Search Results (157)

Thermal energy storage (TES) technologies are essential for renewable energy integration, industrial waste heat recovery, grid flexibility, and improved energy efficiency. Despite advances in sensible heat thermal energy storage (SHTES), latent heat thermal energy storage (LHTES), and thermochemical energy storage (TCES), practical deployment remains constrained by inadequate heat transfer rates, which limit charging and discharging processes, reduce storage utilization, and increase system size and cost. Conventional heat-transfer enhancement approaches, including fins, embedded heat exchangers, conductive additives, porous structures, and flow intensification techniques often introduce trade-offs related to manufacturability, complexity, durability, and energy consumption. Additive manufacturing (AM) has emerged as a promising approach for overcoming these limitations by enabling precise control of internal geometry, porosity, surface-area-to-volume ratio, and fluid pathways. Through the fabrication of architected structures, lattice networks, triply periodic minimal surface (TPMS) geometries, and multifunctional heat-transfer architectures, AM enables geometry-driven optimization of thermal performance that is difficult to achieve using conventional manufacturing methods. These capabilities support the development of compact TES systems with enhanced heat transfer, improved thermal uniformity, and increased energy utilization. This review examines additive manufacturing technologies relevant to TES applications, including powder bed fusion, directed energy deposition, material extrusion, vat photopolymerization, and binder jetting. The relationships among manufacturing processes, material selection, and thermal performance are discussed across SHTES, LHTES, and TCES systems. Particular emphasis is placed on AM-enabled heat-transfer enhancement strategies, phase change material (PCM)-integrated structures, architected thermal networks, embedded heat exchangers, and computational design methodologies such as topology optimization. Current challenges involving material compatibility, scalability, cost, and long-term durability are also evaluated. The review highlights how additive manufacturing is transforming TES design from a material-centered paradigm toward geometry-enabled thermal engineering, creating new opportunities for next-generation energy storage systems. Full article

Buildings account for roughly 37% of energy-related CO₂ emissions, and space cooling already consumes nearly 10% of global electricity. Cooling demand is rising fastest in tropical cities, where air-conditioning could reach 45% of peak load, especially in India by 2050. This review critically examines thermal energy storage (TES) as a flexibility resource across three distinct scales: individual buildings, district heating and cooling networks, and city-level multi-energy systems. Using a Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA)-based search of Scopus, Web of Science, and IEEE Xplore with primary and supplementary strings, 4447 records were identified, of which 174 were included. Each quantitative study was classified by validation level (simulation, laboratory, pilot, or operational) and by the centrality of thermal storage. Sensible, latent, and thermochemical storage technologies are compared using energy density (10–500 kWh/m³), efficiency (40–95%), cycle stability, and technology readiness. The review then evaluates the role of artificial intelligence (AI), machine learning, and Internet of Things platforms in forecasting, predictive control, and operational optimization of TES networks. Thirteen method families, grouped into AI and machine learning methods, optimization methods, control methods, and digital enabling technologies, are assessed against six explicitly defined criteria with evidence-coded scores. Among 47 quantitative studies, 37 (78.7%) are simulation-only, and only four (8.5%) report operational data. Direct TES-AI studies report simulated energy savings of 8–64% and peak load reductions of about 35%, whereas field-validated intelligent control reports 17% energy savings in a single real building experiment. The review also identifies inherent drawbacks of artificial intelligence-based operations, including limited interpretability, high data and computational demands, concept drift, and cyber vulnerabilities that increased peak electric load by 17.4% in a simulated attack. A structural imbalance in the literature is evident: most validated deployments remain at the building-scale, whereas urban-scale evidence is confined to district cooling, aquifer and pit storage, and multi-energy hub studies; no study reports the coordinated operation of distributed TES assets across multiple districts. A conceptual framework and a staged roadmap linking building, district, and urban scales are proposed. Priority research needs include urban-scale pilots in tropical climates, techno-economic assessment, interpretable and drift-robust AI, and interoperability standards that support United Nations’ Sustainable Development Goals 7, 11, and 13. Full article

