Anti-soiling Coatings Research Articles

Substrate controlled hydrophobicity of the Y2O3 films

The development of hydrophobic surfaces is an important factor for clean energy production from solar arrays, enabling their operation at the highest possible efficiencies for the longest possible time, without the need for physical intervention. This work reports the development of hydrophobic Y2O3 thin films on a range of transparent glass substrates. The growth of the Y2O3 films from the mono-hydrate yttrium (III) complex of 1,3-diphenyl-1,3-propanedione [Y(dbm)3(H2O)] is studied using the aerosol-assisted chemical vapor deposition (AACVD) technique. The qualitative evaluation of the deposited films and their hydrophobicity is assessed using several materials characterization techniques, such as scanning electron microscopy, grazing incident X-ray diffraction, Fourier-transform infrared, X-Ray photoelectron spectroscopy, in addition to a surface free energy and water contact angle measurements. This work demonstrates experimentally a relationship between the Y2O3 wettability and its physico-chemical characteristics in terms of surface energy, chemical composition, and morphology which is controlled by the type of glass support used. The water contact angle of the hydrophobic Y2O3 coating grown on the F-doped tin oxide glass reached 128°; currently the first deposited on transparent glass. This film exhibits the highest WCA reported up to date without the need for performing post-reaction surface treatment processes. The hydrophobic nature of the transparent Y2O3 films marks a significant leap forward in the field of anti-soiling coatings suitable for photovoltaic technology.

Sol-gel coatings for solar cover glass: Influence of surface structure on dust accumulation and removal

Soiling of solar cover glass is a major cause for efficiency loss of solar photovoltaic modules. Anti-soiling coatings can be used to reduce the rate of soiling and lower cleaning costs. The efficiency of these coatings has been demonstrated in laboratory and field tests, but the mechanisms and relevant parameters are still not well understood.In this article, we present a study on the influence of surface structure of hydrophilic sol–gel coatings on their anti-soiling performance in terms of both, dust accumulation and subsequent indoor tests for dust removal by wind. The surface structure of the films originates from the addition of colloidal silica particles of different sizes to the sols used for film preparation. In the dust deposition experiments, standardized test dust and dust collected from solar installations were used. Repeated tests were conducted under controlled humidity.In the case of dust deposition, the accumulation of dust particles larger than ∼10 µm is strongly reduced, in relation to bare glass, by the anti-soiling effect of all coatings regardless of their surface structure.For the dust removal via wind, coatings that bear a smoother surface structure are cleaned more easily than coatings with a rougher surface structure.Additionally, larger and rounder dust particles are removed more easily from coatings with a rougher surface structure (structure height over ∼40 nm), while smaller and more irregularly shaped dust particles are removed more easily from coatings with a smoother surface structure.

Contemporary considerations of the utility of self-cleaning coatings for solar power installations-The SolarSkin system

Soiling of conventional Photovoltaic (PV) modules and Concentrated Solar Power (CSP) mirrors significantly affects the efficiency of the system. Although there are several soiling mitigation strategies, none of them has been widely adopted, since effectiveness in real field conditions is often disputed. Anti-soiling coatings are perhaps the most promising solution for solar power projects since they combine low cost and effectiveness. These are broadly categorized into hydrophilic and hydrophobic. Hydrophilic coatings perform better in arid climates, whereas hydrophobic coatings have a wider spectrum of functionality. Most of them however suffer from various drawbacks, such as poor durability and transmittance which restrict the extent of benefits. In addition, there are only a few reliable technologies that can be retrofitted to existing installations. Predicting the efficiency of a given anti-soiling coating in a specific plant is difficult, therefore, the objective of this work was to identify those parameters that are critical to their performance in real outdoor conditions. Focus was given to the drawbacks of current hydrophobic coating systems and the requirements that a modern anti-soiling coating should satisfy in order to be implemented as an effective after-market solution to degraded solar systems. A prominent example of cutting-edge, high-performing self-cleaning technology, i.e. the SolarSkin system developed by BFP Advanced Technologies, is additionally presented. The latter can renovate deteriorated solar collectors, increase the energy yield of the system, and protect it from weathering effects over its expected operational lifecycle. Potential increment of the system’s efficacy as well as maintenance savings are also briefly discussed.

