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TECHNICAL BRIEFS

Analysis of Potential Conversion Efficiency of a Solar Hybrid System With High-Temperature Stage

[+] Author and Article Information
Y. V. Vorobiev

 CINVESTAV-Querétaro, Libramiento Norponiente 2000, Querétaro 76230, QRO, México

J. González-Hernández1

 CIMAV, Miguel de Cervantes 120, Chihuahua 31109, México

A. Kribus

Faculty of Engineering, Tel Aviv University, Tel Aviv 69978, Israel

1

On sabbatical leave from CINVESTAV.

J. Sol. Energy Eng 128(2), 258-260 (Sep 30, 2005) (3 pages) doi:10.1115/1.2189865 History: Received September 20, 2005; Revised September 30, 2005

The analysis is given of hybrid system of solar energy conversion having a stage operating at high temperature. The system contains a radiation concentrator, a photovoltaic solar cell, and a thermal generator, which could be thermoelectric one or a heat engine. Two options are discussed, one (a) with concentration of the whole solar radiation on the PV cell working at high temperature and coupled to the high-temperature stage, and another (b) with a special PV cell construction, which allows the use of the part of solar spectrum not absorbed in the semiconductor material of the cell (“thermal energy”) to drive the high-temperature stage while the cell is working at ambient temperature. The possibilities of using different semiconductor materials are analyzed. It is shown that the demands to the cell material are different in the two cases examined: in system (a) with high temperature of cell operation, the materials providing minimum temperature dependence of the conversion efficiency are necessary, for another system (b) the materials with the larger band gap are profitable. The efficiency of thermal generator is assumed to be proportional to that of the Carnot engine. The optical and thermal energy losses are taken into account, including the losses by convection and radiation in the high-temperature stage. The radiation losses impose restrictions upon the working temperature of the thermal generator in the system (b), thus defining the highest possible concentration ratio. The calculations made show that the hybrid system proposed could be both efficient and practical, promising the total conversion efficiency around 2530% for system (a), and 3040% for system (b).

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Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 1

Scheme of the hybrid system discussed: (a) with high-temperature cell regime and (b) with low-temperature cell

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Figure 2

Calculated temperature dependencies of solar cells efficiency with account of optical system efficiency (αηa, curve 1), and of efficiency of the hybrid system a (curve 2 for K=0.4, curve 3 for K=0.5, curve 4 for K=0.6; parameter α=0.9, h=10W∕m2K, C=50). Curve 5 shows the effect of the TG for K=0.6.

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Figure 3

Percentage of “thermal” radiation in the solar AM1.5 spectrum (curve 1 gives 0.5fT), PV cell estimated efficiency 2 and the total system efficiency as function of band gap of a cell material (α=0.9, K=0.6; ΔT=500K and C=500 for curve 3, ΔT=900K and C=1500 for curve 4).

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