Temperature Based Models for Determining Solar Radiation in the Savannah Region

Abstract

Due to erratic power supply, effort towards the development of alternative energy system is increasing on a daily basis. The quantity of radiation is essential for efficient designing and selecting energy devices for agricultural, industrial, telecommunication and household uses. It requires knowledge of the actual solar radiation (SR) reaching the earth’s surface at the location of interest. In this study, temperature-based methods to determine SR in the savannah region using Abuja (9.05⁰N, 7.49⁰E). Nigeria as a case study was conducted. Hargreaves-Samani, Annandale and Samani models were analyzed and compared with ten years data on SR, and temperatures from 2001 to 2010 from Nigerian Meteorological Agency, NIMET Abuja. The solar declination δ, eccentricity correction factor of the earth’s orbit E_o, and day angle (⁰) were determined to estimate extraterrestrial SR on a horizontal surface. The models were tested in terms of the mean bias error (MBE), root mean square error (RMSE) and the percentage RMSE. The results revealed Hargreaves-Samani is the most fitted followed by Annandale while Samani model is not applicable due to proximity to large water bodies. The extraterrestrial and SR continuously decreases during summer due to absorption, scattering, reflection and transmission by clouds, ozone layer, water vapour, carbon dioxide, smog and other particles while their values increases drastically during winter in agreement with other research findings.