Zero-carbon Power Research Articles

Performance analysis of multi-stack fuel cell systems for large buildings using electricity and heat

The fuel cell market, which utilizes hydrogen as a fuel for zero-carbon power generation to address global warming, continues to grow steadily. In the building sector, where small-scale fuel cells of 10 kW or less have been predominant, there is increasing interest in scaling up fuel cells to increase deployment and reduce system costs. The multi-stack fuel cell system (MFCS), which consists of connecting multiple modules, is one method of configuring large-scale fuel cell systems, offering advantages in system efficiency, durability, and cost. The objective of this paper is to compare and analyze the behavior of the MFCS according to different operation strategies. In particular, it compares the Equivalent operation method, which behaves similarly to the single-stack fuel cell system (SFCS), with others (Daisy-Chain, Electrical Optimization). Unlike previous studies that only focused on the electrical efficiency of MFCS, this study analyzed thermal energy, which is indispensable in building applications, to maximize the effects of MFCS. Simulation of operation strategies based on the electricity and heat demand of a specific residence showed that MFCS outperformed the SFCS in terms of electrical and heat efficiency, hydrogen consumption, degradation, and operating costs.

Development of Detailed and Reduced Chemical Kinetic Models for Ammonia Gas Turbines

Abstract The power generation sector has been recently moving towards decarbonization and there is an increased interest in replacing conventional fossil fuels with fuels that produce reduced/zero carbon emissions. One such fuel is ammonia (NH3). However, ammonia is hard to ignite, has a low flame speed, and produces a significantly large amount of nitrogen oxide (NOx) emissions. Hence, using 100% ammonia as fuel in gas turbines requires significant modifications and the development of novel combustors. Blending hydrogen with ammonia, however, helps in having better control over the combustion properties. Before utilizing hydrogen-blended ammonia in an actual gas turbine combustor, thorough simulation studies are required to evaluate its performance, possible hazards, and emissions. The literature lacks well-validated chemical kinetic models for the combustion of hydrogen-blended ammonia for undiluted mixtures at gas turbine-relevant conditions (~20 bar). Hence, in this work, we develop a detailed chemical kinetic model for hydrogen blended ammonia combustion and validate it with a wide range of experimental data for both dilute and undiluted mixtures relevant to gas turbine operating conditions. The detailed chemical kinetic mechanism was reduced to a smaller version (32 species mechanism) without significant loss in accuracy using the direct relation graph with error propagation (DRGEP) and full species sensitivity analysis. The resultant mechanism can predict a wide range of experimental results with the least cumulative error and will be a valuable tool in CFD simulations that will enable the development of gas turbines for zero-carbon power generation.

Demand Response of Integrated Zero-Carbon Power Plant: Model and Method

Demand Response of Integrated Zero-Carbon Power Plant: Model and Method

Techno-economic assessment of the modified Allam cycle configurations with multi-stage pump/compressor for efficient operation in hot regions

The Allam cycle is renowned for its zero-carbon power generation and high efficiency. However, it faces challenges in hot regions where there is no available cold source for carbon dioxide liquefaction, leading to deterioration in its performance. In this study, a multi-stage pump/compressor is introduced, aiming to enhance the net electric efficiency of the conventional Allam cycle. Various potential enhancement methods are explored and analyzed through comprehensive thermodynamic and economic analyses. Among the configurations under consideration, the Allam cycle combined with two-stage pump/compressor and bypass compressor exhibits the best performance, achieving a 6.71 % increase in the efficiency of the conventional cycle. For the conventional Allam cycle, the efficiency decreases by 0.42 % for every 1 ℃ increase in ambient temperature, however, it is 0.17 % for the Allam-MPC cycle, which indicates it is less responsive to changes in ambient temperature. Moreover, the economic performance of the proposed cycle is better than that of the conventional cycle, which has higher revenue and lower levelized cost of electricity. The capital costs of the modified equipment represent around 1.43 % of the total capital costs of the conventional Allam cycle, and the investment-increment payback period is less than 0.5 years when the ambient temperature exceeds 30 ℃. Sensitivity analyses suggest that the proposed cycle will be more economically viable in hot regions with lower natural gas prices and higher electricity prices. Overall, this study provides a promising approach to improving the performance of Allam cycle in hot regions and offering valuable references for its practical implementation.