The increasing integration of renewable energy sources, particularly solar and wind, has created a growing need for efficient and reliable energy storage technologies (ESTs) because of their intermittent nature. This review critically examines established and emerging ESTs, including batteries, supercapacitors, and mechanical, thermal, hydrogen, and superconducting magnetic energy storage systems, with emphasis on their technical performance, durability, response time, economic feasibility, and environmental considerations. The reviewed technologies exhibit substantial differences in their energy and power characteristics. Lithium-ion batteries, for example, provide an energy density of approximately 100–265 Wh/kg, with reported lifetimes of 2000–10,000 cycles, whereas supercapacitors offer only 5–10 Wh/kg but can withstand more than 100,000 cycles and deliver energy within seconds. Flywheel systems can achieve power densities of 1000–10,000 W/kg and operate for up to 100,000 cycles, while pumped hydro storage has a comparatively low energy density of approximately 0.5–1.5 Wh/kg but can provide service over periods exceeding 50 years. Thermal storage technologies also show considerable potential, with reported energy densities ranging from approximately 0.25 Wh/kg for sensible heat storage to 120–383 Wh/kg for thermochemical storage, depending on the materials and system configuration. Overall, the findings demonstrate that no single storage technology is optimal for all applications. Technology selection should, therefore, consider the required energy and power capacity, response time, lifetime, cost, and environmental impact, particularly when integrating variable renewable energy into modern energy systems. Full article

Photovoltaic–thermal (PVT) collectors coupled to thermochemical energy storage (TCES) can turn intermittent low-grade solar heat into a dispatchable service, but solar intermittency poses a closed-loop control problem. A companion study established the feedback-only lower bound: a 937 kJ accumulated exergy-delivery-deficit benchmark under optimally tuned proportional–integral–derivative (PID) flow control. The corresponding upper bound is quantified here by means of a deliberately idealised search-based predictive controller that, at each 10 s step, enumerates 51 candidate pump rates, predicts the reactor-inlet temperature by a single forward-Euler step, and is granted perfect future irradiance. On the experimentally validated shared plant (matched to the companion baseline), against an optimally tuned PID, the perfect-foresight advantage is marginal: +0.96% daily exergy on synthetic days and +0.07–0.24% on two measured Walailak University monsoon days, all controllers tracking within 6–13 K on the measured days. Under tropical-monsoon irradiance, the 95 °C desorption setpoint is rarely sustained, so the delivered exergy is nearly controller-independent: the perfect-foresight upper bound lies just above the feedback-only lower bound, and together the two results bracket the exergy envelope available to any flow-rate controller of this system. A horizon sweep localises the bottleneck to internal-model fidelity, not anticipation depth. The eight-node plant is validated against measured module temperature (root-mean-square error 3.5 °C, coefficient of determination R² = 0.89) and a copper-tube PVT prototype (1.5 °C; peak hot water up to 79 °C). The central contribution is therefore a rigorously defined, experimentally grounded upper bound showing that, at this scale and latitude, deployability rather than anticipation is the effective design lever. Full article

