Energy Storage and Applications

Molten salt heat exchangers are crucial components in systems requiring high-temperature heat transfer and energy storage, especially in renewable energy and advanced nuclear technologies. Their ability to operate efficiently at high temperatures while offering significant energy storage capacity makes them highly valuable in modern energy systems. They have high thermal stability. In the framework of this research, a computational fluid dynamics (CFD) simulation model of the HITEC molten salt cooling system has been developed. HITEC molten salt is a specialized heat transfer and thermal energy storage medium primarily used in industrial processes and solar thermal power plants. It is a eutectic blend of sodium nitrate, sodium nitrite, and potassium nitrate. COMSOL multi-physics code has been employed in this research. It simultaneously solves the fluid flow, energy, and heat conduction transport equations. Two cases have been investigated in this paper: a water flowing velocity of 1 [m/s] and a water flowing velocity of 10 [m/s]. The results indicate that the maximal surface temperature of the Crofer^®22 H reached 441.2 °C in the first case. The maximal surface temperature of the Crofer^®22 H reached 500 °C in the second case. Crofer^®22 H alloy provides excellent steam oxidation, high corrosion resistance, and thermal creep resistance. The proposed HITEC molten thermal system may be applied in the oil and gas industries and in power plants (such as the Organic Rankine Cycle). Full article

The global decarbonisation strategy has accelerated the shift toward renewable energy and electric transport, demanding advanced electrochemical energy storage systems. Conventional anodes such as graphite and silicon composites face challenges in conductivity, stability and cycling performance. MXenes, a class of two-dimensional (2D) materials, offer promising alternatives owing to their metallic conductivity, tunable surface chemistry and high theoretical capacity. Here, we synthesise and characterise Mo₂TiC₂T_x and V₂CT_x (T = O, OH, F and/or Cl) MXenes for lithium-ion battery anodes and supercapacitors. Unlike Ti₃C₂T_x, which stores charge via intercalation and surface redox reactions, Mo₂TiC₂T_x and V₂CT_x exhibit conversion-type mechanisms. We also identify novel V₂C–VO_x heterostructures, achieving a specific capacitance of 532.4 F g⁻¹ at 2 mV s⁻¹ and an initial capacity of 493.3 mAh g⁻¹ at 50 mA g⁻¹ in lithium half-cells, with a low decay rate of 0.071% per cycle over 200 cycles. Pristine Mo₂TiC₂T_x shows 391.7 mAh g⁻¹ at 50 mA g⁻¹, decaying by 0.109% per cycle. These results experimentally validate theoretical predictions, revealing how MXene structure and transition metal chemistry govern electrochemical behaviour, thus guiding electrode design for next-generation batteries and supercapacitors. Full article

The paper examines the experimental performance of air–rock bed, oil only, and oil–rock bed systems for storing heat suitable for cooking applications. The air–rock bed system is charged using hot air from a compressed air tank, while the oil–rock bed system employs a resistive heating element to heat a small volume of oil, which then circulates naturally. The charging process for the oil systems was controlled by adjusting funnel heights, and temperature measurements were taken using thermocouples connected to a data logger. Both systems can store thermal energy ranging from 4.5 kWh to 8 kWh and achieve temperatures between 150 °C and 300 °C, depending on supply temperatures. The simpler oil–rock bed allows for the direct boiling of water using the high temperature produced, and tests indicated comparable boiling times between systems. The findings suggest that these heat storage systems could enhance the advancement and integration of solar cookers, enabling more flexible cooking options. Full article

The challenge of optimally controlling energy storage systems under uncertainty conditions, whether due to uncertain storage device dynamics or load signal variability, is well established. Recent research works tackle this problem using two primary approaches: optimal control methods, such as stochastic dynamic programming, and data-driven techniques. This work’s objective is to quantify the inherent trade-offs between these methodologies and identify their respective strengths and weaknesses across different scenarios. We evaluate the degradation of performance, measured by increased operational costs, when a reinforcement learning policy is adopted instead of an optimal control policy, such as dynamic programming, Pontryagin’s minimum principle, or the Shortest-Path method. Our study examines three increasingly intricate use cases: ideal storage units, storage units with losses, and lossy storage units integrated with transmission line losses. For each scenario, we compare the performance of a representative optimal control technique against a reinforcement learning approach, seeking to establish broader comparative insights. Full article

