Energy Storage Cycle Research Articles

Modeling of energy carrier in solar-driven calcium-looping for thermochemical energy storage: Heat-mass transfer, chemical reaction and stress response

The solar-driven calcium looping process (CaL) poses a great potential for thermochemical energy storage. The calcium-based particle, a core energy carrier for CaL, however, is prone to fragmentation, significantly reducing the efficiency and stability of energy storage. In this work, a particle scale model for core–shell structured energy carrier that considers the heat transfer, hierarchical reaction, mass transport and thermal stress processes is proposed to study the characteristics of energy storage performance. The multiprocess model confirms that stress failure at the particle center is the main reason of energy carrier fragmentation, resulting from the exceedingly high radial tensile stress. To improve the energy storage performance, the operation conditions and modified particle properties of CaL are investigated. It was found that the thermal stress can be relieved with the reduction of energy carrier temperature, while energy storage efficiency is decreased. In addition, the thermal stress can also be reduced by an appropriate increase in the airflow temperature without sacrificing the efficiency. Moreover, energy carrier can yield a high energy storage efficiency and cycle stability when the radius falls into 300–500 μm.

Thermo-economic performance of a compressed CO2 energy storage system with a flexible gas holder

In recent years, engineers' eyes have been increasingly captured by the compressed CO2 energy storage since it is a competitive electricity storage technology equipped with massive renewable power plants. Nevertheless, how to design an effective system configuration, for instance the scenarios of storing CO2 in high and low pressures, vacillates to the left and right in the researchers. A CO2 energy storage cycle, configured by three section compression/expansion, two-tank heat storage, artificial tank for storing high pressure CO2 liquid and gas holder for storing ambient pressure CO2, is comprehensively examined in this paper. Both the thermodynamic and economic performances are considered. Results demonstrate that the round trip efficiency is capable of arriving at 71 % along with the levelized cost of electricity being 0.1252 $/kWh. Inspiringly, the system is operated with low pressures, charge pressure being 8 MPa and discharge pressure being 6 MPa. The turbomachineries are provided with the 68.18 % share of overall exergy destruction. The high pressure heater carries the largest exergy destruction among heat exchangers. By integrating with low grade waste heat of 39 °C, the efficiency can be further improved to 72.66 % with the levelized cost of electricity being 0.1242 $/kWh. Meanwhile, the discharge pressure should be raised to 6.58 MPa.

Energy and exergy performance evaluation of a novel low-temperature physical energy storage system consisting of compressed CO2 energy storage and Kalina cycle

To improve the overall performance of the Compressed CO2 Energy Storage (CCES) system under low-temperature thermal energy storage conditions, this paper proposed a novel low-temperature physical energy storage system consisting of CCES and Kalina cycle. The thermal energy storage temperature was controlled below 200 °C, and the Kalina cycle was used to optimize the reuse of the stored thermal energy. A thermodynamic model of the integrated system was constructed, and the system performance was analyzed from the energy and exergy perspectives. Several evaluation indicators, such as system exergy efficiency (SEE), round trip efficiency (RTE), system energy density (SED), Kalina exergy efficiency (KEE), and Kalina energy efficiency (KEnE), were defined to evaluate system performance. In addition, the influences of several core parameters (e.g., split ratio (r), storage pressure (ps), turbine efficiency (te), pinch point temperature difference (pt) of heat exchangers, and ambient temperature (T0)) on the system performance were analyzed. The results of the base condition showed that SEE, RTE, SED, KEE, and KEnE were 58.17 %, 59.38 %, 6.32 kWh/m3, 38.62 %, and 8.64 %, respectively. The exergy destruction in heat exchanger 3 was the largest, accounting for 71.7 % of total exergy destruction. The sensitivity analysis results showed that increasing r could increase the SEE of the system, increasing ps could lead to a decrease in the RTE of the system, and increasing T0 could cause the RTE and SED to increase. The increase in te could improve all evaluation indices, while the increase in pt could reduce the system's overall performance. This study provides a new solution for the integrated application and optimal design of CCES systems under low-temperature thermal energy storage conditions.

