Investigation of Cloudiness Patterns and Their Relationship with Solar Radiation in Ibadan, Southwest Nigeria

Cloud cover variability is a critical determinant of surface solar radiation availability, influencing energy yield from photovoltaic systems and agricultural productivity in the tropics. This study investigates seasonal and inter-annual patterns of cloudiness and their relationship with incoming solar radiation over Ibadan, Oyo State, using synoptic cloud cover observations and pyranometer sunshine duration records from the International Institute of Tropical Agriculture (IITA) Ibadan station supplemented by NiMet data for 2018 to 2023. The Angstrom-Prescott regression model was applied to estimate global solar radiation from sunshine hours, and the results were correlated with cloud cover fraction observations using Pearson correlation analysis. Results reveal that mean cloud cover ranges from 3.5 oktas in the dry season to 6.8 oktas at the height of the rainy season, corresponding to a 45 percent reduction in mean daily solar radiation between January and August. The Angstrom-Prescott model produced reliable solar radiation estimates with a root mean square error of 1.37 MJ per square metre per day. A significant inverse correlation between cloud cover and solar radiation confirms that cloud dynamics are the dominant driver of surface radiation variability in Ibadan. Findings have practical implications for the sizing and yield forecasting of rooftop solar photovoltaic systems in Southwest Nigeria. Keywords: cloud cover, solar radiation, Ibadan, photovoltaic, Angstrom-Prescott.