Large-scale Energy Storage Technologies Research Articles

Floating Photovoltaic Systems Coupled with Pumped Hydroplants under Day-Ahead Electricity Market Conditions: Parametric Analysis

The intermittent nature of the solar resource together with the fluctuating energy demand of the day-ahead electricity market requires the use of efficient long-term energy storage systems. The pumped hydroelectric storage (PHS) power plant has demonstrated its technical and commercial viability as a large-scale energy storage technology. The objective of this paper is to analyse the parameters that influence the mode of operation in conjunction with a floating photovoltaic (FPV) power plant under day-ahead electricity market conditions. This work proposes the analysis of two parameters: the size of the FPV power plant and the total process efficiency of the PHS power plant. Five FPV plant sizes are analysed: 50% (S1), 100% (S2), 150% (S3), 350% (S4) and 450% (S5) of the PHS plant. The values of the total process efficiency parameter analysed are as follows: 0.77 for old PHS plants, and 0.85 for more modern plants. The number of daily operating hours of the PHS plant is 4 h. These 4 h of operation correspond to the highest prices on the electricity market. The framework of the study is the Iberian electricity market and the Alto Rabagão dam (Portugal). Different operating scenarios are considered to identify the optimal size of the FPV power plant. Based on the measured data on climatic conditions, an algorithm is designed to estimate the energy production for different sizes of FPV plants. If the total process efficiency is 0.85, the joint operation of both plants with FPV plant sizes S2 and S3 yields a slightly higher economic benefit than the independent mode of operation. If the total process efficiency is 0.77, there is always a higher economic benefit in the independent operation mode, irrespective of the size of the FPV plant. However, the uncertainty of the solar resource estimation can lead to a higher economic benefit in the joint operation mode. Increasing the number of operating hours of the PHS plant above 4 h per day decreases the economic benefit of the joint operation mode, regardless of the total process efficiency parameter and the size of the FPV plant. As the number of operating hours increases, the economic benefit decreases. The results obtained reveal that the coupling of floating photovoltaic systems with pumped hydroelectric storage power plants is a cost-effective and reliable alternative to provide sustainable energy supply security under electricity market conditions. In summary, the purpose of this work is to facilitate decision making on the mode of operation of both power plants under electricity market conditions. The case studies allow to find the optimal answer to the following practical questions: What size does the FPV power plant have to be in order for both plants to be better adapted to the electricity market? What is the appropriate mode of operation of both plants? What is the economic benefit of changing the turbine pump of the PHS power plant? Finally, how does the installation of the FPV power plant affect the water volume of the upper reservoir of the PHS plant? Knowledge of these questions will facilitate the design of FPV power plants and the joint operation of both plants.

Evolution of Vanadium Redox Flow Battery in Electrode.

The vanadium redox flow battery (VRFB) is a highly regarded technology for large-scale energy storage due to its outstanding features, such as scalability, efficiency, long lifespan, and site independence. This paper provides a comprehensive analysis of its performance in carbon-based electrodes, along with a comprehensive review of the system's principles and mechanisms. It discusses potential applications, recent industrial involvement, and economic factors associated with VRFB technology. The study also covers the latest advancements in VRFB electrodes, including electrode surface modification and electrocatalyst materials, and highlights their effects on the VRFB system's performance. Additionally, the potential of two-dimensional material MXene to enhance electrode performance is evaluated, and the author concludes that MXenes offer significant advantages for use in high-power VRFB at a low cost. Finally, the paper reviews the challenges and future development of VRFB technology.

Co-activation for enhanced K-ion storage in battery anodes.