Soiling mitigation potential of glass coatings and tracker routines in the desert climate of Saudi Arabia

AbstractHigh levels of airborne dust, frequent dust storms and infrequent rain events are some of the reasons why soiling can drastically reduce the energy yield of photovoltaic modules in desert areas. There are ongoing and increasing efforts to identify appropriate and economically feasible strategies that can be used to mitigate soiling in deserts. Both innovative tracking with adapted resting positions during night and anti‐soiling coatings (ASCs) are considered as potential solutions to reduce soiling. In this study, the individual mitigation potential of both ASC and tracking routines as well as the combination of the two approaches are investigated. For this, outdoor exposure tests were carried out in desert region of Saudi Arabia. Coated and uncoated glass samples were tested in different tilt configurations: fixed, 1‐axis tracking with horizontal stowage (facing the sky) and 1‐axis tracking with vertical stowage during the night. Both methods indicate significant soiling reductions, especially for the combined solution of ASC and tracking with vertical night stowage, where soiling losses can be reduced by up to 85%. In addition, it has been shown that the relative ASC performance can be improved when using vertical night stowage compared to fixed tilt or standard 1‐axis tracking scenarios.

Understanding Multiple Stressors Which Degrade Antisoiling Coatings: Combined Effect of Rain, Abrasion, and UV Radiation

Antisoiling coatings (ASCs) are nano or microlayer coatings which reduce the settlement of dust on the surface of the PV module and are extensively investigated as a dust mitigation strategy. Since the coating is applied on the outer surface of the PV module, they are exposed to various environmental stressors, and the durability of these coatings is essential. Various studies have reported the effect of individual stressors that degrade ASCs. However, there are very few reports on the impact of the combination of stressors relevant to outdoor field conditions. In this article, we investigate the impact of the combination of the following stressors that degrade ASCs: 1) the combination of the impact of raindrops and acidic water, 2) the combination of UV radiation, the impact of raindrops, and acidic water, and 3) the combination of abrasion, UV radiation, the impact of raindrops and acidic water. The key takeaways from this study are 1) coating life reduced by 21× (average of all coatings) when exposed to the rainy season compared with those exposed to the nonrainy season. 2) All coated samples show lower coating life varying from 10× to 48× when exposed to the impact of raindrops with pH 7 water than those exposed to water immersion/water contact test with pH 7 water. This indicates that, during a rain event, the impact of raindrops hitting the coated surface causes more significant damage than water contact. This study shows that coatings A, B, C, and D are unreliable for long-term use in warm and humid climate zones, considering 25-year module lifetime. However, other chemistries of hydrophobic and hydrophilic solutions could be effective if they exhibit long-term reliability.

Abrasion resistance of spray coated anti-soiling coatings during waterless cleaning of PV modules

Dust deposition on photovoltaic (PV) modules leads to remarkably high energy loss, which has an enormous economic impact on PV plants. Anti-soiling coatings have been extensively studied as a cost-effective dust mitigation strategy in the PV market. However, such coatings applied to the top surface of the PV modules should be resilient to environmental stressors. Coated modules would also need periodic cleaning; thus, such anti-soiling coating must be abrasion-resistant. This article investigated the abrasion-resistant property of 4 types of commercial hydrophobic anti-soiling coatings. The study emulates the effects of different brush designs on the degradation of anti-soiling coatings under low soiling conditions. The samples were subjected to dry brush cleaning. We tested the samples with 3 different brush designs (linear brush 1, linear brush 2 and rotary brush) with a varying packing density of brush bristles. Linear brush 1 had 3.5 times higher packing density of brush bristles than linear brush 2 and rotary brush. By increasing the packing density of brush bristles by 3.5 times, the degradation rates were enhanced by factors varying from 1.2 X to 4.4 X in coated samples when cleaned with linear brush 1, compared to linear brush 2 and rotary brush. Phenylsilicone based coating shows higher degradation rates (varying from 2.9 X to 11.2 X) than fluoropolymer-based coatings. The result indicates a decline of the anti-soiling property as we see an increase in roll-off angle (compared to Mumbai, India’s tilt angle = 19º) with the increase in number of cycles. The results also show that compared to the structural brush design, the packing density of the brush bristle has a strong impact on the coating life. However, the actual coating life in the field would also be dependent on other environmental factors like the amount of dust deposit, moisture etc.

