Solar Selective Surfaces Research Articles

Effect of substrate on graphite and other solar selective surfaces

Solar selective surfaces consisting of a substrate of copper, silver, or nickel underlying a single layer of material of refractive index N = n + ik are compared using the criterion of maximum available power. Copper is shown to be slightly superior to silver, and both are shown to be superior to nickel for operating temperatures of 200 degrees C. For operating temperatures of 100 degrees C and below the three metals are comparable as substrates. The absorptance and emittance properties of graphite films on copper, silver, nickel, and titanium are found. The effect of aging of these films at temperatures up to 400 degrees C is investigated and interpreted in terms of diffusion. Graphite films on copper and silver are candidates for high temperature evacuated collectors.

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A solar-selective surface with an excellent heat-resistance and optical quality has been developed from zirconium/ zirconium carbide stack. The surface film has been prepared by reactive rf-sputtering of pure Zr target in a gas mixture of methane and argon.The composition of the optically optimized film is about 6/1 in atomic ratio of C/Zr, which was determined to be a mixture of ZrC and carbon by ESCA. Solar absorptance and infrared reflectance of the surface are 90 and 95%, respectively. The optical property of the surface was stable up to 800°C.The solar absorptance of the carbon selective-surface can be increased by several percent when a thin oxide layer is overcoated.

The dc sputter coating of solar-selective surfaces onto tubes

A device for coating tubes using reactive or nonreactive dc sputtering is described. The coating of glass tubes with a solar selective surface consisting of a layer of metallic carbides on copper is used as an example. Uniformity of thickness and composition are demonstrated. The cylindrical design of the coating equipment and low manufacturing tolerances make this a low-cost system.

A new solar selective surface

A new waveguide method of providing a selective surface for solar energy applications is described. Some measurements of a vacuum-deposited mesh are given, and elementary theory indicates that ratios of solar absorptance to thermal emittance of 30:1 should be possible at temperatures of about 200°C.