The relative natural abundance of potassium and potentially high energy density has established potassium-ion batteries as a promising technology for future large-scale global energy storage. However, the anodes' low capacity and high discharge platform lead to low energy density, which impedes their rapid development. Herein, we present a possible co-activation mechanism between bismuth (Bi) and tin (Sn) that enhances K-ion storage in battery anodes. The co-activated Bi-Sn anode delivered a high capacity of 634mAhg-1, with a discharge plateau as low as 0.35V, and operated continuously for 500 cycles at a current density of 50mA g-1, with a high Coulombic efficiency of 99.2%. This possible co-activation strategy for high potassium storage may be extended to other Na/Zn/Ca/Mg/Al ion battery technologies, thus providing insights into how to improve their energy storage ability.

Aqueous Zinc-Chlorine Battery Modulated by a MnO2 Redox Adsorbent.

Aqueous zinc-chlorine battery with high discharge voltage and attractive theoretical energy density is expected to become an important technology for large-scale energy storage. However, the practical application of Zn-Cl2 batteries has been restricted due to the Cl2 cathode with sluggish kinetics and low Coulombic efficiency (CE). Here, an aqueous Zn-Cl2 battery using an inexpensive and effective MnO2 redox adsorbent (referred to Zn-Cl2@MnO2 battery) to modulate the electrochemical performance of the Cl2 cathode is developed. Density functional theory calculations reveal that the existence of the intermediate state Clads free radical catalyzed by MnO2 on the Cl2 cathode contributes to the charge storage capacity, which is the key to modulate the electrode and improve the electrochemical performance. Further analysis of the Cl2 cathode kinetics discloses the adsorption and catalytic roles of the MnO2 redox adsorbent. The Zn-Cl2@MnO2 battery displays an enhanced discharge voltage of 2.0V at a current density of 2.5mAcm-2, and stable 1000 cycles with an average CE of 91.6%, much superior to the conventional Zn-Cl2 battery with an average CE of only 66.8%. The regulation strategy to the Cl2 cathode provides opportunities for the future development of aqueous Zn-Cl2 batteries.

Maximizing uninterrupted solar electricity in spectral-splitting photovoltaic-thermal systems integrated with CO2 battery

Solar energy is the most important renewable energy, and its large-scale application is of great significance to achieve carbon neutrality. Photovoltaic (PV) power generation is one of the most important ways of solar energy utilisation. However, it faces two important bottlenecks. Current PV efficiency is far below the Landsberg limit, and more importantly, the intermittent nature of solar energy poses a huge challenge to large-scale energy storage technology, leading to the large-scale discarding of solar power around the world. To handle the issues, a concentrated spectral-splitting photovoltaic-thermal system is integrated with advanced technologies of PV cells and CO2 battery to maximise the uninterrupted utilisation of solar energy, especially optimising the system to achieve full-spectrum utilisation based on the solar spectrum properties. The results show that the round-trip efficiency can achieve higher than 88 %, the power produced by the turbine in discharging phase is higher than the input PV power in the charging phase when the bandgap energy (Eg) is higher than 1.2 eV, and the gap increases evidently as Eg rises. In the extreme case, >68 % of solar utilisation efficiency can be achieved. In the proposed system, CO2 is employed to reduce carbon emissions by harnessing its unique properties rather than simply capturing and burying it as a greenhouse gas, which not only provides a good solution for the intermittent nature of solar photovoltaic power but also obtains higher electrical power in discharging phase than the input photovoltaic power in charging phase, and it is easily scaled up, demonstrating the significant potential of the proposed concept in practical applications.

A Bifunctional Liquid Fuel Cell Coupling Power Generation and V3.5+ Electrolytes Production for All Vanadium Flow Batteries.

All vanadium flow batteries (VFBs) are considered one of the most promising large-scale energy storage technology, but restricts by the high manufacturing cost of V3.5+ electrolytes using the current electrolysis method. Here, a bifunctional liquid fuel cell is designed and proposed to produce V3.5+ electrolytes and generate power energy by using formic acid as fuels and V4+ as oxidants. Compared with the traditional electrolysis method, this method not only does not consume additional electric energy, but also can output electric energy. Therefore, the process cost of producing V3.5+ electrolytes is reduced by 16.3%. This fuel cell has a maximum power of 0.276mW cm-2 at an operating current of 1.75mA cm-2 . Ultraviolet-visible spectrum and potentiometric titration identify the oxidation state of prepared vanadium electrolytes is 3.48 ± 0.06, close to the ideal 3.5. VFBs with prepared V3.5+ electrolytes deliver similar energy conversion efficiency and superior capacity retention to that with commercial V3.5+ electrolytes. This work proposes a simple and practical strategy to prepare V3.5+ electrolytes.