Compressed air seesaw energy storage: A solution for long-term electricity storage

The globe is witnessing a significant energy transformation with an increasing proportion of variable energy sources like wind and solar on the grid. Energy storage solutions are required to enable a seamless integration of these renewable energy sources. This paper presents a novel isothermal compressed air energy storage (CAES) consisting of two floating storage vessels in the deep ocean that operates by balancing the pressure of the upper and lower tanks with the oceanic pressure. The methodology consists of estimating the proposed system's energy storage potential and operational parametrization. Results show that the maximum compression ratio between the two storage vessels is four, which significantly increases the system's efficiency and lowers compression costs. Compressed air seesaw energy storage is a cheap alternative for storing compressed air because it does not require large, pressurized tanks or sand cavers. It is expected to cost between 10 and 50 USD/kWh for electric energy storage and between 800 and 1500 USD/kW for the installed power capacity. Seesaw is an interesting alternative to pumped hydro and hydrogen for long-term energy storage cycles in islands and coastal regions close to the deep sea.

Underground Gravity Energy Storage: A Solution for Long-Term Energy Storage

Low-carbon energy transitions taking place worldwide are primarily driven by the integration of renewable energy sources such as wind and solar power. These variable renewable energy (VRE) sources require energy storage options to match energy demand reliably at different time scales. This article suggests using a gravitational-based energy storage method by making use of decommissioned underground mines as storage reservoirs, using a vertical shaft and electric motor/generators for lifting and dumping large volumes of sand. The proposed technology, called Underground Gravity Energy Storage (UGES), can discharge electricity by lowering large volumes of sand into an underground mine through the mine shaft. When there is excess electrical energy in the grid, UGES can store electricity by elevating sand from the mine and depositing it in upper storage sites on top of the mine. Unlike battery energy storage, the energy storage medium of UGES is sand, which means the self-discharge rate of the system is zero, enabling ultra-long energy storage times. Furthermore, the use of sand as storage media alleviates any risk for contaminating underground water resources as opposed to an underground pumped hydro storage alternative. UGES offers weekly to pluriannual energy storage cycles with energy storage investment costs of about 1 to 10 USD/kWh. The technology is estimated to have a global energy storage potential of 7 to 70 TWh and can support sustainable development, mainly by providing seasonal energy storage services.

Thermodynamic analysis and economic assessment of a novel multi-generation liquid air energy storage system coupled with thermochemical energy storage and gas turbine combined cycle

Liquid air energy storage (LAES) is one of the most promising technologies to balance the demand and supply of electricity, which is attracting more and more researchers' attention, but the system's efficiency is still relatively low. To further improve the round trip efficiency (RTE) and energy utilization rate (EUR) of the LAES system, a novel LAES system coupled with thermochemical energy storage (TCES) and gas turbine combined cycle (GTCC) is proposed in this paper. In addition, based on the baseline liquid air energy storage (B-LAES) system, an improved liquid air energy storage (I-LAES) system is also proposed to utilize the excess air compression heat to produce cold energy or thermal energy under different operation modes. Thermodynamic analysis and economic assessment are performed to evaluate these three systems' performances. Compared with the B-LAES system and the I-LAES system, the LAES-TCES-GTCC system has the highest RTE of 123.07 % and the highest EUR of 88.74 %. The LAES-TCES-GTCC system also has the best economic feasibility, with a net present value of $24.08 million and a dynamic payback period of 7.29 years. For the novel LAES-TCES-GTCC system, enhancing the methanol decomposition pressure, direct normal irradiation, and mass flow of vapor all reduce the EUR. And the EUR reaches the maximum at an inlet air temperature of the throttle valve of −168 °C.

Covalent organic frameworks for next-generation of lithium-ion batteries

The demand to develop lithium-ion batteries (LIBs) is growing as their consumption in various applications rises. In this regard, it is very important to pay attention to materials with suitable properties for use in LIBs. The energy storage capacity, cycle life, weight, and recycling of aging batteries are expected to improve with these materials. Recently, covalent organic frameworks (COFs) have shown great promise for use in cathode, anode, electrolyte, and separators of LIBs due to their numerous properties, including porosity and excellent physical and chemical stability. This review discusses the application of COFs in the next-generation of LIBs. First of all, the Main components, working principles, and characteristics of LIBs are described. After that, the advantages, applications, and synthesis methods of COFs are discussed. Finally, the application of COFs in various parts of LIBs by key features and the associated challenges is highlighted. In this review, we focus on improving batteries by introducing and developing COFs as a new-generation of materials for energy storage applications to overcome the current limitations and provide promising alternatives for current LIBs.

