Abstract

Two-step solar thermochemical cycles (STC) for H2O and CO2 splitting is a promising technology to produce solar fuel. Reaching up to higher solar-to-fuel efficiencies (e.g., >10%) relies on not only the selection of efficient redox materials, but also devising effective solar reactors. We propose a hemispherical STC reactor design with spectral-selective window for solar flux homogenization and solar collection efficiency enhancement. The new geometry effectively increases the percentage of redox oxide between 1500-1700 °C from 89.8% (for a cylindrical geometry) to 97.6% at 15 kW irradiation. A thermodynamic model is developed, taking into account the geometry, reactions, conservations, spectral selectivity and all the major energy losses. Results show that for a typical ceria-based temperature-swing STC in the range of 900-1600 °C combined with inert gas purging and vacuum pumping, the spectral-selective transmissive coating significantly reduces the re-radiation loss by 69.56%. With solar concentration ratio of 5263, the reactor heating rate increases from 172 °C min-1 to 194 °C min-1, decreasing the incident solar energy demand from 703 J g-1oxide to 621 J g-1oxide. More importantly, the solar-to-fuel efficiency increases from 10.58% to 12.14%. Spectral selectivity lowers re-radiation loss (>70%) and effectively maintains high collector efficiency and solar-to-fuel efficiency at low concentration ratios (C<3000).

Abstract

Urban traffic emissions from vehicle fuel pose significant challenges to urban sustainability. Revealing urban traffic emission patterns is crucial for effective urban planning. Current research often overlooks the spatial interaction links facilitated by traffic flows. This oversight limits our ability to map the attribution of emissions from vehicular travels between different locations. To this end, our study introduces a novel perspective and corresponding methodologies to reveal emission patterns of urban traffic. Utilizing extensive, all-day activity data from individual vehicles across multiple types, this research quantifies CO2 and NOX emissions from vehicular travels within the urban center of the case city. This quantification of emissions defines the link weights in the construction of the Urban Traffic Flows Emission Network (UTFEN). Applying complex network theory, this study uncovers emission patterns within UTFEN, ranging from the micro to the macro level. Our findings demonstrate that private car emissions exhibit a bimodal fluctuation throughout the day, whereas truck emissions peak at noon. Micro-level network analysis shows that nodes linked to high-emission links are predominantly situated at the city’s ingress and egress points, with these high-emission links displaying a certain degree of directional consistency. At the macro level, statistical measures expose significant structural differences in networks composed of different vehicle types. Additionally, statistical analysis indicates that the link emission distribution within UTFEN follows a power law distribution, revealing the heterogeneity of emissions of spatial interaction traffic flows. This study offers a network perspective on urban traffic emission patterns, offering data-driven insights critical for formulating sustainable urban traffic strategies.

Abstract

The planning of urban low-carbon energy transition needs to be supported by scientific methods. However, current methods cannot integrate energy and social systems well. Conceptual frameworks can overcome this by expanding the research scope and identifying inter-disciplinary relationships, but it lacks quantitative approaches. This paper proposes an urban low-carbon energy planning method, which uses Fuzzy Cognitive Maps (FCM) to quantitatively integrate energy modeling and stakeholder network maps (SNM) based on Energy systems-Sustainability-Governance-Operation (ESGO) Conceptual Framework. The method includes 5 steps: 1) Propose a Conceptual Framework to explain the interactions between energy and social systems; 2) Energy System Modeling; 3) Social System Modeling; 4) Construct FCM; 5) Multi-scenario Analysis. A case study on Shanxi Transition Comprehensive Reform Demonstration (STCRD) Zone is used to verify the method feasibility. The results indicate that: 1) The method is feasible by depicting the interactions between social relations and energy technology changes; 2) The case study implicates energy saving is preferable in order to achieve carbon emission targets. Stakeholders’ inclination towards low-carbon emissions is inducive to economic growth. Plans need to repeatedly adjust resource allocation and control the transition rhythm according to actual situations while maintaining long-term goals.

