Bulk Energy Storage Research Articles

Study on heat transport analysis and improvement method in a single CaCO3 pellet for thermochemical energy storage

CaCO3/CaO thermochemical energy storage (TCES) pellets have significant advantages in bulk energy storage density, transport, and utilization. However, severe heat transport limitations within the milli-sized CaCO3 significantly affect the TCES efficiency and economy. Currently, investigations on the effect of initial porosity, bulk gas flow velocity, and reaction rate on heat transport and methods of enhancing the heat transport inside the pellet are lacking. In this paper, we developed a mathematical model coupling calcination reaction, mass transfer, and heat transfer to reveal the effects of pellet parameters and operating conditions on heat transport and reaction conversion rate within a CaCO3 pellet. The results show that the size of the CaCO3 pellet, bulk gas temperature, and reaction rate generate the most pronounced impacts on heat transport in a single CaCO3 particle during the TCES process. Furthermore, the heat transport inside the CaCO3 pellet can be improved by appropriately increasing the bulk gas flow velocity. Finally, this paper first numerically investigates the addition of SiC as a thermal conductivity enhancer to improve the heat transport performance inside a CaCO3 pellet. This study can guide the design of high-performance CaCO3 composite pellets and inform the selection of operating conditions for subsequent reactor applications.

Electrolyte Mixtures and Organic Cathode Materials for Rechargeable Aluminum Batteries

Rechargeable aluminum (Al) metal batteries are an emerging energy storage technology ideal for use at a global scale: Al metal is energy dense, low cost, inherently safe, earth abundant, and highly recyclable. Despite such great promise, their technological progress has been hindered by the few electrolytes able to reversibly electrodeposit Al metal at room temperature, coupled with the limited number of positive electrode materials that are compatible with them. In this context, recent progress will be discussed in the development of electrolyte mixtures and organic cathode materials for rechargeable aluminum batteries. Chloroaluminate ionic liquid electrolytes and ionic liquid analogues prepared using mixtures of organic cations and/or neutral solvent species will be presented, which exhibit improved electrochemical properties for aluminum electrodeposition and in aluminum-graphite batteries, over temperatures ranging from ambient conditions down to -60 °C. Different organic structures will also be presented as organic cathode materials for aluminum batteries, where the effects of molecular structure on bulk energy storage properties will be discussed. Molecular-scale understanding of their ionic and electronic charge storage mechanisms will be elucidated through a combination of solid-state nuclear magnetic resonance (NMR) spectroscopy and density functional theory (DFT) calculations. Lastly, by using different electrolytes in combination with an organic cathode, it will be shown that electrolyte speciation can affect the local environments of charge-compensating ions in cycled organic electrodes. Overall, the results and analyses are aimed at developing next-generation rechargeable aluminum metal batteries for diverse energy storage applications.

Investigating the efficiency of a novel offshore pumped hydro energy storage system: Experimental study on a scale prototype

We introduce a novel offshore pumped hydro energy storage system, the Ocean Battery, which can be integrated with variable renewable energy sources to provide bulk energy storage. Its working principle is based on that of conventional pumped hydro storage with notable differences: the Ocean Battery is installed on the seabed, is powered by the hydrostatic pressure at the depth of deployment, and uses conditioned water as a working fluid within a closed hydraulic system to minimize the effects of corrosion and biofouling on the internal system. Herein we focus on the novel aspects of the Ocean Battery to investigate their effects on performance relative to that of conventional pumped hydro storage. Specifically, we present an analytical model that accounts for energy losses in the hydraulic system to predict pressures and flow velocities under different operating conditions and validate model predictions with measurements performed on an experimental small-scale prototype deployed in a relevant sea environment. Following validation, we use the model to estimate the round-trip efficiency of a scaled-up hydraulic system connected to pumps and turbines working at peak efficiencies, with the latter adopted from literature. The round-trip efficiency of such a scaled-up system is shown to be comparable to that of conventional pumped hydro storage.

