Maximum Energy Storage Density Research Articles

Revealing multiphase coexistence of R-O-T phases in BaTiO3-CaTiO3-BaSnO3 electroceramics for energy harvesting and storage response with piezo actuation

The (Ba1-xCax)(SnyTi1-y)O3 piezoelectric ceramics (where x=0.016, y=0.024; x=0.032, y=0.048; x=0.048, y=0.072; x=0.064, y=0.096; x=0.08, y=0.12) were designed by conventional solid state reaction method. The crystal structure for the composition of x=0.064 and y=0.096 (abbreviated as BCST-4) possesses the coexistence of non-centrosymmetric rhombohedral-orthorhombic-tetragonal (R-O-T) tri-lattice symmetries at room temperature, as demonstrated by the structural Rietveld refinement, Raman analysis, and temperature dependence of dielectric study. Because of the R-O-T multiphase coexistence, BCST-4 possesses a superior electromechanical and piezoelectric property viz. kp ∼ 0.45, strain ∼ 0.100 %, d33* ∼ 649 pm/V, and an improved d33 ∼ 452 pC/N, which is comparable to commercially available soft PZT ceramics (d33 ⁓ 370 pC/N). For BCST-4 ceramics, an exceptional electrostriction coefficient Q33 ∼ 0.0434 m4/C2 value was attained. The intrinsic piezo-actuation DC strain was observed to be 130 microstrain (με) and 188 με with ε33 and ε31 modes respectively. The BCST-4 ceramic exhibits a maximum output power of 1.03 mW, a power density of 13.5 µW/mm3, a maximum output current of 88 µA, and an open circuit voltage Vpp of 28 V which successfully glowed ‘SPPU’ panel having 40 red commercial light-emitting diodes (LEDs). The energy storage study reveals that BCST-4 ceramics exhibit a maximum energy storage density (Wrec) of 165.87 mJ/cm3 with efficiency (ƞ) 68.00 %. Therefore, the improvement in electrostriction coefficient, piezoelectric charge coefficient, and energy storage response indicates that BCST-4 ceramic has the potential for actuator, energy harvesting, and energy storage applications.

A novel microgroove-based absorber for sorption heat transformation systems: Analytical modeling and experimental investigation

This study proposes a novel sorber bed design, a stationary thin film microgroove-based absorber, that can address the low specific power and oversized sorber bed issues in existing oscillatory solid sorption heat transformation systems. An analytical heat and mass transfer model is developed for the proposed stationary thin film microgroove-based absorber. A highly-wettable microgrooved aluminum substrate is fabricated by the deposition of a hybrid Al2O3/TiO2 layer, and experimental water uptake measurements are obtained using a custom-built gravimetric large pressure jump setup to validate the analytical model. The model examines how key design parameters affect specific cooling power, cooling power density, and energy storage density. Findings indicate that cycle time and groove depth significantly impact system performance. Also, it is found that there is an optimum groove depth, or film thickness, to achieve maximum power. Trapezoidal grooves achieve higher specific cooling power and cooling power density, while rectangular grooves yield a higher maximum energy storage density. It is experimentally shown that a specific cooling power enhancement of up to 600 % can be obtained compared to the experimental data available for oscillatory sorber beds. Also, the absorption rate of the present sorber bed is up to three times higher than that of falling film absorbers.

Sandwich-structured SrTiO3/PEI composite films with high-temperature energy storage performance

Dielectric capacitors are widely used in aerospace and power systems due to their non-polluting, high power density and fast charge/discharge rates. Polyetherimide (PEI) exhibits excellent temperature tolerance, high withstand voltage and low dielectric loss. However, its relatively low dielectric constant restricts its energy storage density. In this paper, a sandwich-structured composite film with the outer layer of pure PEI and the middle layer of strontium titanate (SrTiO3)/PEI is prepared by the solution casting method. At room temperature, the composite film with 5 vol% two-dimensional (2D) SrTiO3 plates achieves an outstanding energy storage density of 19.46 J cm−3 and an ultra-high energy storage efficiency of 97.05% under an electric field of 630 MV m−1. Furthermore, this composite film exhibits a maximum energy storage density of 10.34 J cm−3 and an energy storage efficiency of 88.13% at 150 °C. Combined with finite element simulation results, it confirms that the synergistic effect of 2D SrTiO3 plates and sandwich-structured can effectively hinder the development of electric trees. This work presents a sophisticated approach to design and preparation of dielectric composites suitable for the applications of high-temperature energy storage.

