## 1 Introduction
From the above deployments, the initial hypothesis that no transposition model has an eminent performance seems true, with the exception of the Perez model, which rightly gives generally better performance than the others because of the many intrinsic parameters and complexity it uses. As far as Saudi Arabia is concerned, there has been no comparison of transposition models to the knowledge of the authors, probably due to the lack of systematic solar radiation measurements on either horizontal or inclined planes. Therefore, such a comparison was performed for the first time for Saudi Arabia in the present work, and this constitutes its novelty. Further, no practical guidelines about the suitability of an isotropic or an anisotropic solar model depending on the solar system configuration-mode exist for Saudi Arabia. This gap is bridged in the present study. The Saudi Arabian National Centre for Science and Technology (SANCST, later renamed to KACST) initiated the Renewable Resource Atlas of the Kingdom of Saudi Arabia in the early 1980s, covering the period 1971-1980. In 1999, a new Solar Radiation Atlas for Saudi Arabia was generated as a cooperation between KACST and the US Deptartment of Energy [27]. A network of 12 solar radiation stations was set-up for this purpose. Later, in 2013, the King Abdullah City for Atomic and Renewable Energy (KACARE) initiated the Renewable Resource Monitoring and Mapping (RRMM) programme with international collaboration. One of the products of this project was a new Renewable Resource Atlas for Saudi Arabia, covering the period 1994-2012 [27]. The first Solar Radiation Atlas for the Arab World (SRAAW) was derived in 2004 [28]. The SRAAW included Morocco, Algeria, Tunisia, Egypt, and the Arabian Peninsula (Saudi Arabia, UAE, Kuwait, Syria, Jordan, Bahrain), and gave the distribution of the monthly and annual mean solar irradiation in the territory. Later in 2019, the World Bank [29] presented a solar atlas for Saudi Arabia exclusively, which includes the distribution of the three solar radiation components (global, diffuse, direct) on the horizontal plane over the country. [PERSON] et al. [24], [PERSON] et al. [30; 31] and [PERSON] et al. [32] applied the methodology developed by [PERSON] and [PERSON] [33] and presented for the first time solar atlases for Saudi Arabia for a solar receiving system (e.g., PV) with: (i) southward fixed-tilt (static system), (ii) fixed-tilt tracking the Sun (one- or single-axis system), and (iii) varying-tilt tracking the Sun (two- or dual-axis system). In these studies, the transposition model used was the isotropic L-J with a near-real ground-albedo value instead of the commonly used 0.2. The present work repeated the calculations of [30; 31; 32] by using an anisotropic transposition model. The model selected was the Hay one, because of its simplicity and its general accuracy, as shown earlier. Despite the growing rate of PV system installation, these solar systems are not free from failures due to malfunctions in the moving parts (in the case of dynamic systems), the prevailing sky conditions (especially overcast conditions), and the temperature sensors on them [34]. Further, a problem with PV parks is associated with the management of the distribution of the energy produced by the so-formed smart grid [35]. The structure of the paper is as follows. Section 2 describes the data collection and data analysis. The analysis includes calculations of the solar energy received by inclined flat-plate surfaces across Saudi Arabia with the three above-mentioned configuration modes and both transposition models (L-J, Hay). Section 3 presents the results of the study: annual, seasonal, and monthly solar energy sums are presented for both transposition models and are compared. Section 4 presents the conclusions and main achievements of the study. Acknowledgements and references follow.