Integrating marine renewable energy (MRE) with conventional energy sources and logically constructing island energy systems is crucial for alleviating island energy supply challenges and helping coastal energy systems achieve a sustainable, low-carbon transition. In this study, the status of marine energy utilisation technologies is reviewed, with a focus on advancements in energy conversion equipment, grid integration, and energy storage. The economic feasibility and environmental sustainability of marine energy systems are comparatively analysed to enhance the development and utilisation of marine energy technology while reducing the economic cost of power generation. Suitable equipment is highlighted for islands, with efficient energy generation strategies proposed to achieve cleaner, localised, and cost-effective island integrated energy system (IIES) design. Island energy facilities vary, and integrated development is crucial for building new energy systems. Based on the types and resources of island energy, IIESs are constructed for hierarchical energy utilisation and multi-energy coupling, coordinating resources to achieve source–grid–load–storage integration. The optimisation of IIESs is reviewed, with a focus on modelling methods, intelligent algorithm development, and system simulation. This study differs from previous research as it considers the integration of marine energy into existing systems to achieve comprehensive integration of multiple energy sources. Additionally, optimisation and solution methods for IIES models are summarised. To integrate complex, multivariable energy systems and create stable and predictable outputs, marine energy and load forecasting methods are explored. Overall, this study supports the advancement of marine energy utilisation, focusing on its progressive integration into island energy systems as the efficiency of marine energy improves. This work aims to inspire the development of new functions and modules based on existing system optimisation and forecasting techniques.

The contribution of Pawel Oclon has been funded by the EU project “Renewable energy system for residential building heating and electricity production–RESHeat”, Grant Agreement #956255. The work of Petar Varbanov has been funded by the Széchenyi István University in Hungary. The authors would like to apologise for any inconvenience caused.

Sustainable energy systems are crucial for reducing carbon emissions because renewable energy sources leave a footprint. The petrochemical industry often suffers from inefficient heat exchange network (HEN) systems, leading to substantial energy wastage. In the current work, a real case study of the residue hydrogenation process was analyzed to identify potential energy savings. A new method combining Pinch Analysis and Thot–Tcold diagram analysis methods was proposed. This graphical analysis method plots the cold-flow temperature of each heat exchanger unit on the x-axis and the hot-flow temperature on the y-axis. By applying the Thot–Tcold diagram to a practical case of residue hydrogenation in Zhejiang, the existing process energy state was evaluated, and HEN was retrofitted to achieve energy savings and carbon emission reduction. Following optimization, the energy recovery amounted to 202.71 GJ/h with an energy recovery rate of 14.3 %. The proposed method saves approximately 4.058 × 10⁵ GJ/y compared to current operations, resulting in an annual cost saving of approximately $ 2.76 M/y, with an investment payback period of less than 0.36 y. This study offers a solution to the energy challenges of industrial residue hydrogenation by enhancing the economic and environmental sustainability of existing process flows.

Liquefied Natural Gas (LNG), as a vital form of natural gas resources, has exhibited a steadily increasing trend in global production and trade volumes. LNG terminals are facing the challenge of how to recover and utilise cold energy in a safe and efficient regasification process, while coordinating with the natural gas pipeline network transport scheduling. This study proposes an integrated regulation and collaborative optimisation approach for natural gas pipeline networks and LNG cold energy cascade utilisation systems. For natural gas pipeline network systems, P-Graph develops multi-period gas-electric interconnected supply chain network to optimise resource allocation. For the LNG cold energy cascade utilisation system, a dual Organic Rankine Cycle (ORC) framework for both power generation and refrigeration is developed, as well as thermodynamic analysis and heat integration techniques are applied to optimise system efficiency. Using a coastal LNG terminal in Zhejiang, China, as a case study, when the LNG regasification flow rate is 62.46 t/h, cold energy generates electricity of 2,335.94 kW and air-conditioning cooling load of 1,651.5 kW, system efficiency reaches 44.75 %. The peak regulation and gas storage effect of LNG is significant, which helps to alleviate that energy shortage in the region, and the coupled system of LNG and natural gas pipeline network improves energy utilisation efficiency and economic benefits for LNG industry chain.

As offshore wind power migrates into deep, remote waters, the traditional single-source electricity-export model faces severe techno-economic fragility, primarily driven by prohibitive offshore transmission costs and finite onshore grid absorption capacity. To overcome these barriers, this structured review examines the transition from standalone wind farms to multifunctional integrated energy systems through a holistic resource-grid-load integration framework, within which generic objectives, balance relationships, operational constraints, and validation approaches are summarized as a standardized modeling reference. On the supply side, the analysis evaluates the spatiotemporal synergy of coupling wind with floating photovoltaics, wave energy converters, marine biomass, and ocean thermal energy, demonstrating how multi-energy complementarity dampens output fluctuations and enhances structural stability. On the demand side, the study critically explores diversified in situ utilization pathways, specifically low-trophic marine ranching, seawater electrolysis for green hydrogen and ammonia (Power-to-X), and the electrification of legacy oil and gas platforms. These demand-side load reconfigurations transform surplus electricity into storable chemical carriers, effectively relieving pressure on long-distance transmission corridors. Furthermore, this review addresses the strict geographic and economic boundary conditions of these pathways, indicating that preferred export and utilization pathways depend on distance, water depth, project scale, metocean conditions, market readiness, and cost assumptions. Finally, by assessing the technology readiness levels and intrinsic limitations of current configurations, this study proposes a three-stage research roadmap, providing the theoretical and methodological grounding necessary for future autonomous deep-sea multi-carrier energy hubs.