Performance of Generated Models with Statistical Tools for Estimation of Solar Radiation in Umudike, Abia State, Nigeria

Abstract

This study presents a comprehensive analysis of the monthly variation in global solar radiation and associated meteorological parameters in Umudike, Nigeria, using both observed and model-predicted data. The monthly mean daily extraterrestrial radiation (Ho) ranged from 33.38 MJ m⁻² day⁻¹ in June to a peak of 37.73 MJ m⁻² day⁻¹ in March. Measured global solar radiation (Hm) exhibited a strong seasonal pattern, with values increasing from 2.65 MJ m⁻² day⁻¹ in August to a maximum of 6.35 MJ m⁻² day⁻¹ in May. Predicted radiation values (Hp) from statistical models closely mirrored this trend, ranging from 2.75 MJ m⁻² day⁻¹ in August to 6.31 MJ m⁻² day⁻¹ in May. Among the models evaluated, Model 9 and Model 10 showed the best agreement with observed values, with minimal deviation during peak and trough periods. The clearness index (K), indicative of atmospheric transparency, ranged from 0.07 in August to 0.18 in May, reflecting the influence of cloud cover and rainfall on solar availability. Maximum daily air temperatures (Tmax) peaked at 34.1°C in February and dropped to 28.7°C in August, while minimum temperatures (Tmin) fluctuated between 21.05°C in January and 23.50°C in April. Sunshine fraction (ϴ) was highest in December (0.47) and lowest in August (0.18). August also recorded the highest monthly rainfall (Ṝ = 312.63 mm), while the highest relative humidity (RH = 87.15%) occurred in July. The consistency between measured and predicted solar radiation, as well as alignment with long-term climatic records (Climate Data, 2025), supports the reliability of the applied models for solar radiation estimation. These insights are crucial for optimizing solar energy harvesting, agricultural scheduling, and climate-resilient infrastructure planning in southeastern Nigeria