Journal of Basic Physical Research. Vol. 1, No. 1 , pp 41-47, November, 2010 Available online at www.jbasicphyres-unizik.org 41 EMPIRICAL MODELS FOR THE CORRELATION OF MONTHLY AVERAGE GLOBAL SOLAR RADIATION WITH SUNSHINE HOURS AT MINNA, NIGER STATE, NIGERIA G. A. Agbo 1, 2 , A. Baba 2 and T. N.Obiekezie 3 1 Department of Industrial Physics, Ebonyi State University, Abakaliki, Nigeria 2 Department of Physics, Ibrahim Babangida University, Lapai, Niger State, Nigeria 3 Department of Physics and Industrial Physics, Nnamdi Azikiwe University, Awka, Anambra State, Nigeria. (Accepted: 4 November, 2010) ABSTRACT Monthly average daily values of global solar radiation and relative sunshine hours over a period of five years (1987-1991) using multi-linear polynomial form of the Angstrom-Prescott model have been developed to estimate global solar radiation at Minna which lies on latitude 09.37°N and longitude 06.32°E and 256.4 m above sea level. It was found that the fourth order polynomial utilizing relative sunshine hours gave the best overall estimate of the total solar radiation in Minna. The correlation coefficient of 0.932 were found in the forth order polynomials and was the highest value compared to order models. The dependency of the developed equation was tested in terms of mean percentage error (MPE), mean bias error (MBE) and root mean square error (RMSE) and were found to have low error values when compared to other models. KEYWORDS: Global solar radiation, Minna, Solar energy, Atmospheric conditions INTRODUCTION Solar energy occupies one of the most important places among the various possible alternative energy sources [1]. It is the energy provided by the sun. The radiation from the sun that is arriving on the earth’s surface is dependent on the atmospheric conditions of the place hence a study of the solar radiation under local atmospheric conditions is very necessary. However, lack of measuring instruments and techniques involved or maintenance culture especially in developing countries has led to unavailability of solar radiation data. In the absence of these measurements there is, therefore, the need to devise a model to predict and estimate the global solar radiation of a place using some meteorological parameters. One of such meteorological parameters used is the sunshine hours. An earlier research carried out by Angstrom was concerned with the relationship between solar radiation and sunshine duration. Since then research in this field has come a long way. A number of researchers have employed sunshine duration to estimate solar radiation, this includes the works of [2], [3], [4], [5], [6] [7], [8], [9] plus his references and [10]. In this work we employ the Angstrom type first order polynomial and several orders of polynomials up to fifth order polynomial to estimate the monthly average daily global solar radiation on horizontal surfaces at Minna, Nigeria. Corresponding author: agbogodwina@yahoo.com 41