H2S Mediated One‐Pot Synthesis of Single Phase Hexagonal CoS Nano‐Spheres: A Pseudocapacitive Electrode for Hybrid Supercapacitors

AbstractDue to their exceptional qualities like high power density, extended cycle life, quick response, rapid charging periods, higher capacitance, and moderate energy density, hybrid (Asymmetric) supercapacitors (HSCs) have become a potential energy storage option as bulk energy storage devices to harness the renewable energy generated through sources such as solar, wind and tidal as an alternative to fossil fuels. Single‐phase hexagonal CoS nano‐sphere was successfully synthesized via the H2S‐mediated one‐pot synthesis route, characterized by crystallographic and microscopic techniques, and further investigated as a potential pseudocapacitive electrode material for use in large‐scale energy storage systems. The CoS electrode showed a superior specific capacitance of 761 F/g at 1 A/g current density from the galvanostatic discharge profile, and a capacitance of 776 F/g at 1 mV/s from the CV curve in 2 M KOH aqueous electrolyte. An aqueous asymmetric hybrid supercapacitor (HSC) device was assembled with activated carbon (AC) as the negative electrode and the CoS as the positive electrode. The device (full cell in HSC mode) results in high energy and power densities of 139.7 Wh/kg and 7.51 kW/kg, respectively, with excellent cyclic stability of up to 87 % after 10000 continuous charge‐discharge cycles. The electrochemical measurements demonstrate high‐rate capacity and good cyclic stability of the CoS nano‐sphere, suggesting a great potential to be used as a supercapacitor electrode.

Carbon-cement supercapacitors as a scalable bulk energy storage solution.

The large-scale implementation of renewable energy systems necessitates the development of energy storage solutions to effectively manage imbalances between energy supply and demand. Herein, we investigate such a scalable material solution for energy storage in supercapacitors constructed from readily available material precursors that can be locally sourced from virtually anywhere on the planet, namely cement, water, and carbon black. We characterize our carbon-cement electrodes by combining correlative EDS-Raman spectroscopy with capacitance measurements derived from cyclic voltammetry and galvanostatic charge-discharge experiments using integer and fractional derivatives to correct for rate and current intensity effects. Texture analysis reveals that the hydration reactions of cement in the presence of carbon generate a fractal-like electron-conducting carbon network that permeates the load-bearing cement-based matrix. The energy storage capacity of this space-filling carbon black network of the high specific surface area accessible to charge storage is shown to be an intensive quantity, whereas the high-rate capability of the carbon-cement electrodes exhibits self-similarity due to the hydration porosity available for charge transport. This intensive and self-similar nature of energy storage and rate capability represents an opportunity for mass scaling from electrode to structural scales. The availability, versatility, and scalability of these carbon-cement supercapacitors opens a horizon for the design of multifunctional structures that leverage high energy storage capacity, high-rate charge/discharge capabilities, and structural strength for sustainable residential and industrial applications ranging from energy autarkic shelters and self-charging roads for electric vehicles, to intermittent energy storage for wind turbines and tidal power stations.

Least cost analysis of bulk energy storage for deep decarbonized power system with increased share of renewable energy

Least cost analysis of bulk energy storage for deep decarbonized power system with increased share of renewable energy

The role of electricity market design for energy storage in cost-efficient decarbonization

The role of electricity market design for energy storage in cost-efficient decarbonization

Hybrid Aqueous Alkaline Zinc/TEMPO Flow Battery: A Sustainable High Voltage Green Energy Storage Device

