Spatial Analysis of Solar Energy Resource Variability Across Nigeria’s Six Geopolitical Zones

Solar energy resource variability across Nigeria's diverse geographical and climatic zones affects the performance and economic viability of photovoltaic installations, yet spatially comprehensive analyses that simultaneously account for seasonal, inter-annual, and inter-zonal variability are limited, constraining the precision of national renewable energy planning. This study conducts a spatial analysis of solar energy resource variability across Nigeria's six geopolitical zones using gridded irradiance datasets from three independent satellite sources: NASA POWER, SARAH-2, and PVGIS ERA5. A 15-year data period from 2008 to 2022 is analysed to characterise seasonal patterns, annual variability coefficients, and spatial gradients in global horizontal irradiance, direct normal irradiance, and photovoltaic power output across a 0.5-degree grid. Geographic information system-based interpolation and spatial autocorrelation analysis are employed to identify resource hotspots and transition zones. Intercomparison of the three satellite datasets is used to quantify data uncertainty relevant to project bankability assessments. Results confirm a pronounced north-south gradient with annual global horizontal irradiance ranging from 1,650 kilowatt-hours per square metre in the South South to 2,200 kilowatt-hours per square metre in the North West. Inter-annual variability is highest in the Middle Belt transition zone and lowest in the semi-arid North West. The study produces Nigeria's first publicly available multi-source solar resource uncertainty map and recommends its integration into the Rural Electrification Agency's project planning toolkit. Keywords: solar resource variability, spatial analysis, Nigeria, geopolitical zones, satellite irradiance data.