Empirical models for the correlation of global solar radiation with meteorological data for Northern Nigeria

Abstract

Sunshine duration hours, minimum and maximum daily temperatures, relative humidity, mean daily temperatures and specific humidity, all as monthly averages for a 60-month time period (1980–1984), have been used to produce 12 different correlations with which the global solar radiation could be estimated for Kano (latitude of 12°02′N, longitude of 8°30′E and an altitude of 454 m) in northern Nigeria. The correlation equations obtained, ranging from the simple Angstrom-type to the one in which all the parameters considered have exponential factors, showed that the equation with the least value of root mean square error to be: ( H / H 0 ) = 0·621 − 0·294 ( n / N ) + 0·178 ( n / N − R − θ ) + 0·491 ( n / N θ ) , while that with the minimum value of the sum of percentage error was: ( H / H 0 ) = 0·567 + 0·054 ( n / N ) − 0·182 ( θ R) , where H , H 0 , n , N , R and θ are the global radiation, extraterrestrial radiation, sunshine hours, maximum duration for which the sunshine recorder is active, relative humidity and the ratio of the minimum to the maximum temperatures, respectively, and all are expressed as average monthly daily values. In calculating the extraterrestrial radiation, the new value of the solar constant of 1367 W m −2 was used.