General Assembly at KIT in Karlsruhe

© H. Nirschl, A. Wolf, KIT

For the last time, the SONAR members gathered and exchanged results, looking back at quite a number of  impressive achievements. A tour of the extensive laboratories and workshops on the campus completed the programme.  

Night of Technology in St. Augustin

© M. Krapp, SCAI

In front of a packed hall, Jan Hamaekers gave a broad audience an introduction to flow batteries in general and AI based approaches for material search in particular.  

Hands-on Workshop in St. Augustin

© C. Steinborn, SCAI

The developments almost complete, SONAR members presented their achievements at our one-day workshop with practical training. For every workpackage, the methods and tools were introduced, for some the users could work with pre-installed examples. We had a lively exchange and enjoyed the event.

IUPAC23+chains in Den Haag

© A. Maaß, SCAI

P. Fischer  gathered speakers from the FLORES network to offer a dedicated session on flow batteries at the five days event, where Astrid gave a report on AI supported search for new electro active materials.


244th ECS Meeting

© D. Gerlach, ICT-extern

D. Gerlach presented his research on techno economics in Gothenburg, Sweden.


© J. Noack

This year taking place in Prague, various members of SONAR participated in the International Flow Battery Forum, giving two talks and presenting four posters, even winning an award for the best poster  speed pitch.  And again, we shared a booth with other projects from the FLORES network.  

General Assembly at DTU in Kopenhagen

© Piotr de Silva, DTU

We had another one-day hybrid meeting hosted by DTU. Those attending in person could also take a tour through the impressive  lab facilities.  

Fraunhofer-SCAI @ E-world

© C. Steinborn, SCAI

Together with colleagues from Computational Finance and Network Evaluation Techniques we had a shared booth in Essen May 2023. Flow batteries received a lot of attention.

New paper on optimization of the microstructure of carbon felt electrodes

© Jia Yu, LCRS

We propose a computational methodology to optimize the microstructure of the carbon felt electrode employed in redox flow batteries. Our objective is to maximize the electrolyte utilization rate in a quantitive manner, which is affected by the fibrous electrode's microstructure. By combining stochastic generation of electrode microstructures, the digital compression of the electrodes, the Lattice Boltzmann Method, and a Bayesian optimization approach, we established our computational workflow that predicts an optimized set of parameters for electrode design. more info

New Paper on Multi-scale Flow Battery Modelling using Mass Transfer Coefficients

© Amadeus Wolff, KIT

A novel multiscale flow battery simulation approach is presented: The mass transfer coefficient is extracted from the 3D-resolved microscale simulations, transferred to the homogenized cell scale and compared to empirical formulations from literature.  The model accounts for flow, mass, and coupled charge transport using Butler–Volmer kinetics. It is suitable to study power density as a function of concentration, velocity, and discharge rate.  more info

SONAR & CENELEST @ Smart Energy Expo in Sydney

© Chris Menictas, UNSW Sydney

SONAR and CENELEST shared a both at the Smart Energy Expo in Sydney / Australia  on 3 -4  May 2023.  The Expo brings the entire renewables industry   together, including manufacturers, distributors, project developers, financiers and many more.  

Girls' Day at Fraunhofer SCAI

© Carina Steinborn, Fraunhofer SCAI

On April 27th, female school students in grades 5 to 10 had the opportunity to take a look at the work and career fields at Fraunhofer SCAI. One of the workshops was about flow batteries and the new electroactive materials. All molecules tested that day were composed by the girls themselves -- the best posolyte/negolyte pair achieved a theoretical OCV of ~ 0.6V!


10th Conference on Advanced Materials and Nanotechnology

© Jens Noack, ICT

On Feb 8th 2023 Jens Noack gave an invited talk about the results of the EU-Australian project SONAR at the ATMN10 in Rotorua / New Zealand.

SONAR General Assembly in Winterthur, Switzerland at ZHAW

© Jens Noack, ICT

On February 1, our penultimate General Assembly took place, this time in hybrid format in Wintherthur / Switzerland at the ZHAW.

During the one-day meeting, the progress made within the individual work packages was presented and the partners had the opportunity to visit the premises of ZHAW..



