Empirical model development for the estimation of clearness index using meteorological parameters

Authors : Fakhar ALAM, Saif Ur REHMAN, Shafiqur REHMAN, Muhammad JAHANGIR, Muhammad SHOAIB, İmran SIDDIQUI, İntikhab ULFAT

Pages : 4429-4441

View : 13 | Download : 6

Publication Date : 0000-00-00

Article Type : Research Paper

Abstract :The clearness index is an indispensable parameter required for the design and analysis of solar energy systems. In the absence of measured values for a specific location, the clearness index can be estimated from other measured meteorological variables. In this study three meteorological parameters, sunshine hours, monthly mean values of the temperature difference insert ignore into journalissuearticles values($\Delta$T);, and cloudiness, are used to develop empirical models for the estimation of clearness index. The empirical models are developed for five major cities in Pakistan insert ignore into journalissuearticles values(Karachi, Multan, Lahore, Islamabad, and Quetta);. For empirical model development, long-term data insert ignore into journalissuearticles values(1991 to 2010); of monthly average clearness index, sunshine hours, average daily minimum and maximum temperatures, and cloudiness have been used. The accuracy of the models has been tested by statistical indicators that include mean percentage error insert ignore into journalissuearticles values(MPE);, coefficient of determination insert ignore into journalissuearticles values(R$^2$);, mean absolute relative error insert ignore into journalissuearticles values(MARE);, mean bias error insert ignore into journalissuearticles values(MBE);, and root mean square error insert ignore into journalissuearticles values(RMSE);. The error analysis revealed that the proposed models are suitable for the estimation of the clearness index. It is also concluded that multiple regression models give better estimates of clearness index for all the stations insert ignore into journalissuearticles values(0.80 $\leq$ R$^{2}$ $\leq$ 0.86); compared to single parameter model and therefore are recommended. The study indicated that clear sky conditions prevail throughout the months at all the investigated sites insert ignore into journalissuearticles values(0.58 $\leq$ K$_T$ $\leq$ 0.68);, which is a good indicator for solar energy utilization. The statistical indicators also suggest that multilinear regression model M-3 gives a better representation of the climate system and using three parameters reduces the uncertainties in the developed model.
Keywords : Clearness index, meteorological variables, cloudiness, sunshine hours, statistical evaluation