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) undergoes regasification before delivery to end users, releasing a large amount of cold energy that is significant for efficient utilization. Therefore, based on the principle of “temperature counterpart, cascade utilization”, this study integrates Pinch Analysis with Total Site Heat Integration (TSHI) to propose two new types of integrated systems for LNG cold energy cascade utilization. The first system, designed for rich-gas LNG, comprises light hydrocarbon separation, cryogenic comminution of rubber, electricity generation by organic rankine cycle, and heat management of data center by direct cooling (LHS-CCR-ORC-DC). The second system, designed for lean gas LNG, replaces the LHS unit with an air separation process (ASP) while retaining CCR, ORC, and DC. Through the synergistic optimization of the Grand Composite Curve (GCC) and total site composite curve (TSCC), the proposed system realizes the cascade and efficient utilization of the LNG cold energy in the whole temperature range (−160 °C to 10 °C). Thermodynamic analysis shows that the energy utilization efficiency of the LHS-CCR-ORC-DC and ASP-CCR-ORC-DC systems is improved by 50.06 % and 40.93 %, respectively, compared with the single cold energy utilization mode. Economic evaluation indicates net present values of 1.81 × 10⁸ $ and 2.32 × 10⁸ $ for the two systems, with levelized costs of energy of 0.062 $/kWh and 0.055 $/kWh, respectively. By replacing fossil‐fuel power generation and compression‐based refrigeration, the integrated systems achieve annual CO2 reductions of 261.84 kt and 238.20 kt, respectively. This study provides theoretical basis and technical support for the efficient utilization of LNG cold energy and for the synergistic optimization of its cascade utilization in industrial parks.