Abstract
Some multi-linear regression equations were developed to investigate the dependence of global solar radiation on a combination of the following parameters: relative humidity, mean of daily temperature, ratio of maximum to minimum daily temperature, relative sunshine hour, rainfall, and the difference of monthly daily maximum and minimum temperature for Kano and Oyo-Nigeria for a span of 30 years (1981-2010). Using the Angstrom model as the base, ten (10) other regression equations were developed by modifying Angstrom equation. The results of statistical indicators: Coefficient of Determination (R<sup>2</sup>), Mean Bias Error (MBE), Root Mean Square Error (RMSE) and Mean Percentage Error (MPE); performed on the model along with practical comparison of the estimated and observed data validate the excellent performance accuracy of the proposed model. The equations with the highest value of coefficient of determination R2 and least value of RMSE, MBE, and MPE are given as: H/H<sub>o</sub>= 0.351 + 0.556(S/S<sub>o</sub>) – 0.268(RH/100) and H/H<sub>o</sub>= 0.110 + 0.409(S/S<sub>o</sub>) + 0.152(RH/100) for Kano and Oyo respectively, where S/S<sub>o</sub> is the relative sunshine duration and RH is the relative humidity. The models can be used for estimating global solar radiation on horizontal surfaces for places with similar latitudes where radiation data are unavailable. Based on overall results, it was concluded that Sunshine duration and relative humidity are the most appropriate combination of climatic variables suitable for the estimation of global solar radiation in the study areas.
Highlights
Solar radiation holds one of the relevant places among the diverse possible options of energy sources
This is in agreement with [17], [18] that a zero value of Mean Bias Error (MBE) is ideal and low Root Mean Square Error (RMSE) and Mean Percentage Error (MPE) is desirable
Multiple regression techniques have been employed in this study to develop several correlation equations to describe the dependence of global solar radiation on some atmospheric data for Kano and Oyo, Nigeria
Summary
Solar radiation holds one of the relevant places among the diverse possible options of energy sources. It is the energy provided by the Sun. Nigeria receives ample solar energy that can be usefully exploited with an annual average daily solar radiation of about 5250Wm-2 day-1 [1]. Nigeria receives ample solar energy that can be usefully exploited with an annual average daily solar radiation of about 5250Wm-2 day-1 [1] This alternates between 3500Wm-2 day-1 at the coastal horizon and 7000 Wm-2 day-1 at the northern periphery. Among the methods developed, are those based on empirical correlation using commonly measured meteorological elements This method has attracted great attention owing to lower data requirement and computation cost [5]
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