Energy Storage Mix Optimization Based on Time Sequence Analysis Methodology for Surplus Renewable Energy Utilization

Increasing the proportion of carbon-free power sources, such as renewable energy, is essential for transitioning to a zero-carbon power system. However, when the rate of grid expansion and flexibility cannot match the rate of renewable energy increase, surplus energy is the result. Surplus energy can be discarded through curtailment or stored and utilized when required. The optimal equipment configuration of the storage system should be determined based on the surplus energy characteristics. This study proposes an optimal energy storage mix configuration method by considering long-term forecasts of surplus energy in the South Korean renewable energy supply and power grid expansion plan. The surplus energy by time slot is comprehensively analyzed considering renewable energy power output, power demand, and power system operation constraints. We calculate the required power and energy of storage devices. Furthermore, we construct a long-term optimal energy storage mix using surplus energy generation patterns and technical and economical characteristics of storage technologies. The total cost minimization was considered as the objective function, comprising three elements: initial construction, equipment replacement, and loss costs for charging and discharging. We propose a time sequence analysis (TSA) method that enables chronological analysis from the starting year to the final target year. The TSA method provides an energy storage mix configuration roadmap that can utilize surplus energy for various years over the entire period, considering the annual increase in surplus energy and commercialization timing of each storage technology. We compare the difference between our proposed TSA method and the method that analyzes only the final target year to validate the superiority of this methodology.

Simultaneous design and operational optimization for flexible carbon capture process using ionic liquids

Carbon capture and storage is an effective way to abate CO2 emissions during the transition to zero-carbon power generation technologies. As renewable electricity sources such as wind and solar photovoltaics become more prevalent, conventional power generation systems are increasingly required to operate at highly variable rates in order to balance intermittent renewable power supply. As a result, post-combustion carbon capture systems integrated with fossil fuel power plants must also operate at variable load. In addition, the solvent regeneration and CO2 compression in capture plants requires substantial amounts of energy and such flexible operation can present an opportunity for operators to take advantage of fluctuating electricity prices, potentially offsetting the cost of carbon capture. This can be achieved through, among others, variable capture rates and utilization of solvent storage. In this paper, we consider a carbon capture system using ionic liquids as a chemical absorption solvent. We study the optimal flexible operation of this system when connected to a natural gas combined cycle power plant under high variable renewable power generation rates. The results show significant cost savings relative to the case of inflexible capture system operation.

Voltage Control Strategy for Low-Voltage Distribution Network with Distributed Energy Storage Participating in Regulation under Low-Carbon Background

With the gradual advancement towards the goal of carbon neutrality, photovoltaic power generation, as a relatively mature zero-carbon power technology, will be connected to the grid in an increasing proportion. A voltage control strategy, involving distributed energy storage, is proposed in order to solve the voltage deviation problem caused by the high proportion of PV connected to the low voltage distribution network (LVDN). A voltage calculation method of the LVDN node with a high proportion of PV is proposed. According to the voltage distribution of the LVDN nodes running throughout the day, fuzzy cluster analysis was used to partition the nodes in the LVDN. A two-objective mathematical model for optimizing distributed energy storage in a partition was constructed, and a particle swarm optimization algorithm was used to solve the model. A voltage control strategy based on sensitivity analysis is proposed, and a mathematical model is established to analyze the relationship between the node current increment and the node off-limit voltage. The mathematical relationship among the node off-limit voltage, node off-limit power and energy storage exchange power is derived, and the voltage deviation of the distribution network can be suppressed by adjusting the injected power of the distributed energy storage. Through case analysis, it is verified that the proposed voltage control strategy can reduce the voltage deviation of the distribution network nodes, effectively solve the problem of the distribution network voltage deviation, and reduce the active power loss.

Research on the adaptability of proton exchange membrane electrolysis in green hydrogen–electric coupling system under multi-operating conditions

The green hydrogen–electric coupling system can consume locally generated renewable energy, thereby improving energy utilization and enabling zero-carbon power supply within a certain range. This study focuses on a green hydrogen–electric coupling system that integrates photovoltaic, energy storage, and proton exchange membrane electrolysis (PEME). Firstly, the impact of operating temperature, power quality, and grid auxiliary services on the characteristics of the electrolysis cell is analyzed, and a voltage model and energy model for the cell are established. Secondly, a multi-operating conditions adaptability experiment for PEME grid-connected operation is designed. A test platform consisting of a grid simulator, simulated photovoltaic power generation system, lithium battery energy storage system, PEME, and measurement and acquisition device is then built. Finally, experiments are conducted to simulate multi-operating conditions such as temperature changes, voltage fluctuations, frequency offsets, harmonic pollution, and current adjustment speed. The energy efficiency and consumption is calculated based on the recorded data, and the results are helpful to guide the operation of the system.

