Degradation of concentrating solar thermal reflectors in acid rain atmospheres

Abstract

Given the importance that concentrating solar power technologies have had in recent years, the interaction between humid atmospheres in which SO 2 is the main pollutant and the metal reflecting layers of the solar concentrators is a major concern that should be addressed. Previous durability studies have urged the importance of designing an accelerated aging test protocol for simulating aggressive industrial atmospheres that solar reflector materials are bound to encounter. Therefore, three types of reflectors were tested in an acid-rain (or Kesternich) chamber at various temperatures and gas concentrations based on the DIN 50018 and ISO 6988 standards. The results showed the significant effect of high SO 2 concentrations rather than high temperatures on silvered-glass reflectors, although synergy should not be disregarded. Strong reductions in specular reflectance were found for one type of silvered reflector compared to another type, highlighting the significance of material processing and its effects on their final performance. Aluminum reflectors were not damaged as much as silvered-glass reflectors, but under microscopic inspection, a wide range of noticeable corrosion defects could be found in all the materials. Comparisons between the most representative Kesternich test and samples from an outdoor industrial site permitted realistic lifetime correlations for commercial silvered-glass reflectors.

Durability Studies of Solar Reflectors Used in Concentrating Solar Thermal Technologies under Corrosive Sulfurous Atmospheres

“…Conversely, no significant signs of corrosion were observed in aluminum reflectors on performing accelerated corrosion tests with both sulfurous gases for 21 days. However, aluminum reflectors are also prone to corrosion according to other studies, especially in the presence of SO 2 in acid rain conditions [25]. These results show prominent corrosion in this reflector type when the surrounding atmosphere is moist and the gas concentration is high.…”

“…Aluminum reflectors may be considered appropriate candidates if not very high specularity values are needed in industrial environments, such as in small collectors for industrial process heat applications. Therefore, despite its lower reflectance, aluminum reflectors can be commercially competitive due to their simpler and more cost-efficient fabrication process, and their slower degradation rate in industrial environments, compared to silvered glass reflectors [25]. In past studies, aluminum degradation has been proven to be rather slow due to its protective SiO 2 layer [22].…”

“…To date, the few research studies conducted on this specific topic are devoted to the effects of humid sulfur-containing atmospheres [21,22], in addition to the studies already carried out by the authors' research group with H 2 S [23] and acid rain [24,25]. These differ from the present study in that the effect of each gas was assessed independently without comparing it to the effects of other gases.…”

Corrosion on silvered-glass solar reflectors exposed to accelerated aging tests with polluting gases: A microscopic study

“…Solar reflectors used in CSP (concentrating solar power) applications are one of the most sensitive components of concentrating solar thermal facilities in terms of their durability. As identified in our previous works [1][2][3][4][5] and by many other references in the literature [6][7][8][9][10][11][12][13][14][15][16][17], surrounding atmosphere of the facilities are frequently affected by corrosive gaseous agents (SO2, H2S and NO2) that are likely to degrade the reflector materials, especially their reflective metallic layers, what may be crucial for their optimal performance.…”

Uncertainty Study of Reflectance Measurements for Concentrating Solar Reflectors

“…The instrument produces a collimated beam to a diameter of 10 mm, so that all of the reflected beam can be collected by the 22-mm-diameter receiver lens. This device has been extensively employed in research activities by a number of institutions [28]- [32].…”