Historical PerspectiveHigh transmittance and highly amphiphobic coatings for environmental protection of solar panels
Graphical abstract
Introduction
Over the past 15 years, photovoltaic energy has faced a fast development as independent market at global level with growing demand in terms of performance with the aim to increase its competitiveness. Solar power represents an abundant and clean source, thanks to environmental compatibility and it's presently regarded as the foremost important renewable energy [1], but still its energy conversion efficiency requires major improvements like technology design and time performance compared with the standard energy sources [2].
The potential of electricity generation from solar energy is, in principle, valid and promising until many alterable and unalterable factors that can govern a PV module's efficiency are not considered.
Many long-term studies analyse degradation rates to determine the performance of PV power plants over time, but monitoring data often resulted highly sensitive to uncertainties. Most of the reasons are found in the environment properties including living presences, both urban or wild, and the global impact of climate change resulting in increasing rain, wind and dust presence will create new standards and parameters to be considered [3].
Dirt coming from various sources, natural and artificial is one of the problems strongly affecting the efficiency of solar panels, even when the modules and components are not yet degraded. The use of surfaces with superhydrophobic and amphiphobic characteristics can help to overcome this problem thanks to their self-cleaning effect. This effect is due to the surface chemistry and structure avoiding water and oil drops interaction with the surface itself. This type of surfaces is widely studied for use in many fields where protection from the environment is required such as in marine, industrial and medical application (antifouling and anti-corrosive coatings, membranes for oil separation, optical windows, for drag reduction, as anti-bacteria for medical equipment and anti-water condensation) [4,5]. The design and fabrication of superhydrophobic and amphiphobic coating for antifouling and anticorrosion purpose have been studied by the authors in marine environment [[6], [7], [8], [9]] and for medical application [10,11].
Amphiphobic and self-cleaning coatings applied on solar panels must be transparent and durable over time for minimizing human intervention while maintaining high efficiency. The durability of amphiphobic coating is a very important, studied and partially unresolved problem because it depends on the type of material used and field of application.
Despite the rising dimension of the problem, the literature linking these topics is not yet satisfactory. By entering several keywords on Web of Science is observed that in 2019 the attention of the scientific community was focused on “organic solar cell” and “perovskite solar cell” (order of magnitude thousands of articles) while the articles regarding durability and solar cell are on the order of hundreds. Another interesting data is about the studies combining water repellence and solar cells, among articles for “hydrophobic solar cell”, only less than 20 for “superhydrophobic solar cell” are found.
Purpose of this work is then matching few different environmental soiling sources affecting a PV module efficiency from natural to anthropic to application of self-cleaning coating solutions at high transmittance.
Section snippets
Dust deposition
Durability and life expectation of a solar panel strongly depend on aging, but also on presence of dust on the panel surface reducing the energy production with significant economic loss [[12], [13], [14]].
The power output decrease of a module due to the dust accumulation is more and more frequently evaluated in the literature. Mainly coming from sands and soil, this phenomenon reduces the transmittance of PV glazing, resulting in the degradation of efficiency [15].
The most common sources of
Requirements for self-cleaning coatings
Self-cleaning technology [48] is an important improvement for solar power applications employing photovoltaic panels. Solar power plants are continuously exposed, as was previously described, to dust storm and to organic/inorganic soil reducing the efficiency of solar panels. A self-cleaning coating allows the cleaning of the panel without any external source. The self-cleaning concept and its use in surface preparation were due to the discovery by Barthlott e Neinhuis [49] of the lotus leaf
Superhydrophobic/amphiphobic transparent coatings preparation
To obtain a superhydrophobic surface is possible to follow two different routes: a) create a rough surface from a low surface energy material, b) modify a rough surface with low surface energy materials. Usually, this behaviour is due to the presence of non-polar groups such as polysiloxanes (-Si-O-Si-), fluorocarbons (CF2/CF3), aliphatic chain (CH2/CH3) or combined structures. Several methods have been used for the fabrication of SH surfaces and often, as we will see, some different techniques
Conclusion
The aim of this review was to investigate the environmental problems which solar panels are subjected to and discuss the recent literature on new solutions to prepare transparent coatings with superhydrophobic and oleophobic properties in order to provide self-maintaining solar panels. The literature shows that the combination of transparency (high transmittance) and superhydrophobicity is not yet very common, and even less common is the simultaneous presence of highly hydrophobic and
Declaration of Competing Interest
None.
Acknowledgements
M. F. and F. C. acknowledge the support of Fondazione Bancaria Compagnia di San Paolo, Torino. This work has been performed within the framework of the Project ANFISOL Design and development of superamphiphobic coatings with self-cleaning properties for photovoltaic panels (ID ROL 20718) funded by the Fondazione Bancaria Compagnia di San Paolo, Torino.
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