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Please use this identifier to cite or link to this item: http://hdl.handle.net/10481/48589

Title: Multi-exposure adaptive threshold technique for cloud detection with sky imagers
Authors: Cazorla Cabrera, Alberto
Husillos, C.
Antón, Manuel
Alados-Arboledas, Lucas
Issue Date: Apr-2015
Abstract: Sky imagers have been used for cloud detection and classification in the last years, and one of the applications of these instruments is the use of cloud information in forecast algorithms for solar power technologies. These algorithms depend on an accurate classification of the complete sky dome cloud cover, but most system fail in the proximity of the sun due to saturation in the images. This work proposes a new method for cloud detection with sky imagers using images taken with different exposure times and applying an adaptive threshold to each one. The use of multiple exposure times avoids the saturation of the image in the vicinity of the sun position, while the adaptive threshold applied to the images helps in the accurate detection of cloud coverage, especially in the circumsolar area. The method is tested with a commercial sky imager, paying special attention to the detection of clouds close to the sun position. A case study is analyzed, showing an accurate detection of clouds in the vicinity of the sun. The method is also validated using statistical values for data recorded during almost one month which cover a great variety of cloudiness cases. For this purpose, the detection of clouds in the sun position is compared against the reduction of the direct normal irradiance (DNI) with respect to a modeled DNI.
Sponsorship: This work was supported by the Andalusia Regional Government through projectsP10-RNM-6299 and P12-RNM-2409,
Spanish Ministry of Economy and Competitiveness through projectsCGL2013-45410-R.
EU through ACTRIS project (EU INFRA-2010-1.1.16-262254).
Publisher: Elsevier
Keywords: Sky imager
HDR (High dynamic range)
Cloud detection
Solar energy
Forecasting
URI: http://hdl.handle.net/10481/48589
ISSN: 0038-092X
1471-1257
Rights : Creative Commons Attribution-NonCommercial-NoDerivs 3.0 License
Citation: Cazorla Cabrera, A.; et al. Multi-exposure adaptive threshold technique for cloud detection with sky imagers. Solar Energy, 114: 268-277 (2015). [http://hdl.handle.net/10481/48589]
Appears in Collections:RNM119 - Artículos
OpenAIRE (Open Access Infrastructure for Research in Europe)

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