Total Energy Storage Capacity Research Articles

Performance optimization of latent heat storage device based on surrogate-assisted multi-objective evolutionary algorithm and CFD method

The design of fin structures and the formulation of heat conductivity enhancers have always been critical factors influencing the performance of latent heat storage devices. However, achieving the optimal parameters of fin structures and the fraction of heat conductivity enhancers when adjusting multiple parameters simultaneously remains a time-consuming and labor-intensive task. In this paper, a combination of machine learning methods and computational fluid dynamics (CFD) was employed to optimize the parameters of fin structures and the mass fraction of expanded graphite with minor computational resources and time costs, thereby obtaining a set of Pareto optimal latent heat storage (LHS) devices that simultaneously considers energy storage power and energy storage capacity. The combination essentially is a surrogate assistant multi-objective evolutionary optimization algorithm, which utilizes batch recommendation strategies to recommend multiple high-quality candidate solutions that achieve a balance between two conflicting optimization objectives in CFD simulations. This method significantly reduces the number of model iterations and saves the time and computational resources required for multi-objective optimization. The results showed that the proposed algorithm only required 80 cases of CFD calculations to obtain two well-fitted Gaussian process models, leading to a 91 % improvement in computational efficiency. According to the recommendations from the algorithm, the LHS device with 78 fins of 2.0 mm thickness and 20 % mass fraction of expanded graphite could achieve the optimal trade-off of energy storage power and energy storage capacity. Compared to the prototype, the energy storage power and total energy storage capacity increased by 46.7 % and 22.1 %, respectively. The method proposed in this study can provide guidance for the optimal configuration design of LHS devices.

Experimental and numerical analysis of cosine wave heat source on thermal storage performance of a conical spiral shell-tube energy storage system

Solar radiation is the main driving force for the energy source of solar collectors, and its intensity determines the amount of energy that solar collectors can absorb. Therefore, the periodicity of radiation intensity will lead to periodic fluctuations in the outlet water temperature of solar collectors. This study numerically investigates the effects of the heat source period, amplitude, inlet flow rate, and steady state heat source temperature on the thermal storage performance of conical spiral shell-tube energy storage systems when the inlet temperature varies periodically as a cosine function using fluent software. The results show that when heat source periods are between 5 and 300 min, compared to the constant heat source, the total energy storage capacity can be increased by a maximum of 7.32 %. The melting time can be shortened by a maximum of 16.31 %. The average energy storage rate and energy storage efficiency can be increased by a maximum of 4.08 % and 0.17 %, respectively. When amplitudes are increased from 0 to 20 K, the melting time, total energy storage capacity, and energy storage efficiency are reduced by 30.21 %, 1.19 %, and 1.64 %, respectively. The average energy storage rate increases by 41.59 %. Furthermore, compared to the constant heat source, increasing the inlet flow rate and steady state heat source temperature has more significant effects on the thermal storage performance under cosine wave heat sources. The results can provide some reference for the optimization of phase change thermal storage systems under unsteady state conditions.

Lignin Functionalized with Catechol for Large‐Scale Organic Electrodes in Bio‐Based Batteries

Lignin, obtained as a waste product in huge quantities from the large‐scale cellulose processing industries, holds a great potential to be used as sustainable electrode material for large‐scale electroactive energy storage systems. The fixed number of redox‐active phenolic groups present within the lignin structure limits the electrochemical performance and the total energy storage capacity of the lignin‐based electrodes. Herein, the way to enhance the charge storage capacity of lignin by incorporating additional small catechol molecules into the lignin structure is demonstrated. The catechol derivatives are covalently attached to the lignin via aromatic electrophilic substitution reaction. The increased phenolic groups in all functionalized lignin derivatives notably increase the values of capacitance compared to pristine lignin. Further, solvent fractionation of lignin followed by functionalization using catechol boosts three times the charge capacity of lignin electrode.

The Capacity Configuration of Energy Storage System in DC Microgrid with Source-storage Integration

The occurrence of a fault in a DC microgrid can significantly jeopardize the system’s safe operation, making it a critical area of research for scholars. One key focus of this research is on developing methods to suppress the fault current, which has become a research hotspot for many scholars. Each distributed power source is connected to DC microgrid through a battery storage system to form a source-storage integration DC microgrid structure, which can have good fault current control ability and obvious improvement effect on reducing the protection technology difficulty of DC microgrid and enhancing the flexibility of distribution network. Compared with the traditional DC microgrid structure, the source-storage integration DC microgrid, whose battery storage system is changed from centralized to distributed, will smooth fluctuations in distributed power output by modifying energy storage planning principles, and also maintain bus voltage and realize fault current control with distributed power sources. Capacity planning principles for energy storage systems proposed in this paper were studied for DC microgrids with source-storage integration, and the total energy storage capacity and power under two DC microgrid structures were compared and analyzed with a scenic complementary power station as an example. Although a DC microgrid with a changed grid structure would require less than a 20% increase in the overall capacity and power of the energy storage system, according to the calculation results, the operation of the microgrid can be significantly improved, the flexibility of power dispatching of the distribution network was enhanced, and the investment cost of fault protection was reduced. Research into the capacity configuration of energy storage systems has demonstrated that DC microgrids with integrated source and storage capabilities hold significant engineering application value and practical significance.

