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| Titel |
Atmospheric extinction in solar tower plants: absorption and broadband correction for MOR measurements |
| VerfasserIn |
N. Hanrieder, S. Wilbert, R. Pitz-Paal, C. Emde, J. Gasteiger, B. Mayer, J. Polo |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1867-1381
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Measurement Techniques ; 8, no. 8 ; Nr. 8, no. 8 (2015-08-25), S.3467-3480 |
| Datensatznummer |
250116543
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| Publikation (Nr.) |
 copernicus.org/amt-8-3467-2015.pdf |
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| Zusammenfassung |
| Losses of reflected Direct Normal Irradiance due to atmospheric
extinction in concentrated solar tower plants can vary significantly
with site and time. The losses of the direct normal irradiance between
the heliostat field and receiver in a solar tower plant are mainly
caused by atmospheric scattering and absorption by aerosol and water
vapor concentration in the atmospheric boundary layer. Due to a high
aerosol particle number, radiation losses can be significantly larger
in desert environments compared to the standard atmospheric conditions
which are usually considered in ray-tracing or plant optimization
tools. Information about on-site atmospheric extinction is only rarely
available. To measure these radiation losses, two different
commercially available instruments were tested, and more than
19 months of measurements were collected and compared at the Plataforma Solar de
Almería. Both instruments are primarily used to
determine the meteorological optical range (MOR). The Vaisala FS11
scatterometer is based on a monochromatic near-infrared light source
emission and measures the strength of scattering processes in a small
air volume mainly caused by aerosol particles. The Optec LPV4
long-path visibility transmissometer determines the monochromatic
attenuation between a light-emitting diode (LED) light source at
532 nm and a receiver and therefore also accounts for
absorption processes. As the broadband solar attenuation is of
interest for solar resource assessment for concentrated solar power
(CSP), a correction procedure for these two instruments is developed
and tested. This procedure includes a spectral correction of both
instruments from monochromatic to broadband attenuation. That means the attenuation is corrected for the
time-dependent solar spectrum which is reflected by the collector.
Further, an absorption correction for the Vaisala FS11 scatterometer is implemented. To optimize the
absorption and broadband correction (ABC) procedure, additional
measurement input of a nearby sun photometer is used to enhance
on-site atmospheric assumptions for description of the atmosphere in
the algorithm. Comparing both uncorrected and spectral- and
absorption-corrected extinction data from 1-year measurements at the
Plataforma Solar de Almería, the mean difference between the
scatterometer and the transmissometer is reduced from 4.4 to
0.57 %. Applying the ABC procedure without the usage of additional
input data from a sun photometer still reduces the difference between
both sensors to about 0.8 %. Applying an expert guess assuming
a standard aerosol profile for continental regions instead of
additional sun photometer input results in a mean difference of
0.8 %.
Additionally, a simulation approach which just uses sun photometer and common
meteorological data to determine the on-site atmospheric extinction at
surface is presented and corrected FS11 and LPV4 measurements are validated with the simulation results.
For T1 km equal to 0.9 and a 10 min time resolution, an uncertainty
analysis showed that an absolute uncertainty of about 0.038 is expected for
the FS11 and about 0.057 for the LPV4. Combining both uncertainties results
in an overall absolute uncertainty of 0.068 which justifies quite well the mean
RMSE between both corrected data sets. For yearly averages several error
influences average out and absolute uncertainties of 0.020 and 0.054 can be expected for the FS11 and the LPV4, respectively.
Therefore, applying this new correction method, both instruments can now be
utilized to sufficiently accurately determine the solar broadband extinction in tower plants. |
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