Doubling the concentration of one-axis tracking parabolic trough collectors by a new second-stage design

Conference · Sat Dec 31 04:00:00 EST 1994

OSTI ID:194854

Brunotte, M; Goetzberger, A; Blieske, U ^[1]

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1. Fraunhofer Inst. for Solar Energy Systems, Freiburg (Germany)

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 the authors 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 focuses 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}. 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} in the NS-direction which still can be concentrated by a factor of n/sin(23.5{degree}). 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.

• OSTI ID: 194854
• Report Number(s): CONF-9404167--; ISBN 0-8194-1564-2
• Country of Publication: United States
• Language: English

Related Subjects

14 SOLAR ENERGY
ANTIREFLECTION COATINGS
COMPOUND PARABOLIC CONCENTRATORS
CONCENTRATOR SOLAR CELLS
DESIGN
PERFORMANCE
SOLAR TRACKING