Analysis of Measurements of Direct Normal and Global Solar Radiation for Maceió, Alagoas State, Northeastern Brazil

Análise das Medidas de Radiação Solar Direta Normal e Global para Maceió, Estado de Alagoas, Nordeste do Brasil

Abstract

Studying solar radiation is essential for human knowledge, since it is present in practically all its activities. Thus, the aim of this work was to analyze the climatic and seasonal variation of direct normal and global solar radiation in the region of Maceió, Alagoas State, Northeastern Brazil with sky conditions characterized by clearness index (K_t). The K_t was determined by the ratio between global solar irradiance and solar irradiance at the top of the atmosphere. The highest occurrences of daily direct normal solar irradiance under conditions of K_t ≥ 0.6 were recorded between 400 W m⁻² and 700 W m⁻² for all seasons. Under conditions of 0.4 ≤ K_t < 0.6, the daily direct normal solar irradiance occurred between 200 W m⁻² and 500 W m⁻² and for conditions of K_t < 0.4, its maximum value was 200 W m⁻². It was observed that the levels of solar incidence in the study region depend on cloud cover conditions, with little influence of seasonality.

Keywords
solar irradiance; climatic and seasonal analysis; sky conditions