Hybrid Electrical Energy Storage Research Articles

An optimal energy co-scheduling framework for smart buildings

The Heating, Ventilation and Air Conditioning (HVAC) system accounts for nearly half of the energy consumption of a typical building. Additionally, the need for HVAC changes over hours and days as does the electric energy price. Level of comfort of the building occupants is, however, a primary concern, which tends to overwrite pricing. Dynamic HVAC control under a dynamic energy pricing model while meeting an acceptable level of occupants' comfort is thus critical to achieve energy efficiency in buildings in a sustainable manner. Finally, there is the possibility that the building is equipped with some renewable sources of power such as solar panels mounted on the rooftop. The presence of Hybrid Electrical Energy Storage (HEES) system in a target building would enable peak power shaving by adopting a suitable charging and discharging schedule for each Electrical Energy Storage (EES) element, while simultaneously meeting building energy efficiency and user comfort requirements. Achieving this goal requires detailed information (or predictions) about the amount of local power generation from the renewable source plus the power consumption load of the building.This paper addresses the co-scheduling problem of HVAC control and HEES system management to achieve energy-efficient smart buildings, while also accounting for the degradation of the battery state-of-health during charging and discharging operations (which in turn determines the amortized cost of owning and utilizing a battery storage system). A time-of-use dynamic pricing scenario is assumed and various energy loss components are considered, including power dissipation in the power conversion circuitry, the rate capacity effect in the batteries, and the self-discharge in the super-capacitor. A global optimization framework targeting the entire billing cycle is presented and an adaptive co-scheduling algorithm is provided to dynamically update the optimal HVAC air flow control and the HEES system management in each time slot during the billing cycle to mitigate the prediction error of unknown parameters. Experimental results show that the proposed algorithm achieves up to 10% in the total electric utility cost compared with some baseline methods.

Toward a Profitable Grid-Connected Hybrid Electrical Energy Storage System for Residential Use

Hybrid electrical energy storage (HEES) systems have the potential to result in considerable cost savings by reducing the electric bills of home users. This paper first presents grid-connected dual-bank HEES system design and management to maximize the electric bill savings for residential users, and subsequently provides a comprehensive sensitivity analysis of the economic feasibility of residential HEES systems. Specifically, the paper describes a daily management policy based on energy buffering strategy with one bank as the main storage bank and the other as the energy buffering bank, and then derive the global design of HEES specifications based on the daily management results. Simulation results prove the effectiveness of energy buffering strategy and show the proposed HEES system is capable of bringing in profits under current input variables. Finally, a detailed analysis is conducted to show how each input variable affects the final design of the proposed residential HEES system and the maximum annual profits it achieves. Together with the design and control mechanism, the proposed analysis provides potential customers with the comprehensive knowledge of how HEES systems can be deployed to achieve savings in their electric bills.

Model predictive control‐based operation management for a residential microgrid with considering forecast uncertainties and demand response strategies

This study proposes a model predictive control (MPC)-based home energy management system for residential microgrid (RM) in which all related information such as the time-varying information of the load demand, electricity price and renewable energy generations, are all taken into account. A novel finite-horizon mixed-integer linear programming problem is iteratively formulated to investigate the optimal control actions of the RM under an MPC framework. Three case studies are conducted to discuss the technical and economic impacts of the responsive electrical and thermal loads, plug-in hybrid electric vehicles, and electrical and thermal energy storage units. Moreover, a sensitivity analysis is performed to demonstrate the superiority of the proposed approach when forecasts of related information are imperfect.

Optimal hybridization and amortized cost study of battery/supercapacitors system under pulsed loads

Hybrid electrical energy storage systems (HESS) show promise for solving the problems and exploiting the benefits of heterogeneous electrical storage systems (ESS). This paper compares the performance of a lead-acid battery/supercapacitors hybrid to that of a battery alone under pulsed loads. Two types of aging protocols, using pulsed and smoothed power, were carried out on VRLA batteries at 40°C. These protocols typically illustrate a single or hybrid battery’s use for an Uninterruptible Power Supply. In HESS, the supercapacitors smooth the power demand applied to the battery, and, when idle, the battery charges the supercapacitors. The same amount of energy is extracted from the battery during both protocols. The experiment indicated that the battery alone performs 150 ten-minute-cycles before reaching the end of its life. In the hybridized battery, the power dissipated was reduced to 36% of that used by the battery alone, and the number of cycles increased by 70%. The use of a hybrid also reduced the battery’s capacity fade by 60% and its increase of internal resistance by 83%. Finally, the amortized cost of the hybrid system was 17.6% less than that of the battery alone.

