Search Results (70)

With the large-scale development of renewable energy such as wind, solar and ocean energy, the demand for energy storage is more urgent. Pumped hydro energy storage (PHES) is one of the fundamental solutions to the problem of intermittent supply of renewable energy. The large-capacity/low-head pumped hydro energy storage (LL-PHES) system with the use of tubular pump turbine is a beneficial extension of traditional PHES systems owing to large flow rate and cheaper civil structures. However, the continuous competition between the “static water pressure difference caused by gravity” and the “pressure increase caused by accelerated impeller rotation” leads to prominent instability in the start-up process of the LL-PHES system under pump conditions. An explicit coupling algorithm is proposed for analyzing the transient characteristics in the start-up process of the LL-PHES system under pump conditions. This algorithm is based on the idea of dimensional transformation, and performs 3D flow calculations and 2D rigid body dynamics equation solution in the pump domain and the flap gate domain, respectively. This algorithm avoids the problems of high computational cost and poor convergence that exist in existing fully three-dimensional coupling algorithms and ensures the efficiency of transient hydraulic characteristic calculation. A comprehensive analysis of the transient characteristics of the LL-PHES system during pump start-up process is conducted using the proposed new algorithm. The entire process of the increase in rotational speed, valve opening, flow rate, and the continuous evolution of blade surface pressure during the start-up process is quantitatively described. The amplitude and spectral characteristics of the alternating pressure on multiple blades are clarified. The evolution law of blade load during the stage of severe pressure fluctuations during the start-up process is explained. The load distribution characteristics of “high in the leading and trailing edge areas and low in the middle” in the blade stream direction is presented. The research results have a direct guiding role in improving the hydraulic design and enhancing the operational stability of LL-PHES systems. Full article

Gravity energy storage systems (GESS) have emerged as a promising long-duration energy storage technology capable of supporting large-scale renewable integration and enhancing grid resilience. However, the modeling framework for the hoisting electromechanical subsystem in wire-rope-based GESS remains underdeveloped, thereby limiting the accurate characterization of its transient grid-connected behavior, dynamic operating response, and cross-domain coupling effects. Existing studies commonly simplify wire ropes and related transmission components as rigid bodies or low-dimensional mechanical elements, failing to adequately account for their flexibility and the resulting high-dimensional nonlinear dynamics. Although related studies in mine hoisting and elevator systems have addressed mechanical vibration phenomena, they primarily focus on mechanical-side effects, such as shock loading and guide-structure response, whereas the mechanism by which flexible mechanical vibrations propagate through electromechanical coupling and influence electrical dynamic performance remains inadequately understood. To address this gap, this study establishes a distributed-parameter model for the wire-rope hoisting mechanism based on Hamilton’s principle and solves the corresponding vibration governing equations using the Galerkin method to capture nonlinear multi-modal dynamics. An electromechanical coupling model is then developed to elucidate how rope-vibration-induced tension fluctuations propagate through the drive chain, resulting in torque ripple, electrical interharmonics, and low-frequency grid-side oscillations. A Bessel-function-based analytical representation is further introduced to explain the formation of interharmonic clusters and beat-frequency phenomena under converter modulation. An experimental prototype is constructed to validate the proposed modeling framework. The measured vibration spectra, beat-frequency characteristics, and torque ripple align closely with analytical predictions, confirming the model’s capability to capture key propagation paths from rope vibration to electromechanical oscillation and grid-side dynamic response. The results provide a solid theoretical foundation for vibration mitigation, dynamic analysis, and control design of hoisting electromechanical subsystems in gravity energy storage applications. Full article

Hydrogen has the potential to revolutionize the aviation industry by transitioning aviation into a zero-carbon industry. However, realizing this vision requires overcoming significant technological challenges, particularly in hydrogen storage, distribution, and safety. The DEMOCRITE (Development of Modular Cryogenic Tank system) project is collaborative research within the EREA, the Association of European Research Establishments in Aviation, focusing on composite cryogenic hydrogen tanks for hydrogen-powered aircraft. This paper addresses the energy storage capability of modular hydrogen tanks and the related A/C integration aspects. Using multiple parameters (weight, center of gravity, passenger count), different tank arrangements are proposed and evaluated in search for the most optimal solution. Pressure management of cryogenic hydrogen tanks is also discussed. Full article