Doping Engineering of M-N-C Electrocatalyst Based Membrane-Electrode Assembly for High-Performance Aqueous Polysulfides Redox Flow Batteries.

Polysulfides aqueous redox flow batteries (PS-ARFBs) with large theoretical capacity and low cost are one of the most promising solutions for large-scale energy storage technology. However, sluggish electrochemical redox kinetics and nonnegligible crossover of aqueous polysulfides restrict the battery performances. Herein, it is found that the Co, Zn dual-doped N-C complex have enhanced electrochemical adsorption behaviors for Na2 S2 . It exhibits significantly electrochemical redox activity compared to the bare glassy carbon electrode. And the redox reversibility is also improved from ΔV=210mV on Zn-doped N-C complex to ΔV=164mV on Co, Zn-doped N-C complex. Furthermore, membrane-electrode assembly (MEA) based on Co, Zn-doped N-C complex is firstly proposed to enhance the redox performances and relieve the crossover in PS-ARFBs. Thus, an impressively high and reversible capacity of 157.5AhL-1 for Na2 S2 with a high capacity utilization of 97.9% could be achieved. Moreover, a full cell PS-ARFB with Na2 S2 anolyte and Na4 [Fe(CN)6 ] catholyte exhibits high energy efficiency ≈88.4% at 10mAcm-2 . A very low capacity decay rate of 0.0025% per cycle is also achieved at 60mAcm-2 over 200 cycles.

Numerical verification on the feasibility of compressed carbon dioxide energy storage in two aquifers

Compressed carbon dioxide energy storage in aquifers (CCESA) is a new large-scale energy storage technology derived from geological carbon dioxide sequestration, compressed air energy storage in aquifers, and compressed carbon dioxide energy storage. However, there have been no practical applications so far. In this study, we present a numerical model that simulates the whole process of gas filling period and daily cyclic period of the subsurface system of CCESA with two wellbores and two aquifers, and reveal the hydrodynamic and thermodynamic properties, energy efficiency, and the influences of wellbore and aquifer locations, injection temperature and injection rate on system performance. The results show that the fluctuation ranges of pressure and temperature in the wellbores and aquifers increase with time, especially in the high-pressure aquifer where the maximum and minimum pressures are 15.96 and 9.78 MPa after 200 days of cycles. The maximum energy efficiency of the system can reach 1.022. Within 100 days of cushion gas filling and 200 days of cycles, the maximum horizontal CO2 transportation distance in aquifers is 198.1 m, indicating a strong sealing effect of the system. The system energy efficiencies of the two target aquifers are very similar for different vertical intervals, while the variations in wellbore pressure and temperature differ significantly, which affects the energy efficiency and stability of the surface plant. Low-temperature CO2 injection is beneficial to improving the energy efficiency of the system. Increasing injection-production rate can directly improve power generation rate, and energy efficiency is also higher for higher flow rates.

A Systematic Study on the Redox Potentials of Phenazine-Derivatives in Aqueous Media: A Combined Computational and Experimental Work.

Phenazines are an emerging class of organic compounds that have been recently utilized in aqueous redox flow batteries, a promising technology for large-scale energy storage. A virtual screening based on density functional theory calculations is used to investigate the redox potentials of around 100 phenazine derivatives in aqueous media containing various electron-donating or electron-withdrawing groups at different positions. The calculations identify the crucial positions that should be functionalized with multiple hydroxy groups to design new anolytes. The combined experimental-computational methodology reported herein guides the development of a new molecule with a record low reversible redox potential as a potential anolyte for aqueous redox flow batteries.

