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Research Papers

Experimental Verification of Optical Modeling of Parabolic Trough Collectors by Flux Measurement

[+] Author and Article Information
Björn Schiricke

German Aerospace Center (DLR), Institute of Technical Thermodynamics, 51170 Cologne, Germanybjoern.schiricke@dlr.de

Robert Pitz-Paal, Eckhard Lüpfert

German Aerospace Center (DLR), Institute of Technical Thermodynamics, 51170 Cologne, Germany

Klaus Pottler, Markus Pfänder

German Aerospace Center (DLR), Plataforma Solar de Almería, 04200 Tabernas, Spain

Klaus-J. Riffelmann

 Flagsol GmbH, Mühlengasse 7, 50667 Cologne, Germany

Andreas Neumann

 Solar Systems Pty. Ltd., 322 Burwood Road, Hawthorn, Victoria 3122, Australia

J. Sol. Energy Eng 131(1), 011004 (Jan 06, 2009) (6 pages) doi:10.1115/1.3027507 History: Received July 09, 2007; Revised January 08, 2008; Published January 06, 2009

In order to optimize the solar field output of parabolic trough collectors (PTCs), it is essential to study the influence of collector and absorber geometry on the optical performance. The optical ray-tracing model of PTC conceived for this purpose uses photogrammetrically measured concentrator geometry in commercial Monte Carlo ray-tracing software. The model has been verified with measurements of a scanning flux measurement system, measuring the solar flux density distribution close to the focal line of the PTC. The tool uses fiber optics and a charged coupled device camera to scan the focal area of a PTC module. Since it is able to quantitatively detect spilled light with good spatial resolution, it provides an evaluation of the optical efficiency of the PTC. For comparison of ray-tracing predictions with measurements, both flux maps and collector geometry have been measured under identical conditions on the Eurotrough prototype collector at the Plataforma Solar de Almería. The verification of the model is provided by three methods: the comparison of measured intercept factors with corresponding simulations, comparison of measured flux density distributions with corresponding ray-tracing predictions, and comparison of thermographically measured temperature distribution on the absorber surface with flux density distribution predicted for this surface. Examples of sensitivity studies performed with the validated model are shown.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

ParaScan-II mounted on the prototype Eurotrough collector at PSA

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Figure 2

The flux measurement sensor of ParaScan-II

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Figure 3

Optical setup of CCD line camera and glass fibers

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Figure 4

Picture of photogrammetric data evaluation with measurement targets on eight facets, the absorber tube, and the module axis

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Figure 5

Measured height deviations of the facets from the ideal parabola in millimeters (smoothed data, expanded scale)

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Figure 6

Transversal slope errors of the facets in milliradians, calculated from the smoothed data. Above: deviations in the x direction (transversal); below: deviations in the y direction (longitudinal).

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Figure 7

Photogrammetry data and ParaScan-II measurement surface in the ray-tracing model

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Figure 8

Comparison of simulated and measured intercept factors

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Figure 9

Comparison of measured flux with simulated flux on the total array for the incidence angles θ=30deg (top), θ=14deg (middle), and θ=5deg (bottom)

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Figure 10

Interval of total array used in Fig. 1

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Figure 11

Comparison of simulated flux (top) with measured temperature profile (bottom)

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Figure 12

Example for a sensitivity study with parameter variation. The combined influence of tracking offset and a displacement of the absorber on the optical efficiency is shown.

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