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Real-Time Uncertainty Specification of All Sky Imager Derived Irradiance Nowcasts

Nouri, Bijan and Wilbert, Stefan and Kuhn, Pascal Moritz and Hanrieder, Natalie and Schroedter-Homscheidt, Marion and Kazantzidis, A. and Zarzalejo, L.F. and Blanc, Philippe and Kumar, Sharad and Goswami, Neeraj and Shankar, Ravi and Affolter, Roman and Pitz-Paal, Robert (2019) Real-Time Uncertainty Specification of All Sky Imager Derived Irradiance Nowcasts. Remote Sensing, 11 (1059). Multidisciplinary Digital Publishing Institute (MDPI). doi: 10.3390/rs11091059. ISSN 2072-4292.

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Official URL: https://doi.org/10.3390/rs11091059


The incoming downward shortwave solar irradiance is harvested to an increasing extent by solar power plants. However, the variable nature of this energy source poses an operational challenge for solar power plants and electrical grids. Intra hour solar irradiance nowcasts with a high temporal and spatial resolution could be used to tackle this challenge. All sky imager (ASI) based nowcasting systems fulfill the requirements in terms of temporal and spatial resolution. However, ASI nowcasts can only be used if the required accuracies for applications in solar power plants and electrical grids are fulfilled. Scalar error metrics, such as mean absolute deviation, root mean square deviation, and skill score are commonly used to estimate the accuracy of nowcasting systems. However, these overall error metrics represented by a single number per metric are neither suitable to determine the real time accuracy of a nowcasting system in the actual weather situation, nor suitable to describe any spatially resolved nowcast accuracy. The performance of ASI-based nowcasting systems is strongly related to the prevailing weather conditions. Depending on weather conditions, large discrepancies between the overall and current system uncertainties are conceivable. Furthermore, the nowcast accuracy varies strongly within the irradiance map as higher errors may occur at transient zones Close to cloud shadow edges. In this paper, we present a novel approach for the spatially resolved real-time uncertainty specification of ASI-based nowcasting systems. The current irradiance conditions are classified in one of eight distinct temporal direct normal irradiance (DNI) variability classes. For each class and lead-time, an upper and lower uncertainty value is derived from historical data, which describes a coverage probability of 68.3%. This database of uncertainty values is based on deviations of the irradiance maps, compared to three reference pyrheliometers in Tabernas, Andalucia over two years (2016 and 2017). Increased uncertainties due to transient effects are considered by detecting transient zones close to cloud shadow edges within the DNI map. The width of the transient zones is estimated by the current average cloud height, cloud speed, lead-time, and Sun position. The final spatially resolved uncertainties are validated with three reference pyrheliometers, using a data set consisting of the entire year 2018. Furthermore, we developed a procedure based on the DNI temporal variability classes to estimate the expected average uncertainties of the nowcasting System at any geographical location. The novel method can also be applied for global tilted or horizontal irradiance and is assumed to improve the applicability of the ASI nowcasts.

Item URL in elib:https://elib.dlr.de/130790/
Document Type:Article
Title:Real-Time Uncertainty Specification of All Sky Imager Derived Irradiance Nowcasts
AuthorsInstitution or Email of AuthorsAuthor's ORCID iDORCID Put Code
Nouri, BijanUNSPECIFIEDhttps://orcid.org/0000-0002-9891-1974UNSPECIFIED
Wilbert, StefanUNSPECIFIEDhttps://orcid.org/0000-0003-3573-3004UNSPECIFIED
Kuhn, Pascal MoritzUNSPECIFIEDhttps://orcid.org/0000-0001-9978-5706UNSPECIFIED
Hanrieder, NatalieUNSPECIFIEDhttps://orcid.org/0000-0002-9671-351X141971487
Schroedter-Homscheidt, MarionUNSPECIFIEDhttps://orcid.org/0000-0002-1854-903XUNSPECIFIED
Kazantzidis, A.Lab. of Atm. Physics, Uni Patras, GreeceUNSPECIFIEDUNSPECIFIED
Pitz-Paal, RobertUNSPECIFIEDhttps://orcid.org/0000-0002-3542-3391UNSPECIFIED
Date:May 2019
Journal or Publication Title:Remote Sensing
Refereed publication:Yes
Open Access:Yes
Gold Open Access:Yes
In ISI Web of Science:Yes
Publisher:Multidisciplinary Digital Publishing Institute (MDPI)
Series Name:MDPI
Keywords:Nowcasting; uncertainty; all sky imager; cloud camera; solar irradiance; irradiance map; DNI; DNI variability classification; cloud modeling
HGF - Research field:Energy
HGF - Program:Renewable Energies
HGF - Program Themes:Concentrating Solar Thermal Technology
DLR - Research area:Energy
DLR - Program:E SW - Solar and Wind Energy
DLR - Research theme (Project):E - Impact of Desert Environment (old), E - Systems Analysis and Technology Assessment (old)
Location: Köln-Porz
Institutes and Institutions:Institute of Solar Research > Qualification
Institute of Networked Energy Systems > Energy Systems Analysis
Deposited By: Kruschinski, Anja
Deposited On:20 Nov 2019 15:19
Last Modified:31 Oct 2023 14:41

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