General performance evaluation method of the heat aided liquid air energy storge system with waste heat utilization

As a large-scale energy storage technology, liquid air energy storge (LAES) system is considered as a promising route to solve the instability of renewable energy. The heat aided LAES system with waste heat utilization (WHU) has been widely concerned for the high electrical efficiency. However, there is no unified theoretical evaluation method for such systems. In this study, the WHU-LAES systems are generalized and unified, and a comprehensive evaluation factor (efficiency improving ability) is proposed. The specific influence modes of the added heat energy on the WHU-LAES system are analyzed: the “allocation effect” shows the heat energy redistribution in the air expansion (AE) subsystem and the follower waste heat utilization system due to the heat integration in the AE subsystem; the “gain effect” is brought by the simultaneous heat integration of the “power increase” subsystems and “consumption reduction” subsystems; the “superposition effect” is revealed and shows the efficiency improving ability is comprehensively determined by the direct benefit, the explicit influence, the “allocation effect” and the “gain effect”. In the end, the efficiency improving ability is applied to the supplementary heat characteristic analysis and the comprehensive evaluation of 8 cases of WHU-LAES systems, which proves the effectiveness of the comprehensive evaluation factor.

Comparative study on the globally optimal performance of cryogenic energy storage systems with different working media

Cryogenic energy storage (CES) has garnered attention as a large-scale electric energy storage technology for the storage and regulation of intermittent renewable electric energy in power networks. Nitrogen and argon can be found in the air, whereas methane is the primary component of natural gas, an important clean energy resource. Most research on CES focuses on liquid air energy storage (LAES), with its typical round-trip efficiency (RTE) being approximately 50% (theoretical). This study aims to explore the feasibility of using different gases as working media in CES systems, and consequently, to achieve a high system efficiency by constructing four steady-state process models for the CES systems with air, nitrogen, argon, and methane as working media using Aspen HYSYS. A combined single-parameter analysis and multi-parameter global optimization method was used for system optimization. Further, a group of key independent variables were analysed carefully to determine their reasonable ranges to achieve the ideal system performance, that is, RTE and liquefaction ratio through a single-parameter analysis. Consequently, a multi-parameter genetic algorithm was adopted to globally optimize the CES systems with different working media, and the energy and exergy analyses were conducted for the CES systems under their optimal conditions. The results indicated the high cycle efficiency of methane and a low irreversible loss in the liquefaction cycle. Moreover, the Joule-Thomson valve inlet temperature and charging and discharging pressures considerably affected the system performance. However, exergy loss in the CES system occurred primarily in the compressor, turbine, and liquefaction processes. The maximum optimal RTE of 55.84% was achieved in the liquid methane energy storage (LMES) system. Therefore, the LMES system is expected to exhibit potential for application in the CES technology to realize the integration of natural gas pipelines with renewable power grids on a large scale. Moreover, the results of study have important theoretical significance for the innovation of the CES technology.

Application Trend Analysis of Compressed Air Energy Storage and Gas Storage

Large-scale energy storage technology is the key to improve the utilization of renewable energy, reducing energy pressure and achieving sustainable development. Among all energy storage technologies, the most promising physical energy storage technique is thought to be compressed air energy storage, featuring qualities including scalability, affordability, durability, and environmental friendliness. Nowadays, with the quick advancement of compressed air energy storage technology, air storage device research has gotten a lot of attention. The material properties of gas storage systems primarily determine their features, and this paper accordingly classifies and summarizes the gas storage devices in this technology, discussing the applications and characteristics of above-ground gas storage devices, natural underground caves and artificial caves. On this basis, it compares various gas storage devices, describes the challenges encountered in the development of gas storage devices, and introduces the development status of compressed air energy storage and gas storage. Finally, it looks ahead to this trend in the hope of achieving sustainable growth.