A versatile approach towards development of easy-to-clean transparent nanocoating systems with pronounced anti-static properties for various substrates

<abstract> <p>Sol-gel is a widely applied method for the development of hydrophobic anti-soiling coatings. Most of them however suffer from serious drawbacks which restrict their generic applicability, especially on surfaces with limited number of hydroxyl groups. This study aims to propose a facile and straightforward strategy for the development of an "one-fits-all" anti-soiling coating with strong adhesion to a variety of hard, non-absorbent surfaces. The structure of the proposed composition is based on a two-component coating system consisting of an organopolysilazane primer and an alkoxysilane topcoat, based on a quaternarized ammonium silane. Morphology and microstructure were systematically studied, while hydrophobicity, adhesion, stability, abrasion and chemical resistance were determined on aluminum and PC substrates. The anti-soiling behavior of the proposed coating system was also evaluated. It was found that the polysilazane primer provided mechanical and chemical robustness regardless of substrate type, while the quaternarized silane offered pronounced easy-to-clean and anti-static attributes. The combination of such attributes within a single sol-gel coating system is highly beneficial for numerous applications.</p> </abstract>

Review of Current State-of-the-Art Research on Photovoltaic Soiling, Anti-Reflective Coating, and Solar Roads Deployment Supported by a Pilot Experiment on a PV Road

The objective of this review paper is to provide an overview of the current state-of-the-art in solar road deployment, including the availability of anti-reflection and anti-soiling coating materials for photovoltaic (PV) technology. Solar roads are built using embedded PV panels that convert sunlight into electricity, which can be stored for later use. Prototypes of solar roads have been tested on various continents, but the lack of suitable PV materials has limited their effectiveness compared to conventional PV systems. By analyzing the existing literature on solar roads and PV materials, including anti-reflection and anti-soiling coatings, we aim to identify gaps in knowledge and propose an action plan to improve the resiliency, durability, and reliability of PV panels in solar road applications. This will enable the deployment of solar roads as a clean, renewable energy source.

Anti-Soiling Coatings for Enhancement of PV Panel Performance in Desert Environment: A Critical Review and Market Overview.

Areas with abundant sunlight, such as the Middle East and North Africa (MENA), are optimal for photovoltaic (PV) power generation. However, the average power loss of photovoltaic modules caused by dust accumulation is extreme and may reach 1%/day, necessitating frequent cleaning which adds to the cost of operations and maintenance. One of the solutions to the problem of PV soiling is to develop anti-soil coatings, where hydrophilic or hydrophobic coatings with spectral characteristics suitable for PV applications are added to the outer layer of PV glass. However, the effectiveness of such coatings depends extensively on climatic conditions and geographical locations. Since coatings add to the cost of solar panels, it is imperative that they are first tested for suitability at the intended location and/or in similar weather conditions prior to their large-scale deployment. This critical review focuses on various anti-dust technologies employed to mitigate the PV soiling issue. The in-depth comparison of the various developed techniques and materials aims at providing a relevant input in adapting the right technology based on particles’ accumulation mechanism, weather conditions, and geographical location. Though the mechanical cleaning process is the most used solution to date, development of thin film anti-dust coating could be a better alternative—when it is relevant—due to its abrasion-free capability, large deployment, economic viability, and durability. This review aims at serving as a reference in this topic, thereby paving the way to adapting efficient anti-dust coatings, especially in the MENA region and/or desert environment at large, where it is the most relevant.

Proposing a sustainable strategy for the fabrication of robust anti-soiling coatings with enhanced antibacterial attributes for non-absorbent substrates

In this paper, we propose a convenient methodology for fabricating a generic structure toward developing a robust, easy-to-clean transparent coating with inherent antibacterial properties for smooth, non-absorbent surfaces, such as glass and plastics. A two-step coating comprising an organopolysilazane primer and an alkoxysilane topcoat, based on positively charged quaternary ammonium silanes, is proposed. The topcoat is co-condensed with the primer to provide a hybrid structure with high wear strength even on surfaces that lack surface hydroxyl groups. Surfaces examined included glass and PMMA. The coated samples were studied in terms of abrasion resistance as well as anti-soiling and antimicrobial performance. It was found that the quaternary silane compound could covalently graft onto the primer acting both as an antibacterial, anti fungicidal, and hydrophobizing agent. The utility of amphoteric surfactants within the coating’s solution was also examined. The resulting structure was transparent and exhibited pronounced self-disinfecting properties with remarkable sustainability. These attributes suggested a dual functionality of the coating, i.e., both anti-soiling and antimicrobial, thus rendering it a potential candidate for numerous industrial and commercial applications.

