Analysis of the GHI Variability Index for the City of Natal - RN

Amorim, Ana Cleide Bezerra, Emiliavaca, Samira de Azevedo Santos, Silva, Bruno do Nascimento e, de Sousa, Alan Rodrigues, Mendonça, João Vítor Fonseca, Lopes, Nicholas Medeiros, Silva, Gabriela Rocha Alves, Lira, André Luiz de Oliveira

ISES Solar World Congress 2025 · Fortaleza, Brazil · 2025-11-03
Published by International Solar Energy Society (ISES)
DOI: 10.18086/swc.2025.04.03

Abstract

Natal, a city located in Northeastern Brazil, is characterized by high levels of solar radiation, making it a strategic site for solar energy generation. However, its coastal setting promotes frequent cloud formation, introducing substantial variability in solar irradiance and influencing the performance of photovoltaic systems. This study investigates cloud cover variability in Natal using the Variability Index (VI) and the Clear-Sky Index (Kt*), based on irradiance data collected by a solarimetric station between 2015 and 2023. Cluster analysis was employed to classify sky conditions. Additionally, an investigation into overirradiance events was conducted for each type of sky. Results indicate that clear-sky conditions are uncommon, with daily VI values typically ranging from 20 to 30. Seasonal patterns reveal a reduction in VI during the rainy season (April–July) and higher variability during the dry months. Four distinct sky condition classes were identified: Clear Sky, Overcast Sky, Variable Part of the Day, and Highly Variable All Day. Overirradiance events occurred across all categories but were most frequent under highly variable conditions. These findings advance the understanding of cloud dynamics in coastal tropical environments and provide valuable insights for optimizing solar energy generation and enhancing grid stability in regions with high solar variability.

Keywords

Solar Energy, Cloudiness, Clear Skies, Northeast Brazil, Overirradiance

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