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Cloud height and tracking accuracy of three all sky imager systems for individual clouds

Nouri, Bijan and Kuhn, Pascal Moritz and Wilbert, Stefan and Hanrieder, Natalie and Zarzalejo, L.F. and Kazantzidis, A. and Blanc, Philipp and Pitz-Paal, Robert (2019) Cloud height and tracking accuracy of three all sky imager systems for individual clouds. Solar Energy, 177, pp. 2013-228. Elsevier. DOI: 10.1016/j.solener.2018.10.079 ISSN 0038-092X

[img] PDF - Postprint version (accepted manuscript)


Solar irradiance nowcasts can be derived with sky images from all sky imagers (ASI) by detecting and analyzing transient clouds, which are the main contributor of intra-hour solar irradiance variability. The accuracy of ASI based solar irradiance nowcasting systems depends on various processing steps. Two vital steps are the cloud height detection and cloud tracking. This task is challenging, due to the atmospheric conditions that are often complex, including various cloud layers moving in different directions simultaneously. This challenge is addressed by detecting and tracking individual clouds. For this, we developed two distinct ASI nowcasting approaches with four or two cameras and a third hybridized approach. These three systems create individual 3-D cloud models with unique attributes including height, position, size, optical properties and motion. This enables us to describe complex multi-layer conditions. In this paper, derived cloud height and motion vectors are compared with a reference ceilometer (height) and shadow camera system (motion) over a 30 day validation period. The validation data set includes a wide range of cloud heights, cloud motion patterns and atmospheric conditions. Furthermore, limitations of ASI based nowcasting systems due to image resolution and image perspective constrains are discussed. The most promising system is found to be the hybridized approach. This approach uses four ASIs and a voxel carving based cloud modeling combined with a cloud segmentation independent stereoscopic cloud height and tracking detection. We observed for this approach an overall mean absolute error of 648 m for the height, 1.3 m/ s for the cloud speed and 16.2° for the motion direction.

Item URL in elib:https://elib.dlr.de/127655/
Document Type:Article
Title:Cloud height and tracking accuracy of three all sky imager systems for individual clouds
AuthorsInstitution or Email of AuthorsAuthor's ORCID iD
Nouri, BijanBijan.Nouri (at) dlr.deUNSPECIFIED
Kuhn, Pascal MoritzPascal.Kuhn (at) dlr.dehttps://orcid.org/0000-0001-9978-5706
Wilbert, StefanStefan.Wilbert (at) dlr.dehttps://orcid.org/0000-0003-3573-3004
Hanrieder, NatalieNatalie.Hanrieder (at) dlr.dehttps://orcid.org/0000-0002-9671-351X
Kazantzidis, A.Univ. of Patras, Patras, GRUNSPECIFIED
Blanc, PhilippEcole des Mines de ParisUNSPECIFIED
Pitz-Paal, RobertRobert.Pitz-Paal (at) dlr.dehttps://orcid.org/0000-0002-3542-3391
Journal or Publication Title:Solar Energy
Refereed publication:Yes
Open Access:Yes
Gold Open Access:No
In ISI Web of Science:Yes
DOI :10.1016/j.solener.2018.10.079
Page Range:pp. 2013-228
Series Name:El Sevier
Keywords:Nowcasting, 3-D cloud modeling, Cloud tracking, Cloud height, All sky imager, Irradiance map
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
Location: Köln-Porz
Institutes and Institutions:Institute of Solar Research > Qualification
Deposited By: Kruschinski, Anja
Deposited On:20 Nov 2019 15:18
Last Modified:10 Feb 2020 12:01

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