The Special Issue "Low-grade thermal energy utilization: technologies and applications" addresses the growing interest in harnessing low-grade thermal energy for sustainable energy systems. This editorial article reviews the articles featured in the issue, highlighting advancements and contributions in various areas of low-grade thermal energy utilization. 1. **Introduction**: The introduction emphasizes the increasing recognition of low-grade thermal energy as a significant resource for sustainable energy systems. It discusses the emergence of innovative technologies and applications, such as power cycles, heat pumps, thermoelectric generators (TEGs), and thermal energy storage solutions. 2. **Overview of Articles Collected**: - **Heat Pumps**: Articles focus on integrating heat pumps with various systems, including seasonal heat storage, solar thermal systems, and ground-coupled heat pumps. Studies highlight improvements in energy efficiency and cost-effectiveness. - **Power Cycles**: Research on power cycles like the organic Rankine cycle (ORC), Kalina cycle (KC), Stirling cycle, and CO₂ cycles is presented. Studies cover working fluid selection, heat transfer optimization, and system integration. - **Thermoelectric Generators (TEGs)**: Articles explore structural optimization, heat transfer, and integration with other systems like photovoltaic (PV) systems. Studies demonstrate significant improvements in power output and system performance. - **Thermal Storage**: Research on thermal storage materials, heat transfer processes, and system integration is discussed. Studies focus on improving storage efficiency and addressing challenges such as supercooling and shape flexibility. - **Solar Thermal Energy Utilization Technologies**: Articles highlight the use of solar thermal energy for freshwater production, solar concentrators, and photothermal conversion fluids. Studies provide insights into system design and performance optimization. - **Other Thermal Energy Technologies**: Research on heat pipes, thermally regenerative electrochemical cycles (TREC), and thermal management technologies is covered. Studies explore innovative designs and applications in geothermal energy, cooling systems, and battery thermal management. 3. **Conclusions**: The Special Issue provides a comprehensive overview of state-of-the-art research in low-grade thermal energy utilization, covering a wide range of technologies and applications. It offers valuable insights and guidance for future research and development in this field. The authors express gratitude to the editorial board, contributors, and reviewers for their contributions to the Special Issue.The Special Issue "Low-grade thermal energy utilization: technologies and applications" addresses the growing interest in harnessing low-grade thermal energy for sustainable energy systems. This editorial article reviews the articles featured in the issue, highlighting advancements and contributions in various areas of low-grade thermal energy utilization. 1. **Introduction**: The introduction emphasizes the increasing recognition of low-grade thermal energy as a significant resource for sustainable energy systems. It discusses the emergence of innovative technologies and applications, such as power cycles, heat pumps, thermoelectric generators (TEGs), and thermal energy storage solutions. 2. **Overview of Articles Collected**: - **Heat Pumps**: Articles focus on integrating heat pumps with various systems, including seasonal heat storage, solar thermal systems, and ground-coupled heat pumps. Studies highlight improvements in energy efficiency and cost-effectiveness. - **Power Cycles**: Research on power cycles like the organic Rankine cycle (ORC), Kalina cycle (KC), Stirling cycle, and CO₂ cycles is presented. Studies cover working fluid selection, heat transfer optimization, and system integration. - **Thermoelectric Generators (TEGs)**: Articles explore structural optimization, heat transfer, and integration with other systems like photovoltaic (PV) systems. Studies demonstrate significant improvements in power output and system performance. - **Thermal Storage**: Research on thermal storage materials, heat transfer processes, and system integration is discussed. Studies focus on improving storage efficiency and addressing challenges such as supercooling and shape flexibility. - **Solar Thermal Energy Utilization Technologies**: Articles highlight the use of solar thermal energy for freshwater production, solar concentrators, and photothermal conversion fluids. Studies provide insights into system design and performance optimization. - **Other Thermal Energy Technologies**: Research on heat pipes, thermally regenerative electrochemical cycles (TREC), and thermal management technologies is covered. Studies explore innovative designs and applications in geothermal energy, cooling systems, and battery thermal management. 3. **Conclusions**: The Special Issue provides a comprehensive overview of state-of-the-art research in low-grade thermal energy utilization, covering a wide range of technologies and applications. It offers valuable insights and guidance for future research and development in this field. The authors express gratitude to the editorial board, contributors, and reviewers for their contributions to the Special Issue.