Innovations in Thermal Energy Systems, Bridging Traditional and Emerging Technologies for Sustainable Energy Solutions

Val Hyginus Udoka Eze^*

• Kampala International University - Western Campus, Bushenyi, Uganda

Thermal energy systems (TES) have historically underpinned global industrialization and power generation, with fossil fuel-based technologies accounting for approximately 81% of the global primary energy supply as of 2024. However, their reliance on finite resources and inherent thermal inefficiencies, often below 40% conversion efficiency in conventional steam power plants, contributes disproportionately to greenhouse gas (GHG) emissions and environmental degradation, responsible for over 35% of global CO₂ emissions. This systematic review critically examines the evolution and transformative innovations in TES over the past two decades, emphasizing the urgent transition toward sustainable, hybridized, and digitally optimized systems. Using the PRISMA methodology, 163 peer-reviewed studies were systematically analyzed to capture trends in technological advancements, including enhancements in the Rankine cycle, deployment of TES solutions such as phase change materials, thermochemical, and nano-enhanced media, and hybrid configurations integrating biomass, concentrated solar power (CSP), and photovoltaic-thermal (PVT) systems. Digitalization emerges as a cornerstone for TES modernization, with artificial intelligence, machine learning, Internet of Things (IoT), and digital twins enabling real-time performance optimization, predictive maintenance, and adaptive control. These tools have demonstrated system efficiency improvements of up to 20–35% and reduced operational downtime by up to 40% in pilot deployments. Waste heat recovery technologies, particularly organic Rankine cycles (ORCs) and thermoelectric generators (TEGs), have achieved energy recovery efficiencies exceeding 80% for low-to medium-grade thermal streams, aligning with circular economy principles. Moreover, modular and containerized TES solutions are gaining traction for decentralized and off-grid applications, especially in healthcare and agricultural cold chains, where they have reduced post-harvest losses by up to 30% and improved vaccine cold storage reliability in sub-Saharan Africa by over 50%. The integration of TES with electrochemical storage and green hydrogen production is also accelerating, positioning TES at the nexus of multi-vector, decarbonized energy platforms. Findings underscore that the future of TES lies in interdisciplinary R&D, material innovation, particularly in nanostructured composites, and enabling regulatory and fiscal policies that support hybrid renewable integration and digitalization. This paradigm shift toward intelligent, low-carbon thermal networks is not only vital to meeting the Paris Agreement targets but also central to achieving global energy equity and long-term sustainability.