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Dependence of the solar absorptance of selective absorber coatings on the angle of incidence

Description: The directional solar absorptances ..cap alpha../sub s/(theta) of samples of a number of selective absorber coatings have been determined. The spectral directional hemispherical reflectances plambda(theta;2..pi..) of each sample was measured over the wavelength range 0.3..mu.. to 2.5..mu.. at angles of incidence theta between 10/sup 0/ and 80/sup 0/. The quantity (1-plambda(theta;2..pi..)) was convoluted over an AM2 solar spectrum to obtain ..cap alpha../sub s/(theta) at each angle of incidence. The solar absorptance at near normal incidence varied from sample to sample and from coating to coating, as expected, given the present state of the art. All the absorptances show similar angular dependences, however. When normalized to unity at normal incidence, the data nearly describe a single curve, for which a power series in theta was found. For comparison, the solar absorptance was also determined for freshly prepared lamp black.
Date: January 1, 1977
Creator: Reed, K A
Partner: UNT Libraries Government Documents Department

Development of surfaces optically suitable for flat solar panels. Final report

Description: This final report contains three principal items. The first describes a simple and novel reflectometer which can separately evaluate the spectral and diffuse reflectivities of surfaces. A phase locked detection system for the reflectometer is also described. The second item is a selective coating on aluminium potentially useful for flat-plate solar collector applications. The coating is composed of strongly bound copper oxide (divalent) and is formed by an etching process performed on an aluminium alloy with high copper content. Because of this one step fabrication process, fabrication costs are expected to be small. Process parameters, however, need further definition. The third item contains conclusions gleaned from the literature as to the required optical properties of flat plate solar collectors.
Date: August 1, 1979
Partner: UNT Libraries Government Documents Department

Methods for reducing heat losses from flat plate solar collectors: Phase III. Final report, May 1, 1977-January 31, 1979

Description: The present study extends earlier studies by examining the effect of the emissivities of both the absorber plate and the glass cover on the honeycomb's ability to suppress free convection, and on the radiative and conductive heat transfer which takes place across the honeycomb in the absence of free convection. By means of heat transfer measurements on ten Mylar honeycombs, this study has shown that the effect of the above emissivities on the suppression of convection by the honeycomb is slight, and can probably be ignored. On the other hand, the measurements also showed that the effect of these emissivities on the non-convective heat transfer is substantial, but not nearly so large as would have been predicted by existing theories. To explain this latter result theories were developed which take into account the important coupling (ignored by previous theories) between the conductive and radiative modes of heat transfer. These new theories predict the measured heat transfer rates to with about +-15%, depending on the emissivities. The results of this study have direct application to evaluating solar collectors which combine a selective surface with a honeycomb.
Date: March 1, 1979
Creator: Hollands, K.G.T.; Raithby, G.D.; Russell, F.B. & Wilkinson, R.G.
Partner: UNT Libraries Government Documents Department

Black germanium selective absorber surfaces. Semi-annual progress report, September 1, 1978-March 1, 1979

Description: It was shown that by controlling the sputtering preparation conditions of noncrystalline Ge films the surface microstructure can be drastically altered by simply etching in 30% H/sub 2/O/sub 2/. The resulting surface has a total reflectance of less than 3% in the solar spectrum. This flat-black surface appearance is shown to be due to a dense array of aligned, needle-like protrusions which have an extremely high aspect ratio and both a cross-sectional area and a separation between needles on the order of the wavelength of solar radiation. A systematic series of thin films were prepared by rf-sputtering with rf-power and Ar gas pressure as the primary preparation parameters and characterizing the various films.
Date: April 23, 1979
Creator: Messier, R F & Vedam, K
Partner: UNT Libraries Government Documents Department

Solar-absorber-selective paint research

Description: Research and development on thickness-sensitive and thickness-insensitive solar paints are discussed. The thickness-sensitive paints include reverse roll coated, gravure printed, and spray coated paints. The coating methods and optical properties of the thickness-sensitive paints are discussed. The thickness-insensitive solar paints include a low emittance flake such as aluminium-flake, and pigment. Durability tests are discussed, including accelerated weathering and humidity durability tests, for the thickness-sensitive coatings. (LEW)
Date: January 1, 1982
Creator: Moore, S.W.
Partner: UNT Libraries Government Documents Department