A phase-change-material-assisted absorption thermal battery for space heating under low ambient temperatures

Solar-driven Absorption Thermal Battery (ATB) is a promising technology for space heating. However, providing heating under low ambient temperatures seriously degrades the storage performance of ATB, which is still a major challenge. Therefore, this study proposed a Phase-Change-Material (PCM)-assisted ATB to recover and store the condensation heat in the charging process. Then, the recovered heat is used to heat the evaporator to strengthen the evaporation-absorption process. This study investigates two different PCMs: organic paraffin and inorganic hydrated salt. The dynamic behaviors and cycle performance of the basic and two PCM-assisted ATBs are compared. Then, parametric studies are conducted for a better system design. Results indicate that the PCM-assisted ATB can significantly enhance the Energy Storage Density (ESD) and slightly improve the Energy Storage Efficiency (ESE). The hydrated-salt-assisted ATB yields the best storage performance with an ESD of 141.5 kWh/m3 and an ESE of 0.78. In contrast, the basic ATB only obtains an ESD of 70.7 kWh/m3 and an ESE of 0.73. The discharging process is strengthened with the increase of phase change temperature, but the charging process is weakened. The maximum ESD of 160.1 kWh/m3 is achieved at the phase change temperature of 28 °C.

Moderation of [Bi3+/Na1+] molar ratio for enhancement of dielectric and energy storage properties of NaNbO3 ceramics

Lead-free (Na1−3xBix)(Nb0.75Ti0.25)O3 (x = 0.0, 0.05, 0.1, 0.125 and 0.15) (NN-BT) ceramics were synthesized using solid-state reaction technique. The effect of Bi3+ into the crystal structure, dielectric, ferroelectric and energy storage properties of NNT ceramics were investigated. Pure NNT shows present perovskite structure with orthorhombic crystal structure at x ≤ 0.125, while Na3NbO8-NaNbO3 composite phase has been detected at x = 0.15. The tolerance factor (τ) decreased from 0.97 (x = 0.0) to 0.82 (0.15) which signified the composition deviated from perovskite structure at 0.15. Significant enhancement of dielectric constant at room temperature has been achieved by increasing Bi-content and the maximum value (∼1500) obtained at 0.1. The largest value of maximum polarization (Pmax) and smallest value of remnant polarization (Pr) were achieved at x = 0.1 due to orthorhombic NaNbO3 and rhombohedral (Na0.5Bi0.5)TiO3 coexistence phases. The substitution of monovalent (Na1+) by trivalent (Bi3+) lead to create sodium vacancies into the A-sites of NNT lattice subsequently increased the cations disorder and charge misfit. The maximum recoverable energy storage density (Wrec = 17.5 J cm−3) and energy storage efficiency (η = 80%) were achieved at x = 0.1, E ∼ 700 kV cm−1. Partially, (NNTB0.1) exhibit an outstanding stability of energy storage properties in terms of temperature range (25 to 150 °C) and frequency stability (2–20Hz). The present results imply the moderation ratio of Bi/Na plays an important role for enhancement of energy storage properties of NaNbO3 anti-ferroelectric ceramics.

Energy-storage performance of NaNbO3-based ceramic capacitor derived from a high DOP glass network structure

