## 1 Introduction  
The knowledge of solar irradiation on tilted surfaces of any mode is significant for engineers who specialise in the design of flat-plate collectors, photovoltaic systems, or any other type of solar energy collecting devices. Solar radiation is recorded on a horizontal plane at fewer sites worldwide than meteorological parameters [1]. On the other hand, solar radiation measurements on inclined surfaces are indeed rare [2,3]. The development of solar radiation models for its estimation on horizontal surfaces was an initiative and need since the beginning of 1950s; nowadays, many such models exist in the international literature [4]. The exploitation of solar energy as a renewable energy source (RES) has triggered the need for the development of solar models that estimate solar energy received by devices with (static or moving) inclined surfaces, such as photovoltaic (PV) systems. A good account of the most usable transposition models (models that estimate solar energy on a tilted surface from its horizontal value) is given in [4]. In practice, these models provide expressions for the estimation of the diffuse solar energy on the tilted surface from its value on horizontal plane, since the direct and ground-reflected solar radiation components can easily be calculated; then, the global tilted solar radiation is the sum of the three components. Nevertheless, the accuracy of such models must be verified against solar radiation measurements. There exist many studies that have tried to estimate and evaluate the accuracy of such transposition models worldwide; e.g., [5; 6; 7; 8]. From these works, it seems that the error derived by the models varies from place-to-place, indicating the need for individual assessments of solar energy estimates by any transposition model used at the place of interest. The following studies are indicative of this conclusion. [PERSON] et al. [9] showed that the (isotropic) Liu-Jordan (L-J) [10], the (anisotropic) Gueymard [11], the Hay [12; 13], the [PERSON] [14], and the Skartveit-Olseth [15] models perform best for Athens, Greece. [PERSON] and [PERSON] [6] found that the L-J and Hay models perform equally well in Amman, Jordan; the isotropic model gives slightly better estimates in the summer, and the Hay one the rest of the year. [PERSON] and [PERSON] [5] evaluated 11 transposition models at Beer Sheva, Israel, and found that the best-performing ones were the [PERSON] [16] and the Muneer [17] models. [PERSON] and [PERSON] [18] used the [PERSON] [19] model to find the optimum fixed orientations for capturing solar radiation in the continental USA. [PERSON] et al. [20] used the L-J model [10] to compute the daily optimum tilt angle as a function of the day-of-the-year and geographical latitude in the range [40\({}^{\circ}\) S, 40\({}^{\circ}\) N]. [PERSON] et al. [8] compared the performances of the Gueymard, the Hay, the Perez [21], and the Skartveit-Olseth models to estimate the solar radiation on surfaces with different tilt angles and orientations at Saint Pierre, Reunion island. They found that the best-performing model is the Perez one, which is more complicated in the analytical expressions and the parameters used than the other three. [PERSON] et al. [22] compared 10 models to estimate the diffuse solar radiation on an inclined surface at Valladolid, Spain. The best-performing model was the [PERSON] one, followed by the [PERSON] model. [PERSON] et al. [23] utilised 15 models (including the Gueymard, the Hay, the Perez, and the Skartveit-Olseth ones) to predict the solar irradiance on sloped surfaces with tilt angles of 45\({}^{\circ}\) and 60\({}^{\circ}\) towards the south; they compared them with solar radiation measurements at Ajaccio, France, and found that the best-performing model was the Perez model. Apart from the use of solar radiation measurements or solar radiation modelling to assess the solar potential in a region, satellite observations and modern statistical methods have been applied to solar radiation or RES in general; e.g., [24; 25; 26].