Aqueous organic redox flow batteries (AORFBs) have number of distinct benefits for large scale energy storage, including synthetically configurable high oxidation/reduction redox potentials and excellent solubility. AORFBs still have poor energy density due to the low cell voltage, which is limited by either catholyte or anolyte. The hybrid RFB inherits the benefits of both aqueous and non-aqueous systems, demonstrating promising characteristics for next generation RFBs such as high potential window and maximum energy density. The hybrid neutral Zinc/TEMPO polymer hybrid flow battery exhibits the limiting cell voltage of 1.4 V, which resulting the low energy density. Herein, we freshly coupled alkaline Zn(OH)4 2−/4-Hydroxy 2,2,6,6-Tetramethylpiperidine 1-oxyl (4HT) as a hybrid RFB system which exhibits the high cell voltage of 2.1 V with 25.32 Wh l−1 energy density. The galvanostatic charge-discharge shows stable performance at 5 to 40 mA cm−2 with the maximum 90% coulombic efficiency. The high rate GCD profile of alkaline Zn(OH)4 2-/4HT at 40 mA cm−2 current density have shown 90% coulombic efficiency and 60% energy efficiency. More importantly, the alkaline-based Zn(OH)4 2−/4HT exhibits remarkable capacity retention of 99.99% over 100 cycles with 25.32 Wh l−1 energy density. Thus, the freshly developed alkaline Zn(OH)4 2−/4HT system would be a potential high voltage RFB for bulk energy storage.

Experimental studies of latent heat storage based solar air heater for space heating: A comparative analysis

There are numerous applications of solar energy technology, among which an air heating system is commonly used for space heating, wood seasoning, industrial drying, etc. Previous research focuses on the bulk usage of different latent heat storages, which is a costly method for performance improvement, especially for solar heating systems. Another major problem with bulk energy storage is that it takes a long time to be charged completely, which results in low-rate air heating at the start. The present research focuses on an economical solution for solar air heating, especially under India's mild cold climatic conditions. About 36 tiny cylindrical containers have been used to carry the two low-cost phase change materials (PCMs), i.e., coconut oil and paraffin wax. These materials have been filled inside the small containers and placed over the solar absorbers of modified models of air heaters, namely, SAHS-2 (with coconut oil) and SAHS-3 (with paraffin). A total of 02 configurations have been developed to conduct the air heating trials on natural and forced convection. To the best of the author's knowledge, likely methodology has not been applied to any air heating system to improve performance for extended hours, especially in a cold climate. Results have been compared with the same size conventional solar heater (SAHS-1) and some other relevant designs of SAHS to observe the significance of PCMs and their appropriateness for air heating. Finally, the model SAHS-3 is found to be the best-configured air heater, capable of performing efficiently under mild cold climates. Experimental studies showed that the best model provides enhanced heat transfer of about 372.81 W/m2 K, thermal efficiency of about 75.9%, a heat loss coefficient of about 4.93 W/m2 K, and outlet air temperature of about 44.07 °C under forced convective operations. The estimated cost of the modified heater is approximately $61, while its payback period is about 4.38 years.

Hydrogen sorption and diffusion in coals: Implications for hydrogen geo-storage

A full-scale hydrogen economy requires a bulk energy storage system to store the excess energy as a buffer and to fulfill the demand constantly. Hydrogen sorption capacity and diffusion behavior in coal quantify its potential to become a well storage candidate from geological formations. In this study, the sorption and diffusion behaviors of eight coals across the major coalfields in the United States in terms of their ranks, fixed carbon content, vitrinite reflectance, vitrinite or huminite content, O/C ratio, and H/C ratio were measured and analyzed. The sorption data shown that all eight coals have considerable sorption capacities, among which the LvB coal has the maximum adsorption capacity of ∼ 1.17 mmol/g, followed by An coal with the maximum hydrogen adsorption capacity of ∼ 0.95 mmol/g and the SemiAn coal of approximately 0.82 mmol/g. The fixed carbon content and typically the O/C ratio are obviously correlated with the maximum hydrogen adsorption capacity in coals, which may be attributed to the oxygen-containing functional groups. Hydrogen has superior diffusive gas deliverability defined by hydrogen effective diffusivity. The effective diffusivities of hydrogen in SemiAn coal decreases from ∼ 0.00156 to ∼ 9.26 × 10-41/s with pressure increases from ∼ 2.45 MPa to ∼ 10.07 MPa, among which the lowest diffusivity at ∼ 10.07 MPa is even ∼ 4 times higher than that of CH4 at equivalent pressure. This is a vantage for a promising field candidate of hydrogen storage in coal with maximized injectivity. The results reveal that the sorption and diffusion behaviors of hydrogen in different rank coals towards the depleted coalbed methane formation with injected hydrogen can serve as a geological “H2-Battery”.

