EMPIRICAL MODEL TO ESTIMATE DAILY GLOBAL SOLAR RADIATION USING AIR TEMPERATURE OVER NIGERIA

Abstract

Solar radiation is a primary driver for many physical, chemical and biological processes on the Earth’s surface. Complete and accurate solar radiation data at a specific region are quite indispensable to the solar energy related research. For locations where measured values are not available, a number of formulae and models have been developed to estimate solar radiation. This study aimed to validate five exiting models for estimating global solar radiation data using temperature measured data for eight stations located in Nigeria and identify the best. The stations used are Lagos, Port Harcourt, Benin, Calabar, Lokoja,, Ilorin, Kaduna and Maiduguri. The stations were selected to represent four main climatic zones in Nigeria. They are the fresh water swamp forest, the rain forest, the guinea Savannah, and the sudanosahel savannah. Two stations were chosen to represent each ecological zones. Daily data of minimum and maximum temperature (◦C), rainfall (mm) and solar radiation (MJ/m2/day) of the stations in Nigeria. were collected from the National Centre for Environmental Prediction (NCEP) and National Centre for Atmospheric Research (NCAR). The data cover a period of fifteen years from 1997 to 2011. The model tested are Hargreaves and Samani model, Annandale model, Bristow and Campbell method, Donatelli and Campbell model and finally the Goodin model. A statistical analysis performed on the results of the calculation are The Root Mean Square Error (RMSE), Mean Bias Error (MBE) and Mean Percentage Error (MPE). 4 xi It was observed that the Models perform well in each of the Stations but perform better as one moves northwards in the climatic belt. In other words, the result of the sudanosahel Savannah is better than the Guinea Savannah and the result obtained at the Guinea Savannah is also better than the Rain forest and so on. This work concludes that empirical models based on temperature give good results in all the stations provided the parameters are correctly adjusted. According to the results, the Goodin Model showed the best estimation for all stations in the climatic zones in Nigeria and therefore is recommended. It is believed that the calculated daily solar radiation values produced by the Goodin model can be used in the design and estimation of the performance of solar applications.