Stationary Battery Systems Research Articles

Model-based lifetime prediction of an LFP/graphite lithium-ion battery in a stationary photovoltaic battery system

Battery degradation is a complex physicochemical process that strongly depends on operating conditions. We present a model-based analysis of lithium-ion battery degradation in a stationary photovoltaic battery system. We use a multi-scale multi-physics model of a graphite/lithium iron phosphate (LiFePO4, LFP) cell including solid electrolyte interphase (SEI) formation. The cell-level model is dynamically coupled to a system-level model consisting of photovoltaics (PV), inverter, load, grid interaction, and energy management system, fed with historic weather data. Simulations are carried out for two load scenarios, a single-family house and an office tract, over annual operation cycles with one-minute time resolution. As key result, we show that the charging process causes a peak in degradation rate due to electrochemical charge overpotentials. The main drivers for cell ageing are therefore not only a high state of charge (SOC), but the charging process leading towards high SOC. We also show that the load situation not only influences system parameters like self-sufficiency and self-consumption, but also has a significant impact on battery ageing. We assess reduced charge cut-off voltage as ageing mitigation strategy.

Performance Analysis of Machine-Learning Approaches for Modeling the Charging/Discharging Profiles of Stationary Battery Systems with Non-Uniform Cell Aging

The number of Stationary Battery Systems (SBS) connected to various power distribution networks across the world has increased drastically. The increase in the integration of renewable energy sources is one of the major contributors to the increase in the number of SBS. SBS are also used in other applications such as peak load management, load-shifting, voltage regulation and power quality improvement. Accurately modeling the charging/discharging characteristics of such SBS at various instances (charging/discharging profile) is vital for many applications. Capacity loss due to the aging of the batteries is an important factor to be considered for estimating the charging/discharging profile of SBS more accurately. Empirical modeling is a common approach used in the literature for estimating capacity loss, which is further used for estimating the charging/discharging profiles of SBS. However, in the case of SBS used for renewable integration and other grid related applications, machine-learning (ML) based models provide extreme flexibility and require minimal resources for implementation. The models can even leverage existing smart meter data to estimate the charging/discharging profile of SBS. In this paper, an analysis on the performance of different ML approaches that can be applied for lithium iron phosphate battery systems and vanadium redox flow battery systems used as SBS is presented for the scenarios where the aging of individual cells is non-uniform.

High-performance aqueous symmetric sodium-ion battery using NASICON-structured Na2VTi(PO4)3

A high-safety and low-cost route is important in the development of sodium-ion batteries, especially for large-scale stationary battery systems. An aqueous sodium-ion battery is demonstrated using a single NASICON-structured Na2VTi(PO4)3 material with the redox couples of V4+/V3+ and Ti4+/Ti3+ working on the cathode and anode, respectively. The symmetric full cell fabricated based on the bi-functional electrode material exhibits a well-defined voltage plateau at ∼1.2 V and an impressive cycling stability with capacity retention of 70% exceeding 1,000 cycles at 10C (1C = 62 mA·g–1). This study provides a feasible strategy for obtaining high-safety and low-cost rechargeable batteries using a single active material in aqueous media.

Model-based Economic Assessment of Stationary Battery Systems Providing Primary Control Reserve

Rapidly decreasing battery prices and high capacity prices on the German primary control reserve (PCR) market promote the attractiveness of battery energy storage systems (BESS) for primary control provision. In order to assess the economic feasibility in this application field, two case studies based on a 2 MWh BESS are performed. By coupling a PCR simulation model with a battery aging model, battery lifetimes are estimated. Costs and revenues occurring during the lifetime are calculated using the net present value approach. The results indicate that a BESS with a power-to-energy ratio of 1:2 is not economically feasible under the current framework. A BESS with a power-to-energy ratio of 1:1 will break even after approximately nine years of operation. Decreasing battery system prices are likely to increase the price pressure on the PCR market leading to decreasing revenues for PCR supply. Battery aging results suggest similar aging behavior for both systems presented due to the prevalence of shallow DoD cycles and the resulting predominance of calendar aging.