Abstract

Electric vehicles are essential for decarbonizing transport, though many challenges lie ahead. One issue that has received recent attention is the gap between real-world battery energy consumption and results from laboratory tests, especially in winter, where the operational status of thermal management system (TMS), including air conditioning (AC) system, varies greatly. Despite the critical importance of TMS for safety anddriving range performance, the precise contribution of TMS to battery and cabin energy consumption remains elusive. Through a comprehensive expermental analysis of the energy flow characteristics and consumption patterns of a certain four-wheel-drive multi-purpose vehicle (MPV) under diverse low-temperature conditions (-7 °C, -20 °C), we elucidated the operational traits of the primary energy-consuming components in cold environments, with particular emphasis on the vehicle’s overall energy consumption. Based on the standardized CLTC-P test procedure, our experimental findings reveal a pronounced increase in the overall energy consumption of EVs in low-temperature environments, with energy consumption recorded as 6.8 kW.h, and 8.9 kW.h, respectively. Notably, the energy consumption attributed to the battery thermal management system accounts for 54.0 %, and 59.8 %, while the propulsion system’s motor drive energy consumption represents 43.8 %, and 38.0 %, respectively. Furthermore, under the two low-temperature conditions, the activation of the air conditioning system incurs an additional energy consumption of 16.60 %, and 18.44 %, respectively. Notably, the energy consumption surge is more pronounced when the air conditioning is activated, with energy consumption increasing by up to 287.65 % at -20 °C, compared with the standard working condition, corresponding to a 74.20 % decline in driving range, which further elucidating the mechanistic effects of temperature variations on the performance of the thermal management system in electric vehicles. These research findings not only contribute to a deeper understanding of the energy utilization status of electric vehicles in adverse climate conditions but also provide crucial guidance for the design of more environmentally sustainable and efficient electric vehicles, thereby promoting the development of sustainable transportation systems.

Abstract

With the excessive use of fossil energy and concern for environmental protection, coal coke gasification as an clean means of energy utilization has received widespread attention worldwide. Coal catalytic gasification is an effective way to realize clean coal utilization. The catalytic gasification technology of coke and CO2 has the advantages of low reaction temperature, small energy consumption and low CO2 emission. In this study, the catalytic effect of alkali metals, alkaline earth metals, transition metals and rare earth on the reaction between coke and CO2 was investigated by using a self-made gas-solid reaction device. It was concluded that in the gasification reaction between coal coke and CO2 at 1173K, the performance of K2CO3 catalyst was the best. Under the condition of wet mixing, the conversion rate of K2CO3 was 98.8%, and τ50% was 40.6min. The metal compound catalyst of Ca, Fe in wet mixing and dry mixing conditions had little effect on the coal coke -CO2 gasification. Thus, K and Ce was kinds of efficient catalyst and will be used as a promising catalyst for coal char CO2 gasification.

Abstract

Isobaric compressed air energy storage is a pivotal technology enabling the extensive deployment of renewable energy in coastal regions. Recently, there has been a surge in research integrating isobaric compressed air energy storage with various renewables. However, there remains a significant shortage of experimental verifications. This paper presents an experimental study on the discharge process of a megawatt isobaric compressed air energy storage system, revealing the regulation characteristics of the start-up, isobaric discharge operation, and shut-down processes. Experiments show that the energy storage system has reliable and rapid regulation characteristics, with vibration less than 41um, cold start time not exceeding 5 min, and shut down within 2 min. The storage system with a flexible storage device can fully utilize the stored compressed air while maintaining stable pressure at the compressor outlet and turbine inlet. The findings of this study lay the foundation for the actual application of isobaric compressed air energy storage systems in the development and utilization of renewable energy along coastal areas.

Abstract

In this study, we systematically investigated an environmental-benign kinetic promoter (L-leucine, L-Leu) coupling magnesium to enhance CO2 hydrate formation at the pressure of 3.5 MPa and temperature of 275.2 K. The induction time (tind) of CO2 hydrate was reduced to 696.65 minutes in the addition of 1.0 wt% L-leu. When magnesium was introduced to enhance CO2 hydrate formation, it showed a superior promotion effect on reducing tind to less than 10 s. In pure water, the dense CO2 hydrate film at the gas-liquid interface blocked the mass transfer and the CO2 gas uptake was 10.44 Vg/Vw. Therefore, magnesium was applied to trig CO2 hydrate nucleation coupling L-leu to realize rapid CO2 hydrate formation, followed by rapid P drop with the CO2 gas uptake of 78.77 Vg/Vw. In the coupling system, CO2 hydrate formation rate was promoted effectively with the t90 of 85.08 min under the static condition. This work contributes to offering considerable enhancement in the kinetic process of CO2 hydrate formation. which can be utilized for various hydrate-based technologies such as CO2 sequestration.