Solar-assisted thermochemical cycles can convert intermittent solar energy into storable chemical fuels. Within the European SULPHURREAL project, elemental sulfur is investigated as a long-term energy-storage medium in a cycle based on H₂SO₄, S, and SO₂. This work investigates an indirect magnesium-mediated route for the disproportionation of SO₂. The proposed cycle consists of three steps: aqueous reaction of SO₂ with MgO to form sparingly soluble MgSO₃; thermal decomposition of MgSO₃ through competing pathways producing elemental sulfur, MgSO₄, MgO, and SO₂; and high-temperature decomposition of MgSO₄ to regenerate MgO and produce sulfur oxides and oxygen. All three steps were experimentally investigated using laboratory-scale reactors, thermogravimetric analysis, X-ray diffraction, ion chromatography, and calorimetric measurements. The sulfur yield was approximately 25% of the theoretical maximum, corresponding to 8.3% relative to the initial SO₂ amount. Complete MgSO₄ conversion was achieved after 90 min at 1100 °C, at which temperature the SO₂-forming pathway accounted for approximately 87% of the gaseous sulfur products. The experimental results were used to establish a preliminary mass and energy balance for the closed-loop process. The calculated gross heat requirement was 5349 kJ mol⁻¹ of sulfur, corresponding to an energy efficiency of 5.5% when heat recovery was not considered. These results demonstrate the technical feasibility of the proposed magnesium-mediated route and provide a quantitative basis for its further development, identifying sulfur selectivity, high-temperature sulfate decomposition, quantitative product recovery, and heat integration as the main priorities for process optimisation. Full article

As the global energy sector and maritime industry transition toward carbon neutrality, Carnot batteries have emerged as a critical technology for flexible, long-duration energy management. Carnot batteries, which operate on a Power-to-Heat-to-Power principle, present a highly promising alternative to conventional electrochemical batteries. The present study provides a review of Carnot battery architectures, systematically evaluating their thermodynamic cycles, working fluids, Thermal Energy Storage media and key turbomachinery components. A comparative assessment of the current literature illustrates that system selection requires balancing round-trip efficiency, Energy Storage Density and Technology Readiness Level. According to the findings of the present study, high-temperature Brayton cycles offer robust baseline efficiencies of 60–80% whereas subcritical Rankine cycles benefit from commercial maturity and can achieve efficiencies exceeding 200% when integrated with cryogenic heat sinks like LNG. It should be clarified that efficiency values exceeding 100% represent “Apparent Round-Trip-Efficiencies (RTE)” resulting from the thermodynamic contribution of external exergy streams, such as LNG cryogenic cold, rather than standalone cycle efficiencies, which are strictly below 100%. In addition, volumetric energy density varies drastically based on the physical phase of the storage medium, scaling from under 1 kWh/m³ for unpressurized water to over 385 kWh/m³ for advanced thermochemical systems. Although most configurations currently remain in the prototyping phase, the technology holds transformative potential for the maritime sector. Carnot batteries can deliver a self-contained, zero-emission electrical power supply to cover the vessel’s electrical load requirements during harbor stays and transit within Emission Control Areas (ECAs) by dynamically capturing and storing shipboard waste heat during open sea transit. Full article

Hydrogen has emerged as a promising energy carrier for sustainable, low-carbon energy systems because of its high energy density and compatibility with fuel cell technologies. This study presents a comprehensive investigation of hydrogen production through the integration of steam methane reforming (SMR), solar photovoltaic (PV) power generation, proton exchange membrane (PEM) electrolysis, hydrogen storage, and PEM fuel cells. A three-dimensional computational fluid dynamics (CFD) model was developed to analyze fluid flow, heat transfer, species transport, and chemical reactions within a catalytic steam methane reformer. The simulation predicted a methane conversion of 94.71%, a hydrogen yield of 3.75 mol H₂/mol CH₄, and an overall efficiency of 63.35%, indicating highly efficient hydrogen production. Sensitivity analyses identify catalyst temperature, inlet temperature, and residence time as the dominant parameters affecting hydrogen yield. Integration with renewable energy systems demonstrated that a hybrid configuration consisting of a 120 kW PV array, a 50 kW PEM electrolyzer, a 6 kW PEM fuel cell, and 6–8 kg hydrogen storage can effectively support sustainable hydrogen production and auxiliary power demands. The proposed framework provides a practical pathway for integrating thermochemical and renewable hydrogen technologies into future energy applications worldwide. Full article