In Situ Electrical Conductivity of LixMnO2 Nanowires as a Function of x and Size

Manganese oxide, MnO2, excels as a hybrid electrical energy storage material: The manganese centers in MnO2 are capable of undergoing a reduction from 4+ to 3+ balanced by the intercalation of lithium ions to form LixMnO2 while its conductive surfaces simultaneously store energy as an electrical double layer capacitor. The highest capacitance and power performance for MnO2 has been obtained for ensembles of nanowires that are 200 nm or less in width and many microns in length. Typically such MnO2 nanowires are attached to a current collector at just one end, and electrical conductivity of the nanowire is therefore required in order to maintain a consistent redox and charge state along its axis. The electrical conductance of the nanowire therefore plays a very important role, and yet this parameter has been measured in few previous studies. In this work, we directly measure the electrical conductance of δ-MnO2 nanowires in situ in 1 M LiClO4, acetonitrile as a function of the equilibrium Li content for nan...

Iron and Titanium-Based Electrode Materials for Sodium-Ion Batteries

In the past two decades, lithium-ion batteries (LIBs) have been successfully used in mobile electronic devices. With the development of hybrid electrical vehicles (HEVs), electrical vehicles (EVs), and energy storage stations, etc., of which a battery needs at least manifold amount of lithium, the cost of lithium would be further driven higher as the lithium metal reserves are limited both in amount and geographical location. Recently, sodium-ion batteries (NIBs) have been proven to be the most attracted alternative rechargeable systems for the potential large-scale production because sodium is much cheaper and more abundant in the Earth’s crust, and the potential of sodium metal is only 0.3 V higher than that of lithium. Therefore, it is urgent for us to develop NIBs to provide sufficient low-cost and safe energy storage devices for our society. Recent studies in NIBs focused on the development of electrode materials. A number of promising electrode materials, including cathodes such as α-NaFeO2-based NaMO2 (M = Fe, Co, Mn, Ni, Ti, etc.) [1, 2], polyanion-based Na3V2(PO4)3 [3], Na3MPO4CO3 [4], Na4Fe3(PO4)2(P2O7) [5], and Prussian blue [6], and anodes such as hard carbon [7], Na2Ti3O7 [8], P2-type Na2/3Co1/3Ti2/3O2 [9], and carboxylate-based materials [10] have already been explored for NIBs. The development of feasible electrode materials by an optimized composition with high capacity, long cycle life, and low cost still remains a challenging issue that warrants further investigation. Looking back to the history, iron (Fe) always has the priority being used when it comes to transition metal oxides because the elemental abundance in the Earth’s crust is of primary importance for large-scale batteries [1, 11]. In this pursuit, herein, O3-type Na[Fe1/3Ni1/3Ti1/3]O2 cathode material and orthorhombic Nax[FeTi]O4 (x = 1 and 4/3) anode materials are synthesized by a solid-state reaction method, and studied as a positive electrode and negative electrodes for NIBs, all tested in a half cell and at 20 ºC, using 1 M NaClO4 in 1:1 weight ratio of propylene carbonate (PC) and dimethyl carbonate (DEC) as electrolyte, and a glass fiber filter (GF/D, Whatman) as separator. The obtained Na[Fe1/3Ni1/3Ti1/3]O2 cathode material has an initial discharge capacity of 115 mAh g-1 under a current density of 10 mA g-1 (0.1 C) in the voltage range of 1.5-4.0 V, and shows reversible discharge capacity values of 91.3, 89.7, 79.2, 69.7, 46.2, and 30.9 mAh g-1, respectively at 0.2, 0.5, 1, 2, 5, and 10 C. The potentials reported in this work refer to the Na+/Na couple. The obtained Na4/3[FeTi]O4 anode material exhibits a first charge capacity of 119.6 mAh g-1 under a current density of 17.7 mA g-1 (0.1 C) in the voltage range of 0.01-2.5 V, and delivers reversible charge capacity values of 84.5, 73.1, 61.4, 47.5, and 36.7 mAh g-1, respectively at 0.5, 1, 2, 5, and 10 C. The even more promising thing is as-prepared orthorhombic Na[FeTi]O4 exhibits an initial charge capacity of about 181 mAh g-1 at 0.1 C, and good cycling performance as well.