Outdoor performance of anti-soiling coatings in various climates of Saudi Arabia

Soiling can significantly reduce the energy yield of PV modules, especially in desert climates due to high airborne dust concentration, frequent dust storms, and rare rain events. The current vast deployment of PV in deserts requires adequate and economically feasible strategies for the mitigation of soiling. In this regard, anti-soiling coatings (ASCs) could be a promising solution as they could significantly reduce the accumulation of dust and resultant soiling losses. To assess the outdoor performance of different ASCs, an outdoor benchmark test setup was designed and installed at eight different locations in Saudi Arabia. The soiling losses have been determined by measuring the transmittance of the samples before and after outdoor exposure for monthly (2 locations) and quarterly (6 locations) exposure periods throughout one full year. Within this study, detailed results are presented for an uncoated reference glass and 3 out of 15 coatings, which have been tested. In addition, a general coating ranking based on average monthly and quarterly soiling losses of the full set of ASCs is also presented. The results indicate huge variations of anti-soiling functionality of the coatings depending on exposure period and location. Overall, both improved and decreased anti-soiling performances have been observed for coatings compared with an uncoated reference glass. An investigation on the correlation between the daily soiling loss and weather parameters indicates that besides precipitation and particulate concentration in the air, also dew and its interaction with the coatings is an important influencing parameter strongly affecting soiling rates. Looking at the two most promising coatings with very low-adhesive properties, the overall performance benefit is higher for a hydrophilic surface in high humid areas (coastal) and a hydrophobic surface in dry areas (central desert). • First of its kind benchmark study for an extended set of anti-soiling coatings (ASC) and locations. • ASC performance evaluation at eight different desert locations in Saudi Arabia. • Soiling rates are higher in coastal areas of Saudi Arabia than in inland regions. • Weather data analysis indicates that dew is an important parameter increasing annual soiling. • Coatings tend to perform either well or poorly in most locations.

Optical Transmission Losses of a TiO2-based Anti-soiling Coating for Use in Outdoor Photovoltaic Applications

Background: Soiling can be a major challenge for photovoltaic (PV) installations, depending on their location, as it reduces transmission and can lead to significant losses. Anti-soiling coatings have been demonstrated to reduce soiling losses and thereby increase PV power production. Objective: This article investigates the applicability of a titanium-dioxide-based anti-soiling coating developed by Photocat under the name “ShineOn” for use with PV installations. The main parameter examined is the optical transmission losses, as this directly translates to performance losses during non-soiled operations. Methods: Measurements of transmittance are carried out using both indoor laboratory setups as well as outdoor PV installations, including measurements of the short-circuit current (Isc), incidence angle modifier (IAM) and spectral transmittance. Investigated samples include both full-sized modules and custom-made mini-modules containing a single solar cell. Results: Both indoor and outdoor measurements show minor transmission losses in the range of 0.3 to 0.6 % and negligible effects on the IAM. Additionally, observations indicate that samples should be coated after lamination, as losses for samples coated before lamination are slightly higher. Conclusion: As the transmission losses due to the ShineOn coating are small and no additional angular- dependent losses were observed, the coating is deemed not to be detrimental for PV applications. Proper assessment of the usefulness requires investigations of the anti-soiling properties, for example, through test installations in regions with high soiling rates.

