Investigating the Applicability of Horizontal to Tilted Sky-Diffuse Solar Irradiation Transposition Models for Key Libyan Cities

The global solar irradiation incident on a tilted surface with different tilt angles is one of the most important requirements for simulating solar energy systems. However, such data is often not available. For this reason scientists, database platforms and commercial software resort to employ transposition models to convert horizontal solar irradiation into tilted solar irradiation incident on any inclined surface at any degree. The present study considered a wide range of the most commonly used horizontal to tilted transposition models around the world. In the absence of measured information, the horizontal solar radiation was obtained from Solargis for six locations in Libya, which were carefully selected to represent all Libyan territories. Three cities were selected in the north (Tripoli, Sirte and Benghazi), a city in the middle (Al-Jufra) and two cities in the south (Sabha and Kufra). The proposed approach was applied to these cities for selected 22 transposition models and for various tilt angles (10°-90°) in order to determine the best model for use in each area at any given tilt angle. According to the obtained results, it is recommended to use Bugler; 1988 model as the most accurate model for the northern and central regions of the country, and Lui&Jordan model; 1963 as the most applicable model for the southern region.