Long-Term Trends in Solar Radiation and Climatic Variability Across Nigeria: Implications for Renewable Energy Potential

Abstract

The increasing demand for sustainable energy and the growing impacts of climate change have intensified the need for reliable assessments of solar energy resources across different regions of the country. Despite the abundant solar energy potential in Nigeria, limited studies have comprehensively assessed the combined influence of climatic variability on solar radiation and photovoltaic energy generation. This study examined the long-term trends of solar radiation and climatic variability across Nigeria and evaluated their implications for the country's renewable energy potential across selected climatic zones. Climatic datasets comprising Global Horizontal Irradiance (GHI), temperature, and relative humidity, spanning a total of 45 years (1981‒2025) were obtained from the NASA POWER database for twelve selected locations representing the Warm Desert (Kukawa), Semiarid (Sokoto, Gombe, and Kano), Tropical Savannah (Abeokuta, Abuja, Minna, Jalingo, Jos, and Ibadan), and Monsoon (Ikot Akpaden and Asaba). The study adopted the Mann-Kendall trend test and Sen’s slope estimator to assess long-term trends in solar radiation and climatic variables, while correlation analysis was employed to investigate the relationships between the study parameters. Additionally, a simplified photovoltaic energy estimation model based on a standardized 2kW photovoltaic system capacity was adopted in this study to estimate the solar photovoltaic energy output. The Mann-Kendall trend analysis revealed a statistically significant decreasing trend in solar radiation across all study locations (p < 0.05), with Z-values ranging from -3.404 to -5.425 and Sen’s slope values ranging from -0.005 today. Temperature showed a significant increasing trend in most locations, with Z-values ranging from 2.299 to 5.645 and Sen’s slope values ranging from 0.009 to 0.067 °C/year, indicating increasing regional warming pattern across the study area. Relative humidity revealed a strong spatial variability, with increasing trends observed in Ikot Akpaden, Asaba, Abeokuta, Ibadan, Sokoto, and Kukawa, while Abuja, Minna, and Jalingo revealed decreasing trends. The Z-values ranged from 1.595 to 5.204, while Sen’s slope values ranged from -0.218 to 0.224 %/year. The correlation heat map revealed that solar radiation correlates negatively with relative humidity, with the strongest negative correlations observed in Abeokuta (-0.72), Ibadan (-0.63), Kukawa (-0.54), and Ikot Akpaden (-0.55). The estimated annual photovoltaic energy output ranged from approximately 2450 kWh/year to 3450 kWh/year for the standardized 2kW photovoltaic system, with northern locations such as Kukawa, Kano, Sokoto, and Gombe exhibiting the highest solar energy potential. These findings demonstrate the strong influence of long-term climatic variability on solar energy resources across the country. The study reveals a clear north-south variation in solar energy potential, pointing out the potential of northern Nigeria for solar energy development and provides essential scientific information for renewable energy panning, sustainable energy policy development, and climate adaptation strategies in Nigeria.