Allocating the capacity of shared energy storage for wind farm groups based on the over-limit power export risk

Energy storage in wind farms can stabilize the fluctuation of wind power output. Shared energy storage can reduce the construction cost of energy storage devices and stimulate the enthusiasm of wind farms to invest in energy storage. The wind power base is composed of multiple wind farm groups. Existing research methods did not consider how to allocate shared energy storage among wind farm groups in the wind power base. This paper proposes an energy storage capacity allocation method for wind farm groups. Firstly, a bilevel model for the shared energy storage allocation is established. The upper-level model optimizes the shared energy storage allocation of each wind farm group with the goal of minimizing the over-limit power export risk in the wind power base; The lower-level model calculates the over-limit power export of each wind farm group according to the energy storage capacity allocation and transfers the value of over-limit power export to the upper-level model. The bilevel model can be converted to a two-stage model that can be solved sequentially; The wind power base in Belgium is used for numerical simulation to verify the effectiveness of the proposed model. Finally, the sensitivity of confidence level, total energy storage capacity, and risk preference factor are analyzed.

Geographic Information System-based Multi-Criteria Decision-Making analysis for assessing prospective locations of Pumped Hydro Energy Storage plants in Morocco: Towards efficient management of variable renewables

The considerable potential offered by wind and Solar Photovoltaic (SPV) energy, at competitive costs, constitutes a real opportunity to reduce CO2 emissions, thus contributing to significant decarbonization. Nevertheless, these sources require energy storage, which remains a key solution to mitigate their intermittency and variability, as they are dispatchable energy production systems. Among these latter, Pumped Hydro Energy Storage (PHES) stands as the most widely adopted technology for utility-scale applications, since it offers numerous advantages. Finding a suitable site for a PHES plant, however, remains a challenge for new project development, as it is highly dependent on topographic and geological site conditions. In this perspective, this paper presents an approach aiming at identifying and classifying appropriate locations for PHES plants based on the Analytic Hierarchy Process (AHP) method along with Geographic Information System (GIS) tools - ArcGIS 10.8. Considering the various PHES topologies, this assessment seeks to explore two: the first uses existing dams and lakes as primary reservoirs (Topology - T2), while the second considers the sea as a lower reservoir (Topology - T4). To our knowledge, this study introduces for the first time two novel decision criteria: evapotranspiration and sea surface salinity. These parameters lead respectively to evaporation losses from the storage reservoirs and corrosion effects on the different components of the installation. The proposed methodology was then applied to the case of Morocco, whereby the results revealed that a total of 1606 potential sites were identified, from which >36 % were deemed highly suitable. Furthermore, a total energy storage capacity of 6862 GWh was estimated from those locations, where about 72 % is represented by T2. This research work, the first of its kind for Morocco, aimed at securing cost-effective sites to help policy- and decision-makers develop strategies tailored to the country's conditions for a wide integration of variable renewables.

Numerical investigation of nano-enhanced phase change material melting in the 3D annular tube with spiral fins

In the annular tube with spiral fins, adding the nanoparticles in phase change material (nano-PCM) can significantly improve the energy storage efficiency. The use of spiral fins coupled with nanoparticles could greatly broaden the application of PCM in the annular tube in the energy storage field. However, the energy storage process of nano-PCM in the annular tube with spiral fins is a research gap that has not been investigated before. In this study, the energy storage process and enhancement rate of this system are numerically investigated, which could provide a reference for the future design of this energy storage system. Results show that the melting rate of PCM added graphene is six times as fast as PCM added Al2O3 in the same situation. Adding 1% graphene into the PCM could significantly enhance the energy storage process. Increasing the volume concentration of nanoparticles of Al2O3 or graphene from 0% to 5% reduces the total energy storage capacity per unit mass of nano-PCMs to 16.53% or 10.87%, but increasing the spiral cycle (the distortion degree of the spiral fin) does not. With the synergistic effects of spiral cycle and nanoparticles, the maximum enhancement rates of energy storage of PCM added Al2O3 or graphene are 40.28% and 92.84%, respectively.

