The aim of this study is to increase the power generation/exergy efficiency and reduce total product cost/environmental contamination of solid oxide fuel cells. Accordingly, three integrated systems are proposed and analyzed from energy, exergy, exergoeconomic, and environmental viewpoints through the parametric study. The first model assesses the combination of a gasifier with a solid oxide fuel cell. In the second model, waste heat of the first model is reused in the Stirling engine to enhance the efficiency and power generation. The last model proposes reuse of the surplus power of the Stirling engine in a proton exchange membrane electrolyzer for hydrogen production. Considering total product cost, exergy efficiency, and hydrogen production rate as the objective functions, a multi-objective optimization is applied based on the genetic algorithm. The results indicate that at the optimum operating condition, the exergy efficiency of the model (a), (b), and (c) is 28.51, 39.51, and 38.03, respectively. Corresponding values for the energy efficiency and the emission rate of the models are 31.13, 67.38, 66.41, 1.147 t/MWh, 0.7113 t/MWh, 0.7694 t/MWh. At the optimum solution point, total product cost associated with the model (a), (b), and (c) is 19.33 $/GJ, 18.91 $/GJ, and 24.93 $/GJ, respectively. If the hydrogen production rate and total product cost considered as the objective functions, at optimum solution point, the rate of hydrogen production and overall product cost would be 56.5 kg/day and 41.76 $/GJ, respectively. Overall, the proposed integrated systems demonstrate decent functionality both in thermodynamic, environmental, and economic aspects.
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