Analysis of Spatial and Temporal Variability of Solar Radiation Across Nigeria’s Six Geopolitical Zones Using Long-Term Satellite Data

Background: Nigeria's solar radiation resource is abundant but spatially variable, with limited ground-based measurement stations creating data gaps that impede accurate solar energy planning across all geopolitical zones. Aim: This study analysed spatial and temporal variability of solar radiation across Nigeria's six geopolitical zones using 20 years of NASA POWER satellite-derived irradiance data. Methods: Monthly global horizontal irradiance, direct normal irradiance, and diffuse horizontal irradiance data for 54 grid points covering all six zones were extracted and analysed. Spatial interpolation using ordinary kriging generated zonal irradiance maps. Temporal trend analysis applied Mann-Kendall tests to detect long-term changes. Results: Mean annual GHI ranged from 4.62 kWh/m2/day in the South West to 6.84 kWh/m2/day in the North West. A statistically significant declining trend of 0.012 kWh/m2/day per year was detected in the South South, attributed to increasing atmospheric aerosol loading. North West and North East zones showed the highest and most consistent solar resources. Conclusion: Nigeria's North West and North East zones are optimal for utility-scale solar deployment, while the South South requires careful aerosol adjustment in resource modelling. The study provides a robust national solar atlas for evidence-based energy planning. Keywords: solar radiation, spatial variability, Nigeria, satellite data, NASA POWER.