Frontiers in Energy最新文献

Intelligent power systems can improve operational efficiency by installing a large number of sensors. Data-based methods of supervised learning have gained popularity because of available Big Data and computing resources. However, the common paradigm of the loss function in supervised learning requires large amounts of labeled data and cannot process unlabeled data. The scarcity of fault data and a large amount of normal data in practical use pose great challenges to fault detection algorithms. Moreover, sensor data faults in power systems are dynamically changing and pose another challenge. Therefore, a fault detection method based on self-supervised feature learning was proposed to address the above two challenges. First, self-supervised learning was employed to extract features under various working conditions only using large amounts of normal data. The self-supervised representation learning uses a sequence-based Triplet Loss. The extracted features of large amounts of normal data are then fed into a unary classifier. The proposed method is validated on exhaust gas temperatures (EGTs) of a real-world 9F gas turbine with sudden, progressive, and hybrid faults. A comprehensive comparison study was also conducted with various feature extractors and unary classifiers. The results show that the proposed method can achieve a relatively high recall for all kinds of typical faults. The model can detect progressive faults very quickly and achieve improved results for comparison without feature extractors in terms of F1 score.

First, a brief introduction is made to the four basic judgments and understandings of the goals of “carbon peaking and carbon neutrality.” Then, an in-depth elaboration is provided on the eight major strategies for achieving the goals of “carbon peaking and carbon neutrality,” including conservation and efficiency priority, energy security, non-fossil energy substitution, re-electrification, resource recycling, carbon sequestration, digitalization and cooperation between countries. Next, eight major implementation paths for achieving the goals of “carbon peaking and carbon neutrality” are discussed in detail, including industrial restructuring; building a clean, low-carbon, safe and efficient energy system, and renewing the understanding of China’s energy resource endowment; accelerating the construction of a new-type power system with a gradually growing proportion of new energy, and realizing the “possible triangle” of high-quality energy system development; utilizing electrification and deep decarbonization technologies to promote the orderly peaking and gradual neutralization of carbon emissions in the industrial sector; promoting the low-carbon transition of transportation vehicles to achieve carbon peaking and carbon neutrality in the transportation sector; focusing on breaking through key green building technologies to achieve zero carbon emissions from building electricity and heat; providing a strong technical support for carbon removal to achieve carbon neutrality; accelerating the construction of the integrated planning and assessment mechanism for pollution and carbon reduction, establishing a sound strategy, planning, policy and action system, and optimizing the carbon trading system. Afterwards, it is particularly pointed out that the realization of the goals of “carbon peaking and carbon neutrality” cannot be separated from the support of sci-tech innovation. Finally, it is stressed that carbon neutrality is not the end, but an important milestone. If viewed from the perspective of future energy, the significance and historical status of the goals of “carbon peaking and carbon neutrality” will be more understandable.

Peer-to-peer (P2P) energy trading is an emerging energy supply paradigm where customers with distributed energy resources (DERs) are allowed to directly trade and share electricity with each other. P2P energy trading can facilitate local power and energy balance, thus being a potential way to manage the rapidly increasing number of DERs in net zero transition. It is of great importance to explore P2P energy trading via public power networks, to which most DERs are connected. Despite the extensive research on P2P energy trading, there has been little large-scale commercial deployment in practice across the world. In this paper, the practical challenges of conducting P2P energy trading via public power networks are identified and presented, based on the analysis of a practical Local Virtual Private Networks (LVPNs) case in North Wales, UK. The ongoing efforts and emerging solutions to tackling the challenges are then summarized and critically reviewed. Finally, the way forward for facilitating P2P energy trading via public power networks is proposed.

