Solar Thermal Collector’s Degradation – Influence of Corrosivity Inside and Outside the Collectors (original) (raw)
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MATERIALS IN SOLAR THERMAL COLLECTORS
A procedure for accelerated life testing of solar absorber surfaces was developed within the framework of the working group MSTC (Materials in Solar Thermal Collectors) of the IEA-SHCP (International Energy Agency -Solar Heating and Cooling Programme). The intensive material and micro-climatic investigations on solar thermal collectors and solar systems within the preceding IEA Task 10 (1985 -1991) as well as further studies in this field by the group itself formed a basis for this work. Examples of the application of the test procedures will be given. The studies on the micro-climatic data in collectors were carried out at 5 different locations and with various collectors. The ambient climate, the ventilation rate of the collector and the isolation material were identified as main influence parameters. Simulation tools for the optimisation of the micro-climate in order to achieve the most favourable micro-climate in terms of corrosivity and a test procedure for the ventilation rate...
Aging tests of components for solar thermal collectors
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Components for solar thermal collectors like glazing materials, absorbers and reflectors are exposed to outdoor weathering and accelerated weathering tests in order to analyze their stability and behavior under different climatic conditions. To measure the degradation on different scales and to identify the processes taking place, the samples are characterized before, during and after the tests with different methods, including FT-IR spectroscopy, contact angle measurement and microscopic technologies such as Atomic Force Microscopy (AFM).
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Typical components for solar thermal collectors like glazing materials, absorbers and reflectors are exposed to accelerated weathering tests to analyze their stability and behavior under different climatic conditions including a saline atmosphere. The samples are characterized before, during and after the tests with different methods, including FT-IR spectroscopy and microscopic technologies like AFM microscopy to measure the degradation on different scales and identify the processes taking place. In this article we focus on the solar reflector.
Durability of different selective solar absorber coatings in environments with different corrosivity
Solar Energy Materials and Solar Cells, 2017
The degradation and durability of different selective solar absorbers surfaces in outdoor exposure testing (OET) sites with different atmospheric corrosivity (maritime/industrial and urban atmospheres) were investigated for the optimization of accelerated aging tests to the qualification in terms of durability of selective solar absorber coatings in different environments. Two Outdoor Exposure Testing (OET) sites were constructed, the climate was characterized and the atmospheric corrosivity categories were determined by corrosion rate measurements of standard specimens (carbon steel, zinc, copper and aluminium) during 12 months, according to ISO 9223, ISO 9225 and ISO 9226:2012. Two Physical Vapour Deposition (PVD) coatings (commercially available) and three paint coatings (commercially available) were also exposed in the two OET sites with evaluation of degradation after 1, 2, 4, 6, 9 and 12 months of exposure in terms of optical properties (solar absorptance and thermal emittance), morphology and chemical evaluation (SEM/EDS and XRD). The selective solar absorber surfaces submitted to OET sites for one year were ranked according to their performance in terms of optical properties and corrosion over time. The results obtained show the relevance of outdoor exposure testing sites, namely in places with high corrosivity as in marine and/or industrial areas as a reliable way to verify the corrosion resistance of new materials and products and the evolution of optical properties degradation of absorber surfaces in the presence of high concentration of contaminants.
Degradation of selective solar absorber surfaces in solar thermal collectors – An EIS study
Solar Energy Materials and Solar Cells, 2017
The selective solar absorber surface is a fundamental part of a solar thermal collector, as it is responsible for the solar radiation absorption and for reduction of radiation heat losses. The most common absorbers are nowadays produced by vacuum deposition, presenting disadvantages, such as lower durability, lower resistance to corrosion, higher cost and complex production techniques. Spectrally selective paints are a potential alternative for absorbing surfaces in low temperature applications, with attractive features such as ease of processing, durability and commercial availability with low cost. Thus, two PVD coatings and three organic coatings obtained by projection on aluminium substrates were studied. Electrochemical impedance spectroscopy (EIS) allows for the assessment of mechanistic information on the degradation processes, especially if equivalent circuits are used, providing quantitative data that can easily relate to the kinetic parameters of the system. EIS measures were carried out in NaCl and Na 2 SO 4 solutions at different immersion times up to 4 weeks. The performance of the coatings, based on coupons as-received and exposed to atmosphere, is discussed and a ranking is proposed.
