Abstract
The present research was designed to locally calibrate Hargreaves-Samani computing model (HS) in twenty-one (21) locations with their corresponding coastal and interior regions in Nigeria employing a single hybrid parameter-based model to obtain the adjusted Hargreaves-Samani coefficient (AHC) for Nigerian environment. To achieve this purpose, meteorological parameters such as extraterrestrial solar radiation, maximum sunshine duration, minimum and maximum temperatures were employed as input parameters to compute the original HS model and equally calibrate the original HS model. The monthly AHCs were obtained by multiplying the 0.17 by the monthly ratio of the observed global solar radiation (H) to H calculated from original HS model. The average value was obtained per station. These observed AHC values were considered as the target values for the development of hybrid parameter-based models (HP) for every station used for calibrating original HS model. On the whole, the result from the statistical indicators confirmed that the locally calibrated HS model performed better than the original HS model in all stations (including coastal and interior regions) investigated. Both the original and calibrated HS models underestimated H at annual timescale, but the calibrated HS model provided closer average values with H, which could confirm the good performances of the calibrated HS model. Therefore, the calibrated HS model obtained in this research could be highly recommended for estimating H in Nigeria when only temperature data are available.
Highlights
Solar radiation is the principal renewable-energy source supporting the biosphere and stimulating the biological, chemical and physical processes in the surface of the earth
The results were used to develop 24 hybrid parameter-based models (HP) models for estimating the monthly mean daily H on the horizontal surface employing extraterrestrial solar radiation, minimum and maximum temperature, and maximum sunshine duration for the 21 stations investigated in the research and their corresponding coastal region, interior region and average of all the stations (Nigerian environment)
The empirical constants of the proposed model, varying Mean bias error (MBE), mean percentage error (MPE), root mean square error (RMSE) and Nash-Sutcliffe coefficient (NS) could be attributed to seasonal variations of the global solar radiation (H) caused apparently by the atmospheric dust, presence of water vapour and ozone, cloudiness, difference in temperature range T and associated atmospheric moisture with the movement of the Hadley cell circulation system along the equatorial line in the atmosphere which differs from one local climate and geographical region to another
Summary
Solar radiation is the principal renewable-energy source supporting the biosphere and stimulating the biological, chemical and physical processes in the surface of the earth. Nigeria is a high insolation country with about an average of 2800 hours/year of of sunshine. Qualification of this renewable-energy capacity that has the energy required to maintain ecology and environment as, they are eco-friendly in that they do not contribute to global warming and production of greenhouse gases, plays a significant role in emerging new energy technologies. Several solar-energy researchers have employed Angstrom-Prescott-Page model globally as a baseline further developing empirical models for estimating global solar radiation using the same parameter, other meteorological parameters, geographical parameters, geometrical parameters and astronomical parameters that will best fit the local climate of their interest Nwokolo [6]
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