0.75(0.4Na2O-0.1K2O-0.5Nb2O5)-0.25(0.87SiO2-0.13BaO) glass-ceramics were prepared by a traditional melting method to optimize the crystallization kinetics. We obtained a glass network with high degree of polymerization (DOP) by crystallization at different temperatures and achieved a high energy storage density. The increase of crystallization temperature has promoted the precipitation of ferroelectric phases Na0.9K0.1NbO3 and NaNbO3 with high dielectric constant (1200–2000), promoted the increases of grain size from 0.76 μm to 1.33 μm, and reduced the gap width from 3.71eV to 3.22eV. When the crystallization temperature increased to 1000°C–1100 °C, Ba2NaNb5O15 with low dielectric constant (∼460) increases, grain boundaries appear, and dielectric constant and BDS decrease. Among all the samples, the sample crystallized at 900 °C showed homogeneous and dense microstructure (grain size∼0.91 μm). The experimental data confirmed that the glass sample crystallized at 900 °C achieves low dielectric loss (<0.005) and high dielectric constant (∼122). The glass sample crystallized at 900 °C sample had a maximum energy storage density of 3.65 J/cm3, a power density of about 54 MW/cm3 and a super-fast discharge speed of 38 ns at 660 kV/cm.

Enhanced energy-storage density in (Pb0.98La0.02)(Zr0.45-xSn0.55Hfx)0.995O3 antiferroelectric ceramics

Antiferroelectric ceramics with unique characteristics of electric-field-induced antiferroelectric to ferroelectric phase transitions and ultra-fast charging-discharging rate, which are demanded in high pulse power devices. In this work, (Pb0.98La0.02)(Zr0.45-xSn0.55Hfx)0.995O3 (PLZSH) antiferroelectric ceramics with x = 0∼0.20 were prepared via a conventional solid-state reaction approach. Incommensurate modulation structure with a 1/n<110> superlattice was observed in AFE at room temperature, which was associated with the unique domain boundaries, contributing the obvious declined AFE-FE phase transition electric field as well as the enhanced energy storage density. It was also observed that the maximum recoverable energy storage density (Wrec) increases from 2.93 J/cm3 (x = 0) to 5.72 J/cm3 (x = 0.15), and the corresponding energy-storage efficiency uprises from 82.4 % to 87.8 % with the increasing x at 280 kV/cm. The superior energy density and efficiency indicate that the obtained PLZSH antiferroelectric ceramics are promising for practical applications in pulse power devices.

Effect of BiFeO3 on the ferroelectric and energy storage properties of (Bi1/2Na1/2)0.94Ba0.06TiO3 based compositions

The compound of (1 − x)[(Bi1/2Na1/2)0.94Ba0.06TiO3)]–xBiFeO3 (BNBT–BF), (0 ≤ x ≤ 0.15) sintered ceramic was processed by chemical route. The XRD patterns revealed the formation of single structured perovskite of Bi1/2Na1/2TiO3 (BNT) ceramics. The temperature-dependent dielectric characteristics indicated different dielectric phase changes in the fabricated compounds. Ferroelectric P–E hysteresis loop showed temperature sweep variations in saturation (P) and residual polarizations (Pr). Storage density (w) increases with temperature. This is due to the presence of AFE (Antiferroelectric) phase at temperatures >120 °C. The energy storage efficiency (η) and the dielectric break down strength (DBS) of the samples were observed to decrease with BF doping. The maximum energy storage density (w) of 0.29 J/cm3 was observed for × = 0.15 at 60 kv/cm.

Performance improvement of Na4SiO4 doped with Li2CO3-K2CO3 for high-temperature CO2 capture and thermochemical energy storage

Na4SiO4 is regarded as a new candidate of high-temperature CO2 sorbent. However, the sorption/desorption temperature of Na4SiO4 is high, and cyclic sorption capacity is low. In this study, Na4SiO4 sorbents doped with Li2CO3-K2CO3 (LiKCO3) were synthesized, and the dynamic, isothermal, and cyclic CO2 capture performances were investigated to improve the performance. The maximum CO2 sorption capacity of Na4SiO4-20LiKCO3 reached 20.64 wt% at 725 °C, and the cyclic sorption capacity was about 50 % higher than that of pure Na4SiO4. The results indicated that LiKCO3 doping could efficiently decrease the optimal sorption/desorption temperature of Na4SiO4. Furthermore, the maximum conversion efficiency and energy storage density of Na4SiO4-20LiKCO3 reached high levels of 95.7 % and 788 kJ/kg, respectively. Finally, the CO2 chemisorption mechanisms on the Na4SiO4 and Na4SiO4-LiKCO3 co-adsorption surfaces were studied via density functional theory calculations. LiKCO3 doping could enhance CO2 adsorption energy and C–OS covalent interaction on the sorbent surface and the energy levels of the CO2/Na4SiO4-LiKCO3 system were reduced. These changes were beneficial to CO2 chemisorption and agreed well with the experimental values. Thus, Na4SiO4 doped with LiKCO3 had high potential for high-temperature CO2 capture and thermochemical energy storage.

