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Research Papers

Techniques to Measure Solar Flux Density Distribution on Large-Scale Receivers

[+] Author and Article Information
Marc Röger

German Aerospace Center (DLR),
Solar Research,
Plataforma Solar de Almería,
Tabernas 04200, Spain
e-mail: marc.roeger@dlr.de

Patrik Herrmann

Technical University of Darmstadt,
Reactive Flows and Diagnostics,
Darmstadt 64287, Germany

Steffen Ulmer, Miriam Ebert, Christoph Prahl

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

Felix Göhring

German Aerospace Center (DLR),
Solar Research,
Cologne 51147, Germany

Commonwealth Scientific and Industrial Research Organisation (CSIRO)

Flux And Temperature MEasurement System (FATMES)

Scanning Camera and Target Measurment System (SCATMES)

French National Centre for Scientific Research (CNRS)

Contributed by the Solar Energy Division of ASME for publication in the JOURNAL OF SOLAR ENERGY ENGINEERING. Manuscript received March 1, 2012; final manuscript received March 7, 2014; published online May 2, 2014. Editor: Gilles Flamant.

J. Sol. Energy Eng 136(3), 031013 (May 02, 2014) (10 pages) Paper No: SOL-12-1062; doi: 10.1115/1.4027261 History: Received March 01, 2012; Revised March 07, 2014

Flux density measurement applied to central receiver systems delivers the spatial distribution of the concentrated solar radiation on the receiver aperture, measures receiver input power, and monitors and might control heliostat aimpoints. Commercial solar tower plants have much larger aperture surfaces than the receiver prototypes tested in earlier research and development (R&D) projects. Existing methods to measure the solar flux density in the receiver aperture face new challenges regarding the receiver size. Also, the requirements regarding costs, accuracy, spatial resolution, and measuring speed are different. This paper summarizes existent concepts, presents recent research results for techniques that can be applied to large-scale receivers and assesses them against a catalog of requirements. Direct and indirect moving bar techniques offer high measurement accuracy, but also have the disadvantage of large moving parts on a solar tower. In the case of external receivers, measuring directly on receiver surfaces avoids moving parts and allows continuous measurement but may be not as precise. This promising technique requires proper scientific evaluation due to specific reflectance properties of current receiver materials. Measurement-supported simulation techniques can also be applied to cavity receivers without installing moving parts. They have reasonable uncertainties under ideal conditions and require comparatively low effort.

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Figures

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Fig. 1

Possible mechanisms of linear moving bars (left: horizontal bar and right: vertical bar)

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Fig. 2

Grabbed CCD image (a1), deskewed and unwinded gray value image in false colors (a2), and image after application of brightness correction matrix and calibration (a3). Image (b) shows the moving bar measurement as reference (open volumetric receiver PSA, ∼225 kW, 13.12.07, 13:20 h).

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Fig. 3

Normalized BRDF values of a volumetric ceramic receiver as a function of zenith and azimuth angle. Comparison of laboratory gonioreflectometer measurements (sketch left and half markers) and measurements with heliostat groups of solar field (full markers, also see Fig. 4).

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Fig. 4

Normalized BRDF value for each heliostat of the CESA-1 heliostat field at PSA, assuming a plane volumetric air receiver at 84 m height, 30 deg inclined, and camera position at the rear of the field

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Fig. 5

Procedure of scanning part of the focus over a stripe-shaped, fixed target

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Fig. 6

Flux density distributions on radiation shield plane in kW/m2 during test 1 (PSA, 19.05.10, 12:50 h, 46 heliostats). Ray tracing simulation (a1). Measurement directly on radiation shield after application of correction matrix and calibration (a2).

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Fig. 7

Moving bar reference measurement shifted to radiation shield plane for test 1, PSA, 19.05.10, 12:50 h

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Fig. 8

Requirements to reach the design specifications. The fields marked in gray show the different measurement objectives.

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