Single-Source, Single-Destination Charge Migration in Hybrid Electrical Energy Storage Systems

In spite of extensive research it is still quite expensive to store electrical energy without converting it to a different form of energy. As of today, no single type of electrical energy storage (EES) element can fulfill all the desirable features of an ideal storage device, e.g., high-efficiency, high-power/energy capacity, low-cost, and long-cycle life. A hybrid EES system (HEES) consists of two or more heterogeneous EES elements, realizing the advantages of each EES element while hiding their weaknesses. HEES systems exhibit superior performance compared with homogeneous EES systems when appropriate charge allocation and replacement policies are developed and used. In addition, charge migration is mandatory because the optimal EES banks for charge allocation and replacement are in general different, and each EES bank has limited storage capacity. This paper formally describes the notion of charge migration efficiency and its optimization. We first define the charge migration architecture and the corresponding charge migration optimization problem. We provide a systematic solution for the single-source, single-destination charge migration problem considering the efficiency variation of the converters, the rate capacity and internal power loss of the storage element, the terminal voltage variation of the storage elements as a function of their state of charge, and so on. We also introduce the optimal solutions for both the time-constrained and -unconstrained versions of the charge migration problem formulations. Experimental results demonstrate significant charge migration efficiency improvement of up to 83.4%.

Principles and Efficient Implementation of Charge Replacement in Hybrid Electrical Energy Storage Systems

Hybrid electrical energy storage systems (HEES) are comprised of multiple banks of inhomogeneous EES elements with difference characteristics. They have been proposed to achieve desired performance metrics of an ideal energy storage device, i.e., high energy capacity, high output power level, low self-discharge, low cost, and long service life. Implementation of appropriate charge management policies enables efficient storage and retrieval of the electrical energy, attaining performance metrics that are close to the respective best values across the constituent EES elements in the HEES system. This paper addresses a global charge replacement problem in HEES systems, namely, how to dynamically select a subset of the EES banks and discharge them to meet the load power demand in a prespecified amount of time. Precisely, the global charge replacement optimization problem is formulated as a mixed-integer nonlinear programming problem, and a hierarchical algorithm is presented to efficiently solve this problem. At the top level the proposed algorithm considers the complete discharging process and allocates the load demand among all available EES banks, whereas at the bottom level it employs convex optimization methods to solve for discharging currents and the voltage level of a shared charger transfer interconnect. A prototype HEES system has been built to demonstrate the energy benefits brought by HEES systems and the efficacy of the proposed charge replacement algorithm.

The Ragone plots guided sizing of hybrid storage system for taming the wind power

The fluctuant behaviors of wind power, and so as their effects on the stability of grid, span across different time scales. Hence, single type of electrical energy storage (EES) cannot level the fluctuation effectively. The high energy density sources (e.g. lead-acid batteries) and high power density sources (e.g. supercapacitors) are complementary in merits such as power density and energy density. As a result, the employment of the hybrid EES (HEES) is hoped to level wind power output more effectively. This work proposes a sizing strategy for determining the capacity allocation between the high energy density sources and high power density sources. The traits of this employed strategy are the introduction of energy-power relationships (Ragone plots) of EES as constraints and taking of the minimization of life cycle cost (LCC) of HESS as objective function; which respectively considers the power and energy storage characteristics of EES integrally, and reflects the economic need of renewable energy integration. The analytical process of the sizing strategy is described in detail. A case study for an analysis of specific wind power output, with the types of EES we adopted in project, is illustrated graphically based on the developed programming software platform.

