Spectrally Selective Coatings for Energy Efficiency and Solar Applications

Abstract

This paper gives a brief survey over some recent work on surface coatings for energy efficiency and solar applications. Specifically, it covers coatings for selective absorption of solar energy (for solar collectors), -selective emission of infrared radiation in the 8-13gm range (for passive cooling devices), -visible transmission combined with near-infrared reflectance (for windows with decreased inlet of solar energy), solar transmission combined with thermal-infrared reflectance (for windows with decreased outlet of thermal radiation), variable transmission of solar or visible radiation (for "smart windows" with dynamic control of radiant energy). One general conclusion from the survey is that the research field embodying these types of coatings remains, with a few exceptions, in a state of rapid progress.

Origin of solar thermal selectivity and interference effects in nickel–alumina nanostructured films

“…Layer 3 corresponds to the composite formed by nanoporous alumina with metallic nanoparticles inclusions (Ni, in the present case). This is in agreement with the fact that the inclusions usually appear just in the porous region closest to the substrate [1,3,11], which has advantages for the device performance [11]. Meanwhile layer 2 is assumed to be a nanoporous alumina region with no inclusions, acting as an antireflective coating.…”

“…The emittance at 100°C [5] differs from the corresponding previous value in less than 0.001. Better results than the previous ones, with absorptance above 0.95 and emittance below 0.07 are reported in the literature [1,[4][5][6][7]14,20]. The main objective here is to demonstrate some of the characteristic features of the preparation process for studying how the optical properties depend on the structure parameters [11].…”

“…Several years ago it was shown that metallic surfaces modified by a ceramic layer with metallic inclusions (or cermet) act as selective surfaces [1,2]. These surfaces increase the efficiency of solar energy conversion into thermal energy.…”

“…Thin films of metal-dielectric composites, like nanoporous alumina (Al 2 O 3 ) with Ni inclusions [3,4], among many others, are currently being widely studied for this application [5][6][7][8][9][10][11][12][13] due to the increased interest in the development and efficient use of renewable energy sources. Several different metal inclusions, like Cu, Au, Ag, Mo, Cr, Co, Pt, and W, have been reported and studied [1,[14][15][16][17][18][19]. Moreover, the development and availability of preparation and characterization techniques of nanostructured materials open new possibilities for the study of this nanostructured films.…”

VO2-based smart coatings with improved emittance-switching properties for an energy-efficient near room-temperature thermal control of spacecrafts

“…It contrasts with the negative emittance switching (i.e. emittance that decreases with increasing the temperature) suitable for other applications such as smart windows [8][9][10] and observed for VO 2 films deposited on low IR-reflecting substrates, such as glass. Second, as aforementioned, it is important in practice to achieve high values of the emittance at high temperature in order to decrease the surface area of the radiator, without reducing the tunability of the emittance.…”