Standards in Flow Batteries

© Jens Noack, ICT

Standards are of great importance for the successful commercialization of new technologies in particular through standardization and to cover the requirements of clients and insurance companies. Last but not least, they also ensure safer and more environment friendly products and can reduce costs and open up new business models. Flow batteries are a new technology in terms of standards and commercialization. more in "Flow Batteries"


History of Flow Batteries

© Jens Noack, ICT

Many far-sighted researchers, who are hardly known today, have laid the foundation for future developments. This article gives an overview of the historical, mostly, scientific developments of flow batteries.  more in "Flow Batteries"  

Quantum Mechanical Modeling of Flow Battery Materials

© Piotr de Silva, DTU

To better understand the theoretical background and limitations of the established modeling methodology and how atomic-scale simulations can help in the development of new flow battery materials, we introduce the fundamental concepts behind atomistic modeling at the quantum-mechanical level, focusing on density functional theory. Atomistic simulations can be used to calculate the basic electrochemical properties of materials, especially the electrolytes as the electroactive components. more in "Flow Batteries"


Mesoscale Modeling and Simulation for Flow Batteries

© Jia Yu, Universite Picardie

The challenge of the multiscale modeling framework mainly comes from the gap between the micro-scale and macro-scale modeling. The microscopic properties obtained from atomistic level approaches are challenging to be associated with macroscopic observables. To bridge this gap, we start with the discussion of electrode kinetics, which is the vital mechanism behind electrochemistry reactions. Three types of kinetic rate calculations were discussed and compared, including the classic approximation of the Butler–Volmer equation, the Marcus–Hush theory, and the Marcus–Hush–Chidsey theory. We also present  the Monte Carlo method, the Dissipative particle dynamics, and the Lattice Boltzmann methods. Advantages and limitations, along with some future modeling perspectives, are also discussed. more in "Flow Batteries"

Continuum Modelling and Simulation of Flow Batteries

© Roman Schärer ZHAW

Find an engineer's approach to cell-scale models. The attention is on flow-battery lifespan issues and the application of robust, physics-based models in device lifetime forecasting. Capacity fade due to membrane characteristics, pumping losses, and cycling efficiencies are described mathematically.
Models based on equilibrium and nonequilibrium thermodynamics allow for a rigorous derivation and incorporation of nonideal electrolyte key metrics, such as chemical activity, as well as transport properties in concentrated electrolytes and transport through membranes.   more in "Flow Batteries"


Pore-scale Modeling of Flow Batteries

Three-dimensional pore-scale models of flow batteries resolve the microstructure of the porous electrode and solve the governing equations for electrolyte flow, reactant and charge transport as well as for the electrochemical reaction. Such models reveal the impact of the microstructure on transport phenomena and cell performance within the electrode. Thereby, they overcome experimental barriers, the limitation of volume-averaged models and can be used to optimize the electrode structure for high-performing batteries. more in "Flow Batteries"

Machine Learning for FB Electrolyte Screening

Machine-learning (ML) techniques allow us to turn sets of independent data points into insights: based on a sufficient body of data that parameterize a given phenomenon, data-driven models can be trained to detect within the training set the underlying patterns and on this basis they can make predictions for new instances. This overview briefly discusses the relevant aspects and the critical issues in this process, starting from the data as the essential ingredients, some ways of representing said data as immediate input to an algorithm while preserving in some sense their original meaning, and various ML techniques that process these data to come up with trained models. more in "Flow Batteries"


WILEY-VCH "Flow Batteries"

© WILEY VCH Flow BAtteries

Everything about flow batteries including a full chapter focussed on modelling: WILEY-VCH “Flow Batteries”, edited by Christina Roth, Jens Noack and Maria Skyllas-Kazacos. ~1300 pages, ~100 figures, 3 volumes.

Upcoming: FLORES workshop on digital twins for flow batteries

September 12 2022, online

Virtual event – free of charge – register now 

A roadmap toward redox flow battery passport

The European Battery Directive foresees monitoring of batteries on their global warming potential and utilization of critical raw materials. FLORES, a network of 13 EU-funded projects, invites speakers to show best practice examples from Lithium-Ion battery applications and other areas to define a roadmap for redox flow batteries towards a battery passport.