Three-Dimensional Porous Sb/Cu2Sb Anode for Na-Ion Batteries

Introduction Over the past few decades, Li-ion batteries (LIBs) have been widely used as power sources for mobile electronic products and power tools [1], and nowadays a much effort has been focused on the use of these batteries in large-scale applications such as electric vehicles, hybrid electric vehicles and electrical energy storage (EES) devices [2]. However, because the amount of the Li resources would not be sufficient to meet industrial needs in the long term, the expansion of the LIBs market takes concern on the sustainable supply of Li and the raising of the Li prices. Thus, in recent years, rechargeable sodium-ion batteries (SIBs) have received great attention as a possible alternative to replace LIBs. Owing to the abundant resource, low cost and a relatively low redox potential (0.3 V above that of Li/Li+), NIBs are expected to be a near-term alternative for large-scale systems such as grid storages.Among the various candidate anode materials, Sb has been considered to be very attractive anode material due to its high theoretical capacity of 660 mAh g-1. However, pure Sb electrode exhibits the poor cycleability because of their significant volumetric changes (up to approximately 390%) that occurs during alloying/dealloying with Na.In a recent communication, we reported that when the porous Cu foam was used as a substrate for the Sn anode in Li-ion batteries, the Cu foam accommodated the volumetric expansion of Sn and effectively inhibited the delamination of the active materials, and hence the cycle performance of the Sn anode was considerably improved [3]. Therefore, the objective of this work is to fabricate the Sb-based electrode using a highly porous Cu foam as a substrate and to examine the electrochemical properties of such electrode for SIBs anode. Experimental. A three-dimensional porous Cu foam was prepared by the electrodeposition at a constant current density of -3 A cm-2 for 4 s from a Cu sulfate electrolytic bath containing 0.2 M CuSO4, 0.7 M H2SO4, 1.2 M (NH4)2SO4and 0.4 mM BTA(benzotriazole). After the Cu foam was prepared, the Sb was electrodeposited on the foam substrate.The electrochemical properties of the Sb/Cu2Sb electrode were investigated using Swagelok-type cells assembled in an Ar-filled glove box. The cell is composed of a sheet of the sb electrode (with an area of 1 cm2) and a Na metal electrode (with an area of 1 cm2) without a separator. Electrolyte was anhydrous propylene carbonate (PC) containing 1 M NaClO4. The charge/discharge characteristics of the electrode were galvanostatically examined at a current density of 0.1 C (based on mass of Sb) between 0.01 V and 1.5 V (vs. Na/Na+). To examine the rate capabilities of the Sb/Cu2Sb electrode, the cell was cycled at different current densities for the following cycles in the voltage ranges between 0.01 and 1.5 V (vs. Na/Na+). Results and discussion. As shown in Fig. 1, the Sb electrodeposit layer was uniformly deposited along the surface of the Cu foam substrate; thus, the prepared electrode exhibits a three-dimensional porous structure with a large surface area. Whereas the cyclic stability of the pure Sb electrode deposited on the smooth Cu sheet is poor, the Sb/Cu2Sb electrode exhibits outstanding cycle stability and excellent rate capability; the charge capacity is sustained at 485.64 mAh g-1 over 120 cycles with a high coulombic efficiency of 97%, and the charge capacity retention is approximately 70% of the capacity at 0.1 C-rate, even at high 3 C-rate. The improvement in the electrochemical performance of the Sb/Cu2Sb electrode is attributed not only to the highly porous structure of the electrode but also to the improvement of bonding between substrate and active materials by the formation of Cu2Sb intermetallic. The sodiation/desodiation reactions of Sb/Cu2Sb with Na+ is proposed based on the ex-situ XRD analysis. After being fully desodiated, the electrode is restored to the crystalline Cu2Sb phase, confirming that the Cu2Sb phase reversibly reacts with Na+[4]. Fig. 1.(a) Surface morphology and (b) cycle performance of the Sb electrode electrodeposited onto the Cu foam substrate [4].

