# Effects of Microbiota on the Soiling Process of PV Modules in Arid Zones of the Atacama Desert
## 4 Conclusions  
This work provides fundamental information about the microbiota present in the soiling deposited on the surface of PV modules in the Atacama Desert. The selected study sites (UA and PSDA) represent different climatic conditions within the same region. In these two locations, the mineralogical composition revealed the presence of hygroscopic materials, such as gypsum at the PSDA and halite at the UA, which, along with favorable atmospheric conditions, facilitated the cementation process. This microbial community, which was dominated by genera adapted to the extreme arid conditions of the Atacama Desert, played a significant role in the biofilm formation. This work demonstrated the capabilities of some bacteria typically found in harsh environments, such as the Atacama Desert, to form biofilms on PV glass in laboratory conditions. In the same way, some of these bacteria may colonize glass surfaces from PV modules that contain salts as a substrate, which may promote the formation of a microbial community dominated by genera adapted to the extreme arid conditions of the Atacama Desert. This microbial community may play a significant role in biofilm formation, which contributes to soiling. As a result, soiling adheres not only due to cementation but also due to biofilm formation. In the case of the PSDA, despite the low TOC concentrations, biofilms composed of the genera _Peribacillus_ and _Kocuria_ were observed. In contrast, the UA exhibited a higher presence of microorganisms that favor biofilm formation, including the genera  
Figure 9: Stages of the soiling process in PV modules considering the contribution of microbiota. The stages considered are the (1) initial deposition of particles (transport and deposition of microbiota); (2) rebound of particles that do not adhere to the surface; (3) accumulation of dirt, microbial colonization, and biofilm formation; and (4) removal and transport of dirt adhered to the surface. Bacillus, Sporosarcina, Bhargavaa, Mesaobacillus Cytobacillus, Caladakilobacillus, and Planococcus. Surprisingly, the presence of toxic heavy metals at the UA soiling was not a factor that prevented biofilm formation. We concluded that the difference in the diversity genera content in the biofilms that formed from the soiling of both sites could be primarily attributed to the location and more important factors than the toxic heavy metals, such as differences in the TOC and fluctuating humidity levels (arid desert and coastal), which directly influenced the microbial diversity and biofilm formation in the laboratory. Under certain conditions, biofilm formation may occur on PV modules installed in the Atacama Desert. This new insight could be a contribution to understanding the soiling formation. Based on the characterization of the microbiota, a new soiling mechanism is proposed that incorporates its biological contributions and complements existing models. The soiling process caused by microbiota was identified to occur in three stages: microbiota deposition, colonization, and biofilm formation. So far, biofilm formation has been demonstrated to occur in virtually any environment, from natural to inorganic materials. However, there is limited information on biofilm colonization on photovoltaic modules. This new soiling mechanism provides insights to develop more effective cleaning strategies and design anti-soiling coatings. In conclusion, the microbiota identified in the soiling samples from the UA and PSDA not only underscored the resilience of microbial life in extreme desert environments but also highlighted its role in the soiling process on solar panels. Understanding these microbial communities is crucial for optimizing maintenance strategies and improving the performance of solar energy systems in arid regions, like the Atacama Desert. This work marks the beginning of ongoing research aimed at understanding the impact of microbiota on the electrical and optical performance of PV modules.