Cooking performance assessment of a phase change material integrated hot box cooker.

Previous research on solar box cookers focusing on the bulk usage of energy storage materials is a costly technique for performance enhancement. Bulk energy storage materials take much time to charge and, thus, result in a low rate of cooking at the start. Therefore, a hot box solar cooker has been developed and experimentally studied for thermal performance enhancement in a hilly region of Uttarakhand, India. A bed of phase change material (paraffin wax) filled with small capsule-shaped containers was prepared (detachable) and placed over the cooking tray of the tested cooker. These containers were vertically positioned over the bed to enhance the heat transfer rate inside the cooker to attain a fast-cooking response. Notably, the combined effect of extended geometry with PCM is an excellent method to increase the efficiency of a solar cooker. As per the author's knowledge, likely techniques have not been studied for a box cooker to achieve a fast-cooking rate in any hilly region up to date. The results of cooking tests show that the cooking plate attained a maximum temperature of about 150°C. It is because of the combined effect of extended fins (vertical capsules) and PCM filled inside them. The results of the experimental study show that the thermal efficiency of the cooker was found to be about 45.7%, the cooking power was calculated about 54.71W, the heat transfer coefficient was estimated about 311W/m2 °C, and the overall heat loss coefficient was computed about 5.71W/m2 °C. This modified cooker costs about $48.19, and the payback period is about 03years and 11months. Cooking trials also showed that the present SBC could cook almost all the dishes commonly cooked in Uttarakhand.

Medium-Voltage Seven-Level Multiplexed Converter for AC Applications

After several decades of technological evolution, power electronics applications have become extremely important for electric/hybrid propulsion systems, smart grids, renewable energy systems, energy saving, and bulk energy storage, besides the typical applications in industrial automation and high-efficiency energy systems. In all these applications, a power conversion system with high efficiency and power density is required without sacrificing the system's power quality. The paper describes the specific characteristics and the scalar modulation strategy of a new multi-level multiplexed inverter topology for medium-voltage AC applications. The proposed power converter configuration is intended for high-power applications aiming to reduce the active device's voltage rating and losses exhibiting a resulting low switching frequency of the power switches. The proposed modulation strategy aims to reduce the computational burden and simplify the implementation process, which are at the basis of any possible industrial adoption. Simulation results and full Hardware-In-the-Loop verification support the analysis. The Hardware-In-the-Loop assessment has enabled the development of a suitable modulation strategy, and the testing of the power converter is a safe environment.

Techno-economic study of a 100-MW-class multi-energy vehicle charging/refueling station: Using 100% renewable, liquid hydrogen, and superconductor technologies

Renewable energies such as the wind energy and solar energy generate low-carbon electricity, which can directly charge battery electric vehicles (BEVs). Meanwhile, the surplus electricity can be used to produce the “green hydrogen”, which provides zero-emission hydrogen fuels to those fuel cell electric vehicles (FCEVs). In order to charge/refuel multi-energy vehicles, we propose a novel scheme of hybrid hydrogen/electricity supply using cryogenic and superconducting technologies. In this scheme, the green hydrogen is further liquefied into the high-density and low-pressure liquid hydrogen (LH2) for bulk energy storage and transmission. Taking the advantage of the cryogenic environment of LH2 (20 K), it can also be used as the cryogen to cool down superconducting cables to realize the virtually zero-loss power transmission from 100 % renewable sources to vehicle charging stations. This hybrid LH2/electricity energy pipeline can realize long-distance, large-capacity, and high-efficiency clean energy transmission, to fulfil the hybrid energy supply demand for BEVs and FCEVs. For the case of a 100 MW-class hybrid hydrogen/electricity supply station, the system principle and energy management strategy are analyzed through 9 different operating sub-modes. The corresponding static and dynamic economic modeling are performed, and the economic feasibility of the hybrid hydrogen/electricity supply is verified using life-cycle analysis. Taking an example of wind power capacity 1898 MWh and solar power capacity 1619 MWh per day, the dynamic payback period is 15.06 years, the profitability index is 1.17, the internal rate of return is 7.956 %, and the accumulative NPV is 187.92 M$. The system design and techno-economic analysis can potentially offer a technically/economically superior solution for future multi-energy vehicle charging/refueling systems.

