EVALUATION OF THE HOURLY DIRECT SOLAR, DIFFUSE AND GLOBAL RADIATION INCIDENT ON TILTED, HORIZONTAL AND VERTICAL SURFACES OVER TRIPOLI
الملخص
This paper has evaluated the direct, diffuse, and global thermal solar irradiance incident on tilted, horizontal and vertical surfaces over Tripoli city, and what is the extent of the influence the slope angle, under suitable climatic conditions on the basis of clear days and dust, dirt, trees and shading that have a negligible effect. Where, the geographical location and climatic conditions play a major role in improving the performance of solar systems. The study includes simulation of three surfaces inclined, horizontal and vertical, considering effect of solar radiation based on the clear sky. Results were obtained using a mathematical model (ASHRAE Mode) developed utilizing the programming language Fortran 90 on the basis of a presentation presented in the form of graphs and patterns showing the monthly average of the hourly direct solar, diffuse and global radiation incident on tilted, horizontal and vertical surfaces and the direct solar radiation on tilted surfaces as function of sloped angle (β) during the daylight hours for four independent months January which represented wintertime, April represented springtime, July represented summertime and October autumn time of the year.
Results show that the higher value of the hourly direct solar radiation for the titled surface 35o was, 1025 W/m2 for the month of October, horizontal surface, 911W/m2 for April, and a vertical surface, 791 W/m2 for January, and with regard to the hourly diffuse solar radiation for titled surface 35o , 224 W/m2 for month July, horizontal surface, 118W/m2 for July, and a vertical surface, 175W/m2 for April, also with regard to the hourly global solar radiation for titled surface 35o , 1195W/m2 for month October, horizontal surface 1001W/m2 for April, and vertical surface 917W/m2 for January at the same conditions. Furthermore, the optimal tilt angle for direct solar radiation in January almost was 55˚, in April the optimal tilt angle was 10˚, in July the optimal tilt angle was 0˚ and in October, the optimal tilt angle is 45˚. It can be noticed from the results that the hourly diffuse solar radiation has a certain value in the first hours of daytime and the last hours, unlike the beam solar radiation; these signs are an evident significance with regard to the Solar Radiation Calculations. However, this study results are useful and satisfactory; they can be applied in reality, with a view to using Photovoltaic Systems to get the necessary electrical energy for the requested load supply. Also, for purpose calculations of the cooling loads and the solar collectors’ performance.