Structure and dielectric properties in Mg/Nb co-substituted bismuth sodium titanate

A systematic study of pseudo-isovalent B site co-substitution of Ti4+ by Mg2+ and Nb5+ in bismuth sodium titanate is presented. A complete solid solution in the Bi0.5Na0.5Ti1−x(Mg1/3Nb2/3)xO3 system is formed. With increasing level of substitution, dielectric anomalies associated with depoling and maximum permittivity temperatures (Td and Tm, respectively) are suppressed and shift to lower temperatures. Variable temperature X-ray powder diffraction on the x = 0.2 composition reveals a non-linear thermal expansion at temperatures below Tm. B-site co-substitution by Mg and Nb has the effect of interrupting the long-range ferroelectric ordering in the system, resulting in lower saturation and remnant polarizations. A maximum energy storage density of 4.14 J cm−3 with a recoverable energy density of 2.35 J cm−3 was obtained for the x = 0.1 composition, while the x = 0.5 composition appears to have the best balance between energy storage and energy efficiency.

Energy Storage Performance and Dielectric Properties of Surface Fluorinated BOPP Films

Various composite films with high energy storage performance and/or dielectric strength have been fabricated. However, due to some reasons, few of them have been used in practice, and BOPP film is still regarded as the state-of-the-art capacitor dielectric film. Previous work has indicated that direct fluorination can improve the dielectric strength of BOPP films. Herein, as a continuation of previous work, the energy storage performance and basic dielectric properties of the surface fluorinated BOPP film are investigated. The charge-discharge experimental results show that the surface fluorinated BOPP sample has the maximum energy storage or release density of 5.27 or 4.43 J/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> , which is 59.8% or 44.6% higher than that of the virgin BOPP sample. The dielectric measurement results indicate that the surface fluorinated BOPP sample has slightly higher dielectric constant and dielectric loss than the virgin BOPP sample. The analyses of physicochemical characteristics reveal that the 0.75 μm thick fluorinated surface layer has a high degree of fluorination. The results of the calculation based on the three-layer dielectric model and the dielectric measurements further show that the fluorinated surface layer has high dielectric constant and loss factor, similar to non-perfluoropolymers. The enhancement of energy storage performance and dielectric strength is mainly attributed to the blocking of the fluorinated layer to electron injection from the cathode, due to a 60% reduction of the interfacial electric field and a decrease in free volume of the surface layer by the fluorination.

Dielectric and Improved Energy-Storage Properties in A-Site Nd3+ Doped Lead-Free 0.88NaNbO3-0.12Sr0.7Bi0.2TiO3 Ceramics

Sodium niobate (NaNbO3)-based antiferroelectric (AFE) ceramics have received significant attention for energy storage applications because of their good performance, low cost, and nontoxicity. However, the existence of the antiferroelectric P phase at room temperature causes large hysteresis, resulting in reduced energy storage efficiency. In this study, 0.88NaNbO3–0.12Sr0.7Bi0.2TiO3 ceramics doped with Nd3+ (i.e., 0.88Na1-3 x Nd x NbO3-0.12Sr0.7Bi0.2TiO3) at x = 0.0 − 0.025 were prepared via conventional solid-state mixed oxide route. The XRD data showed that all samples exhibited an orthorhombic structure. With increasing Nd3+ doping content, the antiferroelectric P (Pbma) phase to R (Pnma) phase transition temperature (T P-R) shifted to lower temperatures. Consistent with the dielectric properties, a transition to a relaxor-like slim P-E loop indicative of an AFE R phase was observed at the composition x ≥ 0.01. This led to an increase in both the recoverable energy-storage density (W rec) and efficiency (η) with an increasing amount of Nd3+ doping level. The maximum recoverable energy storage density (W rec = 0.54 J/cm3) and high energy storage efficiency (η = 93%) were observed at x = 0.025 under an applied electric field of 100 kV/cm. In addition, the optimum composition at x = 0.025 also exhibited excellent temperature stability from 25 °C to 150 °C. This research demonstrates that the NN–SBT–xNd system has the potential for use for high-energy-density pulsed power capacitor applications.

