Abstract
Attenuation of solar radiation between the receiver and the heliostat field in concentrated solar power (CSP) tower plants can reduce the overall system performance significantly. The attenuation varies strongly with time and the average attenuation at different sites might also vary strongly from each other. If no site specific attenuation data is available, the optimal plant design cannot be determined and rough estimations of the attenuation effect are required leading to high uncertainties of yield analysis calculations. The attenuation is caused mainly by water vapor content and aerosol particles in the lower atmospheric layer above ground. Although several on-site measurement systems have been developed during recent years, attenuation data sets are usually not available to be included during the plant project development. An Atmospheric Attenuation (AATTENUATION) model to derive the atmospheric transmittance between a heliostat and receiver on the basis of common direct normal irradiance (DNI), temperature, relative humidity, and barometric pressure measurements was developed and validated by the authors earlier. The model allows the accurate estimation of attenuation for sites with low attenuation and gives an estimation of the attenuation for less clear sites. However, the site-dependent coefficients of the AATTENUATION model had to be developed individually for each site of interest, which required time-consuming radiative transfer simulations, considering the exact location and altitude, as well as the pre-dominant aerosol type at the location. This strongly limited the application of the model despite its typically available input data. In this manuscript, a look-up table (LUT) is presented which enables the application of the AATTENUATION model at the site of interest without the necessity to perform the according complex radiative transfer calculations for each site individually. This enables the application of the AATTENUATION model for virtually all resource assessments for tower plants and in an operational mode in real time within plant monitoring systems around the world. The LUT also facilitates the generation of solar attenuation maps on the basis of long-term meteorological data sets which can be considered during resource assessment for CSP tower plant projects. The LUTs are provided together with this manuscript as supplementary files. The LUT for the AATTENUATION model was developed for a solar zenith angle (SZA) grid of 1°, an altitude grid of 100 m, 7 different standard aerosol types and the standard AFGL atmospheres for mid-latitudes and the tropics. The LUT was tested against the original version of the AATTENUATION model at 4 sites in Morocco and Spain, and it was found that the additional uncertainty introduced by the application of the LUT is negligible. With the information of latitude, longitude, altitude above mean sea level, DNI, relative humidity (RH), ambient temperature (Tair), and barometric pressure (bp), the attenuation can be now derived easily for each site of interest.
Highlights
The design and operation of concentrated solar power (CSP) technologies have to be optimized for the site-dependent conditions so that their potential can be exploited ideally
The look-up table (LUT) for the AATTENUATION model was developed for a solar zenith angle (SZA) grid of 1◦, an altitude grid of 100 m, 7 different standard aerosol types and the standard AFGL atmospheres for mid-latitudes and the tropics
The original AATTENUATION model which was generated for each of the sites individually and which is presented in Reference [19] and validated in Reference [6] is applied by picking the coefficients a, b and DNIclean,sim for each time step using on-site data of direct normal irradiance (DNI), temperature, relative humidity (RH) and bp at four sites in Southern Spain (CIEMAT’s Plataforma Solar de Almería (PSA)) and Morocco (IRESEN’s stations in Missour, Morocco (MIS), Zagora, Morocco (ZAG), and Benguerir, Morocco (BEN))
Summary
The design and operation of CSP technologies have to be optimized for the site-dependent conditions so that their potential can be exploited ideally. As most on-site measurement methods to consider the atmospheric extinction are only applied rarely due to their complexity within the project planning process, in many cases, only one of two standard cases, e.g., typical clear or typical hazy, is considered [5]. This can lead to under- or over-estimations of several percent in terms of the expected annual plant yield [5,8,9].
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