Advances in Gas-Fired Thermophotovoltaic Systems

[+] Author and Article Information
W. Durisch

 Paul Scherrer Institut, PSI, 5232 Villigen PSI, Switzerlandwilhelm.durisch@psi.ch

F. von Roth, W. J. Tobler

 Paul Scherrer Institut, PSI, 5232 Villigen PSI, Switzerland

J. Sol. Energy Eng 129(4), 416-422 (May 16, 2007) (7 pages) doi:10.1115/1.2770749 History: Received August 24, 2006; Revised May 16, 2007

In a first and completely new approach, a vacuum plasma-spray coating technique was used to deposit selective emitting rare-earth oxide films of ytterbia (Yb2O3) on porous silicon-infiltrated silicon carbide foams (Si–SiC). The plasma-spray coating technique offers a new and promising way to produce selective emitting coatings on different refractory substrates with complex geometries. The adhesion and thermal shock stability were tested until a film thickness of 130μm was achieved; the selective emittance of the oxide coating has been found to be dependent on the film thickness. The material combination Si–SiC and Yb2O3, however, needs some major improvement regarding high-temperature stability and high thermal cycling loads. In a different approach, the advantage of low emitting Al2O3 fibers and good thermal matching was combined with Yb2O3 slurry coating of flexible alumina (Al2O3) fiber bundles, formed into a cylindrical shape. The thin fiber structure tried to imitate the famous incandescent mantle emitters of Auer von Welsbach, but with a more rugged structure. Even though the fibers of the woven emitter were thin, the low thermal conductivity of Al2O3 led to a distinct reduction of the surface temperature and emittance, and a shielding effect of the radiation emanating from the hot inner walls by the cooler outer grid structure was inevitable. Optical filters consisting of a water film and of transparent conducting oxides (TCO) have been developed and tested to protect the photocells against overheating and to reflect nonconvertible off-band radiation back to the emitter. The water film led to a significant reduction of the cell temperature and increased cell performance, whereas with the TCO filters only a reduction of the cell temperature was observed.

Copyright © 2007 by American Society of Mechanical Engineers
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Figure 1

Porous Si–SiC foam (65mm×235mm), plasma spray coated with Yb2O3; detail of the porous foam structure shown on the right side; pore size 10ppi

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Figure 2

Ceramic fiber-based tissue emitter, slurry coated with Yb2O3, 50mm×200mm; detail on the right side

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Figure 3

Spectral transmittance of a water film (thickness ca. 4mm), quantum efficiency of a silicon photocell and spectral emittance of an Yb2O3 emitter, according to Schubnell (19)

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Figure 4

Transmittance of water films of different thicknesses (18), representing an almost ideal IR cutoff filter for TPV systems based on ytterbia emitters and silicon photocells

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Figure 5

Measurement test set-up consisting of a water film filter (quartz glass) between incandescent mantle emitter made of Yb2O3 and cylindrical photoreceiver array containing silicon photocells

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Figure 6

Spectral transmittance τ and reflectance ρ of TCO bandpass filter (20); spectral reflectance in the near and middle IR range (right picture)

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Figure 7

Typical external quantum efficiency of SH2 Si photocells (20)

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Figure 8

Photoreceiver installed into a cylinder of polymethylmethacrylate (PMMA) to support the photocells. The array consists of SH2 silicon solar cells from ASE, Heilbronn, Germany.

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Figure 9

Cylindrical photocell generator, manufactured from TPV-tailored silicon cells produced at Paul Scherrer Institut (PSI)

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Figure 10

Influence of vacuum plasma sprayed Yb2O3(100μm) on the output of the photocell generator; Si–SiC foam 65mm×235mm

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Figure 11

Influence of the film thickness of Yb2O3 on the output of the photocell generator; Si–SiC foam 70mm×160mm

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Figure 12

Incandescent woven ceramic fiber emitter, inhomogeneous temperature distribution due to an irregular gas flux



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