This article analyses the possibility of using Li-ion batteries removed from battery electric vehicles (BEVs) as short-term energy storage devices in a near-zero energy building (nZEB) in conjunction with a rooftop photovoltaic (PV) system. The technical and economic feasibility of this solution was compared to that of a standard commercial LIB (Lithium-Ion battery) BESS Battery Energy Storage System). Two generations of the same BEV model battery were tested to analyse their suitability for powering a building. The necessary changes to the setup of such a battery for building power supply purposes were analysed, as well as its suitability. As a result, analyses of profitability over the predicted life span and NPV (net present value) of SLEVBs (second-life BEV batteries) for building power were carried out. The study also conducted preliminary research on the effectiveness of such projects and their pros and cons in terms of security. The author calculates the profitability of a ready-made PV BESS with a set of SLEVBs, estimating the payback periods for such investments relative to electricity prices in Poland. The article concludes on the potential of SLEVBs to support self-consumption in nZEB buildings and its environmental impact on the European circular economy. Full article

Methane, transported as Liquefied Natural Gas (LNG) at −163 °C, is becoming the leading fuel in the decarbonization of the maritime sector within the low-carbon fuels. More than 30 years of knowledge has allowed the development of an extensive offshore supply network that includes regasification plants to store and supply it to the grid, both onshore and offshore. This article first reviews the current state of the sector. Then, the operation of a typical onshore regasification plant and the heat transfer through the storage tanks that causes the generation of boil-off gas (BOG) are analyzed by means of two different methodologies. Finally, and based on the results obtained, the different improvements that can be implemented in this type of installation to improve its energy efficiency and insulation are established, such as, for example, an improvement of more than 4 W/m² by reinforcing the thickness of the materials of the tank dome. Full article

This paper presents a comparative study of data-driven modeling approaches for vanadium redox flow batteries (VRFBs), utilizing Multiple Linear Regression (MLR) and Random Forest (RF) algorithms. Experimental voltage–capacity datasets from a 1 kW/1 kWh VRFB system were digitized, processed, and used for model training, validation, and testing. The MLR model, built using eight optimized features, achieved a mean error (ME) of 0.0204 V, a residual sum of squares (RSS) of 8.87, and a root mean squared error (RMSE) of 0.1796 V on the test data, demonstrating high predictive performance in stationary operating regions. However, it exhibited limited accuracy during dynamic transitions. Optimized through out-of-bag (OOB) error minimization, the Random Forest model achieved a training RMSE of 0.093 V and a test RMSE of 0.110 V, significantly outperforming MLR in capturing dynamic behavior while maintaining comparable performance in steady-state regions. The accuracy remained high even at lower current densities. Feature importance analysis and partial dependence plots (PDPs) confirmed the dominance of current-related features and SOC dynamics in influencing VRFB terminal voltage. Overall, the Random Forest model offers superior accuracy and robustness, making it highly suitable for real-time VRFB system monitoring, control, and digital twin integration. This study highlights the potential of combining machine learning algorithms with electrochemical domain knowledge to enhance battery system modeling for future energy storage applications. Full article

This study analyzed the frequency control challenges within the West Africa Power Pool Interconnected Transmission System (WAPPITS) as it plans to incorporate variable renewable energy (VRE) resources, such as wind and solar energy. Concerns center on the ability of WAPPITS primary frequency control reserves to adapt to high VRE penetration given the synchronization and frequency control problems experienced by the three separate synchronous blocks of WAPPITS. Optimizing solutions requires a better understanding of WAPPITS’ current frequency control approach. This study used questionnaires to understand operators’ practical experience with frequency control and compared these observations to field tests at power plants and frequency response metrics during system events. Eight (8) of ten (10) Transmission System Operators (TSOs) indicated that primary frequency control service was implemented in the TSO, but nine (9) of ten TSOs indicated that the reserves provided were inadequate to meet system needs. Five (5) of ten (10) respondents answered “yes” to the provision of secondary frequency control service, while only one (1) indicated that secondary reserves were adequate. Three (3) TSOs indicated they have AGC (Automatic Generation Control) installed in the control room, but none have implemented it for secondary frequency control. The results indicate a significant deficiency in primary control reserves, resulting in a reliance on under-frequency load shedding for primary frequency control. Additionally, the absence of an AGC system for secondary frequency regulation required manual intervention to restore frequency after events. To ensure the effectiveness of battery energy storage systems (BESSs) and the reliable operation of the WAPPITS with a higher penetration of inverter-based VRE, this paper recommends (a) implementing and enforcing basic primary frequency control structures through regional regulation and (b) establishing an ancillary services market to mobilize secondary frequency control resources. Full article

Green hydrogen, produced through renewable-powered electrolysis, has the potential to revolutionize energy systems; however, its widespread adoption hinges on achieving competitive production costs. A critical challenge lies in optimising the hydrogen production process to address solar and wind energy’s high variability and intermittency. This paper explores the role of artificial intelligence (AI) in reducing and streamlining hydrogen production costs by enabling advanced process optimisation, focusing on electricity cost management and system-wide efficiency improvements. Full article