(Keynote) Non-Destructive Analysis of Electrochemical Systems By Electrochemical Impedance Spectroscopy

The importance of electrochemical impedance spectroscopy (EIS) has grown in accordance with its expanding fields of application. A number of important papers that contributed greatly to the development of this field were published, and the timeline of the refinement of EIS has been well summarized by Orazem and Tribollet.[1] Since we applied to an impedance measurement using FFT on electrochemical systems in 1982,[2] we have proposed many approaches in order to facilitate status evaluation of electrochemical devices on the basis of reaction models of the components and interfaces. In situ observation of electrodeposited lithium was evaluated by EIS and optical microscopy. Microscopic observation indicated that lithium deposited more uniformly in mixture propylene carbonate and 1,2-dimethoxyethane than in sole propylene carbonate solution. The results of morphological evaluation of the electrodeposited lithium using optical microscopy corresponded to the variations in the value of the charge transfer resistance obtained from EIS measurements, showing that the behavior of the charge transfer resistance accurately represented the morphology.[3] Subsequently, we have strenuously investigated lithium ion battery (LIB). The impedance response of the LIB cell is composed of the responses of the two electrodes and the electrolyte with the separator. Elemental processes that affect the impedance response can be assumed as follows; electron migrations in a conductive additive and at interface of active material/current collector, charge transfer processes, a solid state diffusion consists of Warburg. It is difficult to separate the contributions of both electrodes and, if these responses are not separated, the information obtained via the EIS is the internal resistance of the cell only. We have three approaches to overcoming this problem, installation of a reference electrode, separation using a symmetric or temperature-controlled cell.[4] EIS has been utilized to characterize each elemental process of electrochemical devices, because it enables us to analyze dynamics of each elemental process sensitively and separately without destruction of the cell. The equivalent circuit to express each elemental process in a commercial LIB by EIS has been carefully investigated. An equivalent circuit was designed for the analysis of lithium ion batteries with the contributions of a variety of diffusion parameters resulting from the various particle sizes for the cathode and the solid-electrolyte interphase formed on the anode particles, as well as electrochemical reactions and inductive components. The electrochemical impedance of the electrodes in commercial LIB was analyzed to evaluate the proposed circuit at various states of charge[6] and capacity fading were analyzed with continuous charge-discharge cycling.[7] Besides, we have evaluated catalyst layers in direct methanol fuel cell (DMFC)[7] and polymer electrolyte fuel cell (PEFC)[8] using an equivalent circuit composed of transmission line model (TLM) in which primary and secondary pores were considered. As these results, we achieved the detection of the state of the devices from the EIS analysis. The conventional EIS using FRA – potentiostat systems is not easy to measure the impedance of the large-scale LIB because of its low internal resistance. Moreover, FRA – potentiostat system for conventional EIS measurement could not be mounted on the vehicle. Thus, impedance measurement system is needed without using FRA – potentiostat systems. In our study, application of square wave potential for input signals of EIS was investigated in simple electrochemical reaction to verify a new technique called “Square-potential/current electrochemical impedance spectroscopy (SP-EIS, SC-EIS)” which is a method for EIS without using the FRA systems. Introduction of SC-EIS to diagnosis technology of laminated LIBs and the LIB module was discussed.[9] We applied SC-EIS to evaluate a state of a commercial stationary storage battery system with LIB (Fig. 1). This work was partly supported by “Research & Development Initiative for Scientific Innovation of New Generation Batteries” and “Development of Safety and Cost Competitive Energy Storage System for Renewable Energy” from NEDO, Japan.

A Risk Assessment Methodology to Prioritise Risks in Large, Stationary Li-Ion Battery Systems

