Search Results (165)

During the frequent charging, discharging, and storage processes of underground compressed air energy storage systems, the damage and degradation of sealing plugs directly affect the long-term stability of gas storage caverns. Using a self-developed cyclic charging–storage–discharging–restorage gas disturbance rock testing system, this study conducted cyclic gas disturbance tests on sealing plug specimens at different storage pressures, followed by post-disturbance uniaxial compression tests, to investigate the thermodynamic response during cyclic disturbances and elucidate the mechanical property degradation mechanism of sealing plug specimens after cyclic disturbances. The results show that, during a single cycle, the gas temperature exhibits staged responses characterized by compression heating, cooling during high-pressure storage, decompression cooling, and temperature recovery during low-pressure storage. As the storage pressure increases, the heating rate increases from 0.005 to 0.016 °C/s, while the cooling rate increases from 0.023 to 0.055 °C/s. During cyclic charging–storage–discharging–restorage processes, the gas temperature exhibits an overall logarithmic growth trend comprising three stages, namely a rapid increase, a slow increase, and stabilization, with the degree of heat accumulation increasing progressively with storage pressure. Cyclic alternating loading by high-pressure gas aggravates internal specimen damage. With increasing storage pressure, the peak strength of the specimens after cyclic disturbances decreases by 8.14%, 8.99%, 11.58%, and 15.05%, respectively, while the elastic modulus decreases by 2.12%, 6.45%, 8.88%, and 13.49%, respectively. Acoustic emission activity during failure becomes more pronounced, and deformation localization intensifies. With increasing storage pressure, the macroscopic failure mode gradually changes from localized cracking to multiple-crack coalescence and block fragmentation, while the increase in average fracture-surface porosity rises from 7.29% to 37.89%. These results are important for assessing the stability of sealing plugs in underground CAES caverns. Full article

Seasonal energy storage effectively addresses seasonal electricity supply–demand imbalances. This study proposes a cross-seasonal compressed air energy storage system using a depleted gas reservoir as the storage reservoir. A six-stage compression–expansion system with intercooling and reheating is designed. Also, the heat of compression is recovered for district heating, and the expansion of cold energy is for cooling supply, thereby avoiding cross-seasonal heat storage costs. For the YD1 depleted gas reservoir case, the system achieves a round-trip efficiency of 57.85% and an exergy efficiency of 70.9%. The total energy utilization ratio, which represents the combined utilization of the electricity, heating, and cooling outputs relative to the corresponding energy input, reaches 166.6%. Incorporating revenue from the heating and cooling sales, the dynamic payback period is 2.38 years, and the investment recovery ratio reaches 4.40. Parametric analysis indicates that thermodynamic performance improves with the increase in discharge pressure and decrease in discharge power. Economic performance improves with longer daily operating hours and plant lifetime. This study demonstrates that depleted gas reservoirs combined with well-designed surface combined cooling, heating, and power systems offer a new research and development direction for large-scale, long-duration seasonal storage, facilitating renewable energy integration and grid stability. Full article

The reuse of post-mining infrastructure for pumped-storage hydropower may reduce new underground construction while supporting the repurposing of decommissioned mines. This study presents a site-specific preliminary technical and pumping-energy assessment of an underground pumped-storage system using Budryk Shaft II as the lower reservoir. The assessment integrated shaft geometry, hydraulic conditions, turbine–generator selection, pressure-pipeline configuration, structural adaptation, hydraulic isolation, and staged water return. A working water volume of 12,000 m³ was adopted. The proposed generation unit comprises a vertical Pelton turbine operating at a gross design head of 900 m, a rated net head of 837.81 m, and a discharge of 0.71 m³/s. The rated turbine output is 5287 kW, and the turbine is coupled to a 6.3 kV synchronous generator. The three-stage pumping calculation yielded energy demands of 7.037, 19.600, and 37.371 MWh, giving a total of 64.008 MWh. These values are calculation-based estimates derived from the listed nominal pump capacities and powers using a simplified proportional power–flow assumption. At the rated turbine output, the calculated generation time of 4.695 h corresponds to 24.822 MWh of mechanical energy at the turbine shaft. Because verified generator-efficiency data are unavailable, the generated electrical energy and electrical round-trip efficiency cannot be determined exactly. The ratio of turbine-shaft energy to the calculated pumping-energy demand gives an upper-bound energy-return indicator of approximately 38.8%. Further work must verify pump operating points, generator performance, hydraulic transients, structural integrity, shaft sealing, auxiliary-energy demand, and the complete hydraulic connection to the upper reservoir. Full article

