## 1 Introduction  
Installations with tilted solar collectors for exploiting the renewable energy of the Sun have long been available in the market as commercial products. Solar flat-plate panels are nowadays widely used for converting solar energy into electricity (PV installations) or hot water (solar heating systems). These stationary systems consist of solar panels that receive solar radiation (i) at a fixed tilt angle with a southward orientation in the northern hemisphere or a northward orientation in the southern hemisphere; (ii) at a fixed tilt angle following the motion of the Sun; and (iii) at a varying tilt angle following the motion of the Sun, a mechanism that ensures that the solar rays always remain normal to the receiving plane. The mode (i) is widely used because of its lower cost for the static supporting frame of the solar system. The mode (ii), also known as a one- or single-axis system, provides higher solar energy on the inclined surface mounted on a vertical rotating axis, but has a slightly higher cost in order to maintain the moving parts. The mode (iii) is considered the most effective and is known as a two- or double-axis system. It provides the best performance of the solar systems rotating with the aid of a vertical and a horizontal axis, but is associated with higher maintenance costs because of more mechanical moving parts. The first category of solar systems is also called stationary or static, while the other two are dynamic, because of their Sun-tracking ability. [PERSON] et al. [1] examined the mode (i) for the performance of flat-plate solar collectors in Saudi Arabia. This work is a continuation as it investigates the mode (ii) for the solar energy received on single-axis systems across the country. Though static solar systems have received a lot of attention from researchers and solar energy developers, the dynamic ones (and especially the single-axis-mode collectors) have not been neglected either. Much effort has been invested at both the solar-energy-calculation level and the solar-system-development level to improve both the moving and the electronic parts for the Sun-tracking sensors [2; 3]. The calculation of the optimum tilt angle and orientation for receiving maximum solar energy on solar flat-plate collectors has been the objective of various studies that use different strategies for obtaining solar radiation data: solar radiation modelling, e.g., [4; 5]; combining with ground-based solar data, e.g., [6]; or utilising international data bases, e.g., [7; 8]. Recently, a new method was presented by [9] for Greece and was applied in a recent study for Saudi Arabia [1]. The proposed method finds the maximum solar energy received by flat-plate collectors with southward (northward) orientation in the northern (southern) hemisphere. The idea behind this methodology is applied in the present study for solar collectors with constant tilt tracking the Sun. An extensive review of the studies conducted for Saudi Arabia related to the present work can be found in [1]. From the above it is clear that no attempt has been made so far to construct a solar map for Saudi Arabia to show the solar potential on inclined flat planes that track the Sun. This gap is bridged in the present study, which includes three innovations. (i) For the first time, solar maps for Saudi Arabia showing maximum energy on optimally inclined flat surfaces tracking the Sun are derived. (ii) For the second time the three solar energy zones introduced by the same authors for Saudi Arabia [1] are also utilised here. (iii) The notion of the (ground-albedo) correction factor introduced in [1] is also used here, and the shape of the universal curves (representable as nomograms) of this parameter in relation to the tilt angle and the ground-albedo ratio is confirmed. The structure of the paper is as follows. Section 2 describes the data collection and data analysis. Section 3 deploys the results of the study, while Section 4 presents the conclusions and main achievements of the work. Acknowledgements and References follow.