Performing a risk analysis is the basis in all engineered products. No specific methodology exists for stationary batteries. Indications on the needed risk assessment may be derived from standards that cover large stationary Li-ion battery storage systems in their scope [1]. However, they hardly go further than referring to the general risk assessment techniques with as examples Failure Mode and Effect Analysis (FMEA) and Fault Tree Analysis (FTA). Despite this lack of specific guidance, a risk assessment for large battery systems has their uniqueness due to their structure. There are many levels between battery cells and the complete system. Moreover, a huge number of cells are used that must be correctly dealt with in the assessment. In the scientific literature only a few papers are dedicated to risk assessment on batteries. This contribution sets up a complete framework of methodologies and protocols for safety testing of stationary Li-ion batteries for large-scale grid-connected applications. The risk assessment is based on the well-known Failure Mode Effects Analysis (FMEA) method. In a first step, a generic hierarchical system diagram of a stationary battery is developed to be used as the system under study in the FMEA. To improve the completeness and the objectivity of the analysis, improvements to the FMEA methodology are proposed and used. The main goal of these improvements is to limit the dependency on expert judgement and inspiration and to improve the prioritization of risks without adding unnecessary complexity. A core issue is that the method of calculating the Risk Priority Number (RPN) is not sufficient fo large battery systems. This problem was also detected by [2]. The RPN does not take suitable care of the numbers of cells, modules, etc. and has no aggregation per level. Risks that are mitigated on several system levels have to be aggregated in an advanced RPN methodology. This leads to a thorough risk assessment, in which it is easy and meaningful to select the most prominent project risks. This contribution is an outcome of the European FP7 project Stallion. The project has set up safety tests beyond state of the art for stationary Li-ion battery systems. It also resulted in a handbook on battery system safety for the broad audience [3]. [1] Survey on standards for batteries and system integration with them. VITO, 2015. [Online] batterystandards.vito.be.[2] Analysis of Battery Safety and Hazards’ Risk Mitigation. Ashtiani, C.N. 2008, ECS Transactions, Vol. 11, pp. 1-11 .[3] STALLION Handbook on safety assessments for large-scale, stationary, grid-connected Li-ion energy storage systems, DNV GL, Arnhem 2015. [Online] stallion-project.eu Figure 1

Low-Cost Sodium-Ion Batteries (LOCO-NIBs Project)

The LOCO-NIBs (Low-cost Na-ion Batteries) Project funded by Innovate UK aims to investigate novel anode and cathode materials with compositions and morphologies which allow stable insertion and removal of sodium ions for a long number of cycles. This would facilitate the creation of energy storage systems of significantly lower cost due to the abundance of the sodium resources and materials implemented. This collaboration between School of Materials Science and Engineering at Queen Mary University of London (QMUL) and Johnson Matthey (JM) aims to develop low cost and highly performing electrode materials for sodium-ion electrodes based on abundant sodium resources and biomass derived low cost carbon electrodes. This will accelerate the development of sodium ion batteries which could be then integrated into battery modules, creating a new generation of competitive stationary battery systems increasing thus the security of supply, and the use of clean and locally generated energy sources such as solar and wind. Most of the ongoing research in sodium-ion batteries relates to the development of cathodes where replacement of lithium by sodium has been a common route for finding good and low cost electrodes. Thus, a wide range of compounds are being currently studied as cathode materials from oxides to phosphates, fluorophosphates or pyrophosphates. Within this project we aim to investigate cathode candidate materials obtained by replacement or reduction in higher cost metal elements such as Co and Ni, with higher abundance, lower cost elements such as Fe and Mn, while improving cell voltage, capacity and cycling stability through accommodation of volume changes. Much less research has been dedicated in the field to the anode material due to the inability of sodium to insert into graphite along with the formation of a stable solid electrolyte interface layer. Most of the proposed carbon materials as anodes in sodium ion batteries in the literature are expensive and derived from fossil-fuel precursors, using high-energy production techniques. Following successful completion of the project, further development up the supply chain into cells and finally into sodium-ion battery based modules and systems is foreseen. The stationary market is predicted to grow in the near future. It is predicted that over 50,000 modules will be required by 2020. If this was the case then this would require 500 tonnes of combined anode and cathode materials. Interactions with energy companies, OEMS and other end users would also be anticipated, promoting the creation of a supply chain for electrical energy storage that would make an important contribution to economic growth and employment in the UK.

Low-Cost Sodium-Ion Batteries (LOCO-NIBs Project)

