Frontiers in Energy最新文献

Compressed CO₂ energy storage (CCES) system has received widespread attention due to its superior performance. This paper proposes a novel CCES concept based on gas-liquid phase change and cold-electricity cogeneration. Thermodynamic and exergoeconomic analyses are performed under simulation conditions, followed by an investigation of the impacts of various decision parameters on the proposed system. Next, a multi-objective optimization is conducted with the total energy efficiency and total product unit cost as the objective functions. Finally, brief comparisons are made between the proposed system and existing systems. The results indicate that the total energy efficiency of the proposed system reaches 79.21% under the given simulation conditions, outperforming the electrical efficiency of 61.27%. Additionally, the total product unit cost of the system is 25.61 $/GJ. A key component, T1, plays an important role due to its large exergy destruction rate (1.0591 MW) and total investment cost rate (154.85 $/h). Despite this, the exergoeconomic factors of T1 is only 41.08%, indicating that investing in T1 to improve the efficiency is practicable. The analysis shows that a lower CO₂ condensation temperature benefits the proposed system performance. While improving the isentropic efficiencies of the compressors and turbines enhances total energy efficiency, excessive isentropic efficiencies can lead to a significant increase in total product unit cost. Through multi-objective optimization, an optimal favorable operating condition is identified, yielding a compromise result with a total energy efficiency of 111.91% and a total product unit cost of 28.35 $/GJ. The proposed CCES system efficiently delivers both power and cooling energy, demonstrating clear superiorities over previous systems.

Proton exchange membrane (PEM) electrolyzer (EL) is regarded as a promising technology for hydrogen generation, offering load flexibility for electric grids (EGs), especially those with a high penetration of renewable energy (RE) sources. This paper proposes a PEM-focused economic dispatch strategy for EG integrated with wind-electrolysis systems. Existing strategies commonly assume a constant efficiency coefficient to model the EL, while the proposed strategy incorporates a bottom-up PEM EL model characterized by a part-load efficiency curve, which accurately represents the nonlinear hydrogen production performance, capturing efficiency variations at different loads. To model this, it first establishes a 0D electrochemical model to derive the polarization curve. Next, it accounts for the hydrogen and oxygen crossover phenomena, represented by the Faraday efficiency, to correct the stack efficiency curve. Finally, it includes the power consumption of ancillary equipment to obtain the nonlinear part-load system efficiency. This strategy is validated using the PJM-5 bus test system with coal-fired generators (CFGs) and is compared with a simple EL model using constant efficiency under three scenarios. The results show that the EL modeling method significantly influences both the dispatch outcome and the economic performance. Sensitivity analyses on coal and hydrogen prices indicate that, for this case study, the proposed strategy is economically advantageous when the coal price is below 121.6 $/tonne. Additionally, the difference in total annual operating cost between using the efficiency curve anda constant efficiency to model becomes apparent when the hydrogen price ranges from 2.9 to 5.4 $/kg.

The solid oxide fuel cell (SOFC) power system fueled by NH₃ is considered one of the most promising solutions for achieving ship decarbonization and carbon neutrality. This paper addresses the technical challenges faced by NH₃ fuel SOFC ship power system, including slow hydrogen (H₂) production, low efficiency, and limited space. It introduces an innovative a NH₃-integrated reactor for rapid H₂ production, establishes a safe and efficient all-electric SOFC all-electric propulsion system adaptable to various sailing conditions. The system is validated using a 2 kW prototype experimental rig. Results show that the SOFC system, designed for a target ship, has a rated power of 96 kW and an electrical efficiency of 60.13%, meeting the requirements for rated cruising conditions. Under identical catalytic scenarios, the designed reactor, with highly efficient heat transfer, measuring 1.1 m in length, can achieve complete NH₃ decomposition within 2.94 s, representing a 35% reduction in cracking time and a 42% decrease in required cabin space. During high-load voyage conditions, adjusting the circulation ratio (CR) and ammonia-oxygen ratio (A/O) improves system efficiency across a wide operational range. Among these adjustments, altering the A/O ratio proves to be the most efficient strategy. Under this configuration, the system achieves an efficiency of 55.02% at low load and 61.73% at high load, allowing operation across a power range of 20% to 110%. Experimental results indicate that the error for NH₃ cracking H₂ is less than 3% within the range of 570–700 °C, which is relevant to typical ship operation scenarios. At 656 °C, the NH₃ cracking H₂ rate reaches 100%. Under these conditions, the SOFC produces 2.045 kW of power with an efficiency of approximately 58.66%. The noise level detected is 58.6 dB, while the concentrations of CO₂, NO, and SO₂ in the flue gas approach zero. These findings support the transition of the shipping industry to green, clean systems, contributing significantly to future reductions in ocean carbon emissions.

