## 3 Results and Discussion  
The practical results provided the value of the estimated annual radiation using the Hay-Davies model [31] for various land configurations. All the calculations were made for the province of Cordoba, Spain, therefore assuming the same geographical values (latitude = 37.75492\({}^{\circ}\) N; longitude = 5.04548\({}^{\circ}\) W) and the same climatic values throughout the year, varying only the values of inclination \(\beta\) and azimuth \(\chi\) for a fixed panel width \(h=3\ m\) and separation between panel lines \(d=6\ m\). For each inclination \(\beta\) (from 0\({}^{\circ}\) to 45\({}^{\circ}\), 1\({}^{\circ}\) increment) and terrain azimuth \(\chi\) (from \(-60^{\circ}\) to 60\({}^{\circ}\), 5\({}^{\circ}\) increment), the rotation axis was oriented with a wide range of azimuth \(\gamma\) (from \(-20^{\circ}\) to \(20^{\circ}\), 2\({}^{\circ}\) increment). Terrains with negative inclinations were not considered since PV plants are not commonly installed in shaded areas. For facilities located on terrain with a null azimuth (oriented south), independently of its inclination even if it is null, the optimal orientation of the axis of rotation is southward (\(\gamma=0^{\circ}\)). For each value of the inclination of the terrain \(\beta\), it was also observed that the maximum value of irradiance was obtained when the azimuth of the terrain \(\chi\) was 0\({}^{\circ}\). That is, the optimal situation is when the terrain is oriented south and the axis of rotation is directed in the same direction. If the terrain has another orientation, the value of the optimal angle towards which the axis of rotation should be oriented would move in that same direction. This fact is more evident at higher values of the terrain inclination \(\beta\), although in no case will the azimuth axis \(\gamma\) be as high as that of the terrain \(\chi\). The results for a case study with a \(\beta=15^{\circ}\) inclination are presented in Figure 8. Figure 8a shows the variation of radiation with regard to \(\gamma\) when the azimuth of the terrain \(\chi=0^{\circ}\). However, when the terrain was not oriented to the south, as shown in Figure 8b in which the terrain was turned \(\chi=30^{\circ}\), the maximum radiation was obtained by orienting the axis with an azimuth \(\gamma\) of 6\({}^{\circ}\) towards the south. The losses with regard to the maximum radiation obtained in a terrain are shown in Figure 8c, where it is again verified that, by orienting the axis at 6\({}^{\circ}\), these losses can be minimised. Finally, Figure 8d shows the optimal orientation to direct the axis for the different values of the terrain azimuth \(\chi\). In this way it is possible to estimate the orientation that achieves optimal radiation considering the azimuth of the terrain \(\chi\). As already mentioned, for each inclination value the maximum irradiance value was obtained when the terrain had an angle \(\chi=0^{\circ}\). In addition, as the inclination of the terrain increased, the radiation affecting the panels was greater, as seen in Figure 9. The explanation can be found in the latitude for which the calculations were made and in the fact that the direction of the sun is not perpendicular to the horizontal plane. The inclination of the terrain influenced the radiation, increasing until a value of \(\beta\) of around 21\({}^{\circ}\), where the maximum was reached. Figure 8: _Cont._The difference observed between the radiation value for a particular axis azimuth and the maximum capture obtained in the optimum direction was greater as the inclination of the terrain increased. Thus, in low-inclination terrains the difference was low and while for steeper inclinations the losses were considerable. Figure 10 shows that, in the specific case of \(\beta=20^{\circ}\), the losses caused by a bad choice of rotation axis direction can reach values above 7%.