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Journal ArticleDOI

Coatings for enhanced photothermal energy collection I. Selective absorbers

01 Jun 1979-Solar Energy Materials (North-Holland)-Vol. 1, pp 319-341
TL;DR: For economical and efficient utilization of solar energy various types of absorber coatings and preparations can be used for solar collectors as discussed by the authors, and several varieties of commercial and research selective absorbers are reviewed and tabulated for application.
About: This article is published in Solar Energy Materials.The article was published on 1979-06-01. It has received 163 citations till now. The article focuses on the topics: Nanofluids in solar collectors & Absorption (electromagnetic radiation).
Citations
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Journal ArticleDOI
TL;DR: In this paper, the state-of-the-art physical vapor deposited solar selective coatings used for solar thermal applications with an emphasis on sputter deposited coatings for high-temperature applications.

543 citations

Journal ArticleDOI
TL;DR: In this paper, the Advanced Research Projects Agency-Energy (ARPA-Energy) gave DE-AR0000471 and DE-ARM0000181 for the first time, respectively.
Abstract: United States. Advanced Research Projects Agency-Energy (Awards DE-AR0000471 and DE-AR0000181)

483 citations

Journal ArticleDOI
TL;DR: In this paper, the optical properties of (Oxy)nitride materials, including refractive index, reflectance, absorbance, band gap, photoluminescence, and transmittance, are discussed.
Abstract: (Oxy)nitride materials, consisting mainly of transition metal and ionic-covalent (oxy)nitrides, show a vast number of interesting physical and chemical properties due to their substantial structural diversity. The optical properties of these (oxy)nitrides, in combination with their excellent mechanical strength, thermal properties, and chemical stability, enable (oxy)nitrides to be used in a variety of industrial fields, such as photovoltaic, photothermal, photocatalytic, pigment, lighting and display, optoelectronic, and defense industries. The optical properties are extremely related to the electronic band structure of (oxy)nitrides, and can be varied significantly by changing the chemical composition (e.g., the oxygen to nitrogen ratio) and preparation/processing conditions. This article overviews the optical properties (including refractive index, reflectance, absorbance, band gap, photoluminescence, and transmittance) of (oxy)nitride materials that are in the form of thin films, powders, or bulk ceramics, and highlights their applications as antireflection coatings, solar spectral selectivity coatings, visible-light-driven photocatalysts, ecological pigments, phosphors for light-emitting diodes, and transparent window materials.

292 citations

Journal ArticleDOI
TL;DR: In this article, the authors present a review of heat-mirror deposition technology including chemical vapor deposition using hydrolysis and pyrolysis reactions, dc and rf sputtering using reactive, biased and nonreactive techniques, vapor deposition and ion plating.

291 citations

Journal ArticleDOI
TL;DR: The ideal spectral properties are treated, an illustrative experimental example of how well this goal can be realized is given, and a corresponding theoretical curve is shown indicating to what extent the measured results can be theoretically understood.
Abstract: Matter continuously exchanges energy with its surroundings. This exchange can be dominated by radiation, conduction, or convection. In this brief review we discuss how proper design of radiative surface properties can be used for heating and cooling purposes. The desired properties can be understood once it is realized that solar and terrestrial radiation take place in different wavelength ranges and that only part of the solar spectrum is useful for vision and for photosynthesis in plants. These facts allow the possibility of tailoring the spectral absorptance, emittance, reflectance, and transmittance of a surface to meet different demands in different wavelength intervals, i.e., to take advantage of spectral selectivity. One example is the selective surface for efficient photothermal conversion of solar energy, which has high absorptance over the solar spectrum but low emittance for the longer wavelengths relevant to thermal reradiation. Below we discuss the pertinent spectral radiative properties of our ambience. These data are then used as background to the subsequent sections treating four examples of spectrally selective surfaces. The first example is the previously mentioned selective surface for converting solar radiation to useful heat. The second example considers surfaces capable of reaching low temperatures by benefiting from the spectral emittance of the clear night sky. The third example concerns two related types of transparent heat mirror. The fourth example, finally, treats radiative cooling of green leaves; this part is included since it gives a nice example of how nature solves a difficult problem in an elegant and efficient way. This example hence provides an interesting background to the other cruder types of artificial selective surfaces. Throughout our discussion we treat the ideal spectral properties, give an illustrative experimental example of how well this goal can be realized, and—where this is possible—show a corresponding theoretical curve indicating to what extent the measured results can be theoretically understood.

