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Proceedings Paper

Doubling the concentration of one-axis tracking parabolic trough collectors by a new second-stage design
Author(s): Martin Brunotte; Adolf Goetzberger; Ulf Blieske
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Paper Abstract

Economic operation of high-efficiency concentrator solar cells requires solar concentration ratios which up to now can only be achieved with two-axis tracking. In this paper we present a two-stage concentrator approaching concentration ratios up to 300X while being tracked around only one polar axis. Its principle is as follows: A parabolic trough focusses the direct solar radiation onto a line parallel to the polar tracking axis. The half rim angle of this first concentrating stage is chosen to be equal to the sun's maximum declination of 23.5 degree(s). The second stage consists of a row of dielectric, nonimaging 3D-concentrators, which couple the concentrated light directly into square solar cells. The proposed design makes use of the limited divergence of +/- 23.5 degree(s)) in the NS-direction which still can be concentrated by a factor of n/sin(23.5 degree(s)). The performance of the system depends sensitively on how well the angular acceptance characteristic of the second stage matches with the square-shaped angular irradiance distribution in the focal line of the parabolic trough. A new concentrator profile has been found that exhibits an almost ideal square acceptance characteristic with a very sharp cut-off. It is longer than the standard CPC and its slope is reduced towards the exit of the concentrator. A prototype two-stage concentrator has been constructed with a total geometrical concentration of 214X. In outdoor measurements a total optical efficiency of 77.5% was obtained.

Paper Details

Date Published: 9 September 1994
PDF: 10 pages
Proc. SPIE 2255, Optical Materials Technology for Energy Efficiency and Solar Energy Conversion XIII, (9 September 1994); doi: 10.1117/12.185399
Show Author Affiliations
Martin Brunotte, Fraunhofer-Institut fuer Solare Energiesysteme (Germany)
Adolf Goetzberger, Fraunhofer-Institut fuer Solare Energiesysteme (Germany)
Ulf Blieske, Fraunhofer-Institut fuer Solare Energiesysteme (Germany)

Published in SPIE Proceedings Vol. 2255:
Optical Materials Technology for Energy Efficiency and Solar Energy Conversion XIII
Volker Wittwer; Claes G. Granqvist; Carl M. Lampert, Editor(s)

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