## 2 Role of Ports in the Decarbonisation of Maritime Transport  
As mentioned, ports and maritime transport account for approximately 3% of global CO\({}_{2}\) emissions [1]. Consequently, the sector is under growing regulatory and societal pressure to decarbonize its operations and mitigate environmental impacts.  
Ports host several energy-intensive activities. For instance, the 2016 \"GHG Emissions Report of the Port of Valencia\" delineates the port's carbon footprint and identifies the sources of emissions generated by these activities. The report indicates that electricity consumption at the Port of Valencia was 65 Gigawatts-hour (GWh) per year, whereas fossil fuel consumption reached 360 GWh yearly. Additionally, energy demand from berthed ships accounted for 156 GWh per year--equivalent to half of the port's total fuel consumption [11].  
These figures indicate a fossil fuel-to-electricity consumption ratio of approximately 5.5:1, underscoring the need to significantly increase the share of electricity derived from renewable sources and alternative fuels.  
Ports around the world are increasingly adopting advanced solutions to improve energy efficiency, reduce greenhouse gas emissions, and support the shift toward sustainable operations. Key measures include the implementation of energy management systems (EMS) for real-time monitoring and optimization of energy use, and the integration of smart grids and microgrids that manage energy flows dynamically and incorporate multiple renewable sources. Shore-side electricity (SSE), which enables vessels to connect to the local grid while at berth, is also widely used to cut emissions from auxiliary engines. Furthermore, ports are progressively investing in renewable energy sources such as solar photovoltaic (PV), offshore wind, wave, and tidal energy, which reduce fossil fuel dependence and contribute to energy sovereignty.  
Complementary technologies like energy storage systems help stabilize power supply by storing surplus energy and ensuring continuous availability during peak demand or low generation periods. Additionally, digital innovations such as digital twins and artificial intelligence (AI) are transforming energy management in ports. These tools allow for predictive maintenance, scenario modelling, and real-time optimization of operations.  
Figure 1 comprehensively represents the whole marine port power supply system, illustrating the interconnection between renewable energy sources, energy storage facilities, and various port-side energy consumers. On the generation side, the system integrates multiple renewable energy sources--including wind power, solar power, and wave and tidal energy--which are complemented by traditional grid electricity. These energy inputs feed into the port's power infrastructure, which also incorporates diverse energy storage solutions such as batteries, hydrogen storage, and compressed air systems. The stored energy can be flexibly deployed based on demand fluctuations or generation variability. The system then distributes power to a wide array of port operations and consumers, including electric vehicles, shore-side electricity or cold ironing systems (onshore power for berthed ships), cranes, refrigerated storage units, and industrial facilities. A centralized control and distribution unit manages the flow and balance of energy across the system, ensuring efficient, stable, and sustainable operation.