Soiling of photovoltaic panels in the Gulf Cooperation Council countries and mitigation strategies

The use of solar photovoltaic (PV) energy is significantly increasing; thus, PV systems’ efficiency in outdoor working conditions must be optimized. Dust accumulation (or soiling) is one of the most critical external factors affecting the PV efficiency in arid regions. The Gulf Cooperation Council region is showing a tremendous increase in PV deployment. Accordingly, concerns about the maintenance of PV systems in such dusty, water-scarce areas have been raised. This brief review aims at providing an overview of the critical (issues) of PV soiling in the Gulf Cooperation Council. It summarizes findings on dust characteristics in this region and the effects of dust and soiling on PV performance. The review also summarizes various mitigation strategies currently available or under development, with a focus on anti-soiling coatings (ASC). • Soiling is a critical external factors affecting the PV efficiency in GCC. • One main causes of particle sticking to PV modules in arid regions is condensation. • Dusts mostly originate from local soils, construction activities and wind-blow. • A typical monthly decrease of 10% of PV power output is due to soiling in GCC. • Mechanical and passive strategies are used to mitigate dust accumulation.

Characterizing the coverage of anti-soiling coatings on photovoltaic modules

Anti-soiling coatings help protect solar modules against dust deposition. Tapping mode atomic force microscopy phase imaging can be used to ensure these coatings have ample coverage.

Experimental investigation of the anti-soiling performances of different wettability of transparent coatings: Superhydrophilic, hydrophilic, hydrophobic and superhydrophobic coatings

Natural soiling of photovoltaic (PV) panel is an increasing problem especially in arid and desert areas. Finding a strategy that can reduce dust adhesion on PV panels is highly desirable but remains challenging. In this paper, different wettability of transparent coatings including superhydrophilic, hydrophilic, hydrophobic and superhydrophobic coatings were prepared to investigate the importance of surface roughness and surface energy. Their anti-soiling effects were investigated under different airflow velocity and different tilt angles. Dust deposition density, reduced transmittance, the ratio of reduced transmittance between bare glass surfaces and coatings, and PV efficiency reduction were used to characterize dust resistance performances. It is found that dust adhesion on superhydrophilic coatings was eminently governed by their respective high surface energy, with surface roughness rendering lesser contribution towards resisting/adhering effects. However, for other three coatings, further reducing the surface energy had little influence on the improvement of dust-proof ability. A large airflow velocity is beneficial to resist dust adhesion for all four types of coatings. However, a large airflow velocity has a limited ability to improve the anti-soiling effect of superhydrophilic coating under different tilt angles compared with other three coatings. The anti-soiling coatings can be referred to hydrophilic and hydrophobic coatings, not limited to superhydrophobic coating only. The study provides an invaluable guiding significance for preparation of dust-resistant coatings.

Characterization of reliability of anti-soiling coatings using tapping mode-AFM phase imaging

Power loss due to dust deposition on photovoltaic (PV) modules (also referred to as soiling) is a severe challenge to the economic viability of PV deployment in sunbelt countries like India and the Middle East. Anti-soiling coatings are nano/micrometer thick transparent coatings, which mitigate dust deposition on PV module. In this study, Tapping Mode Atomic Force Microscopy (TM-AFM) phase imaging was used to characterize the surface changes of four different commercial hydrophobic anti-soiling coatings as they were subjected to outdoor field exposure tests and three different indoor accelerated stress tests. The anti-soiling coatings were applied via manual spray coating method on solar glass substrates. The phase angle for not-coated glass shows a tight distribution around zero. The phase angle distribution of coated surface showed a larger spread. When the coatings were subjected to different environmental stressors, the phase angle distributions became tighter and, in some cases, collapsed to tight distributions around zero, indicating that the coatings were partly or completely removed from the glass surface. We demonstrate a correlation of the changes in surface coverage identified from phase angle distributions to contact angle and surface roughness, thus establishing TM-AFM phase imaging as a promising approach to characterize anti-soiling coatings subjected to environmental stress. While the analysis of the phase angle distribution is able to resolve the removal of the coating, contact angle and surface roughness cannot do so unambiguously.

+2.5% Improvement in generation utilizing Anti soiling modules based on DSM technology

Accumulation of dust on solar modules decreases the transmittance of photovoltaic glazing, resulting in both deteriorated efficiency and daily energy losses. Actually, the soiling phenomenon in PV systems has been shown to be responsible for a medium- and long-term yield reduction of up to 16% over the first year of outdoor exposure [1].The most prominent origin of dust is driven by wind and soil particles from the ground surface. All over the planet, the properties of dust due to geological, topographical, and environmental ambiences such as relative density, particle structure, surface effects, and vapour content differ from one location to another. In the present study, an exploration of the energy gain observed by Photovoltaic modules coated with DSM Anti-Soiling coating (ASC) installed at 150 MW solar power plant in Andhra Pradesh is presented. The experiment for the analysis of the generation data started on 6 September 2018. Four different slots, one with DSM ASC and the rest with an anti-reflective coating (ARC), with equivalent DC connected load are chosen for analysis. The washing cycle was maintained at an interval of 10 days. The study shows that the modules with ASC generate +2.5% more power than the modules with ARC.

