# Effects of Microbiota on the Soiling Process of PV Modules in Arid Zones of the Atacama Desert
## 1 Introduction  
Soiling refers to the accumulation of dirt on the surface of photovoltaic (PV) modules, which affects their optical properties, and consequently, the economic profitability of projects [1]. This phenomenon has been extensively investigated in recent years due to the widespread adoption of PV in various locations worldwide, including desert, urban, industrial, residential, forested, and rural areas, where implementing cleaning and mitigation plans for this phenomenon is crucial for its profitability and sustainability. It was shown that soiling on PV modules results in a reduction of between 3% and 4% in energy production globally under ideal cleaning scenarios. This decrease in production translates into estimated economic losses of at least EUR 3-5 billion annually [2]. This figure is conservative, as the studies did not include residential installations, where the costs and losses are often even higher. Avoiding these multi-million-dollar losses presents a significant scientific challenge, which involves understanding the phenomenon of soiling in all its aspects to propose improvements in solar technologies in the most diverse places and under the most diverse environmental conditions. Additionally, it was shown that soiling affects different photovoltaic technology types in distinct ways. A study conducted in Mumbai, India, by [PERSON] et al. [3] demonstrated that for a dust density of 1.8 g/m2, the resulting losses in spectral reflectance and quantum efficiency were 17.7% in amorphous silicon cells, 15.7% in cadmium telluride (CdTe), 15.4% in crystalline silicon, and 14.5% in copper indium gallium selenide (CIGS). Traditionally, soiling was comprehensively studied, without clearly distinguishing between the inorganic and organic contributions of dirt, by treating it rather as a unified phenomenon. This approach is due to the critical nature of soiling for plants located in desert areas, where dirt levels are notably high and dominated by inorganic materials, such as quartz, albite, and gypsum, as observed in countries across the Middle East, North Africa, and northern Chile [4; 5]. However, given the diverse locations where PV projects are currently installed, there is a growing need to understand soiling from a broader perspective that includes the organic components, particularly the microbiological component, whose contribution has been underestimated. The state of the art demonstrates a lack of studies on the impact of microorganisms on PV panels, as reflected in the limited availability of scientific literature. [PERSON] et al. [6] noted that between 2013 and 2015, only 1 out of 198 studies focused on microorganisms responsible for soiling in PV technologies. Until the end of 2021, few studies investigated the presence of microorganisms and the development of biofilms on PV modules, as well as the relationship between microbial communities and their impact on PV system performance [7; 8]. Limited research on microbiota in soiling focused on describing and quantifying the diversity of microbial communities associated with PV panels through metagenomic analysis and predicting microbial functions [6; 7]. Another small group of studies focused on understanding the metagenomic analysis of cultivable bacteria by characterizing their adhesive capabilities, UV radiation resistance, and desiccation [9; 10]. Research related to the composition and development of biofilms formed by fungi, algae, bacteria, and cyanobacteria, as well as their impact on the efficiency of crystalline silicon modules, showed a reduction in panel power of at least 7% in six months and up to 11% in 18 months of exposure to the environment [8]. The compositions of microbiota can vary significantly according to the geographical environment and local climatic conditions [11; 12]. This means that the effects of microbiological soiling can differ significantly between different regions, which highlights the need for specific studies adapted to different PV project installation locations.