Inspired lightweight robust quantum Q-learning for smart generation control of power systems

With the continuous development of zero-carbon power systems, more and more models need to be considered in the system, and the dimension of data provided in the system will be higher and higher. The grid frequency will be difficult to be controlled stably. The existing smart generation control (SGC) methods like proportional–integral–derivative (PID), traditional Q-learning (QL), state–action–reward–state–action (SARSA), sliding mode control (SMC), and fuzzy logic control (FLC) have low-performance problems, the curse of dimensionality, and a slow convergence rate in the zero-carbon power system. This work proposes lightweight robust quantum Q-learning (LRQQL) methods to improve the performance of SGC methods and solve these problems. The LRQQL methods are divided into four methods. Two methods apply the idea of quantum normalization to update the action probability and different action selection methods to provide the action with higher performance. Besides, two lighter methods based on the idea of Grover iteration with the less curse of dimensionality and a faster convergence rate are proposed. The LRQQL methods are simulated in the two-area, four-area, and complex four-area systems. The evaluation indexes verify the feasibility of LRQQL algorithms. The LRQQL methods are more than 25% smaller than traditional QL in frequency error, more than 40% smaller than traditional QL in area control error, and more than 40% faster than the QL and SARSA in convergence rate. Meanwhile, the LRQQL methods possess higher adaptivity than PID, QL, SARSA, SMC, and FLC.

Compact and fast-response 150 kW hydrogen-oxygen steam generator

Burning of hydrogen produces high-grade heat, which can be used for zero-carbon power generation and/or heating and in heat-intensive industries. In combination with water electrolysis, hydrogen combustion provides efficient energy storage method for variable renewables. Hydrogen combustion systems are compact, powerful and highly maneuverable in comparison with fuel cells. We present experimental results of fire tests of a water-cooled hydrogen-oxygen steam generator (HOSG). This fast-response device has start-up time less than 15 s to thermal capacity of 147 kW. Temperature of generated steam is within 1173–1273 K, parameters of steam and energy conversion efficiency can be adjusted the water-to-hydrogen ratio. The maximum efficiency of conversion of chemical energy of hydrogen into enthalpy of steam is 98.7%.

Same Goal, Different Pathways for Energy Transition: A More Holistic, Multisector, Community-Driven Approach

Low- and zero-carbon power systems are central to global decarbonization efforts. Costs for renewable energy (RE) and storage have fallen significantly, and advances in technologies and practices have improved the grid flexibility and stability needed to maintain the reliability of high-RE systems. Zero-carbon power systems, in turn, enable deep decarbonization through the electrification of other sectors, including transportation, buildings, and industry.

Microbial-mediated CO2 methanation and renewable natural gas storage in depleted petroleum reservoirs: A review of biogeochemical mechanism and perspective

Renewable natural gas (RNG) production by microbial-mediated CO2 methanation has been identified as a key for future systems relying on renewable and zero-carbon power, which provides a twin dividend of energy-environmental significance and is critical to facilitate China's pledge to be carbon neutral by 2060. Here we provide an overview of the hydrogenotrophic methanation coupled with subsurface CO2 utilization and renewable natural gas storage, giving special focuses on the biogeochemical mechanism and potential applications for renewable energy conversion and storage. Taking injected CO2 and H2 as substrates and subsurface petroleum reservoir as a bioreactor, indigenous methanogenic archaea can induce bio-methane generation by offering essential functional groups and electron carriers. Detailed reviews are provided on the subsurface biogeochemical mechanism including microorganisms, metabolic pathways, environmental conditions, and substrates utilization. Bio-methane-related energy conversion and storage can be achieved by coupling “microbial restoration of methane deposit” (MRMD) with CO2 emission-free power plants, which provides flexibility to balance the unstable power demands and bring additional commercial value for CO2 geological storage. Biological methanation can also be integrated into the “power-gas-power” (PGP) system, yielding advantages in flexibility, large-scale capacity, long-term storage cycle and CO2 emission reduction. The techno-economic status and perspectives are discussed for the purpose of enhancing substrate utilization, energy efficiency and economic feasibility that hold great promise for further practical implementation. Its early potential in northwest China is particularly emphasized. Based on the current technical barriers and energy policy, challenges and future research emphasis of biological methanation in depleted petroleum reservoirs are also presented.

