Abstract

Cryo-compressed vessels have many advantages in storing hydrogen for automotive applications because of large storing density and thermal endurance. However, the cooling power of venting hydrogen in the processes of dormancy and discharge is not fully utilized. A throttling valve can be used to recycle the cooling power. A thermodynamic model is established to analyze the behavior of hydrogen in the insulated pressure vessel with a throttling valve. Different initial pressures and release pressures of hydrogen in the vessel are studied in the processes of dormancy, discharge and driving. The dormancy can be extended 55% with a throttling valve in the vessels of 2 MPa release pressure. The cooling capacity of the throttling valve decreases with the increase of the initial pressure. Simulations of hydrogen storage during the actual driving are performed at different initial pressures. The throttling valve in the lowinitial- pressure vessel can reduce the upper pressure limit of the vessel by 50% which reduces the manufacturing costs obviously. This work introduces the great potential of the throttling valve in the vessel for automotive applications.

Abstract

High-temperature energy storage is very important for solar power systems with advanced thermal cycles. Manganese oxides are considerable materials for high temperature thermochemical energy storage (800-1000℃) due to the merits of low-cost and non-toxic. However, pure Mn2O3/Mn3O4 redox couple suffers low re-oxidation rate and poor cycling stability. Fe-doped Mn2O3 is expected to improve the reaction characteristics, by using a sol-gel synthesis method. The reversibility and cyclic stability are significantly enhanced by the adoption of Fe, verified by over 10 TGA experimental cycles. As to crystallographic analysis, tetragonal spinel and phases cubic spinel were detected in the reduced materials. Jacobsite (MnFe2O4) is regarded as the vital for the promotion, while (Mn0.8Fe0.2)2O3 exhibits good adaptability under different oxygen partial pressure. Lab-scaled honeycomb materials were investigated for over 100 reduction-oxidation cycles, with an average reaction ratio of 87.9%, which indicates an excellent cyclic stability of iron doped manganese oxides for solar thermochemical energy storage.

Abstract

This study aims at exploring the relationship between renewable energy consumption and carbon dioxide emissions in China, and through the significance of renewable energy consumption, the hypothesis of environmental Kuznets curve at individual country level is tested as well as. Autoregressive distributes lag bounds testing approach is employed for empirical analysis. The results show that a quadratic relationship between renewable energy and CO2 emission has been found for the period support EKC relationship, and there exists a negative causality from renewable energy consumption to CO2 emissions.

Abstract

The current centralised, fossil fuel-reliant energy system is experiencing a gradual transition to a more decentralised system, particularly in cities where decentralised energy resources (DER) largely based on renewable sources can help alleviate chronic environmental problems. This transition gave rise to the concept that the pervasion of sensors, embedded systems and ubiquitous network connectivity in urban energy systems (UES) could enhance the overall quality of life through so-called “smart cities” and “smart grids.” A comprehensive analysis of recent reviews of EU-funded projects has elucidated a range of good practices, regarding stakeholder engagement, citizen participation, funding, technologies and demand-side management. Coupled with suitable modelling frameworks accurate analysis of synergies between generation assets, storage solutions and demand-side management (DSM) interventions is possible. Three dominant conceptual models have been identified: the energy hub, the microgrid and the virtual power plant. The technical characteristics can be transferred to the framework structure to be developed for optimising the energy system of the “Fiera del Levante” exhibition complex in the southern Italian city of Bari, which is characterized by a highly variable energy demand scenario. This paper describes the proposed methodology for this case study, which is strongly linked to the Technology Selection and Operation (TSO) model developed at Imperial College London.

Abstract

The evaporative cooling technique has gained growing attention for use in air conditioning systems. A hybrid evaporative pre-cooled air-conditioning system has been proposed. An indirect evaporative heat exchanger (IEHX) is adopted as a pre-cooling device before the conventional mechanical vapour compression unit. The present work aims to develop a numerical model for the IEHX to study the pre-cooling performance by using the room exhaust air as the working air. A computational model has been developed to investigate the heat and mass transfer in the indirect evaporative heat exchanger. It can be inferred that the evaporative pre-cooling unit is able to reduce the air temperature and condense water through the IEHX. Consequently, the hybrid evaporative pre-cooled air-conditioning system is able to achieve a potential energy saving due the pre-cooling effect and the improvement of the chiller’s efficiency.

