Temporal and grid-constrained performance of cold-ironing and photovoltaic generation towards nearly zero energy ports

• Cold-ironing increases port electricity demand by nearly two orders of magnitude • Large-scale photovoltaics reduce but do not eliminate grid dependence in ferry ports • Temporal mismatch, not annual energy sufficiency, limits port decarbonization • Winter and nighttime deficits drive persistent reliance on external electricity supply • System-level planning is required for sustainable port electrification The electrification of ports through cold-ironing is widely promoted as a key pathway toward low-carbon maritime transport, yet its system-level sustainability implications remain insufficiently understood when deployed at scale. This study examines how the integration of cold-ironing and large-scale on-site photovoltaics reshapes the energy dynamics of a ferry-dominated Adriatic port by moving beyond isolated facility loads to a fully electrified port ecosystem. Using high-resolution operational data and a data-driven optimization framework, three progressively integrated scenarios are evaluated, ranging from conventional port operations to comprehensive port-wide electrification. The results reveal that the introduction of cold-ironing increases port electricity demand by nearly two orders of magnitude, fundamentally altering load profiles and creating pronounced temporal variability. Although a photovoltaic installation of 43.55 megawatts generates sufficient annual energy to match total demand, the system remains structurally dependent on the external grid for approximately 30.15 gigawatt-hours per year due to winter scarcity and nocturnal deficits. These findings demonstrate that the primary barrier to port decarbonization is not annual renewable sufficiency but the temporal mismatch between renewable generation and maritime activity. The study provides evidence that achieving sustainable port electrification requires coordinated planning of renewable generation, grid interaction, and operational scheduling rather than reliance on component-level capacity expansion alone, offering critical insights for the design of resilient and realistic port energy transitions.