High penetration of distributed photovoltaic (PV) generation in low-voltage distribution networks can cause voltage violations, limited PV accommodation, and uneven loading among neighboring distribution transformers (DTs). To address these issues, an edge computing-enabled optimal control method is proposed for low-voltage distribution networks organized as distribution transformer clusters (DTCs). An intelligent fusion terminal serves as the edge computing platform and locally performs measurement acquisition, day-ahead schedule generation, intraday rolling correction, safety verification, and control command issuance. In the day-ahead stage, PV generation scenarios are identified from forecast profiles, and scenario-dependent energy storage state-of-charge (SOC) reservation rules and soft open point (SOP) active power balancing schedules are generated. In the intraday stage, PV inverter reactive power, energy storage charging and discharging, necessary PV active power curtailment, and SOP power transfer are coordinated according to real-time measurements. A safety scaling and boundary verification mechanism is further introduced to ensure voltage security and device feasibility without repeatedly solving complex optimization models. Case studies on a three-DT system show that the proposed method reduces overvoltage occurrences in TQ1 by 81.0% and eliminates undervoltage occurrences under four PV scenarios. With SOP-based balancing, total overvoltage and undervoltage occurrences in the DTC are reduced by 4.35% and 88.99%, respectively, while PV utilization and loading ratio balance are improved. The intraday control time is approximately 20 ms, demonstrating the feasibility of real-time rolling control on resource-constrained edge computing platforms. Full article

Liquid Air Energy Storage (LAES) is a promising large-scale storage technology for supporting the sustainable integration of intermittent renewable electricity into power grids, particularly when electricity storage is combined with waste-heat valorization, cryogenic cold recovery, and reduced exergy degradation. In this thermodynamic sense, the present study proposes a sustainability-oriented framework for the comparative and parametric exergetic analysis of LAES systems, integrating the liquefaction and discharge stages within a unified analysis. The assessment focuses on thermodynamic resource efficiency and exergy performance rather than on a complete economic, environmental, or life-cycle evaluation. The objective is to identify the components and operating parameters that most strongly influence performance and to quantify the reductions in exergy destruction and losses achieved through configuration changes and parameter variation. Three Linde–Hampson-based liquefaction configurations are compared, including arrangements with external and intermediate auxiliary pre-cooling. Improved heat-exchanger integration and temperature matching increase the structural liquefaction exergetic indicator from 7.95% in the baseline configuration to 19.28% in the two-RHX configuration. The discharge stage is assessed parametrically with respect to cryogenic pumping pressure, turbine inlet temperature, and expansion architecture. Single-stage and two-stage adiabatic expansions are compared with an ideal isothermal benchmark. The adiabatic configurations provide mechanical-work recovery together with recoverable cooling potential, whereas the isothermal case gives the highest work-recovery benchmark. Under the reference conditions, using the aggregated compressor representation adopted for the main parametric analysis, the two-stage adiabatic configuration reaches a global exergetic efficiency of 15.92% for the improved Linde–Hampson-based chain and 24.87% for the selected Claude–Heylandt reference block. Full article