Melting behavior and heat transfer performance of gallium for spacecraft thermal energy storage application

A typical low melting point metal (LMPM), gallium, is proposed for spacecraft thermal energy storage due to its superior thermal transport properties, and its dynamic melting behavior and heat transfer performance under microgravity are investigated. The role of thermocapillary convection in melting is analyzed, and the dimensionless equations for predicting liquid fraction as well as Nusselt number are developed. The results show that compared with conventional phase change materials including ice and n-octadecane, the utilization of gallium under microgravity can reduce the melting time by 88.3% and 96.4% respectively, while increase the total energy storage capacity by 20.7% and 123.3% respectively. The thermocapillary convection promotes the melting under microgravity, and the promotion effect for gallium is much weaker than that for ice or n-octadecane due to its smaller Marangoni number. The melting time of gallium, ice and n-octadecane under normal gravity are 65.8%, 39.4% and 69.2% less than those under microgravity respectively. The deviations of liquid fraction and Nusselt number predicted by dimensionless equations from numerical results are within ±10%. The results indicate that the thermal energy storage using gallium is effective for temperature control of spacecraft electronic devices under high and periodic heat flux.

Numerical Evaluation of the Transient Performance of Rock-Pile Seasonal Thermal Energy Storage Systems Coupled with Exhaust Heat Recovery

This study seeks to investigate the concept of using large waste rocks from mining operations as waste-heat thermal energy storage for remote arctic communities, both commercial and residential. It holds its novelty in analyzing such systems with an experimentally validated transient three-dimensional computational fluid dynamics and heat transfer model that accounts for interphase energy balance using a local thermal non-equilibrium approach. The system performance is evaluated for a wide range of distinct parameters, such as porosity between 0.2 and 0.5, fluid velocity from 0.01 to 0.07 m/s, and the aspect ratio of the bed between 1 and 1.35. It is demonstrated that the mass flow rate of the heat transfer fluid does not expressively impact the total energy storage capacity of the rock mass, but it does significantly affect the charge/discharge times. Finally, it is shown that porosity has the greatest impact on both fluid flow and heat transfer. The evaluations show that about 540 GJ can be stored on the bed with a porosity of 0.2, and about 350 GJ on the one with 0.35, while the intermediate porosity leads to a total of 450 GJ. Additionally, thermal capacity is deemed to be the most important thermophysical factor in thermal energy storage performance.

Energy Harvesting Communications With Batteries Having Cycle Constraints

Practical energy harvesting (EH) based communication systems typically use a battery to temporarily store the harvested energy prior to its use for communication. The battery capacity can quickly degrade with time if it is subject to repeated shallow charge-discharge cycles. This motivates the cycle constraint which mandates that a battery must be charged only after it is sufficiently discharged and vice versa. We consider a Bernoulli energy arrival model, and a half-duplex battery constraint. In this context, we study EH communication systems with: (a) a single battery with capacity $2{B}$ units and (b) dual batteries , each having capacity of ${B}$ units. The aim is to obtain the best possible long-term average throughputs in point-to-point (P2P) channels and multiple access channels (MAC). For the P2P channel, we obtain an analytical optimal solution in the single battery case, and propose optimal and suboptimal power allocation policies for the dual battery case. We extend these policies to obtain achievable throughput regions in MACs by jointly allocating rates and powers. From numerical simulations, we find that the optimal throughput in the dual battery case can be more than twice of that in the single battery case, although the total energy storage capacity in both cases is $2{B}$ units.

Enhancement of solid-phase thermal conductivity and specific heat of solar salt through addition of MWCNT: new observations and implications for thermal energy storage

Solid-phase thermophysical properties of solar salt (a mixture of NaNO3 and KNO3) influence the performance of sensible heat and latent heat thermal energy storage systems. Solar salt’s lower thermal conductivity imparts kinetic limitation during the discharge cycle and hence its thermal conductivity needs to be enhanced. This work is aimed at studying the influence of MWCNT incorporation on the improvement of solid-phase thermophysical properties of solar salt. Accordingly, experiments were carried out to study the influence of method of MWCNT-solar salt preparation, MWCNT concentration and temperature on solid-phase specific heat and thermal conductivity. Our results reveal that 0.5 wt% MWCNT-solar salt composite prepared by ultrasonication and milling for an appropriate time lead to 18.3% enhancement in the solid-phase thermal conductivity and 18% enhancement in the solid-phase specific heat. In addition, the total energy storage capacity over the temperature range of 50–270 °C (including solid–liquid phase change) is amplified by 11.5%. These results augur well for deployment of the MWCNT-solar salt composite in the thermal energy storage system as a storage medium.

