System integration solutions for urban, industrial, and renewable energy transitions

The energy transition has evolved beyond the search for individual low-carbon technologies, moving instead toward the integration of these solutions into complex infrastructures in urban and industrial settings. This Special Issue synthesizes key research from the 2024 SDEWES conferences - 4th Latin American, 2nd Asia Pacific and 19th SDEWES, highlighting a fundamental shift from technology-centric assessments toward integrated system thinking. Central to this collection is the recognition that flexibility and resilience are now just as vital as cost-efficiency, particularly as energy systems face increasing pressure from climate-driven volatility and infrastructural constraints. The research presented covers several critical pillars of deep decarbonization. It explores urban transformation through integrated planning and energy communities, while advancing power-to-X pathways to address "hard-to-abate" sectors such as heavy industry and maritime transport. Technologically, the contributions evaluate the practical application of direct and indirect electrification, waste heat utilization, carbon-managed waste conversion, wind, wave and hydrogeneration. Methodologically, a clear trend emerges: a move toward high-resolution, dynamic modeling that treats climate-driven variability, spatial and temporal uncertainty as central variables rather than outliers. By addressing the physical, economic, and institutional bottlenecks of the transition, these papers provide an evidence-based framework for real-world implementation.