Subsidized renewables’ adverse effect on energy storage and carbon pricing as a potential remedy

Large-scale energy storage is viewed as a key complementary technology in a power system fed by a large share of intermittent renewable energies (RE). However, subsidies for RE – a well-intended market intervention – may distort price signals, thereby adversely undermining the profitability of energy storages, and thus, adequate investment incentives. This study provides novel causal estimates supporting this notion, using an econometric instrumental-variables framework and data on Austrian pumped storages, operating in the German–Austrian electricity market, characterized by a large share of generously subsidized RE. The findings show that RE significantly depress storage profitability and that further deployment of RE will intensify this effect. This may pose an obstacle against adequate investment in bulk energy storage capacity. Moreover, the results indicate that intensifying carbon pricing would significantly counteract the problem via a market-based price signal. This study contributes to the general debate on the design and effects of environmental regulation and particularly shows that a non-market-based policy for a green technology may adversely affect complementary technologies.

Effect of expanded graphite on the thermal conductivity of sodium sulfate decahydrate (Na2SO4·10H2O) phase change composites

Inorganic salt hydrate phase change materials (PCMs) are of interest for near-room temperature thermal energy storage (TES) systems, but their low thermal conductivity, ~ 0.5 W/m-K, limits their performance. In this work, we report the thermal conductivity and bulk density of composites containing sodium sulfate decahydrate (SSD) Na2SO4·10H2O with three types of graphite: expanded graphite (EG), milled EG (MG), and graphite nanoplatelets (GnP). The effect of these thermophysical properties on TES performance is presented. The composites were made using a readily scalable one-pot synthesis procedure with graphite received as-is. A 583% increase in thermal conductivity (4.1 W/m-K) was achieved with 25 wt% EG. However, as EG fraction increases, bulk density decreases and thermal conductivity plateaus. This ultimately resulted in lower thermal performance at higher EG fractions despite higher thermal conductivity. This highlights the tradeoff between PCM composite properties and performance, and why thermal conductivity is insufficient to describe PCM thermal performance. GnP is added to EG-SSD to increase bulk density and energy storage density, but these density improvements do not offset lower thermal conductivity and thus thermal performance declined. Similarly, MG-SSD composites had a higher bulk density and energy storage density, but lower thermal conductivity and thermal performance than EG-SSD composites at similar compositions. Atomistic molecular dynamics simulations were performed to understand the structure-property relationship of graphite-SSD interfaces. The simulations support the hypothesis that atomic level contact resistance between graphite and SSD increases thermal resistance at the interfaces resulting in effectively lower bulk thermal conductivity in MG-SSD compared to EG-SSD.

Power Electronics: My Life and Vision for the Future [My View

Power electronics has ushered in a new kind of industrial revolution in the 21st century because of its important roles in energy conservation, renewable energy systems (RESs), bulk energy storage, electric and hybrid electric vehicles, and smart grid applications besides its traditional role in high-efficiency energy systems. Future advances in power electronics will occur mainly in two directions: wide-bandgap (WBG) power semiconductor devices and complex smart grid systems.

Design and analysis of biomass-to-ammonia-to-power as an energy storage method in a renewable multi-generation system

To solve the problem of unevenly distributed renewables and increase their penetration, large-scale energy storage is necessary. Green hydrogen is suitable for bulk energy storage; however, it still faces storage problems. Therefore, green ammonia has been proposed as a substitute for hydrogen. The combination of renewables and green ammonia production can achieve cross-sector decarbonization. However, the potential of green ammonia as an energy carrier requires further investigation. This paper reports the design and analysis of a renewable multi-generation system for electricity, heat, and green ammonia, where biomass-to-ammonia-to-power is used as an energy storage method. This concept combines renewable power generation, biomass chemical-looping ammonia production, and direct ammonia fuel cells. The results indicated that the maximum energy and exergy efficiencies were 60.1% and 56.3%, respectively. The system provides 29,582 t·y-1 ammonia and 3,525,305 t·y-1 hot water and captures 171,550 t·y-1 of carbon dioxide. The optimal proportion of key components and relevant design criteria were also determined through sensitivity analysis as well. Compared to systems involving power-to-ammonia-to-power, the higher efficiency, lower electricity consumption for ammonia production, and carbon dioxide capture make biomass-to-ammonia-to-power a promising energy storage method for multigeneration systems.