Standalone DC microgrids offer a promising solution for providing reliable and sustainable electricity to remote communities in developing countries. However, the intermittent nature of solar and wind resources, combined with continuously varying load demand, presents considerable operational challenges in maintaining real-time power balance, stable DC bus voltage, and ensuring reliable continuous supply. Therefore, there is dire need for user-friendly control solutions tailored to the specific needs of isolated communities. As such, this paper presents a coordinated control and power management strategy for an isolated hybrid solar–wind–battery integrated DC microgrid for rural electrification applications. A comprehensive mathematical model of the standalone DC microgrid incorporating photovoltaic generation, wind energy conversion, battery storage, bidirectional DC-DC conversion, and common DC bus dynamics is developed at the very first stage of the proposed coordinated control framework. The framework utilizes principal local device loops and a secondary dynamic power management strategy to ensure efficient renewable power extraction, dynamic source–storage–load coordination, stable DC bus voltage, and real-time energy management within the developed standalone DC microgrid. It is worthwhile to mention that, instead of using synthesized or online available wind speed and solar irradiance data, this research utilized real-time recorded metrological data obtained from the Mehran University Jamshoro, Pakistan. The obtained results establish a stable DC bus voltage regulation within acceptable operating limits, continuous power balance, seamless bidirectional battery operation, and safe battery state-of-charge (SoC) management to prevent deep discharging or overcharging, thus ensuring reliable operation. The overall performance confirms the technical robustness, operational flexibility, and practical suitability of the proposed standalone hybrid DC microgrid architecture for its resilient operation and rural electrification applications. Full article

Lined rock caverns offer a promising option for underground hydrogen, helping to mitigate renewable intermittency and enhance system stability. Considering the geological characteristics of hard rock formations in Southern Ontario, Canada, this study establishes a thermo–gas–mechanical coupled framework that incorporates hydrogen mass and energy evolution in the cavern, gas–wall convective heat exchange, dynamic cavern-volume feedback, and the deformation behaviour of the sealing layer, concrete lining, and surrounding rock. The influences of cavern geometry, sealing material, and in situ stress on the short–term thermodynamic and mechanical responses are further examined. The results show that hydrogen temperature and pressure exhibit clear stage–dependent evolution during the charging–storage–discharging cycle. The comparison between the first and 20th operating cycles indicates that repeated operation mainly causes a moderate adjustment of the cyclic thermal state and temperature–pressure baseline, without changing the overall stage–dependent response pattern. During charging, temperature and pressure increase simultaneously; during storage, both gradually decrease as thermal energy is transferred to the cavern wall; and during discharging, expansion causes pronounced cooling and depressurization, followed by gradual recovery driven by heat transfer from the surrounding rock. Cavern geometry significantly affects stress redistribution around the cavern. The circular cavern shows a relatively uniform stress distribution, whereas the arched cavern is more prone to local stress concentration near the sidewall–floor transition zone. The sealing material mainly influences gas temperature fluctuations through its thermal conductivity. The fibre–reinforced plastic (FRP) sealing layer amplifies thermal fluctuations during cyclic operation, whereas the steel sealing layer promotes heat dissipation through the lining and surrounding rock, thereby moderating cavern–gas temperature variations. In situ stress difference further controls the directional distribution of stresses around the cavern. As the minimum horizontal principal stress increases, compressive stress concentration at the crown and invert becomes stronger, while relative stress release occurs near the sidewalls. These findings provide a thermo–mechanical basis for preliminary cavern–geometry design, comparison of sealing–layer thermal performance, and assessment of in situ stress adaptability for lined rock cavern hydrogen storage in Southern Ontario. Full article