To investigate the dynamic characteristics of key parameters in a piston gravity energy-storage system, an experimental system for novel piston gravity energy storage is designed and developed. Firstly, the structure and working principle of the piston gravity energy-storage system are analyzed. Adopting a modular modeling approach, the system is divided into four core modules, and the piston motion, vertical cylinder chamber pressure, hydraulic actuator, and turbine power models are established. Subsequently, a case study simulation is conducted on the piston gravity energy-storage system to model its dynamic characteristics during discharge conditions, analyzing the variation patterns of key parameters such as the chamber pressure, flow rate, and output power within the system. Finally, the experimental system integrates a digital controller with proportional–integral power regulation and an automatic mode switching logic to enable the constant power closed-loop control, with real-time acquisition of the chamber height, pressure, flow rate, and electrical parameters. The dynamic responses of various system parameters are analyzed. Experimental results indicate that under constant power charging and discharging conditions, the height of the upper chamber exhibits a linear trend, the pressure in the lower chamber is inversely proportional to the height of the upper chamber, and the flow rate remains stable with charging and discharging power. Neglecting energy losses of the pump and hydraulic turbine and only considering friction and hydraulic losses, the charge–discharge efficiency of the energy-storage experimental system is 65%. Full article

Under the background of global change, the threshold for the propagation of meteorological drought to hydrological drought is crucial for drought early warning and water resource management. However, traditional threshold studies often adopt subjective and fixed conditional probabilities and lack the revelation of the driving mechanisms under macroscopic natural geographical differentiation. This study integrates terrestrial water storage anomaly (TWSA) data derived from the Gravity Recovery and Climate Experiment (GRACE) and its Follow-On (GRACE-FO) mission, the standardized precipitation evapotranspiration index (SPEI), and multi-source environmental data to construct an objective threshold identification method based on Copula joint distribution and “system resilience loss”, and combines explainable machine learning to systematically explore the critical threshold for meteorological drought, triggering a TWSA deficit and its driving mechanisms from the perspectives of three major natural regions, the Eastern Monsoon Region (EMR), the Northwestern Arid Region (NAR), and the Tibetan Plateau Region (TPR). The results show that: (1) from 2005 to 2024, the TWSA significantly decreased in nearly half of China’s regions, with significant regional differentiation; (2) the response of the TWSA to meteorological drought has a significant lag (an average of 9–12 months), and shows a spatial pattern of slower in the east and faster in the northwest; (3) the probability of a TWSA deficit and the triggering threshold both have obvious grade dependence and spatial heterogeneity, with the lowest threshold in the northwest arid region, which is the most sensitive; (4) the threshold is driven by the synergy of multiple factors, with “water dominance and energy modulation”, and the dominant factors show regional differentiation; and (5) irrigation agriculture significantly reduces the drought triggering threshold and exacerbates system vulnerability. This study provides a scientific basis for understanding the geographical differentiation laws of drought propagation and regional early warning management. Full article

With the increasing power fluctuations and growing pressure on grid stability resulting from the high penetration of renewable energy, the demand for exploring various energy storage technologies with large-scale, long-duration, and low-cost features has become increasingly urgent. This paper proposes a novel single-track gravity energy storage generation system. This system utilizes non-standardized masses (such as natural rocks) operating stably on an inclined track, and combines coordinated feedforward–feedback electromagnetic torque control, multi-station loading scheduling, and synchronous loading/unloading strategies to effectively smooth the power fluctuations of renewable energy sources such as wind power. The core innovations of this system lie in: (1) utilizing non-standardized mass units to achieve gravity energy storage, thereby expanding the application scenarios and design flexibility of solid gravity energy storage systems; and (2) introducing intelligent scheduling strategies and multi-station loading coordination to effectively smooth the power output fluctuations caused by load randomness, rendering the system insensitive to load variations. Simulation results verify that, for power smoothing in a 10 MW-level wind farm, the system can accurately track the target power and maintain a stable output over a long duration. The power fluctuations are controlled to under 0.2%, even when the total load varies by 10% and the instantaneous load fluctuates by 5%. This system demonstrates the theoretical feasibility and scalability of utilizing natural rock resources in mountainous terrains for long-duration energy storage, providing a novel solution for long-duration power smoothing in renewable energy systems. Full article

Assessing the development potential of gravity energy storage (GES) in mining goafs is vital for the integrating new energy power generation, achieving carbon neutrality goals, and transforming resource-based mining cities. This study proposes an integrated evaluation system using time-series interferometric synthetic aperture radar (InSAR) and a geographic information system (GIS) to assess the safe development potential of GES in goafs. First, a goaf subsidence risk model is constructed based on time-series InSAR. Subsequently, a GES development suitability model is established by integrating environmental parameters including topography and geomorphology. Finally, the GES development potential of goafs is quantitatively evaluated based on energy storage capacity and the Levelized Cost of Gravity Storage (LCOGS). A case study in Yangquan demonstrates that, based on SBAS-InSAR monitoring results from 2021 to 2022, seven out of eight closed mining areas covering a total area of 53.91 km² are suitable for the development of GES facilities. Under defined scenarios, the Nanzhuang Mining Area demonstrates particularly strong potential, with a projected energy storage scale of 410 MWh and an LCOGS of 0.5894 CNY/kWh, indicating good GES development potential. The proposed safety-constrained workflow provides a robust tool to guide GES development in goafs and is transferable to other resource-based and post-mining cities worldwide. Full article

