## 5 Conclusions  
The study was developed to design a grid-connected hybrid power system (PV-FC), and discuss the influence of the major four PV tracking techniques on technical and economic performance of the system. The significant PV tracking techniques included FTSP, HSAT, VSAT, and DAT were considered. Homer Pro was used to perform simulation, calculation, and optimization. Input data such as meteorological condition (solar irradiation and ambient temperature), real agriculture load were considered in Alkharj city, Saudi Arabia. Furthermore, technical and economic data of the system's components came from manufactures. The PV tracking techniques were examined in terms of their influence on techno-economic performance of the proposed system, and the results were assessed and compared in depth. In addition, the optimal design is recommended as the best option for case study. The study found the following key points:  
1. In terms of yearly energy production, the result found that the VSAT was superior in production of the highest power, following by FTSP, DAT and HSAT, respectively.
2. In terms of PV penetration, the result demonstrates that VSAT recorded 772% higher PV penetration of solar energy to the grid, followed by DAT, HSAT, and FTSP, which recorded 674%, 595%, and 563%, respectively.
3. In terms of net purchased energy, VSAT showed the highest of energy sold to the grid than others. Taking the VSAT as the base case that achieved the lowest LCOE, the VSAT can decline 37.65%, 77.5%, and 86.5% of LCOE than FTSP, HSAT, and DAT, respectively.
4. The VSAT showed the lowest CO\({}_{2}\) emission, while DAT presented the highest CO\({}_{2}\) emission. Due to this it was more reliant on the grid. In this context, VSAT can be the lowest environmental effect.
5. The study deduced the vital role of VSAT that optimizes the technical performances and extends to a reduced economic cost of the proposed system. Therefore, VSAT can be highly recommended as the best choice of a grid-connected hybrid (PV-FC) energy system for Alkharj city, Saudi Arabia. The proposed system design method and PV tracker investigation are validated for any location in the world, although the result will be different based on components costs, metrological data.  
Conceptualization: S.M., D.Z. and Y.Z.; Methodology: S.M., D.Z.; Software: S.M.; Validation: S.M.; Formal analysis: S.M.; Investigation: S.M., D.Z., L.W., R.Y. and J.W.; Resources: S.M., Y.Z. and M.L.; Data Curation: S.M., D.Z.; Writing--Original Draft: S.M., D.Z.; Writing--Review and Editing: S.M., D.Z., Y.C., J.L., L.W., R.Y., J.W., Y.Z. and M.L.; Visualization: S.M., D.Z.; Supervision: Y.Z. and M.L.; Project administration: Y.Z. and M.L.; Funding acquisition: Y.Z. and M.L. All authors have read and agreed to the published version of the manuscript.  
This research was funded by National Natural Science Foundation of China (Grant nos. 71974055). This work is supported partially by Natural Science Foundation of Beijing Municipality (L172036), National Natural Science Foundation of China (Grant nos. 51772096), Beijing Science and Technology Project (Z181100005118002), Joint Funds of the Equipment Pre-Research and Ministry of Education(6141A020225), Par-Eu Scholars Program, Science and Technology Beijing 100 Leading Talent Training Project, the Fundamental Research Funds for the Central Universities (2017 ZZD02) and the NCEPU \"Double First-Class\" Program.  
The authors declare no conflict of interest.