Strategic Design of Sector-Coupled Local Energy Systems: A System Planning Framework for the Energy Transition

This study proposes and applies an integrated optimization framework that treats policy targets—such as carbon emission caps—as binding design constraints rather than evaluation metrics. By jointly determining capacity expansion and system operation within a unified system boundary, the framework enables a feasibility-oriented assessment of sector coupling without presupposing its effectiveness. The framework is applied to a regional case study of

Jeollanam-do, Korea, a system characterized by high renewable penetration and persistent grid constraints.

The results demonstrate that sector coupling is not a universally effective solution, but a conditional flexibility option whose value depends critically on grid connectivity and system boundaries. Under constrained grid conditions, coupling electricity with heat and hydrogen provides internal flexibility that reduces renewable curtailment and system cost. As grid connectivity improves, however, the marginal value of sector coupling declines. The analysis further shows that reductions in renewable curtailment do not automatically translate into carbon emission reductions, particularly when surplus renewable energy is absorbed through hydrogen pathways that do not directly displace fossil-based supply within the modeled system.

These findings highlight the importance of evaluating sector coupling as part of an integrated system design problem shaped by grid conditions, policy constraints, and boundary definitions, rather than as an inherently superior technological solution. The proposed framework provides a quantitative basis for identifying the specific conditions under which sector coupling contributes to renewable integration and decarbonization, and for distinguishing them from cases in which it primarily reallocates flexibility without delivering meaningful emission reductions.