Spatiotemporal Assessment of Optimized Solar Radiation for Photovoltaic Applications Across Nigeria: Optimal Tilt Angles, Long-Term Trends, Change Points, and Associations with Climatic Variables

Accurate characterization of solar energy is crucial for PV implementation; however, existing studies in Nigeria have focused on horizontal radiation, site selection, or optimal tilt angle, but not on the combined effects of trends, structural changes, and meteorological factors. This work bridges this gap by conducting a comprehensive spatiotemporal analysis of optimized solar radiation across all 37 administrative regions of Nigeria using NASA POWER data from 1984 to 2025. Thus, this study aims to mathematically determine the optimal tilt angle that achieves the best total solar radiation in different regions of Nigeria. Furthermore, the temporal trends of the maximum total radiation at the optimal angle were analyzed using linear regression and Mann–Kendall tests. The Pettitt, Buishand, and Standard Normal Homogeneity Tests and Segmented Regression were used to detect structural changes, while Spearman’s correlation was used to measure association with meteorological and atmospheric factors. Optimal tilt angles per year were relatively high in northern states of Nigeria, with values of 15.3° in Sokoto and 14.7° in Yobe, while southern states had values of about 9–10°. Optimum annual radiation was highest in Yobe and Sokoto (22.9 MJ m−2 day−1), as against 17 MJ m−2 day−1 in Rivers and Bayelsa. Trends in annual radiation declined in all 37 regions, significantly declining in 33 (89.2%) regions. Change point analysis yielded a total of 29 regions (78.4%), mostly occurring within the 2003–2004 period. The results demonstrate that the amount of cloud cover was the main factor with a negative correlation to solar radiation, while wind variables showed a strong positive correlation. Furthermore, circular-linear regression showed statistically significant regional correlations between wind direction and solar radiation. The current findings have important implications for urban planning and city planning in Nigeria, as data on the availability and variability of solar energy resources, precisely defined in terms of geographical location, can be used in designing and determining the sizes of rooftop solar power plants, as well as in integrating renewable energy sources within urban areas, which is a key pillar for the sustainability of cities. Moreover, these results could also form the basis for incorporating solar energy resource trends into urban energy plans in Nigeria, particularly with regard to cities experiencing rapid growth and increasing energy demand. The novelty of this study is a comprehensive framework that unites the orientation of PV, the quantity of resources, temporal variations, regime shifts, and atmospheric variables in Nigeria.