Mathematical modeling and in-depth analysis of 10 kW-class iron-vanadium flow batteries

The iron-vanadium flow batteries (IVFBs) employing V2+/V3+ and Fe2+/Fe3+ as active couples are regarded as promising large-scale energy storage technologies, benefited from their outstanding combination of system reliability, long cycling life and capital cost. In this paper, to thoroughly investigate the performance of IVFB system and accordingly optimize its design and operation, an in-depth analysis is conducted by the development of a stack-level dynamic model. A 10 kW stack composed of 60 single cells is engaged for simulation, and the results demonstrate that: i) the optimal system efficiency is obtained at the flow factor of two; ii) the premature cut-off and additional system efficiency loss can arise at high current densities; iii) electrodes with medium-sized thickness, long side and low height, proper porosity and compression ratio are favoured in practice; iv) adopting high flow rates to enhance thermal behaviors is undesirable; v) outstanding thermal behaviors is potentially realized for systems of long discharge duration and operated at appropriate current density in surroundings of proper temperature. Such in-depth investigations can not only be of great significance for the design, manufacture and management of IVFBs, but also provide a cost-effective way to predict and optimize the behavior and performance for large-scale IVFBs.

All-Iron Semi-Flow Battery Based on Fe3O4@CNTs 3-Dimensional Negative Electrode

Low-cost large-scale electrochemical energy storage technology is of great significance for the efficient utilization of clean and renewable energy. In this work, a novel all-iron semi-flow battery is designed using a 3-dimensional Fe3O4/Carbon nanotubes (CNTs) negative electrode and K4Fe(CN)6/ K3Fe(CN)6 aqueous solution as the positive electrolyte. Fe3O4 is coated onto CNTs through the co-sedimentation method. It is revealed that two steps of redox reactions of Fe3O4 exist in the charge and discharge processes and hydrogen evolution happens along with the reaction of Fe(OH)2 to Fe. It is proved to be effective to control hydrogen evolution by adjusting the capacity of the positive electrolyte. As a result, the coulombic efficiency and energy efficiency can achieve 99.3% and 73.1% at 10 mA·cm−2, respectively. The specific capacity at 10 and 20 mA·cm−2 reach 397.8 and 260.6 mA h·g−1 with Bi2S3 as the additive to the negative electrode. Compared with previous works, the specific capacity and coulombic efficiency are notably improved. Moreover, benefiting from the low cost of the active materials (38.9 $·kw h−1), the alkaline aqueous all-iron semi-flow battery could be promising as a low-cost battery technology for large-scale energy storage in the future.

Synthesis of V2O5 Nanoribbon–Reduced Graphene Oxide Hybrids as Stable Aqueous Zinc-Ion Battery Cathodes via Divalent Transition Metal Cation-Mediated Coprecipitation

Aqueous zinc-ion batteries (AZIBs) are an emerging sustainable and safer technology for large-scale electrical energy storage. Here, we report the synthesis of hybrid materials consisting of V2O5 nanoribbons (NRs) and reduced graphene oxide (rGO) nanosheets as AZIB cathode materials by divalent metal cation-mediated coprecipitation. The divalent metal ions M2+ (Zn2+ and Mn2+) effectively neutralize the negative charges on the surface of microwave-exfoliated crystalline V2O5 NRs and graphene oxide (GO) nanosheets to form a strongly bound assembly. After thermal annealing in a nitrogen atmosphere, GO is converted into rGO with higher electrical conductivity while the layers in V2O5 NRs are expanded by M2+ intercalation. When only Zn2+ ions are used during coprecipitation, the produced Zn-V2O5 NR/rGO hybrid shows a very high reversible specific capacity of ∼395 mAh g–1 at 0.50 A g–1 but suffers from poor stability. This is improved by mixing Mn2+ with Zn2+ ions during coprecipitation. The (Mn + Zn)-V2O5 NR/rGO hybrid shows a slightly lower specific capacity of ∼291 mAh g–1 at 0.5 A g–1 but a substantially improved long-cycling stability and better rate performance due to the stronger binding of Mn atoms in the V2O5 host that serve as stable pillars to support the expanded V2O5 layers.