Thermochemical energy storage (TCES) has emerged as one of the pivotal technologies for enhancing the stability and efficiency of energy systems, owing to its advantages including high energy storage density, low heat loss and long-term energy storage capability. Among various TCES technologies, solid–gas reaction-based TCES exhibits tremendous potential in medium- and high-temperature applications. This paper first overviews the research progress of solid–gas reaction-based TCES technologies. Focusing on four major TCES material systems, namely hydroxides, carbonates, metal oxides and metal hydrides, it discusses their energy storage mechanisms, material modification strategies, and reaction kinetics, as well as approaches to improve thermal conductivity and cycling stability. Subsequently, reactor types (including fixed bed, moving bed and fluidized bed reactors) applicable to different materials and the latest research progress of diverse reaction systems are elaborated in detail, and the optimal designs of heat transfer performance for the four reaction materials in corresponding reactors are clarified. Based on the comparative analysis, the Ca(OH)₂/CaO system is identified as the most promising material system for engineering deployment, owing to its moderate operating temperature, low material cost, and validated pilot-scale performance. The intrinsic complementarity between material modification strategies and reactor heat transfer enhancement is also elucidated, providing a theoretical foundation for scalable implementation. Full article

Photovoltaic–thermal (PVT) collectors co-generate electricity and heat—natural front ends for thermochemical energy storage (TCES)—provided the heat transfer fluid stays above the reactor’s desorption temperature. Using an eight-node model of a 0.6834 m² collector at 8.64° N whose thermal core is partially validated against measured data from the same tropical–coastal site (rooftop PV module temperature, RMSE 3.8 °C; prototype absorber-to-water heat transfer, RMSE 1.3 °C), flow-regulated to the ≈95 °C SrCl₂/NH₃ desorption threshold, we quantify the energy and exergy delivered for charging under tropical–monsoon intermittency. The 95 °C setpoint operation, the ≈5.3 h charging window, and all reported exergy yields are simulated: the built prototype delivered hot water peaking at 79 °C and did not reach the 95 °C setpoint. On a measured clear-sky day (clearness index K_t = 0.52), the collector yields 1.38 kWh of energy but only 0.43 kWh of exergy (first-law efficiency ≈ 38%; gross exergy efficiency ≈ 13%); across a 30-seed synthetic-intermittency ensemble, the exergy yield is 0.678 kWh at ≈14% gross exergy efficiency (≈52% combined first-law efficiency). In both cases, the thermal stream dominates the energy output while the electrical stream dominates the exergy output—on the sunlit day, the exergy is about 80% electrical—because 95 °C heat carries a Carnot factor (exergetic quality factor, 1 − T_a/T₇, at the instantaneous ambient dead state) of only ≈0.18 and an integrated Bejan/Kotas thermal-exergy quality of only ≈0.09. The controller holds the outlet within 1.4 K of the setpoint for ≈5.3 h, whereas no fixed flow in the 0.5–5.0 L min⁻¹ range ever reaches it: feedback control is a structural enabler, not an optimisation. On overcast days, the threshold is never reached and charging heat collapses to zero, leaving a PV-only generator. Exergy delivery is nonetheless nearly controller-independent: the accumulated exergy delivery deficit after a 50% irradiance drop is 937 kJ, a controller-independent value changing only 1.3% across a systematic 4 × 4 gain sweep (K_p 0.33–2.7×, K_d 0.25–5× of nominal), and predictive control improves it by ≤1%. For PVT–TCES at this scale, the decisive lever is deployability, not control sophistication. Full article