Gravity energy storage with suspended weights for abandoned mine shafts

This paper investigates the potential of using gravity energy storage with suspended weights as a new technology for redeveloping abandoned deep mine shafts. The technology has relatively low energy density, but has advantages including a power capacity decoupled from its energy capacity, no cycle-limit and the potential to be combined with compressed air energy storage. It is currently being trialled in the United Kingdom, targeting abandoned coal mines. The paper presents analysis for sizing the suspended weight to maximize the energy storage capacity, given a mine shaft’s physical dimensions. In addition, it is shown that the power capacity of the system’s motor and power electronics determine the maximum ramp-rate, and therefore the range of power system services that can be provided. A case study is presented, estimating the total energy storage capacity which could be obtained by converting abandoned mines in the United Kingdom Midlands, using geographic information system data from the United Kingdom Government Coal Authority Abandoned Mine Catalogue.

Plate type heat exchanger for thermal energy storage and load shifting using phase change material

The study presents an experimental investigation of a thermal energy storage vessel for load-shifting purposes. The new heat storage vessel is a plate-type heat exchanger unit with water as the working fluid and a phase change material (PCM) as the energy storage medium. The thermal characteristics of the heat exchanger such as heat transfer coefficient, effectiveness, efficiency, water exit temperature, heat storage rate, total energy storage capacity and storage time were experimentally evaluated as a function of various inlet conditions. The compact parallel plate design showed an enhanced the performance compared to conventional storage systems with an effectiveness up to 83.1% even when a PCM of low thermal conductivity is used. The proposed phase change energy storage system not only can deliver substantial benefits as a thermal energy storage medium, but also provides cost savings in infrastructure, equipment, and maintenance/operations compared to conventional systems.

Synthesis of amorphous nickel–cobalt–manganese hydroxides for supercapacitor-battery hybrid energy storage system

In this work, amorphous nickel–cobalt–manganese hydroxide (NiCoMn–OH) was hydrothermally synthesized using a mixed solvent strategy and used as positive electrode materials for supercapacitor-battery hybrid energy storage system. The experimental results show that the mixed solvent is indispensable to form the amorphous phase of NiCoMn–OH, which exhibits significantly improved electrochemical activity and rate capability in comparison with the crystalline counterpart because of more grain boundaries and ion diffusion channels in the former phase. A strong synergy between the transition metal ions in the amorphous NiCoMn–OH is found to significantly contribute to the electrochemical activity, rate capability and cycling stability. In addition to battery behavior, the amorphous NiCoMn–OH exhibits pseudocapacitive behavior, which contributes approximately 40% to the total energy storage capacity. The pseudocapacitive property significantly enhances the rate performance. The robust synthesis method described in this paper was also used to fabricate the NiCoMn–OH porous network on Ni foam, which shows a specific capacity close to its theoretical value, indicating a complete utilization of the electroactive material. Furthermore, a supercapacitor-battery hybrid cell fabricated with the amorphous NiCoMn–OH as the positive electrode and reduced graphene oxide (RGO) as the negative electrode exhibits both high-energy and high-power performances with a specific energy of 42.8 Wh kg–1 at a specific power of 749 W kg–1 or a specific energy of 19.9 Wh kg–1 at a specific power of 20.9 kW kg–1.

Пропускная способность ограничителей перенапряжений в составе вакуумных выключателей постоянного тока

The article presents the results from numerical simulation and experimental investigation of the throughput capacity of Type 0PN-TP-3.0/4-UKhL 3 metal-oxide surge arresters (MOSA) used as part of a high-speed automatic DC vacuum circuit breaker for the maximal voltage equal to 4.1 kV. The vacuum circuit breaker operation principle isbased on forced lymaking the disconnected current to pass through zero by means of arranging opposite discharge of a pre-charged capacitor. A numerical model is proposed, whichhas been implemented in the Matlab 6.5 software package using the Sim Power Systems library. The applicability of the model has been experimentally confirmed in disconnecting a current by a vacuum circuit breaker through simulating a short-circuit fault current with different current growth rates. The investig a tions were carrie doutata heavy-current high-voltage test bench realizing an oscillatory circuit involving a capacitor bank for the maximal voltage of up to 6 kV and the total energy storage capacity of up to 1.8 MJ. The numerical model satisfactorily describes the processes in disconnecting acurrentina DC vacuum circuit breaker with forcedly making the current to cross zero. The model also make sit possible to estimate the amount of energy dissipated in the MOSA unit in disconnecting a short-circuit fault current. Byusing the proposed model itis also possible to estimate the number of parallel-connected MOSAs in disconnecting emergency currents in traction DC power supply networks with an inductance ranging from 5 to 15 mH.

