AATTENUATION—The Atmospheric Attenuation Model for CSP Tower Plants: A Look-Up Table for Operational Implementation

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.

Roadmap to Advance Heliostat Technologies for Concentrating Solar-Thermal Power

“…Hybrid attenuation measurement combining in-field measurement and advanced correction models [50], [51], [52] Available…”

“…However, important distinctions must be made between closed loops and open loops in heliostat control, as the distinction is not always clear and there is significant overlap. [18], [51], [52]. Given examples state that a typical signal or effect in a control loop may flow through components starting from the control room, to the controller, then to an actuator, an encoder, a sensor on the heliostat, mirror and surface normal influencers such as drives, to the target.…”

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“…Camera-based methods also exist (Ballestrín et al 2018), and at least three such options are commercially available. Sengupta and Wagner (2012) and Hanrieder et al (2016Hanrieder et al ( , 2020 presented models to derive the attenuation based on only conventional DNI measurements. Polo, Ballestrín, and Carra (2016) and Polo et al (2017) estimated the attenuation based on AOD data.…”

Optimization of CSP Plants with Thermal Energy Storage for Electricity Price Stability in Spot Markets

“…The TES system uses a thermo-solar grade molten salt. Molten salt technology is used as it is a mature technology that can ensure correct performance and match the project requirements [30], being the most extensively used storage system. For the heliostat field, the design point parameters used in the SAM are shown in Table 3.…”