Impact of experimentally measured relative permeability hysteresis on reservoir-scale performance of underground hydrogen storage (UHS)

Underground Hydrogen Storage (UHS) is an emerging large-scale energy storage technology. Researchers are investigating its feasibility and performance, including its injectivity, productivity, and storage capacity through numerical simulations. However, several ad-hoc relative permeability and capillary pressure functions have been used in the literature, with no direct link to the underlying physics of the hydrogen storage and production process. Recent relative permeability measurements for the hydrogen-brine system show very low hydrogen relative permeability and strong liquid phase hysteresis, very different to what has been observed for other fluid systems for the same rock type. This raises the concern as to what extend the existing studies in the literature are able to reliably quantify the feasibility of the potential storage projects. In this study, we investigate how experimentally measured hydrogen-brine relative permeability hysteresis affects the performance of UHS projects through numerical reservoir simulations. Relative permeability data measured during a hydrogen-water core-flooding experiment within ADMIRE project is used to design a relative permeability hysteresis model. Next, numerical simulation for a UHS project in a generic braided-fluvial water-gas reservoir is performed using this hysteresis model. A performance assessment is carried out for several UHS scenarios with different drainage relative permeability curves, hysteresis model coefficients, and injection/production rates. Our results show that both gas and liquid relative permeability hysteresis play an important role in UHS irrespective of injection/production rate. Ignoring gas hysteresis may cause up to 338% of uncertainty on cumulative hydrogen production, as it has negative effects on injectivity and productivity due to the resulting limited variation range of gas saturation and pressure during cyclic operations. In contrast, hysteresis in the liquid phase relative permeability resolves this issue to some extent by improving the displacement of the liquid phase. Finally, implementing relative permeability curves from other fluid systems during UHS performance assessment will cause uncertainty in terms of gas saturation and up to 141% underestimation on cumulative hydrogen production. These observations illustrate the importance of using relative permeability curves characteristic of hydrogen-brine system for assessing the UHS performances.

A comprehensive evaluation of wind-PV-salt cavern-hydrogen energy storage and utilization system: A case study in Qianjiang salt cavern, China

With global energy consumption increasing year by year, the industrial sectors of the world’s countries have never been more urgent in achieving carbon reduction. Renewable energy plays a crucial role in the industrial decarbonization process. As the most mature renewable energy technology, wind and photovoltaic power generation have made significant progress in recent years. However, the intermittent characteristics hinder the efficient use of renewable energy. Existing research provides sufficient support for the flexible scheduling of large-scale renewable energy. Hence, this paper proposes a combined energy system composed of wind power-photovoltaic-energy storage salt cavern with hydrogen as the energy scheduling carrier. The system mainly realizes energy conversion through electrolytic water equipment and fuel cells. Then, Qianjiang City, Hubei Province, is taken as the analysis object, and the working conditions of each component in the system are optimized with the help of an improved particle swarm optimization algorithm. According to the results, the system’s contribution to the energy system is discussed, and the system's economy and carbon reduction effect is studied. The analysis proves that the improved particle swarm optimization algorithm has a stronger solving ability. The combined energy system can effectively improve the economy and renewable energy utilization rate, meet the regional electricity demand, and significantly reduce carbon emissions. The economic analysis of the system shows that the operation and maintenance cost of hydrogen storage salt caverns accounts for the largest proportion of the total cost, about 60 %. Compared with several existing large-scale energy storage technologies, it is found that the energy efficiency of the whole system is only about 40 % due to the limitation of technology maturity. Nevertheless, the flexibility of the hydrogen storage system layout is relatively high. The required underground space volume is only equivalent to 1/6 and 1/2 of pumped storage and compressed air storage with the same scheduling capacity. The system will provide a theoretical support for the optimization of energy pattern and layout.

