Hybrid and All-Electric Civil and Military Ships: From Maritime Decarbonisation Drivers to Integrated Energy System Architectures

The maritime sector is undergoing rapid change due to stricter environmental regulations, shifting policies, and growing concerns about energy security and operational resilience. In this landscape, hybrid and all-electric ships (AES) are gaining recognition as effective solutions for reducing emissions, boosting efficiency, and harnessing alternative energy sources. Nonetheless, many electrification initiatives mainly target propulsion, while the entire onboard energy infrastructure, including generation, storage, distribution, power conversion, and energy management, is often developed separately. This paper investigates hybrid and AES systems linking maritime decarbonisation goals to the development of integrated onboard energy architectures. It starts with an overview of key international, European, and Portuguese policies that impact maritime decarbonisation, emphasising their influence on both the commercial and military sectors. The literature review then charts the evolution of onboard power systems, showing the shift from mechanical propulsion to integrated power solutions. Finally, it analyses different architectural configurations, energy storage technologies, alternative energy sources, and energy management strategies found in current research. Our analysis shows that adopting hybrid and AES systems requires a comprehensive system-level strategy that links power generation, storage, distribution, operational profiles, and energy management. By combining policy initiatives, technological progress, and current research, our review highlights the crucial role of integrated energy system architectures in the development of future hybrid and AES systems. We also identify key research gaps, such as multi-domain modelling, consistent performance metrics, mission-oriented energy management, and assessments of long-term robustness and operational sustainability.