Hydrophilic fillers for anione exchange membranes of alkaline water electrolyzers

Alkaline water electrolysers are widespread in many industries, including systems with hydrogen cycle of energy storage. One of the problems of modern alkaline water electrolysers is insufficient purity of generated electrolysis gases relative to electrolysis systems with solid-polymer electrolyte. In this regard, work on modification of existing porous diaphragms is actively carried out. One new area of research is the impregnation of new hydrophilic fillers into the composition of existing diaphragms and the transition to ion-solvate membranes. In this work the synthesis of zirconium hydroxide hydrogel inside a porous diaphragm with the hydrophilic filler TiO2 was carried out. This synthesis makes it possible to obtain a membrane with anion-exchange properties. A possible mechanism of OH- hydroxyl ion transfer by immobilized K+ ion was also proposed. The obtained results demonstrated the resistance of the membrane to concentrated alkaline solutions.

Electrochemical Properties of Tin-Antimony Sulfide Nanocomposites Synthesized by Hydrothermal Method as Anode Materials for Sodium Ion Batteries

Tin-antimony sulfide nanocomposites were prepared via hydrothermal synthesis and a N2 reduction process for use as a negative electrode in a sodium ion battery. The electrochemical energy storage performance of the battery was analyzed according to the tin-antimony composition. The optimized sulfides exhibited superior charge/discharge capacity (770 mAh g-1 at a current density of 100 mA g-1) and stable lifespan characteristics (71.2 % after 200 cycles at a current density of 500 mA g-1). It exhibited a reversible characteristic, continuously participating in the charge-discharge process. The improved electrochemical energy storage performance and cycle stability was attributed to the small particle size, by controlling the composition of the tin-antimony sulfide. By optimizing the tin-antimony ratio during the synthesis process, it did not deviate from the solubility limit. Graphene oxide also acts to suppress volume expansion during reversible electrochemical reaction. Based on these results, tin-antimony sulfide is considered a promising anode material for a sodium ion battery used as a medium-to-large energy storage source.

Thermodynamic analysis and optimization of a multi-stage Rankine cycle power system combining with hydrate energy storage for liquefied natural gas cold energy utilization

Natural gas (NG) as a primary energy source plays an important in industrial systems. Natural gas generally needs to be converted into liquified natural gas (LNG) during transportation and stored at a low temperature (around-162 °C), which contains a large amount of cold energy that can be used. The discharge of cold energy into the ocean or atmosphere will cause not only energy waste but also environmental pollution. In order to recover LNG cold energy more efficiently, a novel LNG cold energy utilization system integrating Organic Rankine cycle (ORC), transcritical CO2 cycle (TRCC), CO2 energy storage and seawater ice-making cycle and combustion power system is proposed and investigated in this study. Energy analysis and exergy analysis were studied in details. The exergy efficiency and net electric generation (NEG) were analyzed and optimized using the optimizer in Aspen HYSYS. The results reveal that, exergy loss ratio of combustion power system and CO2 energy storage system are relatively larger than that of other subsystems. In addition, The ORC performance of six working fluids was analyzed. The NEG of R290 and R1270 as working fluid of ORC is significantly higher than that of the other four working fluids. Under the condition of basic process simulation, the NEG of ORC and TRCC is 223.7 kW and 216.4 kW, respectively. The total exergy efficiency reaches 39.01 %. After parameter optimization in the optimizer, the total NEG of ORC and TRCC increases by 6.9 % from 440.1 kW to 470.6 kW and the exergy efficiency can reach 39.8 %.

Dynamic Voltage Unbalance Constrained Economic Dispatch for Electrified Railways Integrated Energy Storage

The cophase traction power supply system (CTPSS) is a promising solution in the smart electrified railways to effectively eliminate the neutral section, improve regeneration braking energy (RBE) utilization and mitigate voltage unbalance (VU). It works by coordinating the power flow distribution (PFD) among the energy storage (ES), power flow controller, and traction transformer. However, the conventional dispatch considering VU mitigation may result in increasing extra operation costs and accelerating ES aging. Therefore, driven by the day-ahead forecasted information, a dynamic VU regulation strategy is proposed to draw up the VU compensation schedule (VU-CS), which can satisfy the probabilistic limitations of power quality standards. Consequently, a Copula-based VU dependence model is developed to transform the VU-CS into the PFD constraint set of CTPSS. Meanwhile, an ES degradation model is introduced to quantify the system operation cost within different scenarios. Taking the PFD as a VU regulation constraint, an economic dispatch scheme of CTPSS is established to obtain a minimum operation cost and maximum RBE utilization. Finally, case study tests verify the efficiency of the proposed approach. The results show that scheme can improve ES cycle life and decrease cost under the probabilistic limitations of VU.