Demonstration system of pumped heat energy storage (PHES) and its round-trip efficiency

Among the known energy storage technologies aiming to increase the efficiency and stability of power grids, Pumped Heat Energy Storage (PHES) is considered by many as a promising candidate because of its flexibility, potential for scale-up and low cost per energy storage unit. Whilst there are numerous demonstration systems under development, as it stands the only PHES demonstration system to be realised at scale is located in Hampshire, UK. This paper aims to present the results and analysis obtained from its commissioning and testing as part of an on-going study. The system was designed to offer a nominal power size of 150 kWe and energy storage capacity of 600 kWhe for an 8-hour storage cycle. This work presents evidence of the system Round-trip efficiency (RTE), which is considered as a fundamental performance metric for large-scale energy storage technologies. Recorded Pressure-Volume (P-V) measurements from recent heat pump/engine testing at part-load offers useful insight in terms of overall performance. Models are also developed to simulate the system to finally predict the performance at full-load conditions. The system and principle of operation are described first, followed by mathematical modelling outlining heat transfer mechanism and associated key losses involved in thermodynamic processes within components, and finally results are presented and compared at different operating conditions using different working gases. The results show good agreement with earlier studies, which indicate that expected electricity-to-electricity RTE is quite comparable to other mature technologies such as Pumped Hydropower Storage and Compressed Air Energy Storage. The cyclic operation of the system is also discussed. One-off storage cycle results in lower RTEs compared to a load-levelling cyclic operation where the efficiency is significantly improved due to stable packed-bed behaviour and better utilisation after an initial transient state.

Multi-objective thermo-economic optimisation of Joule-Brayton pumped thermal electricity storage systems: Role of working fluids and sensible heat storage materials

Pumped-thermal electricity storage (PTES), with the advantages of reduced geographical constraints, low capital costs, long lifetimes and flexible power ratings, is a promising large-scale energy storage technology for future power systems. In this work, thermo-economic models of Joule-Brayton PTES systems with solid thermal reservoirs (STRs) and liquid thermal stores (LTSs) were developed, and detailed parametric analyses of the two systems were performed. The results reveal that elevated maximum charging temperatures are beneficial for both thermodynamic and economic performance, and that there are optimal values for the packed-bed void fraction, heat-exchanger effectiveness and turbomachine polytropic pack from a thermo-economic perspective for the two PTES system variants. Multi-objective thermo-economic optimisation of PTES systems at a fixed power capacity (10 MW) and discharging duration (6 h) was also conducted. It is found that helium is the best working fluid candidate for both PTES systems, and that the best options for the storage material are magnetite for PTES systems with STRs, and the combination of Hitec XL + Therminol 66 + Butane for PTES systems with LTSs. In the investigated design space for both systems, PTES systems with STRs are more attractive as the total purchase cost is lower for the same roundtrip efficiency as PTES systems with LTSs. Using the technique for order of preference by similarity to the ideal solution decision-making method, and a selected weighted matrix (1:1), the optimal solutions amongst the Pareto front solutions were determined. The optimal roundtrip efficiency and total purchase cost are 71.8 % and 37.7 M$ for PTES systems with STRs, and are 56.0 % and 36.0 M$ for PTES systems with LTSs, respectively. The conclusions and proposed approach can provide useful guidance for the further development, design and optimisation of PTES technology.

Development of flow battery technologies using the principles of sustainable chemistry.

Realizing decarbonization and sustainable energy supply by the integration of variable renewable energies has become an important direction for energy development. Flow batteries (FBs) are currently one of the most promising technologies for large-scale energy storage. This review aims to provide a comprehensive analysis of the state-of-the-art progress in FBs from the new perspectives of technological and environmental sustainability, thus guiding the future development of FB technologies. More importantly, we evaluate the current situation and future development of key materials with key aspects of green economy and decarbonization to promote sustainable development and improve the novel energy framework. Finally, we present an analysis of the current challenges and prospects on how to effectively construct low-carbon and sustainable FB materials in the future.