The LOCO-NIBs (Low-cost Na-ion Batteries) Project funded by Innovate UK aims to investigate novel anode and cathode materials with compositions and morphologies which allow stable insertion and removal of sodium ions for a long number of cycles. This would facilitate the creation of energy storage systems of significantly lower cost due to the abundance of the sodium resources and materials implemented. This collaboration between School of Materials Science and Engineering at Queen Mary University of London (QMUL) and Johnson Matthey (JM) aims to develop low cost and highly performing electrode materials for sodium-ion electrodes based on abundant sodium resources and biomass derived low cost carbon electrodes. This will accelerate the development of sodium ion batteries which could be then integrated into battery modules, creating a new generation of competitive stationary battery systems increasing thus the security of supply, and the use of clean and locally generated energy sources such as solar and wind. Most of the ongoing research in sodium-ion batteries relates to the development of cathodes where replacement of lithium by sodium has been a common route for finding good and low cost electrodes. Thus, a wide range of compounds are being currently studied as cathode materials from oxides to phosphates, fluorophosphates or pyrophosphates. Within this project we aim to investigate cathode candidate materials obtained by replacement or reduction in higher cost metal elements such as Co and Ni, with higher abundance, lower cost elements such as Fe and Mn, while improving cell voltage, capacity and cycling stability through accommodation of volume changes. Much less research has been dedicated in the field to the anode material due to the inability of sodium to insert into graphite along with the formation of a stable solid electrolyte interface layer. Most of the proposed carbon materials as anodes in sodium ion batteries in the literature are expensive and derived from fossil-fuel precursors, using high-energy production techniques. Following successful completion of the project, further development up the supply chain into cells and finally into sodium-ion battery based modules and systems is foreseen. The stationary market is predicted to grow in the near future. It is predicted that over 50,000 modules will be required by 2020. If this was the case then this would require 500 tonnes of combined anode and cathode materials. Interactions with energy companies, OEMS and other end users would also be anticipated, promoting the creation of a supply chain for electrical energy storage that would make an important contribution to economic growth and employment in the UK.

Scientific Measuring and Evaluation Program for Photovoltaic Battery Systems(WMEP PV-Speicher)

Abstract Grid parity of residential photovoltaic (PV) power generation and retail electricity prices makes self-consumption of solar power increasingly interesting for private households. Residential PV Battery Systems provide the opportunity to store solar energy that is not locally consumed during the day and make it available for self-consumption in the evening, thus cutting the electricity bill. Moreover, decentralized stationary battery systems are a promising technology to deal with grid problems that can arise due to high local penetration of solar power generation. Because relatively high system costs for small stationary battery systems still pose an obstacle for a broad market launch, the German Federal Government has issued a market incentive program to stimulate the market and boost technology development of PV Battery Systems. In order to additionally gain a better understanding of the technology under realistic operating conditions, an accompanying scientific monitoring program has been established from the beginning. This paper outlines the most important terms and conditions of the market incentive program, the methodology of the monitoring program and presents first results of the current market situation of government-funded PV Battery Systems in Germany.

Effect of the mass transport limitations on the stability window of electrolytes for metal-ion batteries

Stationary battery systems have been proposed as plausible alternative for the storage of renewable energy sources in power grid. For this application aqueous electrolytes are preferred, which offer several important advantages compared to organic electrolytes i.e. non-flammability, cost effectiveness, as well as higher ionic conductivity, solubility and thermal capacity. This work was undertaken to investigate the influence of pH on the electrochemical stability window of aqueous electrolytes for metal-ion batteries. The pH was deliberately controlled in the range from pH 2 to 11. Electrochemical chronopotentiometry method served for the electrochemical stability window measurements. It has been observed that the pH critically influenced the measured dynamic stability window, which shows a maximum and almost pH independent value for pH ranging from 5 to 9. The presence of buffering ions and gelling agents strongly affects the dynamic stability window of the electrolyte through the transport overpotential.

Comparison of decentralised and centralised grid‐compatible battery storage systems in distribution grids with high PV penetration

AbstractBecause of the high amount of installed solar power systems in Europe and especially Germany, the low‐voltage distribution grids reach their maximum capacities during periods of high insolation. As an alternative to grid reinforcement, local battery storage systems can be used to store the surplus generation and limit the feed‐in power of the solar power systems. For this purpose, decentralised photovoltaic (PV) home storages in single households and larger stationary battery systems supplying a whole local grid area can be called into action. In this paper, a grid‐compatible storage operational strategy is simulated using standard load profiles and statistically generated realistic load profiles for use with both storage types. The goal of this research is to investigate a grid‐compatible and also economic storage operation when using centralized large‐scale batteries instead of PV home storage systems in a low‐voltage distribution grid with a high degree of decentralised PV generation. Results show that large‐scale systems provide advantages regarding grid‐related operation and economic feasibility and therefore represent a useful alternative to home storage systems. Additionally, it can be shown that depending on which storage type is simulated, different requirements are imposed. The simulation of decentralised home storages needs real load profiles in order to receive realistic results, while the operation of large‐scale battery storages can be simulated using standard load profiles. Copyright © 2014 John Wiley & Sons, Ltd.

