**Michael Castro, Myron Alcanzare, Eugene Esparcia, Jr. \* and Joey Ocon \***

Laboratory of Electrochemical Engineering (LEE), Department of Chemical Engineering, University of the Philippines Diliman, Diliman 1101, Philippines; mtcastro1@up.edu.ph (M.C.); mtalcanzare1@up.edu.ph (M.A.)


Received: 15 January 2020; Accepted: 23 April 2020; Published: 4 May 2020

**Abstract:** Freshwater in off-grid islands is sourced from rain, groundwater, or mainland imports, which are unreliable, limited, and expensive, respectively. Sustainable freshwater generation from desalination of abundant seawater is another alternative worth exploring. Model-based techno-economic simulations have focused on reverse osmosis desalination due to its low energy consumption and decreasing costs. However, reverse osmosis requires frequent and costly membrane replacement. Other desalination technologies have advantages such as less stringent feedwater requirements, but detailed studies are yet to be done. In this work, a techno-economic comparison of multi-effect distillation, multi-stage flash, mechanical vapor compression, and reverse osmosis coupled with solar photovoltaic-lithium ion-diesel hybrid system was performed by comparing power flows to study the interaction between energy and desalination components. Optimization with projected costs were then performed to investigate future trends. Lastly, we used stochastic generation and demand profiles to infer uncertainties in energy and desalination unit sizing. Reverse osmosis is favorable due to low energy and water costs, as well as possible compatibility with renewable energy systems. Multi-effect distillation and multi-stage flash may also be advantageous for low-risk applications due to system robustness.

**Keywords:** desalination; multi-effect distillation; multi-stage flash; mechanical vapor compression; reverse osmosis; renewable energy
