Process-Constrained H₂-to-NH₃ Transition Boundary for Rural Microgrids

Rural renewable microgrids can convert surplus wind-turbine (WT) and photovoltaic (PV) power into H₂ for re-electrification or NH₃ synthesis. However, the boundary governing H₂ allocation between microgrid balancing and NH₃ synthesis remains unclear. This study proposes a process-aware H₂-to-NH₃ transition boundary integrating sustained WT-PV surplus, hydrogen storage tank (HST) reserve, ammonia storage tank (AST) headroom, local NH₃ demand, and Haber-Bosch (HB) operating limits. In the deterministic 8760-h simulation, Case III reduces WT-PV curtailment to 1.18% and supplies 50.25% of local NH₃ demand. Relative to Case II, it also lowers net operating cost and equivalent CO₂ emissions by 1.61% and 0.35%, respectively. These results indicate the operational value of jointly considering microgrid states and process constraints in H₂ allocation.