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Research Papers

Measurement of Solar Radiance Profiles With the Sun and Aureole Measurement System

[+] Author and Article Information
S. Wilbert

German Aerospace Center (DLR),
Institute of Solar Research,
Plataforma Solar de Almería (PSA),
Ctra. de Senés s/n km 4,
Apartado 39, Tabernas 04200, Spain,
e-mail: stefan.wilbert@dlr.de

B. Reinhardt

DLR, Institut für Physik der Atmosphäre,
Oberpfaffenhofen, Wessling 82234, Germany

J. DeVore

Visidyne, Inc.,
429 Stanley Drive,
Santa Barbara, CA 93105

M. Röger

DLR, Institute of Solar Research, PSA,
Ctra. de Senés s/n km 4,
Apartado 39, Tabernas 04200, Spain

R. Pitz-Paal

DLR, Institute of Solar Research,
Linder Höhe,
Köln 51147, Germany

C. Gueymard

Solar Consulting Services,
P.O. Box 392,
Colebrook, NH 03576

R. Buras

Meteorologisches Institut München,
Ludwig-Maximilians-Universität,
Theresienstr. 37, München 80333, Germany

1Present address: Meteorologisches Institut München, Ludwig-Maximilians-Universität, Theresienstr. 37, 80333 München, Germany.

Contributed by the Solar Energy Division of ASME for publication in the Journal of Solar Energy Engineering. Manuscript received February 29, 2012; final manuscript received March 27, 2013; published online June 25, 2013. Assoc. Editor: Werner Platzer.

J. Sol. Energy Eng 135(4), 041002 (Jun 25, 2013) (11 pages) Paper No: SOL-12-1061; doi: 10.1115/1.4024244 History: Received February 29, 2012; Revised March 27, 2013

Due to forward scattering of direct sunlight in the atmosphere, the circumsolar region closely surrounding the solar disk looks very bright. The radiation coming from this region, the circumsolar radiation, is in large part included in common direct normal irradiance (DNI) measurements, but only partially intercepted by the receivers of focusing collectors. This effect has to be considered in the performance analysis of concentrating collectors in order to avoid overestimation of the intercepted irradiance. At times, the overestimation reaches more than 10% for highly concentrating systems even for sky conditions with relevant DNI above 200 W/m2. The amount of circumsolar radiation varies strongly with time, location and sky conditions. However, no representative sunshape measurements exist for locations that are now of particular interest for concentrating solar power (CSP) or concentrating photovoltaics (CPV). A new sunshape measurement system is developed and analyzed in this study. The system consists of the sun and aureole measurement instrument (SAM), an AERONET sun photometer and postprocessing software. A measurement network is being created with the presented system. The uncertainty of this system is significantly lower than what was obtained with previous devices. In addition, the spectral optical properties of circumsolar radiation are determined. As a result, the necessary information for CSP and CPV systems, and a basis for the development of modeling methods for circumsolar radiation, can now be achieved.

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References

Figures

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Fig. 1

Photo of the SAM Series 400 (left) next to the Cimel sun photometer (right) at one of DLR's meteorological stations at Plataforma Solar de Almería (PSA)

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Fig. 2

Block diagram of the SAM instrument (400 series)

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Fig. 3

Deviation of CSR calculated for LBL measurements from all sites after artificially deleting the radiance between 0.26 deg and 0.52 deg, interpolating and integrating

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Fig. 4

Example for the spectral scaling algorithm with actual radiance measurements from Ref. [19]

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Fig. 5

Left: spectral CSR from reference sunshapes (MYSTIC, thick lines and markers), and scaling results (thin) based on the sunshape at 670 nm. Next to the y axis the broadband CSRs are shown. Right: markers and colors used for the different combinations of τc,550 and τa,550.

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Fig. 6

Deviation of the broadband CSR obtained with the scaling algorithm from the reference CSR plotted versus the broadband CSR obtained using the scaling algorithm. Different markers refer to different solar zenith angles.

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Fig. 7

Deviation between the broadband CSR obtained with the scaling algorithm and the reference values, plotted as a function of the broadband CSR for SZA = 60 deg. Different markers correspond to different atmospheric conditions. The number in the legend is the effective radius Reff of the cloud particles in μm, the first small letters correspond to the aerosol type (ca, continental average; mp, maritime polluted; mc, maritime clean; de, desert), the capital letters describe the cloud particle type (WA, spherical water droplet; SC, ice crystal formed as solid column; PL, ice crystal formed as plate). Points belonging to water clouds are connected with dashed lines to distinguish them from the points belonging to ice clouds. For ice clouds, one color and marker shape represents one combination of aerosol type and particle shape. The filled squares with crosses correspond to an effective radius of 80 μm, the filled markers stand for 5 μm and the empty markers for 20 μm.

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Fig. 8

Ratio of the broadband CSR to the spectral CSR at 670 nm plotted versus the broadband CSR for the reference data and SZA = 60 deg. The markers are the same as in Fig. 7.

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Fig. 9

Overall uncertainty ΔCSRBB in broadband CSR for the new (SAM-based) instrument and the older DLR sunshape camera as a function of CSRBB

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Fig. 10

Broadband CSR, DNIexp, and intercept factors for EuroDish and EuroTrough plotted versus time at PSA (Apr. 28, 2011)

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