Abstract

In this paper, the peaking capability of the thermal power unit is maximized, and the wind power accommodation as much as possible. A mathematical model of in depth peak load cycling of the thermal power unit under the condition of wind power integration is proposed, and optimal operation of thermal power unit in depth peak load cycling. Based on the actual data of a provincial power grid in China, the economics of the thermal power unit in depth peak load cycling scheme under large-scale wind power integration are analyzed. The research results show that the adoption of thermal power unit in depth peak load cycling scheme can not only stabilize wind power fluctuation, solve the problem of wind power accommodation, but also save the generation cost of thermal power unit, making it feasible to ”depth peak load cycling and wind power accommodation”.

Abstract

A reliable prediction of energy consumption is crucial for a reasonable building energy management. Considering the uncertain principles of annual electricity consumption with limited datasets, a modified grey interval prediction model abbreviated as BOGIM(1,1) is proposed in this paper. Firstly, the changing patterns of annual series were detected, in order to lower the uncertainty. Afterwards, the predicted intervals were obtained with modified BOGIM(1,1), in which various weakening and enhancing buffer operators were added simulate different future operation scenarios. Finally, the adaptability of this model is summarized based on recognized patterns and predicted accuracy. Specifically, 92 office buildings in Beijing of China were adopted to test the BOGIM(1,1) model. Results show that this proposed model outperforms the traditional GM(1,1) by improving the prediction accuracy for almost 90% of the buildings up to 18.45%, and it is more applicable for target-oriented energy policies.

Abstract

An appropriate battery model is crucial for accurate state of charge (SOC) estimation of lithium-ion batteries. A complex battery model can improve the accuracy, however, it leads to high computational cost. In this paper, the second-order resistor-capacitor (RC) model is selected due to its superiority in good balance between accuracy and complexity. Different factors, including RC parameters of battery model, relationship between open circuit voltage (OCV) and SOC, and measurement noise are investigated to extract the ones that significantly affect the accuracy of SOC estimation based on Kalman filters. The results revealed that in comparison with the resistors, the polarization capacitors have no obvious influence on the SOC estimation. In addition, the voltage measurement noise has greater influence on the SOC estimation compared with the current measurement noise. These results can be potentially used to guide us in deciding which parameters should be separately identified online and offline so as to achieve a proper balance between model accuracy and complexity.

Abstract

This present study uses a panel of 24 countries over the period of 1990-2015 to analyze proposed determinants of energy consumption in Africa. The panel is categorized into LI, LMI and UMI African economies. Applying econometric tests and DCCE estimator through a specified DHPD model, issues of heterogeneity and cross-sectional reliance were considered. Our established findings indicated that, GDP, OP, URB, and POPg are potential drivers of EC when capital stock and labor are used as control variables. Further, with the exception of URB-EC, POPg-EC, POPg-GDP, and POPg-URB nexus whose direction of causality were common across country groups, variations occurred for the causalities amid GDP-EC, OP-EC, OP-GDP and URB-GDP nexus for the different income level groups. We therefore conclude that, factors unique to the various country groups in terms of income levels influence the causal affiliations between analyzed variables. Policy recommendation are briefly discussed.

Abstract

Solid oxide fuel cell (SOFC) was integrated with internal combustion engine (ICE) due to its high operating temperature for improving the energy conversion efficiency in this work. In the SOFC-ICE hybrid energy conversion system, the SOFC anode off-gas with high temperature and combustible fuels is used as the ICE fuel for additional power generation. To evaluate the thermo-economic performance, the thermo-economic model of the hybrid system is developed for the economic analysis. The results showed that the specific electric energy cost (SEEC) of the hybrid system is 3.75 ￠/kWh, which is lower than that of a standard power plant. Through the further analysis, the capital investment cost of the system with the net output power of 470 kW is 50.5 k$, which includes the capital cost of auxiliary devices such as heat exchanger and compressors. In addition, the SOFC accounts for about 35% of the system’s capital cost. The annual cost of the system under the cycle life of 10 years is calculated to be approximately 15.6 k$. Moreover, the influence of operating parameters on thermo-economic performance of the hybrid system is also investigated to optimize the thermo-economic performance. Finally, the corresponding payback period of this system is approximately 6.8 years and the annual return on investment is 4.6%. These results reveal that the proposed NG-fueled SOFC-HCCI engine hybrid system presents a broad market prospect in the practical applications.