Novel “open-sorption pipe” reactor for solar thermal energy storage

In the last decade sorption heat storage systems are gaining attention due to their high energy storage density and long term heat storage potential. Sorption reactor development is vital for future progress of these systems however little has done on this topic. In this study, a novel sorption pipe reactor for solar thermal energy storage is developed and experimentally investigated to fulfill this gap. The modular heat storage system consists of sorption pipe units with an internal perforated diffuser pipe network and the sorption material filled in between. Vermiculite–calcium chloride composite material was employed as the sorbent in the reactor and its thermal performance was investigated under different inlet air humidity levels. It was found that, a fourfold increase of absolute humidity difference of air led to approximately 2.3 times boost in average power output from 313W to 730W and an 8.8 times boost of average exergy from 4.8W to 42.3W. According to the testing results, each of three sorption pipes can provide an average air temperature lift of 24.1°C over 20h corresponding to a system total energy storage capacity of 25.5kWh and energy storage density of 290kWh/m3.Within the study, vermiculite–calcium chloride performance was also compared with the widely investigated Zeolite 13X. Vermiculite–calcium chloride showed a good cyclic ability at regeneration temperature of 80°C with a steadier thermal performance than Zeolite. Energetic and exergetic cyclic efficiencies varied in the range of 0.69→0.61 and 0.21→0.14 in the cycles performed with vermiculite–calcium chloride whilst energetic and exergetic cyclic efficiencies of Zeolite testing were between 0.72→0.48 and 0.25→0.06.

Thermophysical and Mechanical Properties of Hardened Cement Paste with Microencapsulated Phase Change Materials for Energy Storage.

In this research, structural-functional integrated cement-based materials were prepared by employing cement paste and a microencapsulated phase change material (MPCM) manufactured using urea-formaldehyde resin as the shell and paraffin as the core material. The encapsulation ratio of the MPCM could reach up to 91.21 wt%. Thermal energy storage cement pastes (TESCPs) incorporated with different MPCM contents (5%, 10%, 15%, 20% and 25% by weight of cement) were developed, and their thermal and mechanical properties were studied. The results showed that the total energy storage capacity of the hardened cement specimens with MPCM increased by up to 3.9-times compared with that of the control cement paste. The thermal conductivity at different temperature levels (35–36 °C, 55–56 °C and 72–74 °C) decreased with the increase of MPCM content, and the decrease was the highest when the temperature level was 55–56 °C. Moreover, the compressive strength, flexural strength and density of hardened cement paste decreased with the increase in MPCM content linearly. Among the evaluated properties, the compressive strength of TESCPs had a larger and faster degradation with the increase of MPCM content.

The economics of hybrid energy storage plant

Energy storage technologies all have different characteristics that make them suitable to particular purposes. A hybrid energy storage (HES) arrangement can take advantage of these differences. An example of this is a compressed-air energy storage plant with a flywheel mounted on the same shaft as the motor/generator and turbo machinery, where the flywheel would be used for high-frequency transactions with the grid while the compressed air store, with lower efficiency but also lower cost per unit of energy storage, could be used for longer term storage. This paper reports an algorithm which can be used to find the maximum arbitrage value achievable with a given HES plant for a given set of electricity prices. This is used in an optimisation routine to find the configuration of hybrid flywheel/compressed air plant that maximises potential arbitrage value. With realistic costs and efficiencies, it is found that the maximum annual return on investment is 0.29%, corresponding to a plant with 10% of its total energy storage capacity in the form of flywheel and the rest as compressed air.

Energy-storage capacity of the mitochondrial proton-motive force

Resting state respiration of rat-liver mitochondria in the presence of oligomycin was rapidly blocked with cyanide and the dissipation of the membrane potential was followed with a tetraphenylphosphonium-sensitive electrode. From the rate of this dissipation and the electric capacitance of the mitochondrial membrane the energy stored in form of the membrane potential was calculated as about 7 μJ/mg protein. In the absence of oligomycin, dissipation of the membrane potential was slower, as it was partly compensated by proton ejection by mitochondrial ATPase hydrolyzing endogenous ATP. This allowed to calculate the total energy storage capacity of the proton-motive force. It amounted to the equivalence of 3.3 nmol ATP/mg protein or about 130 μJ/mg protein. The stoichiometry of proton-pumping ATPase utilizing endogenous ATP was estimated as three protons per molecule ATP.