Attributes of Bi-Directional Turbomachinery for Pumped Thermal Energy Storage

Abstract In this paper, we (i) present a methodology for determining the aerodynamic performance of bi-directional turbomachines for pumped thermal energy storage, i.e., turbomachines designed to operate as a compressor in one direction, and then as a turbine in the opposite direction, (ii) carry out performance computations for such turbomachines, and (iii) propose principles for conceptual design of these devices. Focus is placed on using the energy storage cycle not only to identify the novel requirements placed on bi-directional turbomachines but also to estimate the effect of these requirements on the efficiency of the energy storage process. In particular, the difference between aerodynamic loading in forward and in backward operation causes the blading to work at incidences leading to the performance below maximum efficiency, resulting in a lower round-trip efficiency. The description of the design principles includes determination of the number of stages, definition of nondimensional parameters for blading selection, and optimization of two-dimensional blading for bi-directional operation. The assessment of stage count shows the relationship between relative Mach number, pressure ratio, and round-trip efficiency. The nondimensional parameters are assessed through a bi-directional analogue to existing “Smith charts,” for the efficiency of single-direction turbomachines, as a function of camber and stagger. The blade shape evaluation and optimization show how the blade profile can be modified to address the requirements of a bi-directional turbomachine, enabling an increase in round-trip efficiency of two percentage points compared to a baseline double circular arc configuration.

Enhanced energy storage properties and large electrostrictive effect of Bi0.35Na0.35Ba0.09Sr0.21Ti(1-x)(Al0.5Nb0.5)xO3 relaxor ceramics

Ferroelectric ceramics have good piezoelectric and ferroelectric properties and can be used for energy storage equipment and actuators. Nevertheless, current research on dielectric capacitors has only focused on the energy storage density, but ignored efficiency. Moreover, conventional piezoelectric materials have a large strain hysteresis. In this work, (Al0.5Nb0.5)4+ (AN) complex ions doped 0.7Bi0.5Na0.5TiO3-0.3Ba0.3Sr0.7TiO3 (BNBST) ceramics were prepared. Doping AN destroyed the long-range ordered ferroelectric domains and generated polar nano regions, resulting in a gradual thinning and inclination of polarization hysteresis loops and an increase in relaxor degree. For BNBST-3AN ceramics, a Wrec of 1.52 J/cm3 and a η of 92.1% were achieved at 150 kV/cm. Meanwhile, BNBST-3AN ceramics had good energy storage temperature stability and cycling performance. The AN doping reduced the strain hysteresis in BNBST ceramics. BNBST-2AN ceramics exhibited a longitudinal electrostrictive coefficient Q33 ∼ 0.0292 m4/C2 and a field-induced strain of 0.25% with low strain hysteresis (6.67%). Furthermore, BNBST-4AN ceramics had superior dielectric temperature stability from 24 to 270 °C. All results show that BNBST-100xAN ceramics have great promise for energy storage devices and actuators.

Thermodynamic analysis of a novel absorption thermochemical energy storage cycle with double compression coupled two-stage generation