Electrochemical Properties of Electrodeposited Sn Anodes for Na-Ion Batteries

Introduction Over the past few decades, Li-ion batteries (LIBs) have been widely used as power sources for mobile electronic products and power tools, and nowadays a much effort has been focused on the use of these batteries in large-scale applications such as electric vehicles, hybrid electric vehicles and electrical energy storage (EES) devices. However, because the amount of the Li resources would not be sufficient to meet industrial needs in the long term, the expansion of the LIBs market takes concern on the sustainable supply of Li and the raising of the Li prices. Accordingly, in recent years, rechargeable Na-ion batteries (SIBs) have received great attention as a possible alternative to replace LIBs. Owing to the abundant resource, low cost and a relatively low redox potential (0.3 V above that of Li/Li+), NIBs are expected to be a near-term alternative for large-scale systems such as grid storages [1].Despite the high specific capacity, pure Na metal is inappropriate as an anode material for practical applications of NIBs because the dendiritc deposition of sodium during charging can cause the severe safety problems as well as the reduced capacity and increasing electrode impedance. To overcome these problems, the research for finding suitable electrode materials which have high specific capacity, low irreversible loss, high coulombic efficiency and long cycle life for SIBs have been extensively conducted. Among the various candidate materials, Sn is one of the most attractive anode materials because of its high theoretical capacity and low reaction potential. When assuming complete sodiation of Sn into Na15Sn4, the capacity of Sn is approximately 847 mAh g-1[1], which is substantially higher than the reversible capacity of carbonaceous materials (approximately 250 mAh g-1) [2]. In this study, the electrochemical performance and the sodiation/desodiation mechanisms of electrodeposited Sn were investigated based on previous studies. Herein, two Sn electrodes that have completely different morphologies and crystal structures were prepared by electrodeposition, and their electrochemical properties for Na-ion battery applications were examined, with an emphasis on the effects of the morphology and the phase structure of Sn on the cyclability of the electrodes. Experimental. Two different Sn electrodes were prepared by electrodeposition from different electrolytes. The electrodeposition of Sn was performed in a two-electrode cell that consists of a smooth Cu sheet as the cathode and a Sn plate as the anode. A constant current density of -10 mAcm-2 was applied for 4 min at room temperature. The electrochemical properties of the Sn electrodes were investigated using Swagelok-type cells assembled in an Ar-filled glove box. The cell is composed of a sheet of the Sn electrode (with an area of 1 cm2) and a Na metal film (with an area of 1 cm2) without using a separator. The electrolyte was anhydrous propylene carbonate (PC) containing 1 M NaClO4 and 0.5 vol.% fluoroethylene carbonate (FEC). The charge/discharge characteristics of the electrode were galvanostatically examined at a current density of 50 mA g-1 between 0.001 and 0.65 V (vs. Na/Na+). Results and discussion. Two Sn electrodes that have completely different morphologies and crystal structures were successfully prepared by electrodeposition. One consists of coarse and isolated particles, but the other exhibits a compact thin layer composed of fine grains. Both electrodes showed excellent reversibility via three conjugated sodiation/desodiation reactions. Nevertheless, the particle-type Sn electrode had the poor cycle performance due to the electrical isolation of the active materials. In contrast, the layer-type Sn electrode showed a stable cycle performance in which the charge capacity was maintained at 607.51 mAh g-1after 40 cycles, which corresponds to 98.21% of its initial charge capacity. The difference in the cyclability of the electrodes was attributed to the morphology of the Sn electrodeposits and to the bond between Sn and the Cu substrate.

Charge Allocation in Hybrid Electrical Energy Storage Systems

A hybrid electrical energy storage (HEES) system consists of multiple banks of heterogeneous electrical energy storage (EES) elements placed between a power source and some load devices and providing charge storage and retrieval functions. For an HEES system to perform its desired functions of 1) reducing electricity costs by storing electricity obtained from the power grid at off-peak times when its price is lower, for use at peak times instead of electricity that must be bought then at higher prices, and 2) alleviating problems, such as excessive power fluctuation and undependable power supply, which are associated with the use of large amounts of renewable energy on the grid, appropriate charge management policies must be developed in order to efficiently store and retrieve electrical energy while attaining performance metrics that are close to the respective best values across the constituent EES banks in the HEES system. This paper is the first to formally describe the global charge allocation problem in HEES systems, namely, distributing a specified level of incoming power to a subset of destination EES banks so that maximum charge allocation efficiency is achieved. The problem is formulated as a mixed integer nonlinear program with the objective function set to the global charge allocation efficiency and the constraints capturing key requirements and features of the system such as the energy conservation law, power conversion losses in the chargers, the rate capacity, and self-discharge effects in the EES elements. A rigorous algorithm is provided to obtain near-optimal charge allocation efficiency under a daily charge allocation schedule. A photovoltaic array is used as an example of the power source for the charge allocation process and a heuristic is provided to predict the solar radiation level with a high accuracy. Simulation results using this photovoltaic cell array and a representative HEES system demonstrate up to 25% gain in the charge allocation efficiency by employing the proposed algorithm.

