Thermoelectric oxide modules tested in a solar cavity-receiver
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Clemens Suter Department of Mechanical and Process Engineering, ETH Zurich, 8092 Zurich, Switzerland
Matthias Trottmann Solid State Chemistry and Catalysis, Empa, Swiss Federal Laboratories for Materials Science and Research, CH-8600 Duebendorf, Switzerland
Aldo Steinfeld Department of Mechanical and Process Engineering, ETH Zurich, 8092 Zurich, Switzerland; and Solar Technology Laboratory, Paul Scherrer Institute, 5232 Villigen, Switzerland
Anke Weidenkaff a) Solid State Chemistry and Catalysis, Empa, Swiss Federal Laboratories for Materials Science and Research, CH-8600 Duebendorf, Switzerland (Received 8 December 2010; accepted 15 April 2011)
Four-leg thermoelectric oxide modules (TOMs) consisting of two p-type (La1.98Sr0.02CuO4) and two n-type (CaMn0.98Nb0.02O3) thermoelectric (TE) legs were produced with a manufacturing quality factor between 30 and 60%. The pressed sintered TE legs revealed 90% of the theoretical density to ensure a sufficient mechanical stability of the TE modules. The legs were connected electrically in series and sandwiched thermally in parallel between two Al2O3 plates serving as absorber and cooler, respectively. A solar cavity-receiver packed with an array of TOMs was subjected to concentrated thermal radiation with peak solar radiative flux intensities exceeding 600 kW/m2. Temperature distributions in the cavity, open-circuit voltage (VOC), and maximum output power (Pmax) were measured for different external loads and solar radiative fluxes (qin). Finally, the solar-to-electricity conversion efficiency (g) was calculated. I. INTRODUCTION
Oxide materials are promising candidates for hightemperature thermoelectric (TE) applications. In contrast to conventional TE materials based on Bi2Te3, which are toxic and have limited chemical stability above T ;523 K in air, they are temperature-stable, oxidation-resistant, and nontoxic.1–4 Oxide materials, especially with perovskitetype structure, can be easily synthesized with controllable composition and TE properties.5–8 The low costs of these materials are beneficial as well. The advantage of Bi2Te3based TE materials is the better performance9,10 expressed by the figure-of-merit, ZT 5 S2T/qj, where S is the Seebeck coefficient, q is the electrical resistivity, and j is the thermal conductivity.11 The maximum conversion efficiency is thermodynamically limited by the Carnot efficiency.12 The performance and conversion efficiency of TE modules depend not only on the properties but also on the compatibility factors of the used TE materials, on the geometrical factors of the TE
II. EXPERIMENTAL
a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2011.125
The TE legs consisted of synthesized La1.98Sr0.02CuO4 (p-type)17 and CaMn0.98Nb0.02O3 (n-type).6 Both materials
J. Mater. Res., Vol. 26, No. 15, Aug 14, 2011
http://journals.cambridge.org
module, and on the quality of the electrical and thermal contacts.11,13,14 The direct conversion of solar irradiation into electricity at high temperatures has recently b
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