• An energy storage cycle obtaining low T g and higher COP and ESD was proposed. • COP using LiNO 3 -[BMIM]NO 3 /H 2 O working fluid was 12.5 and ESD was up to 406 kJ·kg −1 . • This cycle was able to use the low-valley electricity for energy storage. Use of valley electricity for thermochemical energy storage that can be applied to building refrigeration is an important method for adjusting the natural fluctuations in the power grid and improving the energy efficiency of the system. This paper proposes an absorption thermochemical energy storage cycle of double compression coupled with two-stage generation to reduce the generation temperature and achieve a higher coefficient of performance and energy storage density. Based on the thermophysical properties of LiBr/H 2 O and LiNO 3 -[BMIM]NO 3 /H 2 O, the thermodynamic performance of this cycle under various working conditions was studied by MATLAB. The results showed that under the same working conditions, the temperature of the generator using LiNO 3 -[BMIM]NO 3 /H 2 O was 34 K lower than that using LiBr/H 2 O. The coefficient of performance of this new cycle using LiNO 3 -[BMIM]NO 3 /H 2 O was obtained at 12.5, which was much greater than that using LiBr/H 2 O at 7.9. Moreover, the former also achieved a larger energy storage density of 406 kJ/kg. The cycle using the LiNO 3 -[BMIM]NO 3 /H 2 O working fluid not only exhibited better performance, but was also able to effectively use valley electricity and play the role of “peak cutting and valley filling”.

Fabrication of a new rGO@PPy/SS composite electrode with high energy storage and long cycling life for potential applications in supercapacitors

Electrochemical synthesized PPy/SS and rGO@PPy/SS electrodes are individually characterized from the point of their morphological and structural properties by the SEM, EDX and FTIR techniques. Electrochemical measurements, for instance, CV, EIS, and MS are performed to obtain the supercapacitive behaviour of the electrodes in an aqueous solution of 0.1 M KOH. All the morphological and structural studies confirm the molecular occurrence of PPy and rGO@PPy, and the homogenous distribution of the material onto the SS substrate. The specific capacitances of the electrodes show up as 104.22 F g−1 and 122.53 F g−1 respectively for PPy/SS and rGO@PPy/SS at 10 mV s−1 scan rate. The energy density of rGO@PPy/SS is 212.5 Wh kg−1 at the current density of 6 A g−1 while the energy density of PPy/SS is 116.66 Wh kg−1 at the same scan rate. This considerable increase is also shown for the power densities of the electrodes as from 4516.12 W kg−1 to 6219.51 W kg−1 at 6 A g−1 by insertion of rGO into PPy/SS. Likewise, with this insertion, an impressive improvement in the cyclic stability of the electrode is seen from 59.5% to 97.6%. In the light of these results, rGO@PPy/SS is considered an extremely promising material for supercapacitor investigations.

Effects of Ti-doping on energy storage properties and cycling stability of Pb0.925La0.05ZrO3 antiferroelectric thin films

Pb0.925La0.05Zr1-xTixO3 (PLZT, x = 0.5%∼5.5%) thin film were fabricated on Pt(111)/TiO2/SiO2/Si substrates by sol–gel method. In the Zr-rich region, the saturation polarization strengthens with increasing Ti content due to the change of ion-radius. On the other hand, the switching field decreases, which means the enhancement of ferroelectricity. The phase structure and polarization of the films can be tuned by a small amount of Ti doping, and then the energy storage characteristics of the thin films can be modulated. The results showed that a large energy storage density (Wrec) of 49.7 J/cm3 and efficiency (η) of 54% were achieved in the x = 1.5%. Moreover, the x = 1.5% sample displayed excellent cycling stability up to 1 × 106 cyclings, which demonstrated that La and Ti co-doped films can be considered as potential candidates for future energy storage devices.

A double-effect/two-stage absorption refrigeration and thermal energy storage hybrid cycle using dual working fluids

• The hybrid cycle can get a generation temperature of 385 K and a COP of 2.37. • This cycle can work below 273.15 K with a high ESD over 300 kJ·kg −1 . • It realized combined cooling and heating for 24 h using dual working fluids. To improve the flexibility of absorption thermal energy storage (ATES) cycle, including lower the generation temperature, larger the operating temperature region and combined cooling and heating for 24 h, a double-effect/two-stage absorption refrigeration and thermal energy storage hybrid cycle using LiBr/H 2 O and LiBr-[BMIM]Br/C 2 H 5 OH working fluids is proposed in this paper. The cycle includes an absorption heat pump (AHP) sub cycle and an ATES sub cycle. Based on the measured thermophysical properties, the thermodynamic performance of this new cycle under different working conditions was calculated by MATLAB. According to the results, the hybrid cycle obtained a low generation temperature of 385 K, attributed to the utilization of the low-temperature working fluid LiBr-[BMIM]Br/C 2 H 5 OH. Moreover, the evaporation temperature of 268.15 K expanded the operating region of the hybrid cycle, and the highest COP and ESD of 2.37 and 394 kJ·kg −1 were obtained at that temperature, respectively. More importantly, the cycle realized combined cooling and heating all day long, with a cooling output temperature range of 268.15–278.15 K and a heating output temperature range of 321–344 K, which can fully meet the demands of commercial and civilian applications. To further verify the feasibility of the cycle, the model sensitivity and chemical potential achieved in the hybrid cycle were analyzed.

