# Solar Potential in Saudi Arabia for Southward-Inclined Flat-Plate Surfaces
## 4 Conclusions and Discussion
Three innovations appeared in the present study: (i) For the first time, solar maps for Saudi Arabia of the maximum energy received on optimally-inclined flat surfaces towards south were derived; (ii) for the first time, three energy zones were identified in Saudi Arabia for solar applications; (iii) universal curves (nomograms) of CF in relation to the tilt angle and \(\rho_{\rm g}/\rho_{0}\) were derived. Based on the adopted methodology, some guidelines can be given here to interested solar energy scientists and/or solar energy entrepreneurs for applying them in their territory. If a solar radiation station exists in the area, hourly or daily values of the solar global horizontal radiation must be collected for a climatological period of 10 years at least. If no solar radiation exists, then data from a relative website (e.g., BSRN, GEBA, PV-GIS, ARM) can be obtained. In the extreme case that this option is not possible, use of a solar energy model can be made to derive the anticipated data from other available variables (e.g., meteorological parameters). Then, transposition of the selected data from horizontal to inclined planes towards the local south must take place by varying the tilt angles in a range that includes the geographical latitude of the site. In the next step, the annual solar energy sums on the inclined planes have to be calculated and the highest energy sum must be selected; then the corresponding tilt angle is the optimum for the site. The transposition can be achieved by selecting the wishful model (the L-J model is sufficient). It is recommended that a near-real ground albedo value is used in these calculations; if knowledge of this value is not available for the site, use of the nomogram of Figure 11 can be made to correct the solar energy sums by selecting the appropriate tilt angle. Finally, monthly solar energy sums can be estimated and regression lines be derived that can be used as guidelines for estimating the expected solar energy on flat planes with the selected tilt angle. As far as the significance of the results of the present study is concerned in the solar industry and the society of Saudi Arabia, this can be summarized in the following. The solar industry has now a rule for the inclined parts of the solar system-support frames; the inclined surfaces of the supporting frames must have angles of \(20^{\circ}\), \(25^{\circ}\) or \(30^{\circ}\) depending on the SEZ to be installed. It is assumed that the orientation of the supporting frame has to be towards south. This rule may reduce installation costs because of the standardisation of the supporting frame. On the other hand, the society may get indirect benefits from governmental initiatives regarding policies that promote renewable energy sources in Saudi Arabia (and especially solar energy sources) because of the new knowledge gained through the present work. Data collection, data analysis, writing--review and editing, A.F. ; conceptualisation, methodology, data collection, data analysis, writing--original draft preparation, H.D.K. ; writing--review and editing, E.R. ; writing--review and editing, M.A. All authors have read and agreed to the published version of the manuscript. Researchers would like to acknowledge the support provided by the Deanship of Scientific Research (DSR) at the King Fahd University of Petroleum and Minerals (KFUPM) for funding this work through project no. DF181010. Informed Consent Statement: Not applicable. **Data Availability Statement:** The solar radiation data and the ground-albedo ones for Saudi Arabia are publicly available and were downloaded from the PV-GIS platform ([[https://ec.europa.eu/jrc/en/pvgis](https://ec.europa.eu/jrc/en/pvgis)]([https://ec.europa.eu/jrc/en/pvgis](https://ec.europa.eu/jrc/en/pvgis))) and the Giovanni website ([[https://giovanni.gsfc.nasa.gov/giovanni/](https://giovanni.gsfc.nasa.gov/giovanni/)]([https://giovanni.gsfc.nasa.gov/giovanni/](https://giovanni.gsfc.nasa.gov/giovanni/))), respectively.