General Polynomial for Optimizing the Tilt Angle of Flat Solar Energy Harvesters Based on ASHRAE Clear Sky Model in Mid and High Latitudes

Abstract

The aim of this study was to identify the opportunity of optimising the collection of solar energy as far as it is available in order to increase its utilisation. The second aim of this study was to enhance the performance of solar energy harvesters that depend on it through the appropriate determination of optimum solar collector tilt angles. In this study, ASHRAE clear sky model is applied to calculate the solar radiation; and the fundamental solar energy equations were programmed to determine optimum tilt angles in any location on the earth. The optimum tilt angle was presented in a polynomial form to enable the most convenient use of the function of latitude angle on a Julian day in a monthly, seasonal and an annual manner. According to the comparison between the obtained results with those of the local measured authoritative data and those of NASA published data, it can be safely recommended that these polynomials be used especially in mid and high latitudes ( > 20°) in the two hemispheres. The presented study could serve as a reference for the domestic solar electrical and thermal applications.