Physical Science International Journal

Reliable knowledge of local meteorological variability is a prerequisite for technically sound siting and grid integration of a utility-scale solar photovoltaic (PV) farm. This study statistically analysed eleven years (2015–2025; N = 132 monthly observations) of rainfall amount, rainfall rate, relative humidity and sunshine duration for Rivers State, Nigeria, and translated the results into practical guidance for solar PV development in support of Sustainable Development Goal 7 (Affordable and Clean Energy), Goal 13 (Climate Action) and related goals. Descriptive statistics, one-way analysis of variance (ANOVA), Pearson correlation, ordinary least-squares regression and the non-parametric Mann–Kendall/Sen's-slope trend tests were applied, and regression-based proxy-forecast models for sunshine duration and global horizontal irradiance (GHI) were developed and validated on a 2024–2025 hold-out sample. All four variables showed pronounced and statistically significant seasonal variation (ANOVA p < 0.001) but no statistically significant inter-annual trend over the study period (Mann–Kendall p > 0.05 in all cases), indicating a strongly seasonal but climatologically stable resource base. Sunshine duration averaged 7.68 ± 1.54 h/day (CV = 20.0%) and was strongly and significantly negatively correlated with relative humidity (r = − 0.827) and rainfall amount (r = − 0.723, p < 0.001 in both cases). The best-performing proxy model (sunshine and rainfall jointly predicting GHI) achieved a hold-out R² of 0.802 and MAPE of 3.90%, supporting its use for month-ahead solar-resource forecasting. Using the Angstrom–Prescott relation calibrated for Port Harcourt, estimated GHI averaged 6.03 kWh/m²/day (mean clearness index 0.61), with an indicative mean PV capacity factor of 19.6%, rising above 23% in the December–February dry season and falling to about 17% during the June – October rains. A composite site-suitability index built from the standardised sunshine, rainfall and humidity series identified December–February as the optimal window for civil works, panel installation and peak energy yield, and June–October as the period of highest cloud cover, soiling risk and grid-integration variability. These findings support siting solar PV assets on well-drained upland sites away from flood-prone terrain, sizing inverters and battery/storage buffers to accommodate pronounced wet-season output dips, and scheduling major construction and maintenance during the dry season, which collectively strengthen the technical and economic case for grid-connected solar deployment in Rivers State.