This review explores the development of energy storage technologies and governance frameworks in the Asia-Pacific region, where rapid economic growth and urbanisation drive the demand for sustainable energy solutions. Energy storage systems (ESS) are integral to balancing renewable energy fluctuations, improving grid resilience, and reducing greenhouse gas emissions. This paper examines the role of international organisations, including the United Nations, International Energy Agency (IEA), and International Renewable Energy Agency (IRENA), in promoting energy storage advancements through strategic initiatives, policy frameworks, and funding mechanisms. Regionally, the Asia-Pacific Economic Cooperation (APEC), the Association of Southeast Asian Nations (ASEAN), and the Asian Development Bank (ADB) have launched programs fostering collaboration, technical support, and knowledge sharing. Detailed case studies of Japan, Thailand, and China highlight the diverse policy approaches, technological innovations, and international collaborations shaping energy storage advancements. While Japan emphasises cutting-edge innovation, Thailand focuses on regional integration, and China leads in large-scale deployment and manufacturing. This analysis identifies key lessons from these frameworks and case studies, providing insights into governance strategies, policy implications, and the challenges of scaling energy storage technologies. It offers a roadmap for advancing regional and global efforts toward achieving low-carbon, resilient energy systems aligned with sustainability and climate goals. Full article

Electric vehicles are increasingly being used for green transportation in smart urban mobility, thus protecting environmental biodiversity and the ecosystem. Energy storage by electric vehicle batteries is a critical point of this ecologically responsible transportation. This storage is strongly linked to the different external managements related to its capacity state. The latter concerns the interconnection of storage to energy resources, charging strategies, and their complexity. In an ideal urban context, charging strategies would use wireless devices. However, these may involve complex frames and unwanted electromagnetic field interferences. The sustainable management of wireless devices and battery state conditions allows for optimized operation and minimized adverse effects. Such management includes the sustainable design of devices and monitoring of complex connected procedures. The present study aims to analyze this management and to highlight the mathematical routines enabling the design and control tasks involved. The investigations involved are closely related to responsible attitude, “One Health”, and twin supervision approaches. The different sections of the article examine the following: electric vehicle in smart mobility, sustainable design and control, electromagnetic exposures, governance of physical and mathematical representation, charging routines, protection against adverse effects, and supervision of complex connected vehicles. The research presented in this article is supported by examples from the literature. Full article

Composite electrolytes for applications in electrochemical energy technology, i.e. in batteries and supercapacitors, are gaining increasing attention. In the absence of a commonly accepted definition a ternary combination of materials, e.g. a polymer with an electrolyte salt or electrolyte salt solution and a third conductivity-enhancing constituent, is assumed as a definition of a composite electrolyte in the following review. Relevant fundamentals and reported research results up to explanations of the observed effects and improvements are reviewed. Future perspectives and directions of further research are indicated. Full article

We report on the first stage of an energy systems integration project to develop hybrid renewable energy generation and storage of hydrogen for subsequent use via research-based low regret system testbeds. This study details the design and construction of a flexible plug-and-play hybrid renewable power and hydrogen system testbed with up to 50 kW capacity aimed at addressing and benchmarking the operational parameters of the system as well as key components when commissioned. The system testbed configuration includes three different solar technologies, three different battery technologies, two different electrolyser technologies, hydrogen storage, and a fuel cell for regenerative renewable power. Design constraints include the current limit of an AC microgrid, regulations for grid-connected inverters, power connection inefficiencies, and regulated hazardous area approval. We identify and show the resolution of systems integration challenges encountered during construction that may benefit planning for the emerging pilot, or testbed, configurations at other sites. These testbed systems offer the opportunity for informed decisions on economic viability for commercial-scale industry applications. Full article

Green hydrogen and ammonia are forecast to play key roles in the deep decarbonization of the global economy. Here we explore the potential of using green hydrogen and ammonia to couple the energy, agriculture, and industrial sectors with India’s national-scale electricity grid. India is an ideal test case as it currently has one of the most ambitious hydrogen programs in the world, with projected electricity demands for hydrogen and ammonia production accounting for over 1500 TWh/yr or nearly 25% of India’s total electricity demand by 2050. We model the ambitious deep decarbonization of India’s electricity grid and half of its steel and fertilizer industries by 2050. We uncover modest risks for India from such a strategy, with many benefits and opportunities. Our analysis suggests that a renewables-based energy system coupled with ammonia off-take sectors has the potential to dramatically reduce India’s greenhouse emissions, reduce requirements for expensive long-duration energy storage or firm generating capacity, reduce the curtailment of renewable energy, provide valuable short-duration and long-duration load-shifting and system resilience to inter-annual weather variations, and replace tens of billions of USD in ammonia and fuel imports each year. All this while potentially powering new multi-billion USD green steel and maritime fuel export industries. The key risk for India in relation to such a strategy lies in the potential for higher costs and reduced benefits if the rest of the world does not match their ambitious investment in renewables, electrolyzers, and clean storage technologies. We show that such a pessimistic outcome could result in the costs of green hydrogen and ammonia staying high for India through 2050, although still within the range of their gray counterparts. If on the other hand, renewable and storage costs continue to decline further with continued global deployment, all the above benefits could be achieved with a reduced levelized cost of hydrogen and ammonia (10–25%), potentially with a modest reduction in total energy system costs (5%). Such an outcome would have profound global implications given India’s central role in the future global energy economy, establishing India’s global leadership in green shipping fuel, agriculture, and steel, while creating an affordable, sustainable, and secure domestic energy supply. Full article

