Co-Design of a Methane-Fueled SOFC–MGT System with Phase Change Material and Battery Storage for Resilient and Efficient Distributed Generation

Methane, as the primary constituent of natural gas and biogas, is a critical feedstock for high-efficiency distributed power generation via Solid Oxide Fuel Cell–Micro Gas Turbine (SOFC–MGT) hybrids. However, under dynamic load conditions typical of grid-support applications—such as duck-curve ramps and ±30% step transients—these methane-fueled systems experience rapid thermal excursions and reformer instability, accelerating stack degradation and forfeiting significant efficiency. To address this, we present a co-design framework that systematically integrates thermal energy storage (phase change material, PCM) and electrochemical storage (battery) within the SOFC–MGT architecture. The SOFC model was calibrated at 1073 K, and the PCM and battery models were compared with published data (maximum deviations: SOFC 13%, PCM 2.2%, battery 6.3%); the reformer and MGT models were not validated. A heuristic Simple Additive Weighting (SAW) matrix is first used only as a qualitative screening step to confirm that all four candidate topologies are structurally feasible; no topology is eliminated or selected at this stage. Battery-Dominant obtains the highest SAW score (200) because SAW is fully compensatory: its high performance, dynamic stability and load-following ratings offset its weaker thermal buffering. All four topologies are then ranked with AHP and TOPSIS using metrics derived from 168 h transient simulations. Both methods, which share the same criterion weights and decision matrix, place the PCM-Integrated configuration first (AHP-weighted score 7.95; TOPSIS Ci = 0.790), with priority weights of 40.7% for efficiency and 31.0% for thermal stability. Battery-Dominant ranks second in both AHP (6.44) and TOPSIS (Ci = 0.384) because of double-conversion losses. A weighted-sum genetic algorithm then yields 75.0% peak and 68.2% average net electrical efficiency, defined as net AC output divided by the methane LHV input, including inverter (95%), battery round-trip and MGT parasitic losses. Under the same 168 h transient profile, this is 1.45 percentage points above the conventional series SOFC–MGT topology (66.75%). It is 12.2–13.2 percentage points above the 55–56% reported for conventional SOFC–MGT hybrids in steady-state studies. In the model, the PCM reduces the standard deviation of stack temperature by 46% relative to the no-PCM case (for the assumed heat-transfer coefficient), and the battery supplies 82% of the load-power deviations resolved at 1 min resolution. These results are model-based. The main limitations, including the SOFC voltage correlation, extrapolation below the 1073 K validation temperature, and the unvalidated reformer kinetics, are discussed.