Implementation of real-scale systems for rainwater harvesting, treatment and reuse of greywater in residential areas is challenging because several factors should be considered for full adoption and satisfaction of decision-makers, urban developers and users. Technological, construction, operational, social (acceptance), impact on water resources, regulatory, and economic factors are involved. This study presents the implementation of a full-scale hybrid system for rainwater harvesting, treatment and reuse of greywater in a residential building located in Monterrey, Nuevo León, Mexico. The study included intervening in the hydraulic infrastructure of an already constructed residential building for collecting greywater, harvesting and collecting rainwater, designing and constructing an 80 m² controlled natural soil treatment system (CNSTS) and a 65 m³ storage tank for treating and storing rain and greywater. Furthermore, the full-scale hybrid system was monitored under real operating conditions for a two-month period to assess its performance. Results showed that the CNSTS has the potential to replace up to 2835 m³ year⁻¹ of potable water, equivalent to 65% of the building’s annual water consumption. The CNSTS achieved removal efficiencies of up to ~90% for Chemical Oxygen Demand, 90% for surfactants, and 50% for total nitrogen. Most of the measured parameters complied with the corresponding limits established by the Mexican standards NOM-003-SEMARNAT-1997 for non-potable water reuse, NOM-001-SEMARNAT-2021 for wastewater discharges, and NOM-127-SSA1-2021 for potable water with the exception of methylene blue active substances (surfactants), which exceeded the permissible limit during the initial monitoring stage, highlighting the need for further optimization of the system’s vegetative cover. Based on these findings, conceptual designs and preliminary evaluations were conducted for additional buildings, resulting in potable water substitution rates above 90% with investment payback periods of 2 to 5 years, depending on the water demand and the water catchment potential. Full article

Wind power producers face increasing market risks in electricity spot markets because output uncertainty may lead to large imbalance penalties and unstable revenues. This study aims to improve the market participation performance of wind farm consortia by coordinating day-ahead bidding, real-time deviation correction, and internal revenue allocation. The main novelty of this study is the integration of consortium-level bidding, shared energy storage leasing, and post-settlement revenue-cost allocation within a unified decision-allocation framework. A two-stage coordinated bidding model is developed for a wind farm consortium that leases shared energy storage to mitigate real-time power deviations. A Shapley value-based allocation mechanism is further introduced to distribute consortium revenue, while the shared energy storage leasing cost is allocated using an additional revenue-proportional fairness rule. Case studies show that the proposed strategy can reduce deviation penalties, increase the final net revenue after leasing cost, and maintain fair incentives among consortium members. Sensitivity analyses further demonstrate that the economic performance of the consortium is affected by storage size, charging/discharging efficiency, and wind farm output correlation. The proposed framework provides a practical decision-making reference for wind power aggregation, shared energy storage utilization, and coordinated participation in electricity spot markets. Full article

Reliable state of health (SOH) estimation plays an important role in the safe and stable operation of lithium-ion battery energy storage systems. Nevertheless, the nonlinear degradation characteristics and complex aging behaviors of batteries hinder accurate SOH estimation. This study proposes a Whale Optimization Algorithm (WOA)-optimized Convolutional Neural Network (CNN)–Temporal Convolutional Network (TCN)–Temporal Pattern Attention (TPA) framework for lithium-ion battery SOH estimation. Multiple health factors are extracted from charge–discharge curves to characterize battery degradation behaviors. Neighborhood-based imputation and Hampel-Median Absolute Deviation (MAD) correction are employed to handle missing values and local outliers, while Pearson correlation analysis is applied to evaluate the relevance of extracted features. CNN module captures local degradation patterns, TCN module learns long-term aging dependencies, and TPA mechanism enhances the representation of critical degradation stages. Furthermore, WOA adaptively optimizes key hyperparameters to improve model performance and robustness. The proposed framework is validated using NASA and CALCE battery datasets. Experimental results demonstrate that, compared with the CNN-TCN model, the proposed method reduces RMSE by 7.49–50.81% on NASA datasets and 15.83–60.38% on CALCE datasets, achieving higher estimation accuracy and stability. Full article