Abstract

China’s carbon emissions from the building sector have exceeded 50% of the national total emissions. Energy saving and carbon reduction in the building sector is of great significance to China’s “doublecarbon” strategy. In this study, the future development of the building sector in Shaanxi Province is divided into a baseline scenario (BAS), a low-carbon peak scenario (LCS), and an enhanced low-carbon scenario (ELS), using static forecasts and Monte Carlo simulations. The results show that the probability of BAS peaking before 2030 is only 19.9%; the peak time of LCS is around 2030, and its probability of peaking before 2030 is 65.05%; and in ELS, the probability of peaking is 2026, and the probability of peaking before 2030 is 99.9%. The peaks of BAS, LCS and ELS are 101.97 million tons, 97.97 million tons and 91.28 million tons, respectively, indicating that the enhanced energy conservation measures and the adjustment of the energy-use structure have an obvious effect on the control of carbon emissions. The results of the thesis provide a reference for the formulation and implementation of energy conservation and emission reduction policies and measures in the building sector, and provide suggestions for the path to carbon peaking in the building sector.

Abstract

Solar thermochemical cycling, in which concentrated solar energy is used to split water and produce hydrogen, is considered a promising way to produce green hydrogen in the future. Nonetheless, it encounters issues, including elevated reaction temperatures and significant deoxygenation losses. Here, we propose a high-efficiency solar thermochemical cycling system for hydrogen production driven by carbonaceous agents and establish a thermo-kinetic model for isothermal pressure-swing cycles. Carbon monoxide is introduced as a reducing agent into the reduction reaction, decreasing the Gibbs free energy of oxygen vacancies generated by metal oxygen carriers to lower the reduction temperature while consuming oxygen to create an extremely low oxygen partial pressure environment. This system avoids the problem of large energy losses in traditional deoxygenation methods such as inert sweeping gases and vacuum pumps; moreover, it achieves a synergistic decrease in the reaction temperature and oxygen partial pressure during the thermochemical cycle. The theoretical solar energy to fuel conversion efficiencies of this system under isothermal cycling at 1300 °C can reach 19.89% and 23.77% with only water heat recovery when CeO 2-δ and Ce0.80 Zr0.20 O2-δ are used as oxygen carriers, respectively. This research contributes a fresh idea to the problem of the high reaction temperatures and large irreversible losses in the solar thermochemical cycle for hydrogen production.

Abstract

To address climate change, distributed energy system shall explore a synergistic pathway towards high efficiency and low carbon emissions while ensuring the continuity, stability and variety of energy supply. We propose a novel distributed energy system featuring the integration of methanol steam reforming, metal alloy-based hydrogen separation, proton exchange membrane fuel cells and CO2 capture. Methanol, as a convenient, stable, and economical medium for hydrogen storage and on-demand power generation, serves as a transition fuel between current and future energy systems. Using the toxicity-resistant LaNi4.3Al0.7, hydrogen is absorbed from methanol reformate gas containing CO and water vapor at 180 °C and then released through isothermal depressurization. Simultaneously, the tail gas from the hydrogen separation unit undergoes oxy-fuel combustion, achieving CO2 capture with low energy consumption. Subsequently, the proton exchange membrane fuel cells efficiently convert hydrogen to electricity, with the waste heat being exchanged to supply hot water. The models of reformer, metal alloy-based hydrogen separation unit and proton exchange membrane fuel cells are validated by experimental data from the literature. The analysis demonstrates that at 100 mol h-1 methanol flow rate, 250 °C reaction temperature and 8 bar absorption pressure, total electrical efficiency and total energy efficiency of the proposed system are 40.05% and 88.00%, respectively, which are 5.99 and 1.2 percentage points higher than those of the reference system with conventional pressure swing adsorption method. Meanwhile, the total exergy efficiency of the proposed system is 43.38%, which is 5.5 percentage points higher than the reference system. The system enables an efficient on-demand supply of power and heat, the potential for reducing CO2 emission, and compatibility with future energy systems.