Evaluation of a high-performance evaporative cooler-assisted open three-phase absorption thermal energy storage cycle for cooling

Absorption thermal energy storage is promising for long-term storage of solar energy with both cooling and heating output purposes. Recently, the three-phase absorption thermal energy storage attracts significant attention due to its high energy storage density. However, its operation suffers from the vacuum operation and crystals blockage of piping systems, especially for the cooling output scenario. To resolve these issues, a three-phase absorption thermal energy storage in humid air for cooling is proposed, in which the dehumidification via three-phase absorption drives the evaporative cooling. Airflow is used for heat and mass transfer, which avoids vacuum operation and crystal blockage simultaneously. Comprehensive analysis considering the thermodynamic status of both working pair and humid air is carried out, with LiCl-H2O, LiBr-H2O, and CaCl2-H2O. Results showed that high ESD (energy storage density) of 563 kWh/m3 and COP (coefficient of performance) of 1.22 can be achieved under typical summer operating conditions, which are 3.2 and 2.1 times higher than that of the conventional cycle, respectively. Such simultaneous enhancement in ESD and COP has not been achieved by low-grade energy-driven sorption thermal storage yet, showing its great potential in real applications.

Thermodynamics analysis of a combined cooling, heating and power system integrating compressed air energy storage and gas-steam combined cycle

The electrical energy storage (EES) with large-scale peak shaving capability is one of the current research hotspots. A novel combined cooling, heating and power (CCHP) system with large-scale peak shaving capability, the compressed air energy storage integrated with gas-steam combined cycle (CAES-GTCC), is proposed in this paper. In the presented system, the methanol absorbs the compression heat through the cracking reaction avoiding the application of a thermal energy storage system in compressed air energy storage (CAES) system, and the generated cracked gas is burned to drive the gas-steam combined cycle (GTCC) for generating electricity. During discharging, part of the gas diverted from the GTCC heats the air that is about to enter the air turbine in CAES to increase the total output power of the system. Moreover, the coupled system could output heating energy and cooling energy at the same time as electricity to realize the energy cascade utilization. By building the thermodynamic model of the system, the thermodynamic performance of the system and the influence of various important parameters on the performance of the system are analyzed. The results show that the output power of the CAES-GTCC during discharging accounted for 157.09% of the total output power during the general period. Furthermore, the energy efficiency of CAES-CTCC can reach 90.81% when the electrical efficiency of the CAES and equivalent electric efficiency of the CAES-GTCC are 48.07% and 74.51%, respectively. Based on the second law of thermodynamics, the exergy efficiency of the CAES-GTCC is expected to be 52.89%.

Integration and conversion of supercritical carbon dioxide coal-fired power cycle and high-efficiency energy storage cycle: Feasibility analysis based on a three-step strategy

The emission peak/carbon neutrality calls for significantly improved coal-fired power plants. Sustainability of the power plants is critical to meeting the net zero targets in 2050/2060. In this context, it is necessary to investigate the integration and conversion of the supercritical carbon dioxide coal-fired power cycle and the supercritical carbon dioxide energy storage cycle. In this work, the thermodynamic model and performance criteria are firstly presented. After comparison of the two cycles, a three-step strategy for the development of the power cycle is proposed and assessed. First step: when coal still plays an important role as a main energy resource, the integrated tri-compression coal-fired supercritical compressed carbon dioxide energy storage cycle has the highest round-trip efficiency of 56.37%. Second step: with the challenge in utilization of coal energy, a trade-off among the performance criteria must be struck in the integrated cycle with various heat sources. Third step: the adiabatic supercritical compressed carbon dioxide energy storage cycle is proposed, and a high round-trip efficiency of 72.34% is achieved in the split expansion cycle. The present research provides not only a new prospect of the conventional power plants but also design guidance for the supercritical carbon dioxide energy storage cycle.