Phase change energy storage technology has great potential for enhancing the efficient conversion and storage of energy. While triply periodic minimal surface (TPMS) structures have shown promise in improving heat transfer, research on their application in phase change heat transfer remains limited. This paper presents numerical simulations of composite phase change materials (PCMs) featuring TPMS skeletons, specifically gyroid, diamond, primitive, and I-graph and wrapped package-graph (I-WP) utilizing the lattice Boltzmann method (LBM). A comparative analysis of the effects of four TPMS skeletons on enhancing the phase change process reveals that the PCM containing the gyroid skeleton melts the fastest, with a complete melting time of 24.1% shorter than that of the PCM containing the I-WP skeleton. The PCM containing the gyroid skeleton is further simulated to explore the effects of the Rayleigh (Ra) number, Prandtl (Pr) number, and Stefan (Ste) number on the melting characteristics. Notably, the complete melting time is reduced by 60.44% when Ra is increased to 10⁶ compared to the case with Ra at 10⁴. Increasing the Pr number accelerates the migration of the mushy zone, resulting in fast melting. Conversely, the convective heat transfer effect from the heating surface decreases as the Ste number increases. The temperature differences caused by the local thermal non-equilibrium (LTNE) effect over time are significant and complex, with peaks becoming more pronounced nearer the heating surface. This study intends to provide theoretical support for the further development of TPMS skeletons in enhancing the phase change process.

Geothermal energy is clean and renewable, derived from the heat stored within accessible depths of the Earth’s crust. The adoption of a single-well system for medium-deep and deep geothermal energy extraction has attracted significant interest from the scientific and industrial communities because it effectively circumvents issues such as downhole inter-well connections and induced seismicity. However, the low heat transfer capacity in geothermal formations limits the heat extraction performance of single-well systems and hinders their commercial deployment. This review covers various enhancement concepts for optimizing the heat transfer within single-well systems, emphasizing critical parameters such as heat transfer area, heat transfer coefficient, and temperature difference. Additionally, it presents the thermo-economic evaluation of different configurations of single-well borehole heat exchangers and superlong gravity heat pipes (SLGHPs). The SLHGP, utilizing phase-change heat transfer, is recognized as a highly effective and continuously productive technology, capable of extracting over 1 MW of heat. Its pumpless operation and ease of installation in abandoned wells make it cost-effective, offering a promising economic advantage over traditional geothermal systems. It also highlights the challenges and potential research opportunities that can help identify gaps in research to enhance the performance of single-well geothermal systems.

This study explores the structural, electronic, and optical properties of tin-based halide perovskites, MSnX₃ (M = Li, Na; X = Cl, Br, I), under varying pressure conditions. Using volume optimization and the Perdew-Burke-Ernzerhof generalized gradient approximation (PBE-GGA) method, it analyzes these perovskites in their cubic Pm (Pm bar{3} m) phase. The findings reveal that the lattice constants of these compounds decrease as pressure increases, with more pronounced changes observed when anions are substituted from Cl to I. The electronic analysis shows that these materials maintain their direct band gap nature under pressures, although the band gaps narrow with increasing pressure and larger anion sizes. Notably, Li/NaSnCl₃, Li/NaSnBr₃, and Li/NaSnI₃ may exhibit metallic behavior at pressures exceeding 5 GPa. Optical studies reveal significant pressure-induced enhancements in static dielectric constant and optical absorption, especially in the visible spectrum, highlighting the potential of these perovskites for solar cell applications. The refractive index increases with pressure, indicating a higher material density and enhanced optical performance. Additionally, the extinction coefficient and electron energy loss function provide insights into the energy absorption and scattering characteristics, which are crucial for improving the efficiency of optoelectronic devices. This comprehensive analysis underscores the potential of these tin-based halide perovskites for advanced optoelectronic and photovoltaic technologies.