Background/Objectives: In pole vaulting, the capacity to store elastic energy within the pole (E_pole) significantly influences performance. This study investigated the characteristics of E_pole storage by analyzing the box reaction force and vector angle. Methods: Eight male pole vaulters, including World Championships participants, were examined. A motion capture system (VICON) and force plates (Kistler) were used to measure the vector angle (angle between the compression force (CF) and box reaction force vectors) and horizontal velocity of the center of gravity (COG) (Vcogh). E_pole was calculated as the integral of the CF (estimated from the box reaction forces), and pole bending displacement. The relationships between each variable and the peak height of COG (HP) were assessed using Pearson’s product–moment correlation coefficients. Results: HP correlated with Vcogh in the pole plant (PP) (r = 0.82) and E_pole (r = 0.94). Vaulters with a higher HP maintained a vector angle < 2° between 20% and 80% of the pole bending phase, indicating closer directional alignment between the box reaction force vector and pole chord direction, whereas vaulters with lower HP exhibited larger vector angles (4–8°), associated with a relative reduction in the axial component of force transmitted to the pole. Conclusions: A smaller vector angle effectively enhanced the CF, thereby increasing pole bending and promoting greater accumulation of E_pole. Therefore, maintaining a small vector angle may enable more effective force transmission along the pole chord, and vector angle characteristics and PP horizontal velocity may assist appropriate pole selection and training strategies to enhance elastic energy storage and performance. Full article

This paper presents a patented design of a gravity flow rack with an energy recovery system, intended for pallet storage in first-in–first-out (FIFO) and last-in–first-out (LIFO) modes. Compared with conventional flow racks, the proposed solution integrates control of load-unit motion dynamics with energy recovery, thereby reducing losses and stabilising pallet flow. A Rack Energy Performance Index (REPI) is proposed to enable quantitative assessment of the energy consumption of storage racks in intralogistics applications. The research methodology comprised: (i) development of the mechanical architecture and pallet guidance principles; (ii) numerical modelling in the MSC Adams environment at Technology Readiness Level 3 (TRL-3); and (iii) validation using a full-scale prototype installed in a logistics centre. Operational tests confirmed stable operation, the required throughput, and the capability for energy compensation and recovery during storage cycles. The results indicate that energy-recovering racks can support the design of energetically passive warehouses. Full article

This study presents a review of passive linear gravity compensation (GC) mechanisms. Linear GC is defined as the realization of a displacement-independent constant upward force along a vertical axis to balance the gravitational load over the entire stroke. This paper focuses on passive systems that counteract gravity solely through mechanical or magnetic energy storage elements, without relying on external power sources. The main energy sources in passive systems—springs, permanent magnets, counterweights, and fluid pressure—are surveyed with emphasis on their ability to generate a constant force. Representative spring-based constant-force mechanisms, cam–spring linkages, and quasi-zero-stiffness magnetic gravity compensators are summarized, together with their applications in vibration isolation systems. Finally, reported performance data are compiled to outline the practical operating envelope of passive linear GC in terms of force level, stroke, and equivalent stiffness. This review reveals that permanent-magnet-based approaches are advantageous for short-stroke, high-precision applications, whereas spring-based mechanisms offer superior suitability for long-stroke requirements due to their greater design flexibility. Consequently, this review provides a strategic selection guideline based on the inherent trade-offs of energy-storage elements to meet specific application requirements. Full article

Gravity storage has become an important development direction of physical energy storage technology due to its high energy conversion efficiency and low site selection difficulty. However, the existing gravity energy storage systems based on pure mechanical transmission still have shortcomings, such as low reliability and high operation and maintenance costs, which seriously limit their promotion. To overcome this obstacle, this paper proposes a linear-motor direct-drive gravity energy storage system (LMDD-GESS) with a simpler structure and higher energy conversion efficiency. The cableless flux-switching permanent magnet linear motor (SFPMLSM) is used to replace the traditional wire rope or chain transmission mechanism and fundamentally eliminates frictional losses. Firstly, in terms of the SFPMLSM, the thrust fluctuation is suppressed through the integrated design of the permanent magnet and armature winding on the mover side and the optimization of the end magnetic blocks. In terms of the system grid connection, the double-closed-loop PI control of the machine side and the three-level coordination strategy of the grid side are established, and the in-phase carrier PWM modulation and harmonic feedback compensation algorithm are used to improve the quality of grid connection. The speed curve optimization and multi-machine-switching scheme are designed to achieve smooth power output. The simulation results show that the proposed system significantly improves the operation efficiency and power output stability and provides a reliable gravity energy storage solution for the high proportion of new energy grids. Full article

