Diurnal Variation of Solar Radiation, Ambient Temperature, Panel Temperature and Relative Humidity across some selected locations in Nigeria.

Abstract

This study presents a comprehensive analysis of the diurnal variation of solar radiation, ambient temperature, panel temperature, and relative humidity across selected locations in Nigeria. The objective is to examine how these environmental parameters influence photovoltaic (PV) module performance from both an experimental and solid-state physics perspective. Photovoltaic energy conversion is fundamentally governed by semiconductor processes within a p–n junction, where incident photons with energy hν≥E_ggenerate electron–hole pairs. The efficiency of charge carrier separation and transport is strongly influenced by temperature-dependent parameters such as carrier mobility, intrinsic carrier concentration, and recombination rates. Consequently, environmental variables introduce dynamic operating conditions that directly affect PV output. The results obtained from the locations exhibit a consistent diurnal pattern, with solar radiation increasing from near-zero values in the early morning to peak values ranging between approximately 900–1400 W/m² around midday (12:00–14:00 hrs), followed by a gradual decline toward evening. Correspondingly, both ambient and panel temperatures increase with solar irradiance, with panel temperatures consistently exceeding ambient temperatures by several degrees due to heat accumulation and limited convective cooling. Peak panel temperatures were observed in the range above 40°C, depending on location and module type. Relative humidity showed an inverse relationship with solar radiation and temperature, decreasing during peak irradiance periods and increasing during early morning and late evening hours. This behavior is attributed to atmospheric thermodynamics, where increased temperature reduces relative humidity through enhanced evaporation and air expansion. From a solid-state standpoint, the elevated panel temperatures observed across all locations contribute to a reduction in PV efficiency through increased carrier recombination and reduced open-circuit voltage. Comparative analysis of the different locations reveals notable spatial variations in peak irradiance and thermal behavior, reflecting the influence of local climatic conditions such as cloud cover, humidity levels, and atmospheric clarity. Inland and high-radiation locations exhibited sharper irradiance peaks and higher panel temperatures, while more humid regions showed moderated irradiance profiles and relatively lower thermal gradients. The findings highlight the critical interplay between environmental conditions and semiconductor physics in determining PV performance. The results emphasize that while high solar irradiance enhances photocurrent generation, excessive thermal loading reduces efficiency, thereby necessitating careful consideration of location-specific conditions in PV system design and deployment. This study provides valuable empirical data for optimizing photovoltaic systems in tropical environments and contributes to a deeper understanding of how diurnal environmental variations influence solid-state device performance in real-world applications.