Artificial linear brush abrasion of coatings for photovoltaic module first-surfaces

Natural soiling and the subsequent requisite cleaning of photovoltaic (PV) modules result in abrasion damage to the cover glass. The durability of the front glass has important economic consequences, including determining the use of anti-reflective and/or anti-soiling coatings as well as the method and frequency of operational maintenance (cleaning). Artificial linear brush abrasion using Nylon 6/12 bristles was therefore examined to explore the durability of representative PV first-surfaces, i.e., the surface of a module incident to direct solar radiation. Specimens examined include silane surface functionalized-, roughened (etched)-, porous silica-coated-, fluoropolymer-coated-, and ceramic (TiO2 or ZrO2/SiO2/ZrO2/SiO2)-coated-glass, which are compared to monolithic-poly(methyl methacrylate) and -glass coupons. Characterization methods used in this study include: optical microscopy, ultraviolet–visible–near-infrared (UV-VIS-NIR) spectroscopy, sessile drop goniometry, white-light interferometry, atomic force microscopy (AFM), and depth-profiling X-ray photoelectron spectroscopy (XPS). The corresponding characteristics examined include: surface morphology, transmittance (i.e., optical performance), surface energy (water contact angle), surface roughness, scratch width and depth, and chemical composition, respectively. The study here was performed to determine coating failure modes; identify characterization methods that can detect nascent failures; compare the durability of popular contemporary coating materials; identify their corresponding damage characteristics; and compare slurry and dry-dust abrasion. This study will also aid in developing an abrasion standard for the PV industry.

Accelerated aging tests and characterizations of innovated anti-soiling coatings for solar receiver glasses

Durability tests of solar materials are crucial to guarantee the profitability of the Concentrated Solar Power (CSP) plants and to ensure a proper efficiency during their lifetime. As solar mirrors and absorbers, optical performances of receiver glasses are affected by soiling phenomenon and surface degradations, especially in desert and coastal environments. Indeed, the deposition of dust particles, salts, organic materials or any other contaminants present in the solar field or around the CSP installation sites can generate an important optical loss. Some coatings have been developed by a manufacturer to avoid the deposition of a soiling layer on the glass surface and to keep good optical performances. Their formulations are confidential but this paper presents the results and the comparison of the four different anti-soiling coatings, deposited on glass substrates and subjected to several accelerated aging tests. The conclusion of this work will help the manufacturer to make a choice about the most durable coating for industrialization.

Degradation of Hydrophobic, Anti-Soiling Coatings for Solar Module Cover Glass

Soiling of solar module cover glass is a serious problem for solar asset managers. It causes a reduction in power output due to attenuation of the incident light, and reduces the return on investment. Regular cleaning is required to mitigate the effect but this is a costly procedure. The application of transparent hydrophobic, anti-soiling coatings to the cover glass is a promising solution. These coatings have low surface energy and contaminants do not adhere well. Even if soiling does remain on the coated surface, it is much more easily removed during cleaning. The performance of the coatings is determined using the water contact angle and roll-off angle measurements. However, although hydrophobic coatings hold out great promise, outdoor testing revealed degradation that occurs surprisingly quickly. In this study, we report on results using laboratory-based damp heat and UV exposure environmental tests. We used SEM surface imaging and XPS surface chemical analysis to study the mechanisms that lead to coating degradation. Loss of surface fluorine from the coatings was observed and this appeared to be a major issue. Loss of nanoparticles was also observed. Blistering of surfaces also occurs, leading to loss of coating material. This was probably due to the movement of retained solvents and was caused by insufficient curing. This mechanism is avoidable if care is taken for providing and carrying out carefully specified curing conditions. All these symptoms correlate well with observations taken from parallel outdoor testing. Identification of the mechanisms involved will inform the development of more durable anti-soiling, hydrophobic coatings for solar application.