The rapid growth of graphics processing unit (GPU)-accelerated AI workloads has made data centers significant sources of medium-grade waste heat, creating both a sustainability challenge and an urban decarbonization opportunity. This paper presents the Cascaded Exergy-Economic Valorization (CEEV) framework, a three-stage system that converts data-center waste heat through (1) an organic Rankine cycle for GPU liquid-cooling loops at 65–85 °C; (2) a transcritical CO₂ heat pump, upgrading residual heat to 75–90 °C; and (3) thermochemical energy storage using SrBr₂·6H₂O for seasonal heat banking. The framework introduces two metrics: the Exergy Value Index (EVI, $/kJ) and the Levelized Cost of Stored Heat (LCSH, $/kWhth). Results for a 10 MW liquid-cooled data center across three climate zones show cascade exergy utilization of 31.2–38.7%, operational cost reductions of 15–25%, 20-year NPV of $2.2–8.4 million, and payback periods of 5.8–7.8 years. The simpler HP (heat pump) +TCES (thermochemical energy storag) configuration achieves higher deterministic Net Present Value (NPV) because it preserves the full waste-heat temperature for the heat pump; however, the full three-stage cascade becomes preferable when electricity prices exceed approximately $50/MWhe, when revenue diversification is valued, or when real-options flexibility is important. Real-options analysis shows that traditional NPV undervalues cascaded waste-heat recovery investments by 18–32%. Even without carbon credit revenue, NPV remains positive at $1.6–6.1 million, confirming that district-heating sales and electricity revenue alone can support investment. The CEEV framework advances sustainable data-center development by providing quantifiable tools for waste-heat performance assessment, supporting policy instruments such as the EU Energy Efficiency Directive and the German EnEfG, and aligning with SDGs 7, 9, 11, and 13. Full article

Industrial processes consume large amounts of thermal energy, while many recoverable heat streams remain unused because heat sources and sinks differ in time, temperature level, power demand, and operating schedule. Thermal energy storage (TES) can decouple heat supply from heat demand and support waste heat recovery, peak-load reduction, process heat electrification, and flexible operation of continuous, batch, and intermittent processes. This narrative review assesses industrial TES from a process integration perspective rather than from a storage-material perspective alone. Sensible, latent, thermochemical, sorption-based, hybrid, and steam-based storage systems are compared with respect to delivery temperature, storage duration, charging and discharging power, response time, heat losses, reliability, integration complexity, and techno-economic feasibility. Sector-specific opportunities are discussed for the iron and steel, cement, ceramics, chemical and petrochemical, pulp and paper, and food and beverage industries. The review shows that deployment is constrained less by the availability of storage concepts than by heat exchanger limitations, inconsistent Key Performance Indicator (KPI) definitions, unclear system boundaries, scarce long-term operating data, and insufficient coupling with pinch analysis, heat exchanger network design, control, and safety requirements. A practical technology-selection workflow and a research roadmap are proposed for scalable, reliable, and economically viable industrial TES deployment. Full article

Under the global energy transition and the decarbonisation of building heating, cross-seasonal thermal energy storage has emerged as a crucial technology to address the seasonal mismatch between renewable energy supply and demand. This study proposes and evaluates a modular composite thermal storage system that integrates thermochemical and phase change storage modulars. An intelligent control strategy is adopted to achieve functional decoupling and coordinated operation. Taking a residential district in Beijing, China, as a case study, three system scenarios are constructed: a full thermal storage system, a hybrid storage system supplemented with off-peak electricity, and a fully electric system. The results show that the hybrid system maintains the same annual solar energy utilisation as the full storage system while reducing the levelised cost of heat by 33%. The modular strategy reduces the scale of the storage system and enhances operational flexibility. Among the three scenarios, the hybrid system achieves the best balance in terms of storage efficiency, grid interaction, and cost-effectiveness. This study provides strategic insights and design references for the engineering application of cross-seasonal thermal storage systems, contributing positively to the decarbonisation of district heating. Full article