Off-grid residential microgrids in tropical regions require storage architectures capable of maintaining renewable electricity supply under variable solar resources, evening demand peaks, and diverse household consumption levels. In PV–battery–hydrogen systems, however, economic indicators can be difficult to interpret when software-reported costs are compared directly with externally calculated LCOE values based on different accounting conventions. This study presents a metric-reconciled techno-economic reconstruction approach for retained PV–battery–hydrogen microgrid configurations serving off-grid residential demand in Chetumal, Mexico. The objective is not to introduce a new global optimization or to claim the universal superiority of a specific architecture, but to separate archived HOMER Pro benchmark outputs from an external techno-economic model (TEM). The TEM reconstructs net present cost, scheduled replacements, salvage treatment, discounted delivered electricity, HOMER-derived LCOE, TEM-derived LCOE, sensitivity indicators, and storage role metrics using declared accounting assumptions. The approach is applied to two representative residential demand scenarios of 16.67 and 53.42 kWh/day. Both retained configurations achieved a 100% renewable fraction with negligible unmet load. Battery discharge increased from 827.12 kWh/year in the low-demand case to 6125.52 kWh/year in the high-demand case, highlighting the increasing role of the battery in short-duration balancing. In contrast, the hydrogen pathway acted as a delayed-backup layer by converting surplus PV electricity into hydrogen and later recovering it through PEM fuel cell generation. The TEM closely matched the HOMER-derived LCOE benchmark, with deviations below 4%, yielding TEM-derived LCOE values of 0.3320 and 0.3571 USD/kWh for the low- and high-demand cases, respectively. Sensitivity analysis showed that delivered electricity, discount rate, PV cost, and battery cost were the main LCOE drivers, while deterministic multi-parameter scenarios confirmed the combined influence of financing, component costs, O&M, PV degradation, and electricity delivered. Overall, the proposed approach provides an auditable basis for metric reconciliation, early-stage technology assessment, and storage role interpretation in tropical off-grid microgrids. Future extensions should include architecture-level re-optimization, flexible loads, degradation-aware modeling, and part-load component behavior. Full article

Affected by moisture cohesion, wet rice seeds exhibit poor flowability and frequent arching blockage during silo discharging, which seriously restricts stable grain storage and conveying. To address this issue and reveal its intrinsic flow mechanism, this study establishes a discrete element method (DEM) model for wet rice seed-silo systems adopting the Hertz-Mindlin with Johnson-Kendall-Roberts (JKR) contact model, which incorporates surface energy to reflect moisture-induced cohesive effects. The model is verified via physical silo discharge tests, with consistent flow patterns, wall pressure error below 3.7% and discharge time error of 2.14%. EDEM parametric simulations are conducted to analyze velocity fluctuation at different silo heights. Coordination number and normalized contact force distribution are adopted to assess micro-contact force distribution in discharge areas, and a force chain extraction algorithm is used to explore variations in force chain length and orientation. Results demonstrate that during discharge, average particle velocity drops from silo bottom to top with growing fluctuation amplitude, presenting obvious stratified flow and intense upper-layer velocity pulsation. Weak contacts dominate wet rice seed groups and conform to exponential decay distribution. The force chain network undergoes three evolution phases: formation, force arch generation and collapse. Quantitative analysis reveals long force chain proportion falls steadily from 81.40% to 3.68% throughout discharge. Short force chains rise to 60.54% in the arch-forming stage and reach 96.32% after arch collapse. Horizontal force chains account for a maximum of 71.09% during arch formation, while vertical ones decline from 99.52% initially to 61.57% post collapse. This research offers mechanical references and quantitative parameters for the design and operation of silos for wet granular farm grains like rice seeds, and is particularly relevant to post-harvest engineering, grain storage safety, and agricultural machinery design. Full article

In modern power systems, the rapid growth of renewable energy capacity, such as wind and solar photovoltaic (PV) power, has led to a decline in system equivalent inertia and primary frequency regulation margin. At the same time, net load fluctuations have intensified across multiple time scales, making it more likely for the RoCoF, frequency nadir, and quasi-steady-state frequency deviation to approach safety limits following disturbances. To achieve a balance between frequency security and economic operation, this paper proposes a two-stage stochastic frequency-security-constrained unit commitment (FSC-SUC) model tailored for scenarios with high renewable energy penetration. The day-ahead hourly dispatch stage jointly determines the on/off status and reference output of synchronous units and the reservation of slow frequency regulation capacity, as well as energy storage charging and discharging plans, SoC trajectories, and the reservation of fast frequency regulation capacity. The intraday minute-level real-time dispatch stage accommodates prediction errors through scenario-based rescheduling and ensures the deliverability of both slow and fast frequency regulation capabilities via commitment consistency constraints. To address the challenge of directly embedding frequency nadir constraints into mixed-integer optimization, this paper employs a modeling approach that combines analytical criteria with linear surrogate constraints. The RoCoF and quasi-steady-state frequency deviation are specified via aggregated analytical constraints, while the nadir is embedded into the main problem after generating samples offline using a simplified frequency response model and training a polyhedral linear surrogate for external approximation. The safety margin is then calibrated using high-quantile residuals from the validation set to ensure conservativeness. Case studies on the IEEE 33-bus system under different renewable penetration levels demonstrate that the proposed method significantly reduces the probability of frequency nadir violations and load-loss risk with only a modest cost increase while also improving coordination between fast and slow frequency regulation. Full article