Liquid metal-based microchannel heat sinks (MCHSs) suffer from the low heat capacity of coolant, resulting in an excessive temperature rise of coolant and heat sink when dealing with high-power heat dissipation. In this paper, it was found that expanded space at the top of fins could distribute the heat inside microchannels, reducing the temperature rise of coolant and heat sink. The orthogonal experiments revealed that expanding the top space of channels yielded similar temperature reductions to changing the channel width. The flow and thermal modeling of expanded microchannel heat sink (E-MCHS) were analyzed by both using the 3-dimensional (3D) numerical simulation and the 1-dimensional (1D) thermal resistance model. The fin efficiency of E-MCHS was derived to improve the accuracy of the 1D thermal resistance model. The heat conduction of liquid metal in Z direction and the heat convection between the top surface of fins and the liquid metal could reduce the total thermal resistance (R_t). The above process was effective for microchannels with low channel aspect ratio, low mean velocity (U_m) or long heat sink length. The maximum thermal resistance reduction in the example of this paper reached 36.0%. The expanded space endowed the heat sink with lower pressure, which might further reduce the pumping power (P). This rule was feasible both when fins were truncated (h₂ < 0, h₂ is the height of expanded channel for E-MCHS) and when over plate was raised (h₂ > 0).

The increasing use of distributed energy resources changes the way to manage the electricity system. Unlike the traditional centralized powered utility, many homes and businesses with local electricity generators have established their own microgrids, which increases the use of renewable energy while introducing a new challenge to the management of the microgrid system from the mismatch and unknown of renewable energy generations, load demands, and dynamic electricity prices. To address this challenge, a rank-based multiple-choice secretary algorithm (RMSA) was proposed for microgrid management, to reduce the microgrid operating cost. Rather than relying on the complete information of future dynamic variables or accurate predictive approaches, a lightweight solution was used to make real-time decisions under uncertainties. The RMSA enables a microgrid to reduce the operating cost by determining the best electricity purchase timing for each task under dynamic pricing. Extensive experiments were conducted on real-world data sets to prove the efficacy of our solution in complex and divergent real-world scenarios.

Wind power (WP) is considered as one of the main renewable energy sources (RESs) for future low-carbon and high-cost-efficient power system. However, its low inertia characteristic may threaten the system frequency stability of the power system with a high penetration of WP generation. Thus, the capability of WP participating in the system frequency regulation has become a research hotspot. In this paper, the impact of WP on power system frequency stability is initially presented. In addition, various existing control strategies of WP participating in frequency regulation are reviewed from the wind turbine (WT) level to the wind farm (WF) level, and their performances are compared in terms of operating principles and practical applications. The pros and cons of each control strategy are also discussed. Moreover, the WP combing with energy storage system (ESS) for system frequency regulation is explored. Furthermore, the prospects, future challenges, and solutions of WP participating in power system frequency regulation are summarized.

In modern times, worldwide requirements to curb greenhouse gas emissions, and increment in energy demand due to the progress of humanity, have become a serious concern. In such scenarios, the effective and efficient utilization of the liquified natural gas (LNG) regasification cold energy (RCE), in the economically and environmentally viable methods, could present a great opportunity in tackling the core issues related to global warming across the world. In this paper, the technologies that are widely used to harness the LNG RCE for electrical power have been reviewed. The systems incorporating, the Rankine cycles, Stirling engines, Kalina cycles, Brayton cycles, Allam cycles, and fuel cells have been considered. Additionally, the economic and environmental studies apart from the thermal studies have also been reviewed. Moreover, the discussion regarding the systems with respect to the regassification pressure of the LNG has also been provided. The aim of this paper is to provide guidelines for the prospective researchers and policy makers in their decision making.

Alkali carbonate-based sorbents (ACSs), including Na₂CO₃- and K₂CO₃-based sorbents, are promising for CO₂ capture. However, the complex sorbent components and operation conditions lead to the versatile kinetics of CO₂ sorption on these sorbents. This paper proposed that operando modeling and measurements are powerful tools to understand the mechanism of sorbents in real operating conditions, facilitating the sorbent development, reactor design, and operation parameter optimization. It reviewed the theoretical simulation achievements during the development of ACSs. It elucidated the findings obtained by utilizing density functional theory (DFT) calculations, ab initio molecular dynamics (AIMD) simulations, and classical molecular dynamics (CMD) simulations as well. The hygroscopicity of sorbent and the humidity of gas flow are crucial to shifting the carbonation reaction from the gas—solid mode to the gas—liquid mode, boosting the kinetics. Moreover, it briefly introduced a machine learning (ML) approach as a promising method to aid sorbent design. Furthermore, it demonstrated a conceptual compact operando measurement system in order to understand the behavior of ACSs in the real operation process. The proposed measurement system includes a micro fluidized-bed (MFB) reactor for kinetic analysis, a multi-camera sub-system for 3D particle movement tracking, and a combined Raman and IR sub-system for solid/gas components and temperature monitoring. It is believed that this system is useful to evaluate the real-time sorbent performance, validating the theoretical prediction and promoting the industrial scale-up of ACSs for CO₂ capture.

