Analysis of Cloud Cover Related to Overirradiance Events Using Allsky Camera

Costa, Moisés Elias Nascimento Rufino, Amorim, Ana Cleide Bezerra, Emiliavaca, Samira de Azevedo Santos, Mendonça, João Vítor Fonseca, Silva, Gabriela Rocha Alves, de Sousa, Alan Rodrigues, Mutti, Pedro Rodrigues, Silveira, Artur Manoel Guimarães

ISES Solar World Congress 2025 · Fortaleza, Brazil · 2025-11-03
Published by International Solar Energy Society (ISES)
DOI: 10.18086/swc.2025.04.02

Abstract

Overirradiance is an atmospheric phenomenon that occurs when solar irradiance at the surface exceeds the values expected for a clear sky, due to the interaction of radiation with certain cloud formations. These events, generated by atmospheric optical mechanisms such as Mie scattering and reflection, have relevant implications for the operation of photovoltaic power plants. The objective of this study was to visually analyze the occurrence of overirradiance events using images from all-sky cameras, focusing on identifying the characteristics of sky coverage at times of peak irradiance. The data were collected at the solarimetric station of the Institute for Innovation in Renewable Energy (ISI-ER) in Natal-RN, using pyranometer data (1 minute) and images from an allsky camera (15 minutes). Events with irradiance greater than 1000 W/m² occurring between July and October 2015 were selected after applying a quality assurance procedure. The results revealed that the presence of fragmented and semi-transparent clouds (such as Altocumulus) and clouds with bright edges (such as Cumulus) was often associated with the events analyzed, favoring the momentary intensification of radiation on the surface. The combination of overirradiance data with allsky images proved to be an effective tool for characterizing the atmospheric conditions responsible for this type of event.

Keywords

irradiance extremes, cloud cover, cloud enhancement, atmospheric optics, allsky camera

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