This paper presents a comparative analysis of Flywheel Energy Storage Systems (FESS) employing Permanent Magnet Synchronous Machines (PMSMs) and AC Brushless DC (AC-BLDC) machines for fast and efficient frequency regulation. The study examines their electromechanical behavior during the key operational stages of charging, standby, and discharging, with a focus on mitigating inrush current and enhancing overall system efficiency. MATLAB/Simulink models were developed to evaluate machine dynamics, electromagnetic behavior, and harmonic distortion during their operation. The results show that electromagnetic effects, particularly inrush current, commutation harmonics, and inverter limitations, significantly influence torque smoothness, efficiency, and overall system performance. PMSMs demonstrate superior torque quality, lower Total Harmonic Distortion (THD), and more stable energy conversion under Field-oriented Control (FOC), making it well suited for high-performance FESS applications. In contrast, the AC-BLDC machine exhibits higher torque ripple and elevated THD due to six-step commutation but offers a simpler drive topology and cost advantages. The findings offer practical insights for selecting machines and controllers in high-speed FESS designs and emphasize the importance of mitigating transient electromagnetic effects to enhance efficiency and reliability in modern grid support applications. Improved modeling incorporating magnetic saturation, frequency-dependent iron losses, and inverter constraints is essential for accurate performance prediction. Future work includes Hardware-In-the-Loop (HIL), Power-HIL validation, and DlgSILENT PowerFactory co-simulation to confirm dynamic performance under grid-connected operation. Full article

The adoption of lithium-ion batteries (LIBs) as secondary rechargeable batteries across many industries, including consumer electronics, electromobility, industrial tools, and electrical energy storage, is on the rise. As lithium-ion batteries approach the end of their life, there is a need to assess them for the possibility of a secondary application or reuse for a less demanding application. The extra connections of individual cells, BMS, temperature sensors, and other components to form a compact battery pack pose a challenge for second-life assessment, which usually prefers to separate individual cells for testing before discarding very bad cells for recycling and grading cells with substantive capacity based on their remaining capacity. This is a high cost for the second-life assessment. This work seeks to investigate an approach that avoids dismantling the battery pack into individual modules, cells, and BMS by including a BMS feature that allows the capacity and power ratings to be rescaled onboard after its first use. A set of cells with different chemistries was used in this work: a nickel–cobalt–aluminium oxide cathode with a silicon-doped graphite anode (NCA-GS), a nickel–cobalt–aluminium oxide cathode and graphite, and a lithium–nickel–manganese–cobalt oxide (NMC) cathode with a graphite anode (NMC-G) with various ageing states and behaviours. Their internal resistance and capacity at the beginning and end of life were compared. The scaling factor was obtained by finding the square root of the ratio of the internal resistance at EOL to that at BOL. With the current obtained by multiplying the cycling current rate by the rescaling factor, the surface temperature profile of the aged cells during cycling became the same as the temperature at the beginning of life. The relaxation voltage after discharge to 0% SOC and charge to 100% SOC was used to set the low and high cut-off voltages, respectively. This contributed significantly to reduced ageing and to a lower temperature rise in the spent cells. This set the stage for rescaling or derating battery systems without separating the individual cells, which is a huge cost for second-life use of lithium-ion batteries. BMS can be designed with configurable voltage and current limits, so that when repurposed for a second life, only a simple configuration or firmware update may be necessary. Full article