In this work, using fractured shale cores, isothermal adsorption experiments and core flooding tests were conducted to investigate the performance of injecting different gases to enhance shale gas recovery and CO₂ geological storage efficiency under real reservoir conditions. The adsorption process of shale to different gases was in agreement with the extended-Langmuir model, and the adsorption capacity of CO₂ was the largest, followed by CH₄, and that of N₂ was the smallest of the three pure gases. In addition, when the CO₂ concentration in the mixed gas exceeded 50%, the adsorption capacity of the mixed gas was greater than that of CH₄, and had a strong competitive adsorption effect. For the core flooding tests, pure gas injection showed that the breakthrough time of CO₂ was longer than that of N₂, and the CH₄ recovery factor at the breakthrough time (left({{R_{{rm{C}}{{rm{H}}_4}}}} right)) was also higher than that of N₂. The ({R_{{rm{C}}{{rm{H}}_4}}}) of CO₂ gas injection was approximately 44.09%, while the ({R_{{rm{C}}{{rm{H}}_4}}}) of N₂ was only 31.63%. For CO₂/N₂ mixed gas injection, with the increase of CO₂ concentration, the ({R_{{rm{C}}{{rm{H}}_4}}}) increased, and the ({R_{{rm{C}}{{rm{H}}_4}}}) for mixed gas CO₂/N₂ = 8:2 was close to that of pure CO₂, about 40.24%. Moreover, the breakthrough time of N₂ in mixed gas was not much different from that when pure N2 was injected, while the breakthrough time of CO₂ was prolonged, which indicated that with the increase of N₂ concentration in the mixed gas, the breakthrough time of CO₂ could be extended. Furthermore, an abnormal surge of N₂ concentration in the produced gas was observed after N₂ breakthrough. In regards to CO₂ storage efficiency (left({{S_{{rm{storage - C}}{{rm{O}}_2}}}} right)), as the CO₂ concentration increased, ({S_{{rm{storage - C}}{{rm{O}}_2}}}) also increased. The ({S_{{rm{storage - C}}{{rm{O}}_2}}}) of the pure CO₂ gas injection was about 35.96%, while for mixed gas CO₂/N₂ = 8:2, ({S_{{rm{storage - C}}{{rm{O}}_2}}}) was about 32.28%.

The effect of oxygen vacancies on the adsorption and activation of CO₂ on the surface of different phases of ZrO₂ is investigated by density functional theory (DFT) calculations. The calculations show that the oxygen vacancies contribute greatly to both the adsorption and activation of CO₂. The adsorption energy of CO₂ on the c-ZrO₂, t-ZrO₂ and, m-ZrO₂ surfaces is enhanced to 5, 4, and 3 folds with the help of oxygen vacancies, respectively. Moreover, the energy barrier of CO₂ dissociation on the defective surfaces of c-ZrO₂, t-ZrO₂, and m-ZrO₂ is reduced to 1/2, 1/4, and 1/5 of the perfect surface with the assistance of oxygen vacancies. Furthermore, the activation of CO₂ on the ZrO₂ surface where oxygen vacancies are present, and changes from an endothermic reaction to an exothermic reaction. This finding demonstrates that the presence of oxygen vacancies promotes the activation of CO₂ both kinetically and thermodynamically. These results could provide guidance for the high-efficient utilization of CO₂ at an atomic scale.