Method of sputter etching a surface

Description: A surface is textured by co-sputter etching with a target and a seed material with the surface at a pre-selected temperature. By pre-selecting the temperature of the surface while sputter etching, it is possible to predetermine the reflectance properties of the etched surface. The surface may be textured to absorb sunlight efficiently and have minimal emittance in the infrared region so as to be well-suited for use as a solar absorber for photothermal energy conversion.
Date: February 26, 1982
Creator: Henager, C.H. Jr.
Partner: UNT Libraries Government Documents Department

Glass-heat-pipe evacuated-tube solar collector

Description: A glass heat pipe is adapted for use as a solar energy absorber in an evacuated tube solar collector and for transferring the absorbed solar energy to a working fluid medium or heat sink for storage or practical use. A capillary wick is formed of granular glass particles fused together by heat on the inside surface of the heat pipe with a water glass binder solution to enhance capillary drive distribution of the thermal transfer fluid in the heat pipe throughout the entire inside surface of the evaporator portion of the heat pipe. Selective coatings are used on the heat pipe surface to maximize solar absorption and minimize energy radiation, and the glass wick can alternatively be fabricated with granular particles of black glass or obsidian.
Date: August 6, 1981
Creator: McConnell, R.D. & VanSant, J.H.
Partner: UNT Libraries Government Documents Department

Microstructure of a black chrome solar selective absorber

Description: The structure of Harshaw Chemicals' CHROM-ONYX type of black chrome/metal selective absorber was studied to gain a better understanding of its influence upon the mechanism of wavelength selectivity. Spectral reflectance measurements were performed on seven samples. In this study, the best selectivity was found by these measurements to be 1.0 micron of black chrome on copper and 0.7 micron of black chrome on nickel. Both transmission and scanning electron microscopy were employed to study microstructure and chemical composition. As a result of the combined studies, some effects of black chrome thickness and the metallic substrate were determined. It was found that black chrome consisted of a very fine metallic distribution of particles of chromium, possibly suspended within a matrix of an oxide of chromium. This combination was, in turn, agglomerated into larger particles within the 0.05--0.3 micron size range. These larger particles formed a network which constituted the surface coating.
Date: August 1, 1978
Creator: Lampert, C.M.
Partner: UNT Libraries Government Documents Department

Low temperature flat-plate collector space/water heating

Description: Low temperature flat plate collector designs can take many different forms and make use of a variety of materials. Collectors can be liquid heaters, air heaters, heat-pipe exchanged, or a hybrid arrangement when combined with passive systems. They can be factory-manufactured modules, site assembly of factory-manufactured components, factory-manufactured into transportable housing, or completely site-constructed. Material selection for all components must be evaluated with respect to operating parameters, performance, durability, and above all, life-cycle costing.
Date: January 1, 1978
Creator: Moore, S.W.
Partner: UNT Libraries Government Documents Department

Solar collectors. Part II. Recent developments and future performance data and economic analysis

Description: The concepts, materials, and collector types indicative of recent developments in solar collector research for increasing thermal performance are listed by category. The categories are: selective surfaces, honeycombs, all-glass evacuated tube collectors, non-tracking concentrating collectors, tracking concentrating collectors, and heat pipe collectors. (MHR)
Date: January 1, 1978
Creator: Collier, R.K.
Partner: UNT Libraries Government Documents Department

Solar reflectance, transmittance, and absorptance of common materials

Description: The solar reflectance, transmittance, and absorptance of common materials used for solar collector fabrication have been compiled for easy reference. The data are derived from solar weighted averaging techniques and can be used for initial calculations of collector performance.
Date: October 1, 1979
Creator: Butler, B.L.; Call, P.J.; Jorgensen, G.L. & Pettit, R.B.
Partner: UNT Libraries Government Documents Department