This paper introduces a novel stochastic multi-objective optimization framework for the integration of gravity energy storage (GES) with renewable resources—photovoltaic (PV) and wind turbine (WT)—in distribution networks incorporating demand response (DR), addressing key gaps in uncertainty handling and optimization efficiency. The GES plays a pivotal role in this framework by contributing to a techno-economic improvement in distribution networks through enhanced flexibility and a more effective utilization of intermittent renewable energy generation and economically viable storage capacity. The proposed multi-objective model aims to minimize energy losses, pollution costs, and investment and operational expenses. A new multi-objective enhanced weighted average algorithm integrated with an elite selection mechanism (MO-EWAA) is proposed to determine the optimal sizing and placement of PV, WT, and GES units. To address uncertainties in renewable generation and load demand, the two-point estimation method (2m + 1 PEM) is employed. Simulation results on a standard 33-bus test system demonstrate that the coordinated use of GES with renewables reduces energy losses and emission costs by 14.55% and 0.21%, respectively, compared to scenarios without storage, and incorporating the DR decreases the different costs. Moreover, incorporating the stochastic model increases the costs of energy losses, pollution, and investment and operation by 6.50%, 2.056%, and 3.94%, respectively, due to uncertainty. The MO-EWAA outperforms conventional MO-WAA and multi-objective particle swarm optimization (MO-PSO) in computational efficiency and solution quality, confirming its effectiveness for stochastic multi-objective optimization in distribution networks. Full article

The International Energy Agency (IEA) asserts that worldwide electricity demand is rising exponentially every year. Energy storage is the cornerstone of electricity demand. Gravity-based energy storage systems represent the optimum alternative for energy storage systems. They offer zero carbon emission, environmental sustainability, cost-effectiveness, geographical flexibility, long-duration storage, and scalability ranging from 0.5 to 10 GWh. This research introduces a novel design to confirm the workability of the gravity energy storage model. It validates the feasibility of the system through the drive train setup. The drive train model involves storing potential energy by elevating the stack weight using solar photovoltaic input and releasing the weight to generate electrical energy using the gravitational field. The gravity motion is theoretically proven by the mathematical analysis, drive train control system transfer function model, and golden ratio-based design. Solidworks simulation model enhances the working of the drive train setup. Through hardware iterative experimental results with different load profiles, validate the performance metrics. The gravity energy storage system’s feasibility is demonstrated by its scalability in comparison with battery energy systems. Gravity-based energy storage is the best option for utility-scale renewable energy grid integration, since it has a low energy density, medium and large capacity, long-lasting storage, and high scalability. Full article

This paper presents an optimized control strategy based on a Doubly Fed Induction Generator (DFIG) and Gravity Energy Storage System (GESS) for AC voltage support in unbalanced grid conditions. The presented control aims to achieve precise rotational speed control, voltage stabilization, and harmonic component suppression. The optimization strategy responds to voltage and frequency fluctuations in an unbalanced grid. Based on Grid-Forming (GFM) control, it adjusts the DFIG’s operating state in real time. This ensures stable voltage support and mitigates harmonic distortion caused by the unbalanced grid. Simulation results, under a weak grid (SCR = 3) and unbalanced (0.9 p.u. voltage sag) conditions, validate the strategy, which reduces rotor current THD from 12.57% to 1.71% and maintains precise speed tracking during a 0.8 p.u. to 0.7 p.u. load change. The results demonstrate that the presented control method effectively improves grid power quality. It also enhances system stability and reliability. This approach provides strong support for integrating renewable energy into unbalanced grids. Full article

In order to ensure the reliable operation of a gravity energy storage system and reduce a converter’s cost and power rating, this paper proposes a gravity energy storage system (GESS) based on a doubly fed induction generator (DFIG). To address the issues of low inertia and limited grid-support capability, a speed-adaptive droop control strategy is introduced. The droop curve can be adjusted automatically according to the speed variation. Thereby, the GESS can effectively provide grid support through rotor-speed control. A simulation model of the DFIG-based GESS is developed in MATLAB/Simulink 2024b, and the grid-support capability of the proposed control strategy is verified under various operating conditions. Full article