Hybrid cooling and heating absorption heat pump cycle with thermal energy storage

This study presents a hybrid cooling/heating absorption heat pump with thermal energy storage. This system consists of low- and high-pressure absorber/evaporator pairs, using H2O/LiBr as the working fluid, and it is driven by low-temperature heat source of 80 °C to supply cooling and heating effects simultaneously. Using solution and refrigerant reservoirs, the system can store thermal energy in the form of chemical potential owing to the concentration glide. Applying the building cooling/heating temperature conditions, the operating concentration range of the system is constrained to 0.49–0.59 LiBr mass fraction. In this range, a system performance analysis is conducted through simulation modeling. The maximum total COP of the hybrid heat pump cycle reaches 0.80, which is same as the maximum COP of the single-effect absorption chiller with the same operating conditions. In storage mode, the maximum total COP is reduced to 0.30 due to the lack of internal heat recovery, while a maximum energy storage density (ESD) of 402.4 kJ/kg is achieved. In particular, the performance of the storage mode is dominantly affected by the solution circulation ratio, indicating the design criteria for the proposed system.

Improvement in dielectric properties and energy storage performance of barium strontium niobate glass ceramics by Sm2O3 addition

High power density and high energy density glass ceramics have important applications in the field of miniaturized, lightweight and integrated pulsed power devices. Barium strontium niobate glass ceramics with different additive amount of Sm2O3 were successfully prepared. The effects of different additions of Sm2O3 on the phase composition, dielectric properties, breakdown strength, interfacial polarizations and energy storage properties of glass ceramics were investigated. The results of phase structure show that Ba0.5Sr0.5Nb2O6 of tungsten bronze structure and BaAl2Si2O8 two phases are precipitated from the glass matrix. The optimum Sm2O3 addition can increase the Ba0.5Sr0.5Nb2O6 phase content of tungsten bronze structure in the glass ceramics, thus increasing the dielectric constant of strontium barium niobate glass ceramics. A moderate amount of Sm2O3 addition improves the microstructure of the barium strontium niobate glass ceramics and reduces the interfacial activation energy of the glass ceramics, thus increasing the breakdown strength of the glass ceramics. For 3 mol% Sm2O3 addition, the breakdown strength of the glass ceramics reaches 1590 kV/cm with a corresponding dielectric constant of 98.4 and a maximum energy storage density of 12.44 J/cm3, which is 2.62 times higher than that of the barium strontium niobate glass ceramics without Sm2O3 addition. It is concluded that the increased energy density of glass ceramics can be attributed to the fact that the appropriate additive amount of Sm2O3 (1–3 mol%) increases the crystallinity of the glass ceramics and at the same time reduces the interfacial activation energy of the glass ceramics, thus increasing the dielectric properties of the glass ceramics with respect to the breakdown strength.

Achieving high electrical homogeneity in (Na2O, K2O)–Nb2O5–SiO2-MO (M = Ca2+, Sr2+, Ba2+) glass-ceramics for energy storage by composition design

The Na2O–K2O–Nb2O5–SiO2 glass matrixes modified by alkaline-earth metals oxide MO (M = Ca2+, Sr2+ and Ba2+) with different field strength (Fs) are prepared. The degree of polymerization (DOP) of the glass network structure is enhanced with the addition of MO. The (35-x)Na2O–5K2O–40Nb2O5–20SiO2-xMO glass are crystalized at the exothermic peak 916 °C as evidenced by an exothermic peak in thermal analysis. The crystallization kinetics are analyzed by crystallization activation energy (Ec) which increases with the addition of MO facilitating the homogenous nucleation. The crystallinity and the fraction of crystalline phase of the glass-ceramics are analyzed by structural refinements. The dielectric permittivity and polarization of the glass-ceramics are researched. The electrical homogeneity of glass-ceramics is discussed on different scales. On the grain scale of the glass-ceramics, the uniform microstructure prevents the free charge from accumulating. On the glass network scale, the tight glass network structure prevents large interface polarization caused by the accumulating of space charge. A large binding energy (W) or minimum hopping distance (Rm) prevents the electrons from hopping. Kelvin probe force microscopy (KPFM) is used to test the potential of the interface polarization as direct evidence of the electrical homogeneity. The magnitude of the breakdown strength (BDS) of the glass-ceramics is affected by the electrical homogeneity of the glass-ceramics. The average value of BDS is 1780 kV/cm for the Na2O–K2O–Nb2O5–SiO2–BaO glass-ceramics. The maximum potential energy storage density of 23.1 J/cm3 is obtained for the Na2O–K2O–Nb2O5–SiO2–BaO glass-ceramics with x = 3.

