**5. Conclusions**

A fuzzy MILP model has been developed for the optimal operational adjustment of an off-grid micro-hydropower-based polygeneration system under varying drought intensity scenarios. The polygeneration system produces electricity, purified water, and ice, which are the basic needs of an off-grid community. The model accounts for the integration of the process units to give the optimal operational adjustments needed to partially satisfy the community demands for each product output, based on fuzzy constraints. Unlike conventional MILP formulations, the fuzzy bounds provide an optimal solution that gives a more balanced compromise on the reduction of outputs of the facility. A variant of the model also considers the minimization of the fuel consumption of the back-up diesel generator set. Case studies that consider different turbine configurations and diesel back-up options were solved to illustrate the model capabilities. This modelling framework is useful for off-grid electricity systems which have been established and have failed to take into consideration system disruptions resulting from the effects of climate change. The model provides decision-makers with a systematic procedure for identifying the optimal operational adjustment to ensure that the community product demands are satisfied during abnormal conditions. Furthermore, the model can provide insights on the managemen<sup>t</sup> of external sources of energy.

Future work can apply this model formulation to a broader range of integrated polygeneration systems and consider multi-period models to accommodate variations in product demands. In addition, the potential for the use of alternative methods such as fuzzy P-graph [41] to deal with problems of this class should also be explored together with an examination of the availability and performance of alternative operating conditions.

**Author Contributions:** All authors contributed to the completion and publication of the study. R.R.T. conceptualized the general idea of the paper. I.A.V.M.III provided key technical information on off-grid microhydro plants. R.R.T., K.B.A., and A.T.U., contributed on the development of the model. K.B.A. thoroughly verified and validated the model. A.T.U. prepared and edited the manuscript, and responsible for drawing the figures. I.A.V.M.III, K.B.A., and R.R.T. revised and reviewed the manuscript.

**Funding:** This research was funded by Philippine Commission on Higher Education (CHED) PHERNet Project.

**Acknowledgments:** The research is supported by the Philippine Commission on Higher Education (CHED) PHERNet Sustainability Studies Program and the De La Salle Science Foundation (DLS-SFI) for the publication cost. The pioneering work of the late Godofredo Salazar is acknowledged in establishing the Center for Microhydro Research at De La Salle University.

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