The use of a fully renewable energy system (RES) to power mid- and low-scale off-grid systems is an attractive alternative solution to replace fossil fuel technologies in order to meet the ever-growing demand and tackle environmental problems. In this study, the design optimization of a hybrid solar biogas, Organic Rankine Cycle (ORC-Toluene) and Air Gap Membrane Distillation (AGMD) for desalination and electric power generation is presented. Three objective functions namely, maximizing power and water production, and minimizing the unit exergy product costs has been formulated. The turbine efficiency, top ORC vapor temperature and ORC condenser temperature has been selected as the decision variables. The non-dominated sorting genetic algorithm (NSGA-II) has been employed to solve the optimization problem and produce a Pareto frontier of the optimal solutions. Further, the TOPSIS approach has been used to select the optimal solution from the Pareto set. The study constitutes the first attempt to holistically optimize such a hybrid off-grid cogeneration system in a robust manner. It is found that the proposed system is capable of generating 1960 kW of electricity and 8 ð‘˜ð‘”ð‘š2â„Žâ„ freshwater with 11 $/GJ unit exergy product costs.
Keywords Hybrid solar biogas, Organic Rankine Cycle, Air gab membrane distillation, multi-objective optimization, TOPSIS.