Synthesis, stability, and heat transfer behavior of water and graphene nanoplatelet-based nanofluid for cool thermal storage applications

This study aims to synthesize stable nano-enhanced phase change materials (NEPCM) using deionized (DI) water and graphene nanoplatelets (GNPs) with the aid of three different surfactants (CTAB, SDBS, and GA). The study also investigates the dynamic behavior of the NEPCM during solidification and melting in a spherical encapsulation. GA-GNP dispersion showed prolonged stability based on zeta potential distribution (ZP) and UV–vis absorbance after 60 days of preparation. The effect of GNP concentration (0.25, 0.50, 0.75, and 1.00 wt%) on the heat transfer properties of the NEPCM was investigated using differential scanning calorimetry (DSC), temperature-time (T-t) profiles, and TC measurements. The maximum energy storage density decreased by 8.56 % and 15.3 % for 1.00 wt% GNPs added to DI-water during melting and crystallization, respectively, at a heating rate of 5 K/min. The thermal conductivity (TC) increased by 59.1 % and 10.8 % in the solid and fluid circumstances, correspondingly. Transient temperature results showed that GA significantly reduced super cooling (SC) by 47.6 % and eliminated it completely at a concentration of 1.00 wt% GNP-NEPCM. The maximum reduction in solidification rate was 26.4 % with 1.00 wt% GNP-NEPCM at a −7 °C constant heat transfer fluid (HTF) temperature. The melting duration was reduced by 33 % by adding 0.50 wt% GNPs, while the melting duration was prolonged at a concentration of 1.00 wt% due to the viscosity augmentation of molten layers. In conclusion, the proposed stable NEPCM formulation has great potential for use as an energy-efficient storage medium in the CTES system.

High Energy Storage Performance of PZO/PTO Multilayers via Interface Engineering.

Antiferroelectric thin-film capacitors with ultralow remanent polarization and fast discharge speed have attracted extensive attention for energy storage applications. A multilayer heterostructure is considered to be an efficient approach to enhance the breakdown strength and improve the functionality. Here, we report a high-performance multilayer heterostructure (PbZrO3/PbTiO3)n with a maximum recoverable energy storage density of 36.4 J/cm3 due to its high electric breakdown strength (2.9 MV/cm) through the heterostructure strategy. The positive effect of interfacial blockage and the negative effect of local strain defects competitively affect the breakdown strength, showing an inflection point at n = 3. The atomic-scale characterizations reveal the underlying microstructure mechanism of the interplay between the heterointerface dislocations and the decreased energy storage performance. This work offers the potential of well-designed multilayers with high energy storage performance through heterostructure engineering.

Energy harvesting performance of a novel polymer-nanocrystal composite of P(VDF-TrFE)/ZnO QD films

Novel PVDF-TrFE/ZnO quantum dot (QD) nanocomposite films stabilized with organic ligands (TEA) were fabricated using a spin-coating technique by varying the filler composition in the range of; 0, 0.15, 0.25, 0.35 and 0.50 % by weight with a thickness of 200–300 nm. The analysis of the particle size using UV–Vis, XRD and TEM confirmed that the QD size was in the range of 2–3.5 nm. The incorporation of 0.15 wt% ZnO QDs into the P(VDF-TrFE) copolymer exhibited the highest dielectric constant (ε’ = 13.9), remnant polarization (Pr = 10.02 µC/cm2) and pyroelectric coefficient (49 μC/m2K). The micelle-like crystallites and the elongated rod-like crystallites have achieved their optimum growth for the 0.15 wt% polymer nanocomposite. The maximum energy storage density, Ue calculated at 100 Hz is 1.18 Jcm−3 and the highest energy harvesting performance at 1 kHz, FE, is 19.5 J m−3K2 obtained from the 0.15 wt% P(VDF-TrFE)/ZnO QD polymer nanocomposite.

