Effect of substrate on graphite and other solar selective surfaces

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Abstract
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°C. For operating temperatures of 100°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°C is investigated and interpreted in terms of diffusion. Graphite films on copper and silver are candidates for high temperature evacuated collectors.