264 citations

References
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Journal ArticleDOI
TL;DR: In this paper, an introduction to the theory that must be mastered in order to engineer and evaluate the performance of solar energy systems is presented, and the authors build the necessary background and information in successive chapters, culminating in a section on representative applications.
Abstract: This book is an introduction into the theory that must be mastered in order to engineer and evaluate the performance of solar energy systems. An important goal in solar energy applications is the ability to calculate output from a proposed design application and thereby establish the value of the energy delivered and a fair price for the system. To this end the authors build the necessary background and information in successive chapters, culminating in a section on representative applications. (WDM)

229 citations

Journal ArticleDOI
TL;DR: The spectral reflectance properties of a commercially prepared black chrome on steel have been measured as discussed by the authors, and the results indicate absorptivity-to-emissivity (αϵ) values of 9·8, 13.8, 8·0 and 1·00, respectively.

178 citations

Journal ArticleDOI
TL;DR: In this paper, the impact of selective absorber coatings and antireflection coatings on both flat plate and concentrating type solar collectors is covered. And the results of durability life tests on a high-temperature stable, vacuum-evaporated absorber coating consisting of layers of Al 2O3−Mo−Al2O3 are reported.
Abstract: The applications and requirements for thin film coatings in solar−thermal power systems are reviewed. The substantial impact of selective absorber coatings and antireflection coatings on both flat plate and concentrating type solar collectors is covered. The results of durability life tests on a high−temperature stable, vacuum−evaporated absorber coating consisting of layers of Al2O3−Mo−Al2O3 are reported. This coating was unaffected by 500 h at 930°C. Other tests included thermal cycling, thermal shock, ultraviolet irradiation, and solar wind simulation. An electroplated solar absorber coating for low−temperature applications (<200°C) has been developed which has a solar absorption of 0.96 and an infrared emittance of 0.07 at 100°C. A chemically etched antireflection coating for glass has been investigated. Solar transmission of 0.97 is possible with this low−cost technique.

135 citations

Journal ArticleDOI
TL;DR: In this article, a new approach to the conversion of solar energy to heat is proposed, which consists of a dense array of metal whiskers grown with spacings of a few wavelengths of visible light, and achieves significant optical absorption by trapping the light by a geometric maze effect.
Abstract: A material has been developed which allows a new approach to be made to the conversion of solar energy to heat. It consists of a dense array of metal whiskers grown with spacings of a few wavelengths of visible light. The material selected has low emissivity, and achieves significant optical absorption by trapping the light by a geometric maze effect. We have deomonstrated that absorption of normal incidence light is greater than 98% from 0.5 to 40‐μm wavelengths, and hemispherical emissivity at 550 °C can be made less than 0.26. Since surfaces can be made of a single refractory element, such as W, high‐temperature solar conversion (550 °C) should be maintained with good surface stability.

134 citations

Journal ArticleDOI
TL;DR: In this article, the optical constants of Cr2O3/Cr films over the composition range up to 35 vol% Cr were determined and it was found that films containing 29 vol%Cr are nearly optimum for this application.
Abstract: Excellent selective black absorbers for solar radiation, with solar absorptivity of over 0.9 and infrared emissivity of less than 0.1, have been obtained by using rf sputtering to coat metal substrates with a Cr2O3/Cr cermet film, then with a Cr2O3 antireflection coating. By determining the optical constants of Cr2O3/Cr films over the composition range up to 35 vol% Cr, it was found that films containing 29 vol% Cr are nearly optimum for this application. The optical and chemical properties of absorbers made with such films are quite similar to those obtained with electroplated Cr‐black coatings. This similarity suggests that the electroplated coatings are actually Cr2O3/Cr cermets comparable in composition and microstructure to the sputtered films.

94 citations