Rapid load transition for integrated solid oxide fuel cell – Gas turbine (SOFC-GT) energy systems: A demonstration of the potential for grid response

Rapid load transition is an essential requirement for integrated energy systems to maintain grid resilience as more renewable resources are added to the grid. Integrated solid oxide fuel cell – gas turbine (SOFC-GT) systems can provide high efficiency and low carbon emissions over a broad range of turndown. These hybrids also have the potential to enable rapid grid response. The challenge has been to demonstrate effective control strategies to manage load transitions. In the present study, a load transition of ∼50% was achieved in 10 s using a novel but simple strategy. Power demand on the SOFC and the GT were ramped down concurrently. During this transition, the SOFC anode fuel was manipulated to maintain SOFC fuel utilization while the cathode inlet air flow and temperature were also manipulated to thermally protect the SOFC. This study was conducted using the Hybrid Performance (Hyper) facility at the National Energy Technology Laboratory (NETL) in a co-simulation environment with the Idaho National Laboratory (INL)’s grid-simulation. The load ramping strategy was tested using a hardware-based cyber-physical simulation methodology. The results demonstrate a high-fidelity representation of SOFC-GT hybrid dynamics and validation of the control strategy. Thermal and electrochemical transients indicated that the SOFC was well protected during rapid load turndown without violating operability constraints. This demonstration revealed the non-linear nature of tightly coupled SOFC-GT system components, especially the non-linear response of SOFC cathode air flow and inlet temperature controls. These results highlight the needs and challenges in developing adaptive automatic controls for autonomous rapid load transitions. This work demonstrates that SOFC-GT hybrids are a viable option to provide the fast-ramping characteristics essential to accommodate high levels of variable renewable power while maintaining grid resilience, reliability, and environmental performance. The results also demonstrate the utility of co-simulation in advancing the tightly-coupled integrated energy systems needed to meet goals for zero-carbon power generation.

Research Needs for Realization of Zero-Carbon Power Grids with Selected Case Studies

The attainment of carbon neutrality requires a research agenda that addresses the technical and economic challenges that will be encountered as we progress toward 100% renewable electricity generation. Increasing proportions of variable renewable energy (VRE) sources (such as wind turbines and photovoltaic systems) render the supply-and-demand balance of VRE-dominated power grids difficult. The operational characteristics and effects of VRE inverters also require attention. Here, we examine the implications of the paradigm shift to carbon neutrality and summarize the associated research challenges in terms of system planning, operation, and stability, and the need for energy storage integration, demand-side participation, distributed control and estimation, and energy sector coupling. We also highlight the existing literature gaps, and our recent studies that can fill in the gaps, thereby facilitating the improvement of grid operation and estimation. The numerical results of comparative case studies are also provided on the operational stability and economics of power grids with a high level of VRE sources, assisting stakeholders in establishing specific roadmaps and making relevant decisions.

Technologies and economics of electric energy storages in power systems: Review and perspective

Current power systems are still highly reliant on dispatchable fossil fuels to meet variable electrical demand. As fossil fuel generation is progressively replaced with intermittent and less predictable renewable energy generation to decarbonize the power system, Electrical energy storage (EES) technologies are increasingly required to address the supply-demand balance challenge over a wide range of timescales. However, the current use of EES technologies in power systems is significantly below the estimated capacity required for power decarbonization. This paper presents a comprehensive review of EES technologies and investigates how to accelerate the uptake of EES in power systems by reviewing and discussing techno-economic requirements for EES. Individual EES technologies and power system applications are described, which provides guidance for the appraisal of specific EES technologies for specific power system services. Plausibly required scales and technology types of EES over different regions are then reviewed, followed by discussions on storage cost modelling and predictions for different EES technologies. Opportunities and challenges in developing scalable, economically viable and socio-environmental EES technologies are discussed. The paper explores EES's evolving roles and challenges in power system decarbonization and provides useful information and guidance on EES for further R&D, storage market building and policy making in the transition to zero-carbon power systems.

Joint Optimization for Coordinated Charging Control of Commercial Electric Vehicles Under Distributed Hydrogen Energy Supply

The transition to the zero-carbon power system is underway accelerating recently. Hydrogen energy and electric vehicles (EVs) are promising solutions on the supply and demand sides. This brief presents a novel architecture that includes hydrogen production stations, fast-charging stations, and commercial EVs. The proposed architecture jointly optimizes the hydrogen energy dispatch and the EV charging location selection and is formulated by a time-varying bilevel bipartite graph (T-BBG) model. We develop a bilevel iteration optimization method combining the linear programming (LP) and the Kuhn–Munkres (KM) algorithm to solve the joint problem whose optimality is proved theoretically. The effectiveness of the proposed architecture on reducing the operating cost is verified via case studies in Shanghai. The proposed method outperforms other strategies and improves the performance by at least 13%, which shows the potential economic benefits of the joint architecture. The convergence and impact of parameters are assessed.