Application of Advanced Vibrational Spectroscopy in Revealing Critical Chemical Processes and Phenomena of Electrochemical Energy Storage and Conversion.

The future of the energy industry and green transportation critically relies on exploration of high-performance, reliable, low-cost, and environmentally friendly energy storage and conversion materials. Understanding the chemical processes and phenomena involved in electrochemical energy storage and conversion is the premise of a revolutionary materials discovery. In this article, we review the recent advancements of application of state-of-the-art vibrational spectroscopic techniques in unraveling the nature of electrochemical energy, including bulk energy storage, dynamics of liquid electrolytes, interfacial processes, etc. Technique-wise, the review covers a wide range of spectroscopic methods, including classic vibrational spectroscopy (direct infrared absorption and Raman scattering), external field enhanced spectroscopy (surface enhanced Raman and IR, tip enhanced Raman, and near-field IR), and two-photon techniques (2D infrared absorption, stimulated Raman, and vibrational sum frequency generation). Finally, we provide perspectives on future directions in refining vibrational spectroscopy to contribute to the research frontier of electrochemical energy storage and conversion.

Distributed Optimal Control of DC Microgrid Considering Balance of Charge State

State-of-charge (SoC) imbalance and bus voltage deviation are two of the main problems in autonomous dc microgrids. Based on this concern, this paper presents an improved dual-quadrant SoC weighted control strategy and a distributed optimization control method to achieve SoC balance, ensuring accurate power-sharing and bus voltage recovery. Firstly, this paper couples the injected/released power with the current SoC and observed average SoC value to weight the droop coefficient, which is based on the charge/discharge mode for the energy storage system. Then a secondary controller is designed based on distributed optimal control to eliminate the bus voltage deviation caused by the line impedance difference. The proposed optimal control method optimizes the average bus voltage to the nominal value and achieve accurate power-sharing by constructing the correlated variables and voltage independent intermediate variables exchanged among bulk energy storage units (ESUs). Since the voltage observer cannot accurately observe the true average bus voltage under the communication delay, the proposed distributed optimal control method without the voltage observer can ensure that the average bus voltage is optimized to the nominal value, thus improving the robustness of the control system. Finally, the correctness and effectiveness of the proposed method are verified in Simulink/MATLAB.

Various methodologies to improve the energy efficiency of a compressed air energy storage system

AbstractIntermittency characteristic of renewable energy sources can be resolved using an energy storage technology. The function of the energy storage system is to store the excess energy that is produced from various renewable energy sources during the off‐peak hours and releases the same energy during the peak hours. The energy that is produced from the renewable energy sources can be stored in different forms such as Mechanical, Electrical, Electrochemical, Thermal, Chemical energy etc. Among all these forms of stored energy, a CAES technology under the Mechanical form of energy is the most cost effective for the bulk energy storage purpose. It involves a combined operation of various components such as Compressor/Expander, Gas turbine, combustion chambers, heat exchangers, generator unit, and underground compressed air storage. This article focuses to review the detail of various CAES systems such as D‐CAES, A‐CAES, I‐CAES etc. Additionally, it presents various technologies that are used to improve the energy efficiency and applicability of the CAES system. It is found that a maximum RTE of the C‐CAES, A‐CAES, and I‐CAES are 54%, 71%, and 80%, respectively. In addition, the RTE of the modified CAES systems such as LP‐CAES, PH‐CAES, and SC‐CAES are about 90%, 80%, and 60 to 80%, respectively.