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Soiling of photovoltaic (PV) systems compromises their performance causing a significant power loss and demanding periodical cleaning actions. This phenomenon raises great concerns in the solar energy field, thus leading to notable research efforts over the last decades. Soiling is caused by a dual action of dust deposition and biofouling. However, surprisingly, the microbiological contribution to PV soiling is often overlooked or underestimated. In this study, a variety of qPCR-based methods have been developed to quantify the microbial load of fungi, bacteria and phototrophs on PV panels. These protocols were evaluated by comparison with culturedependent methods, and were implemented with real solar plants for two years. The results show that the developed molecular methods are highly sensitive and reliable to monitor the microbial component of the soiling. Fungal biomass was clearly dominant in all analysed PV modules, while bacteria and phototrophs showed much lower abundance. Light microscopy and qPCR results revealed that melanised microcolonial fungi and phototrophs are the main biofilm-forming microorganisms on the studied solar panels. In particular, the fungal qPCR protocol is proposed as a useful tool for monitoring of PV soiling, and investigating the microbial contribution to specific soiling cases.
Materials are subject to environmental constraints that include biological, chemical and physical factors. To gain confidence about durability and long-term performance of any material, environmental resistance testing procedures have to be amended with modern simulation procedures that include biological components. In fact, any environmentally exposed surface at temperatures lower than 121 °C will be home to microbial growth, even at high salt concentrations, extreme pH, environmental pollution, low water potential, and intense irradiation – everywhere where water is liquid and available. As a consequence, complex microbial ecosystems called biofilms are self-sufficient and found on almost all solid-air-water interfaces. Obviously, environmental changes perturb biofilm development but over a number of seasons, these changes result in relatively stable microbial communities peculiar and adapted to a particular niche and material. Certain microbial settlers are indicative of, and in a real sense mark, a particular biofilm and can, thus, be considered as “reference organisms”. Characteristic reference organisms’ peculiar to specific material-inhabiting communities can be isolated, identified, characterised and used in standard test procedures as well as research into materials science (materials improvement). In this presentation classical microbiological, genetic and molecular methods for studying reference organisms and their roles in materials deterioration will be presented. We will present a set of different reference organisms that are currently in focus of our research and testing development.
Microbial colonization affects the efficiency of photovoltaic panels in a tropical environment
(2015)
Sub-aerial biofilm (SAB) development on solar panels was studied in São Paulo. After 6, 12 and 18 months' exposure, photovoltaic panels were covered by increasing proportions of organic matter (42%, 53% and 58%, respectively). Fungi were an important component of these biofilms; very few phototrophs were found. Major microorganisms detected were melanised meristematic ascomycetes and pigmented bacterial genera Arthrobacter and Tetracoccus. While diverse algae, cyanobacteria and bacteria were identified in biofilms at 6 and 12 months, diversity at a later stage was reduced to that typical for SAB: the only fungal group detected in 18 month biofilm was the meristematic Dothideomycetes and the only phototrophs Ulothrix and Chlorella. Photovoltaic modules showed significant power reductions after 6, 12 (both 7%) and 18 (11%) months. The lack of difference in power reduction between 6 and 12 months reflects the dual nature of soiling, which can result from the deposition of particulates as well as from SAB fouling. Although 12-month old SAB demonstrated an almost 10-fold increase in fungal colonization and a higher organic content, the larger non-microbial particles (above 10 µm), which were important for efficiency reduction of lightly-biofilmed panels, were removed by high rainfall just before the 12-month sampling.
Sub-aerial biofilms (SABs) are ubiquitous microbial communities that develop at the interface between hard surfaces and the atmosphere. Inherent SAB 'core-settlers' include phototrophic algae, cyanobacteria, heterotrophic bacteria and microcolonial fungi (MCF). SABs do not simply cover hard surfaces; they interact with them in myriads of ways and bind to the underlying substrate. Secretion of extracellular mucilage aids adhesion, while organic acids and acidic polysaccharides weather the surface. As protection against solar radiation, many members of the SAB consortia produce shielding pigments while the phototrophic inhabitants are laden with photosynthetic pigments. All absorb light of many wavelengths and in addition, the cells themselves scatter light. Both effects change the spectra of incoming radiation (including wavelengths that are converted to electricity by photovoltaic cells) and decrease its intensity. To quantify these effects on SABs as complex entities of organisms and pigments, we measured the spectral properties of model and natural biofilms transferred to glass. Here we show that SABs growing on solar panels and other substrates scatter incident radiation between 250 nm up to 1800 nm and block up to 70% of its transmission. Model biofilms have the advantage that their microbial components can be 'tuned' to resemble natural ones of different compositions thus providing a novel materials-testing tool.