Thermochemical energy storage using coupled metal hydride beds of Mg-LaNi5 composites and LaNi5 based hydrides for concentrated solar power plants

• A MHTES system is proposed for CSP plant application. • Energy storage and recovery temperatures are estimated. • PCIs of Mg based composites and LaNi 5 based alloys are measured. • Reaction enthalpy and entropy are evaluated using van’t Hoff equation. • The performance of the MHTES system is analyzed thermodynamically. • The effect of operating temperatures on the performance of the MHTES is studied. Thermochemical energy storage based on coupled hydride beds is an attractive option for Concentrated Solar Power plant applications due to its efficient long term and high energy storage density. In the coupled system, a high temperature metal hydride (HTMH) bed is coupled with a low temperature metal hydride (LTMH) bed. In the present study, Mg-LaNi 5 composite hydrides are taken as HTMHs due to their high absorption capacity and high reaction enthalpy, and LaNi 5 based alloys are taken as LTMHs as these hydrides are ideal for hydrogen storage at ambient conditions. The thermodynamic properties such as reaction enthalpy and entropy are evaluated by measuring Pressure Concentration Isotherms of Mg- x wt% LaNi 5 ( x =20 and 30) composites, LaNi 4.7 Al 0.3 and LaNi 4.6 Al 0.4 . A new methodology for storing and recovering thermal energy together with upgradation of the quality of energy is established. Methodology to determine the minimum energy storage temperature and maximum energy recovery temperature is proposed. The quality of the thermal energy will be improved by increase in delivery temperature. Thermodynamic analysis is performed using measured properties to evaluate the performance parameters such as heat upgradation, coefficient of performance (COP), and energy storage density (ESD). Maximum COP and ESD of 0.705 and 418.841 kJ/kg, respectively is obtained for hydride pair Mg-5wt% LaNi 5 -La 0.8 Ce 0.2 Ni 5 . Maximum degree of upgradation of 34°C is obtained using the hydride pair Mg-20wt% LaNi 5 -LaNi 4.7 Al 0.3 . The effects of variation of heat source temperature, regeneration temperature and ambient temperature on the performance of the MHTES is studied. It is observed that the regeneration temperature is a significant parameter that influences the performance of the MHTES.

Thermo-economic analysis of combined transcritical CO2 power cycle based on a novel liquefied-biomethane energy storage system

The Chinese government has been encouraging to accelerate the development of energy storage systems to support the rapid growth of renewable energy power generation. For the purpose of achieving flexible and economic energy storage, in this study, a combined transcritical CO2 power cycle is added to biomethane plants to form a liquefied-biomethane energy storage system. A mathematical model that includes terms of energy, exergy, and economy is established to assess the performance of the combined transcritical CO2 power cycle. The effects of critical parameters on the thermo-economic performance are studied. A sensitivity analysis is used to evaluate the extent of the influence of critical parameters. According to the simulation results, the characteristics of the liquefied-biomethane energy storage system are calculated and evaluated. The results show that at a liquefied-biomethane mass flow rate of 1 kg/s, the maximum net power output of the combined transcritical CO2 power cycle reaches 909.81 kW by adjusting the pressure and temperature. High turbine inlet temperature, pump pressure ratio, and methane purity have positive effects on system performance. Among these, the inlet temperature of turbine 2 is the most sensitive factor. Simultaneously, the maximum energy storage density and round-trip efficiency of the liquefied-biomethane energy storage system are 106.8 Wh/L and 52.7 %, respectively. Benefiting from less upfront equipment investment, the lowest power capital cost of the liquefied-biomethane energy storage system is 885.3 $/kW. In conclusion, the liquefied-biomethane energy storage system integrated with a combined transcritical CO2 power cycle exhibits good performance in terms of power output and economy.