Optimal charge control strategies for stationary photovoltaic battery systems

Battery systems coupled to photovoltaic (PV) modules for example fulfill one major function: they locally decouple PV generation and consumption of electrical power leading to two major effects. First, they reduce the grid load, especially at peak times and therewith reduce the necessity of a network expansion. And second, they increase the self-consumption in households and therewith help to reduce energy expenses. For the management of PV batteries charge control strategies need to be developed to reach the goals of both the distribution system operators and the local power producer. In this work optimal control strategies regarding various optimization goals are developed on the basis of the predicted household loads and PV generation profiles using the method of dynamic programming. The resulting charge curves are compared and essential differences discussed. Finally, a multi-objective optimization shows that charge control strategies can be derived that take all optimization goals into account.

Interdependencies of Home Energy Storage between Electric Vehicle and Stationary Battery

Decentralized power generation in private homes, especially by photovoltaic systems, is already common in Germany. The developments of batteries, both for electric vehicles (EV) and for stationary storage might lead to a mass market for those batteries. In this paper we evaluate the economy of stationary battery storage with photovoltaic system at home in the context of available EV and its integration level into the home. Therefore, we use an optimization model with one year detailed operation planning and maximize the net present value of the storage investment. We integrate restriction functions for the technical parameters of the storage systems and limit EV availability and usage on the basis of German mobility studies for single vehicles. The results show, that an investment in a stationary battery system in combination with a photovoltaic system is profitable in Germany under the assumptions considered. The observed high numbers of battery cycles lead to strong requirements for battery lifetime, i. e. cycle stability and long calendar life time. Therewith, Li-ion batteries are a promising technology. In combination with an EV, the net present value of the stationary battery system is smaller when the EV is integrated into the home by controlled charging or the vehicle to home (V2H) concept, which allows discharging into the home system. The size of the EV battery, the availability at daytime and the load curve of the home are the main influencing factors for the profitability of the battery system.

Error detection for PHEV, BEV and stationary battery systems

Battery cells being electrically disconnected resulting from degradation, mechanical stress, or corrosion can lead to hazardous situations during operation of electric vehicles or storage systems in stationary applications. The mentioned errors can be acceptable in some cases when cells or cell strings are connected in parallel, but the failure is to be detected in order to guarantee the reliable and safe operation of the battery system. A method enabling the estimation whether individual battery cells are faulty (cell error or electrically disconnected) by evaluating the mean impedance and capacity information of cell groups is introduced and validated.

Design of Power Converters for Renewable Energy Sources and Electric Vehicles Charging

This paper describes the design and construction of new series of power converters equipped with liquid cooling system. This power series is created for project ENET – Energy Units for Utilization of non Traditional Energy Sources. First power converter is determined for stationary battery system use, the second one is used as an inverter/rectifier for a small solar plant system and the last power inverter is used as a fast charger for electric vehicles. Energy balance is performed for the fast charger converter, which is solved using numerical simulations of the system.

Optimal management of stationary lithium-ion battery system in electricity distribution grids

The present article proposes an optimal battery system management model in distribution grids for stationary applications. The main purpose of the management model is to maximise the utilisation of distributed renewable energy resources in distribution grids, preventing situations of reverse power flow in the distribution transformer. Secondly, battery management ensures efficient battery utilisation: charging at off-peak prices and discharging at peak prices when possible. This gives the battery system a shorter payback time. Management of the system requires predictions of residual distribution grid demand (i.e. demand minus renewable energy generation) and electricity price curves (e.g. for 24 h in advance).Results of a hypothetical study in Great Britain in 2020 show that the battery can contribute significantly to storing renewable energy surplus in distribution grids while being highly utilised. In a distribution grid with 25 households and an installed 8.9 kW wind turbine, a battery system with rated power of 8.9 kW and battery capacity of 100 kWh can store 7 MWh of 8 MWh wind energy surplus annually. Annual battery utilisation reaches 235 cycles in per unit values, where one unit is a full charge-depleting cycle depth of a new battery (80% of 100 kWh).

Full Cell Design and Performance for Stationary Li-ion Battery System

not Available.

Full Cell Design and Performance for Stationary Li-Ion Battery System

not Available.