Compressed air energy storage (CAES) is an effective technology for mitigating the fluctuations associated with renewable energy sources. In this work, a hybrid cogeneration energy system that integrates CAES with high-temperature thermal energy storage and a supercritical CO₂ Brayton cycle is proposed for enhancing the overall system performance. This proposal emphasizes system cost-effectiveness, eco-friendliness, and adaptability. Comprehensive analyses, including thermodynamic, exergoeconomic, economic, and sensitivity evaluations, are conducted to assess the viability of the system. The findings indicate that, under design conditions, the system achieves an energy storage density, a round-trip efficiency, an exergy efficiency, a unit product cost, and a dynamic payback period of 5.49 kWh/m³, 58.39%, 61.85%, 0.1421 $/kWh, and 4.81 years, respectively. The high-temperature thermal energy storage unit, intercoolers, and aftercooler show potential for optimization due to their suboptimal exergoeconomic performance. Sensitivity evaluation indicates that the operational effectiveness of the system is highly sensitive to the maximum and minimum air storage pressures, the outlet temperature of the high-temperature thermal energy storage unit, and the isentropic efficiencies of both compressors and turbines. Ultimately, the system is optimized for maximum exergy efficiency and minimum dynamic payback period. These findings demonstrate the significant potential of this system and provide valuable insights for its design and optimization.

The environmental impacts of hydrogen production can vary widely depending on the production energy source and process. This implies that the collection and management of sustainability data for hydrogen production globally is desired to ensure accountable development of the sector. Life cycle assessment (LCA) is an internationally recognized tool for environmental impact assessment. Integrating LCA in the holistic evaluation of the hydrogen value chain is desirable to ensure the cleanness and sustainability of the various available hydrogen production pathways. The objective of this review is to evaluate the methodology used in assessing the life cycle impact of hydrogen production including proposed documentation such as the guarantee of origin (GO) and certification schemes, and review case studies from Australia. An analysis of the sustainability strategies and schemes designed by the Australian government, aimed at mitigating climate change and promoting the hydrogen economy, was conducted. The case studies that were discussed identified the preferred available scaled routes of clean hydrogen production to be water electrolysis, which is based on technologies using renewable energy. Other dominant technologies which incorporate carbon capture and storage (CCS) were envisaged to continue playing a role in the transition to a low carbon economy. Additionally, it is critical to assess the greenhouse gas (GHG) emissions using appropriate system boundaries, in order to classify clean hydrogen production pathways. Harmonizing regulatory stringency with appropriate tracking of renewable electricity can promote clean hydrogen production through certification and GO schemes. This approach is deemed critical for the sustainable development of the hydrogen economy at the international level.

Carbon dioxide, as a greenhouse gas, is expected to be converted into other useful substances by the electrocatalytic CO₂ reduction reaction (CO₂RR) technology. The electrocatalytic cell, or electrochemical cell, used to provide the experimental environment for CO₂RR plays an irreplaceable role in the study of this process and determines the success or failure of the measurements. In recent years, electrolytic cells that can be applied to in-situ/operational synchrotron radiation (SR) characterization techniques have gradually gained widespread attention. However, the design and understanding of electrolyte systems that can be applied to in-situ/operational SR technologies are still not sufficiently advanced. In this paper, the electrocatalytic cells used to study the CO₂RR processes with in-situ/operando SR techniques are briefly introduced, and the types and characteristics of the electrolytic cells are analyzed. The recent advancements of in situ/operando electrolytic cells are discussed using X-ray scattering, X-ray absorption spectroscopy (XAS), light vibration spectroscopy, and X-ray combined techniques. An outlook is provided on the future prospects of this research field. This review facilitates the understanding of the reduction process and electrocatalytic mechanism of CO₂RR at the atomic and molecular scales, providing insights for the design of electrolysis cells applicable to SR technologies and accelerating the development of more efficient and sustainable carbon negative technologies.