A domestic CHP system with hybrid electrical energy storage

CHP (combined heat and power) is widely regarded as one of the most promising technologies to resolve energy-related problems, such as primary energy saving, emission reducing etc. Domestic CHP is the energy system applied to the household sector to supply both electric and heat energy to users. Due to the dissimilar characteristics between household electricity and heat demands, conventional off-grid CHP systems may not satisfy both of the demands simultaneously. This study developed a domestic CHP system in which an engine-based CHP fuelled by biofuels was integrated with a hybrid electric energy storage system and operated under FEL (following electric load) energy management strategy. Experimental tests validate the feasibility of this application and the results show that the system can satisfy the fluctuant energy demands in a domestic dwelling. The overall energy efficiency has been improved by 47.86% compared to conventional CHP.

Lithographically Patterned Gold/Manganese Dioxide Core/Shell Nanowires for High Capacity, High Rate, and High Cyclability Hybrid Electrical Energy Storage

We describe the fabrication of arrays of nanowires on glass in which a gold core nanowire is encapsulated within a hemicylindrical shell of manganese dioxide. Arrays of linear gold (Au) nanowires are first prepared on glass using the lithographically patterned nanowire electrodeposition (LPNE) method. These Au nanowires have a rectangular cross-section with a width and height of ≈200 and 40 nm, respectively, and lengths in the 1 mm to 1 cm range. Au nanowires are then used to deposit MnO2 by potentiostatic electrooxidation from Mn2+ solution, forming a conformal, hemicylindrical shell with a controllable diameter ranging from 50 to 300 nm surrounding each Au nanowire. This MnO2 shell is δ-phase and mesoporous, as revealed by X-ray diffraction and Raman spectroscopy. Transmission electron microscopy (TEM) analysis reveals that the MnO2 shell is mesoporous (mp-MnO2), consisting of a network of ≈2 nm fibrils. The specific capacitance, Csp, of arrays of gold:mp-MnO2 nanowires is measured using cyclic voltammetry. For a mp-MnO2 shell thickness of 68 ± 3 nm, core:shell nanowires produce a Csp of 1020 ± 100 F/g at 5 mV/s and 450 ± 70 F/g at 100 mV/s. The cycle stability of this Csp, however, is extremely limited in aqueous electrolyte, decaying by >90% in 100 scans, but after oven drying and immersion in dry 1.0 M LiClO4, acetonitrile, dramatically improved cycle stability is achieved characterized by the absence of Csp fade for 1000 cycles at 100 mV/s. Core:shell nanowires exhibit true hybrid energy storage, as revealed by deconvolution of Csp into insertion and noninsertion components.

Mesoporous Manganese Oxide Nanowires for High-Capacity, High-Rate, Hybrid Electrical Energy Storage

Arrays of mesoporous manganese dioxide, mp-MnO(2), nanowires were electrodeposited on glass and silicon surfaces using the lithographically patterned nanowire electrodeposition (LPNE) method. The electrodeposition procedure involved the application, in a Mn(ClO(4))(2)-containing aqueous electrolyte, of a sequence of 0.60 V (vs MSE) voltage pulses delineated by 25 s rest intervals. This "multipulse" deposition program produced mp-MnO(2) nanowires with a total porosity of 43-56%. Transmission electron microscopy revealed the presence within these nanowires of a network of 3-5 nm diameter fibrils that were X-ray and electron amorphous, consistent with the measured porosity values. mp-MnO(2) nanowires were rectangular in cross-section with adjustable height, ranging from 21 to 63 nm, and adjustable width ranging from 200 to 600 nm. Arrays of 20 nm × 400 nm mp-MnO(2) nanowires were characterized by a specific capacitance, C(sp), of 923 ± 24 F/g at 5 mV/s and 484 ± 15 F/g at 100 mV/s. These C(sp) values reflected true hybrid electrical energy storage with significant contributions from double-layer capacitance and noninsertion pseudocapacitance (38% for 20 nm × 400 nm nanowires at 5 mV/s) coupled with a Faradaic insertion capacity (62%). These two contributions to the total C(sp) were deconvoluted as a function of the potential scan rate.