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Solar collector design with respect to moisture problems
Solar Energy, 2003
Humidity inside the collectors is one factor that can be minimised to keep the most favourable microclimatic condition for the internal materials of the collector. This microclimate inside the collector is an important factor in determining the service lifetime of an absorber coating. During the design of the collector, the location and size of ventilation holes, properties of the insulation materials and dimension of the solar collector box are parameters that have to be taken into account for the optimisation in order to achieve the most favourable microclimate to prevent corrosion.
Refocus, 2006
S olar thermal collectors have developed many diverse forms in the nearly onehundred and twenty years since their first invention; ranging from solar ponds to dish and heliostat collectors. The total solar collector area installed worldwide is now estimated to be over 58×10 6 m 2 . For medium temperature water heating and for space and industrial process heating applications most solar collectors are either: flat plate, in which the absorbing surface area is the same as the overall collector area, or tubular in which the absorber is contained within an evacuated glass tube. The latter may include either within or outside the tube, a line-axis parabolic mirror to focus solar energy onto the absorber. Though temperatures of 40 to 70 o C are attained easily by flat plate collectors, the use of solar selective surfaces and reflectors together with the intrinsic heat retention of an evacuated tube collector means significantly higher operating temperatures are feasible. Solar collectors have a history stretching back nearly 120 years. Yet, taking advantage of new materials and manufacturing processes, they continue to develop to more effectively satisfy the requirements of many diverse applications. With larger scale manufacturing and more installers, in many markets their installed price continues to fall. These factors have rendered solar water heating viable economically in an increasingly large number of countries. Brian Norton of Dublin Institute of Technology and Steve Lo of the University of Ulster discuss technical developments in this core component of most solar thermal applications.
Accelerated Aging Tests for Solar Absorber Coatings
Proceedings of EuroSun 2018, 2018
The need of a higher role of solar energy within the energy mix in the coming decades obliges the systems to increase their performance and reliability. It is demanded that the solar absorbers, as the key component of solar thermal systems, should be low cost with high efficiency for extended lifetimes under different kinds of environments. Commercially, there are two different types of solutions as selective solar absorbers coatings: coatings obtained by physical vapor deposition (PVD) and by paint coatings (PC). These coatings present different physical and chemical characteristics. Therefore, it is important to know how these coatings degrade over time in different environments. Results obtained with two different PVD coatings and three PC, under different accelerated aging tests, are presented. The aging tests performed included different environmental stress corrosion conditions: temperature, humidity, chlorides, sulphur dioxide and nitrogen oxides. Cyclic variation of corrosion promoting gases (sulfur dioxide and nitrogen dioxide), higher humidity, salt spraying and drying seem to be an aging test that reflects the different environments where the solar thermal collectors are exposed. In addition to the contaminants, drying / wetting cycles also play an important role in degradation mechanisms of absorber coatings.
Effect of Chromium Trioxide Coating on the Thermal Performance of Solar Thermal Collector
Karbala International Journal of Modern Science
This paper compared the thermal performance of two solar collectors. The first collector is coated by a dark black absorbent solar collector, and the second one coated by the chromium trioxide. The results of the second collector show a better selectivity in terms of greater radiation absorption, and less emission compared to the first collector. At the minimum solar irradiance time, the absorbed energy is increased from 908.28J to 1221.5J, and the thermal efficiency is improved from 37.3% to 50.1% when the chromium trioxide coating is used. Besides, at the maximum solar irradiance time, the absorbed energy is increased from 1340.5J to 1528.4J, and the thermal efficiency is improved from 63.9% to 78.9%. After three months exposing the collectors to outdoor conditions, the chromium trioxide coated collector show superior thermal performance over dark black coated collector. At the minimum solar irradiance time, the absorbed energy is increased by 877J and the thermal efficiency is improved by about 34% when the chromium trioxide coating is used. In addition, the absorbed energy and thermal efficiency are also increased from 501.1J and 20% to 1440.7J and 62.2% respectively when the solar irradiance is at its maximum value