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Proceedings Paper

Optimization of silver-based heat mirrors using a genetic algorithm
Author(s): Thomas Eisenhammer; Michel P. Lazarov; R. Sizmann
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Paper Abstract

Heat mirrors based on thin silver and dielectric films for thermal solar energy applications at elevated temperatures (200 - 300 degree(s)C) are studied numerically. The well known three layer design dielectric/silver/dielectric can be improved by additional anti-reflective films. Thicknesses and selection of dielectrics of these more complex designs are optimized with a genetic algorithm. At absorber temperatures above 200 degree(s)C and for bulk optical constants the optimal sequence with five layers contains two silver films: dielectric/silver/dielectric/silver/dielectric. This design is compared to optimal designs with four and five layers, but only one silver layer. The five layer design with two silver layers allows a reduction in hemispherical emittance in comparison to the design with only one silver layer. An improvement of 14% in the figure of merit at a solar radiant flux of 500 W/m2 and an absorber temperature of 300 degree(s)C is possible. However, optical constants of thin silver films differ substantially from bulk optical constants. Thickness dependent optical constants modeling experimental data were evaluated within a Drude model. The figure of merit is generally smaller than for bulk optical constants. For the design with two silver layers, the figure of merit is smaller than for designs with one silver layer, except at the highest investigated absorber temperature of 300 degree(s)C.

Paper Details

Date Published: 25 November 1992
PDF: 9 pages
Proc. SPIE 1727, Optical Materials Technology for Energy Efficiency and Solar Energy Conversion XI: Selective Materials, Concentrators and Reflectors, Transparent Insulation and Superwindows, (25 November 1992); doi: 10.1117/12.130491
Show Author Affiliations
Thomas Eisenhammer, Ludwig-Maximilians-Univ. Muenchen (Switzerland)
Michel P. Lazarov, Ludwig-Maximilians-Univ. Muenchen (Germany)
R. Sizmann, Ludwig-Maximilians-Univ. Muenchen (Germany)


Published in SPIE Proceedings Vol. 1727:
Optical Materials Technology for Energy Efficiency and Solar Energy Conversion XI: Selective Materials, Concentrators and Reflectors, Transparent Insulation and Superwindows

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