ASSESSMENT OF SOLAR RESOURCE AVAILABILITY AND ITS CLIMATIC DRIVERS AT A REPRESENTATIVE GRID POINT IN THE GAMBIA

Abstract

Assessment of long-term solar resource variability and its climatic controls is essential for sustainable photovoltaic deployment in data-scarce regions. This study evaluated solar resource availability and its climatic drivers at a representative central grid point in The Gambia (13.45° N, 15.38° W) using monthly NASA POWER satellite- and reanalysis-derived estimates from 1998 to 2025. Solar radiation (All-sky surface shortwave (solar) downward irradiance), Clear-sky surface shortwave downward irradiance, cloud cover, air temperature, specific humidity, wind speed, and precipitation were analyzed using descriptive climatology, clear-sky index assessment, Mann-Kendall trend analysis, correlation analysis, and multiple linear regression on both raw and deseasonalized datasets. The results showed that solar resource availability was consistently high during the dry season (November to May), with clear sky index values ranging from 0.90 to 0.96, whereas atmospheric transmissivity was markedly lower during the monsoon season, reaching a low of 0.760 in August. Long-term trend analysis revealed no statistically significant change in solar radiation over the research period, despite minor drops in August and September. After adjusting for seasonal impacts, cloud quantity emerged as the most important predictor of solar radiation fluctuation. Simultaneously, the apparent positive correlations between temperature and wind speed reflected shared seasonal cycles rather than direct physical controls. These findings highlight The Gambia's substantial and seasonally variable solar irradiance resource and indicate cloud fluctuation as the primary atmospheric restriction for solar resource assessment, photovoltaic planning, operational forecasting, and climate-resilient energy policy, providing a point-scale baseline for future multi-site assessment across the country.