Emission Tech CT80 AAA solar simulator was used, together with an Xe (300 W) lamp, simulating ASTM G173 norm conditions, i.e., 1.5 air mass and 1 sun illumination (100 mW/cm\({}^{2}\)). Intensity was adjusted using the c-Si (2 \(\times\) 2 cm) reference cell, while IV curves were measured with a Keithley 2400 source meter. Uncertainty on standard test conditions (STC) for IV parameters was 0.31% for the short-circuit current (I\({}_{\text{sc}}\)), 0.52% for the current at the maximum power point (I\({}_{\text{mpp}}\)), 0.07% for the open-circuit voltage (V\({}_{\text{oc}}\)), 0.18% for voltage at the maximum power point (V\({}_{\text{mpp}}\)), 0.36% for maximum power (P\({}_{\text{mpp}}\)), 0.36% for efficiency, and 0.55% for the fill factor (_FF_).