The Value of Inter-Regional Coordination and Transmission in Decarbonizing the US Electricity System

Summary Preventing global warming in excess of 1.5°C–2°C requires a transition to zero-carbon electricity systems by midcentury along with the widespread electrification of other sectors. Current state-level renewable portfolio standards and regional transmission arrangements do not capture the benefits of inter-regional transmission or coordination of planning and dispatch for renewable-energy integration. Here, using a co-optimized capacity-planning and dispatch model over 7 years of hourly operation, we show that inter-state coordination and transmission expansion reduce the system cost of electricity in a 100%-renewable US power system by 46% compared with a state-by-state approach, from 135 $/MWh to 73 $/MWh. Sensitivity analyses show that reductions in the cost of photovoltaics, wind, and lithium-ion batteries lead to the lowest electricity costs for systems in which transmission expansion is allowed, while cost reductions for nuclear power or long-duration energy storage lead to greater electricity cost reductions for isolated systems.

A power demand resilience analysis of the residential and commercial areas for Fengshan smart green community in Taiwan

As global climate change intensifies, extreme catastrophic weather. As a result, the vulnerability of power infrastructure gradually worsens, leading to an increased threat of power supply disruption. In order to cope with the threat of possible power supply disruption and to accommodate more residents in the event of a disaster, backup power generation and storage facilities are necessary should establish in residential and commercial areas. This study establishes a software analysis model of power demand resilience in the residential area, analyzes various power demand resilience scenarios, and discusses the operation of reasonable backup power generation and energy storage facilities, and power load management and control strategies. In the future, these software tools will be used to analyze the rational allocation and operation strategies of disaster prevention at power facilities in similar situations. This study takes the Fengshan Smart Green Community as the reference field, and extends the simulated facilities as the area of power demand resilience analysis, in an integrated residential area and a commercial area. This study has completed four case studies, including: (1) baseline scenario, (2) “use of diesel generators” scenario, (3) “expanding lithium battery capacity” scenario, and (4) “expanding lithium battery capacity and controlling lithium battery power output in the integrated residential area” scenario. The conclusions of this study include: (1) To cope with the intensified global climate change, adequate deployment of various backup power generation and storage facilities to enhance power resilience can effectively mitigate the threat of power supply disruption. (2) According to the case study results, there is sufficient solar photovoltaic in the residential area of Fengshan Smart Green Community. However, the energy storage and power supply capacity of lithium batteries are insufficient, and it is challenging to perform the backup power function. (3) To supply electricity to the power management system and the medical and shelter area adequately, this study suggests Fengshan Smart Green Community strengthens the power storage and power supply capacity of lithium batteries. (4) Solar photovoltaics are zero-carbon power; it can be a priority backup for power demand resilience. However, solar power is not available when there is insufficient sunshine. (5) The use of a diesel generator can flexibly assist the solar photovoltaic and lithium batteries to ensure the adequate power supply. (6) The use of diesel generators for power generation during a time of crisis is not pollution-free. However, their use for management in a crisis or disaster situation is in order when other power supply backups are insufficient or have failed. The critical findings include: (1) Solar photovoltaics are zero-carbon power; it can be a priority backup for power demand resilience. However, solar power is not available when there is insufficient sunshine. (2) The use of diesel generators for power generation during a time of crisis is not pollution-free. However, their use for management in a crisis or disaster situation is in order when other power supply backups are insufficient or have failed.

Perspectives on oxygen-based coal conversion towards zero-carbon power generation

Projections made by credible institutions indicate that coal will continue to provide a major fraction of the global electricity mix for many decades to come. Assuming the validity of these projections and building on this likely scenario, this perspective article proposes oxygen-based coal conversion as a sustainable pathway for zero-carbon power generation, albeit not without its own challenges. The century-old tradition of burning coal in air is no longer sustainable. Achieving zero-carbon coal power dictates full capture of CO2 emissions. Unfortunately, renewable power is still far from fully displacing coal-based power despite major gains. Also, renewables are inherently non-dispatchable sources constrained severely by lack of utility-scale electricity storage. Moreover, prospects for total conversion of power generation to natural gas presents its own challenges due to uncertain impacts of hydraulic fracturing on the environment. It is highly likely that we will need both coal and natural gas for electricity production. Accordingly, this article proposes a roadmap that emphasizes rapid transitioning of coal-based (and natural gas-based) power generation from air-based combustion to oxygen-based conversion. The latter excludes nitrogen from entering the process stream and offers easy capture of CO2 to achieve zero-carbon electricity generation with significant savings on water demand.

Technology evaluation of zero-carbon power generation systems in Japan in terms of cost and CO2 emission

Technology evaluation of zero-carbon power generation systems in Japan in terms of cost and CO2 emission