More recently, researchers and the industrial community have started researching DC appliances and DC microgrids as a means of increasing the end-to-end efficiency of systems. Given the fluctuating nature of renewable resources, energy storage becomes mandatory in powering households with minimal AC grid supply, and rechargeable battery packs with maximum power point tracking controllers with inverters are used. However, this approach is not the most efficient due to losses in the power converters used in the energy supply path, while short life and environmental concerns of battery storage also come into play. With the rapid development of commercial super-capacitors, with longer life, higher power density and wider operational temperature range, this device family can be at the center of a new development era, for power converters for DC homes and DC appliances. The new family of converters and protection systems known as supercapacitor-assisted techniques is a unique new approach to minimize or eliminate batteries while improving the ETEE. These new SCA techniques are based on a new theoretical concept now published as supercapacitor-assisted loss management theory. In this paper, we will demonstrate how we extend SCALoM theory to develop SCA converters for whiteware, with the example of a DC-converted commercial double-door refrigerator with implementation details. Full article

This paper presents a study on the addition of liquefied biomass of different lignocellulosic forest residues as a means to enhance the co-electrolysis process leading to the production of synthesis gas, composed of H₂, CO, CO_2, and O₂, also known as syngas_, with the aim of a subsequent conversion into methane and methanol. Tests were made on a 1 kW prototype unit and showed that the use of liquefied biomass clearly enhances the reaction leading to syngas production. The optimisation study performed showed that the best results are obtained with an addition of 2.5% mass of liquefied biomass obtained from Acacia melanoxylon and operating conditions of a pressure of 4 bar gauge and a temperature of 110 °C. Full article

Battery Energy Storage Systems (BESSs) are critical in modernizing energy systems, addressing key challenges associated with the variability in renewable energy sources, and enhancing grid stability and resilience. This review explores the diverse applications of BESSs across different scales, from micro-scale appliance-level uses to large-scale utility and grid services, highlighting their adaptability and transformative potential. This study also includes advanced applications such as mobile energy storage, second-life battery utilization, and innovative models like Energy Storage as a Service (ESaaS) and energy storage sharing. Additionally, it discusses the integration of machine learning (ML) and large language models (LLMs), including advanced reinforcement learning (RL) algorithms, to optimize BESS operations and ensure safety through dynamic and data-driven decision-making. By examining current technologies, modeling methods, and future trends, this review provides a comprehensive overview of BESSs as a cornerstone technology for sustainable and efficient energy management, leading to a resilient energy future. Full article

Stability studies remain a crucial aspect of power systems dynamic analysis, and are typically explored in three main categories: numerical methods, linearization techniques, or direct methods, which utilize Lyapunov energy functions. This paper belongs to the third category, and highlights the usefulness of the Popov stability criterion in the analysis of nonlinear power system models. The main advantage of this criterion is that it provides conditions for global asymptotic stability of an equilibrium point, for a nonlinear dynamic system. We show a general method to apply this stability criterion, and examine its uses in several specific applications and case-studies. The results are demonstrated by analyzing the stability of a system that includes a grid-connected storage device and a renewable energy source. Full article

The precise determination of the specific heat capacity of lithium-ion cells is essential for thermal management design. Though, varying influences and insufficient parametric analyses are found in the literature. Therefore, a simple and inexpensive measurement setup is utilized to measure the specific heat capacity of cells independent of their format and dimensions. A comprehensive parametric analysis is performed assessing the effect of cell casing, cell chemistry, temperature, state-of-charge, and state-of-health. For the first time ever, a predictive analysis on material level is conducted allowing for understanding the individual factors in detail. Thus, an analytical approach for calculating the specific heat capacity can be validated by comparing predictive values to experimental data for the first time. It is found that the cell format has a significant influence on the specific heat capacity due to varying mass fractions and housing materials. Furthermore, the cell chemistry and corresponding layer thicknesses are of high importance, too. By selecting specific heat capacities for individual materials from the general literature, the analytical prediction matches the experimental data and is thus validated for the first time ever. Moreover, temperature has a positive linear effect on the specific heat capacity which can increase by up to 15% over the operating range. Furthermore, the positive temperature dependency improves the charging performance. Finally, neither SOC nor SOH significantly affect the specific heat capacity of lithium-ion cells. Full article