Mobile thermal energy storage (M-TES) demonstrates significant commercialization potential in industrial waste heat recovery, distributed heating, and clean heating applications, which is primarily based on three technical pathways: sensible heat storage, latent heat storage using phase change materials (PCMs), and thermochemical heat storage. The updated status of M-TES, mainly on PCMs and thermochemical ones, and the challenges facing application were reviewed, and potential development trends were discussed in the present study. Sensible heat storage is relatively mature and cost-effective; however, it suffers from low energy density and comparatively high heat loss during storage and transport. Latent heat storage utilizes the phase transition enthalpy of PCMs to store thermal energy, offering higher energy density and near-isothermal heat release, making it a focal point of current academic and industrial research. Nevertheless, latent heat storage still faces technical bottlenecks, including low thermal conductivity, phase separation, and supercooling of PCMs. Thermochemical heat storage relies on reversible chemical reactions to convert and store thermal energy as chemical energy, theoretically achieving the highest energy density and minimal heat loss. However, due to its technical complexity and high system cost, thermochemical storage remains largely in the early stages of research and demonstration. Overall, as a bridge between heat supply and demand, the development trend emphasizes the design of high-performance composite PCMs, enhanced system integration, and intelligent operational management. However, its large-scale deployment is still constrained by challenges related to energy density, heat transfer enhancement, long-term material stability, and techno-economic feasibility. Full article

The escalating global challenge of waste management, combined with the urgent need to reduce greenhouse gas emissions, has intensified interest in waste-to-energy (WtE) technologies as integrated solutions for sustainable energy recovery. This review critically examines advanced WtE technologies through three interconnected dimensions: the strength of the evidence base supporting performance and environmental claims, the challenges associated with scalability and system integration, and the implications of these technologies for net-zero energy transitions. The analysis covers thermochemical, biochemical, and hybrid conversion pathways, including pyrolysis, gasification, hydrothermal liquefaction, and anaerobic digestion, with particular emphasis on identifying inconsistencies in the literature and clarifying key uncertainties. A persistent gap between laboratory-scale performance and commercial-scale operation is identified and characterised across conversion pathways. Its principal drivers of feedstock heterogeneity, heat transfer limitations, and operational complexity are examined. Environmental assessments are shown to be highly sensitive to system boundary definitions and carbon accounting methodologies, with lifecycle results varying substantially depending on energy substitution assumptions and biogenic carbon treatment. The integration of WtE within circular economy frameworks demonstrates that energy recovery is most effective when positioned as a complement to material recycling rather than a substitute. The roles of combined heat and power configurations, district heating, carbon capture and storage, and emerging reactor technologies in advancing net-zero contributions are assessed. Significant data gaps are identified in long-term operational performance, modelling transparency, and reporting standardisation. The review concludes that WtE technologies represent valuable components of integrated waste and energy management systems, but their long-term contribution to decarbonisation requires careful system design, sound operational strategies, and harmonised performance evaluation frameworks. Full article

Brewer’s spent grain (BSG) is one of the major by-products of the brewing industry and an abundant lignocellulosic stream with potential for energy recovery and broader biorefinery use. This review evaluates the main BSG-to-energy pathways, including anaerobic digestion (AD), combustion/co-combustion, pyrolysis, gasification, and hydrothermal processes (HTC/HTL), with emphasis on technical performance, environmental aspects, implementation constraints, and integration into brewery systems. Particular attention is given to the effect of BSG heterogeneity, high moisture content, protein and ash composition, and storage instability on process selection and operability. In addition to summarizing pathway-specific evidence, the manuscript proposes a harmonized comparative framework and an integrated technical–economic–environmental interpretation of BSG valorization options. The analysis shows that wet-feed-compatible pathways, especially AD and hydrothermal processing, are generally better aligned with the intrinsic properties of fresh BSG, whereas thermochemical routes usually require more intensive feedstock conditioning and tighter control of ash-related and gas cleaning risks. The review also highlights that long-term operational reliability, scale-up constraints, and utility integration are as important as nominal conversion efficiency when assessing practical deployment. Current evidence suggests that the most realistic implementation strategies are context-dependent and should be selected according to brewery scale, energy demand profile, available heat integration, and acceptable operational risk. Future research should prioritize harmonized reporting, long-term industrial validation, and the development of robust hybrid systems and brewery-integrated biorefinery configurations. Full article