**5. Conclusions**

The RO desalination systems have favorable properties due to high turndown capabilities and low energy use. Coupled energy-RO systems provide a low energy generation cost and the lowest water generation cost due to the efficient energy use of RO. Its high turndown allows for compatibility with RE-favored generation and makes it a future-proof investment as RE installations increase in the future. RO-RE systems have greater resistance to fuel price surges, providing resiliency against the decreasing fuel supply and current political climate.

MED and MSF are easier to implement given the present configuration on off-grid islands in the Philippines. These desalination technologies are more compatible with diesel-favored generation, which is the status-quo on Philippine off-grid islands. The MED and MSF systems are robust against weather patterns, making them a viable investment in the Philippines. These technologies may also have niche applications where diesel prices are low or if small water storage units are preferable.

**Author Contributions:** Conceptualization, methodology, validation, and formal analysis was done by M.C. and J.O. Writing—original draft preparation was done by M.C. and M.A. Writing—review and editing and supervision was done by M.A., E.E.J., and J.O. Funding acquisition was done by J.O. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research is part of the Energy Research Fund (ERF) project entitled "ElectriPHI—Electrification Planning in Small Off-grid Islands in the Philippines" funded through the University of the Philippines Office of the Vice-President for Academic Affairs (UP OVPAA) and the Senate Committee on Energy led by Sen. Sherwin T. Gatchalian.

**Acknowledgments:** J.O. would like to acknowledge the Federico Puno Professorial Chair Award and the US-ASEAN Science & Technology Fellowship. M.C. would like to acknowledge the Department of Science and Technology Science Education Institute (DOST-SEI) Merit Scholarship Program.

**Conflicts of Interest:** The authors declare no conflict of interest.