More info

New Paper about Electrochemical Interface Dynamics

July 2022

© Jia Yu

SONAR partner CNRS presents a 3D kinetic Monte Carlo model to study the electrode-anolyte interface of a methyl viologen-based organic redox flow battery. This model captures various electrode processes, such as ionic displacement and degradation of active materials.

More info

Sustainability of Flow Batteries

FLORES: Joint review about LCA

Suggested product system and functional unit definition for LCA of Flow Batteries.

A transition from fossil to renewable energy requires the development of sustainable electric energy storage systems capable to accommodate an increasing amount of energy, at larger power and for a longer time. Flow batteries are seen as one promising technology to face this challenge and should not shy away from competition when it comes to sustainability goals. Based on a review of 20 relevant life cycle assessment studies, this paper explored relevant methodological choices regarding the phases: goal and scope definition, inventory analysis, impact assessment and interpretation.

More info

Participation of SONAR at the International Flow Battery Forum in Brussels

From June 28 – 30, the annual International Flow Battery Forum (IFBF) took place in Brussels, Belgium. SONAR was represented by several participants with posters and a presentation. Results from the SONAR project and standardization of redox flow batteries were reported. In addition, SONAR organized a joint workshop with its sister project COMPBAT on the topic of "Modeling and Simulation" before the actual program of the IFBF began.


SONAR was further represented together with FLORES, the European network of EU projects on redox flow batteries, at a booth in the exhibitors' area. Participants of the IFBF made extensive use of the opportunities to obtain information and to exchange experiences. This year, IFBF had nearly 300 participants from a variety of countries around the world.

Joint workshop of COMPBAT and SONAR in Brussels

June 27-29, Brussels / Belgium

On June 27, 2022, the two sister projects COMPBAT and SONAR hosted a joint workshop on Modeling and Simulation in Brussels as part of the annual International Flow Battery Forum (IFBF). COMPBAT and SONAR are developing, within the framework of Horizon2020 funded EU projects, high-throughput screening methods for the efficient search of new active materials for future organic redox flow batteries.

At the one-day workshop, presentations on "Screening of flow battery couples at the atomic / molecular level" and "Assessment of flow battery opportunities at the cell and system level" were given by project participants from both projects in the morning. In the afternoon, Dr. Astrid Maaß from the SONAR project presented the development status of the high-throughput screening method currently under development using the RedoxFox demonstrator and discussed its industrial application. Furthermore, a panel discussion with different participants from academia and industry took place on the topic "Opportunities for international collaborations". Finally, the workshop ended with a poster session with results from the two projects COMPBAT and SONAR. The workshop was attended by about 50 participants from a variety of countries around the world.

SONAR General Assembly in Amiens, France

June 2022

On June 15, 2022, the 6th General Assembly of SONAR was held in Amiens, France at the Laboratoire de Réactivité et Chimie des Solides (LRCS). The special thing about this meeting this time was that the participants had decided to hold a physical meeting, whereby it was only the first General Assembly at all after the Kick-Off Meeting 2020 in person.

During the one-day meeting, the results of the individual work packages were presented, as well as the way forward in SONAR was discussed. Furthermore, the participants had the opportunity to visit the premises of the LRCS.




Participation in the 241st meeting of the Electrochemical Society

May 2022 Vancouver / Canada


Daniel Gerlach, Prof. Dr. Piotr de Silva and AA/Prof. Dr.-Ing. Jens Noack from SONAR attended this year’s 241st spring meeting of the Electrochemical Society in Vancouver, Canada. Together, they gave two keynote lectures, three additional lectures and chaired two sessions in the area of redox flow batteries and computational electrochemistry.

SONAR attended the 32nd ISE Topical Meeting in Stockholm

June 2022

The 32nd Topical Meeting of the International Society of Electrochemistry (ISE) with the topic "Experimental and Modelling Tools for Electrochemical Energy Devices" took place in Stockholm, Sweden from June 20 – 22, 2022. Among the participants and as an invited speaker was also AA/Prof. Dr. Jens Noack, project coordinator of SONAR with a presentation of the results achieved so far in the project.

The International Society of Electrochemistry is one of the two leading electrochemical societies worldwide and organizes different conferences in the field of electrochemistry every year. The 32nd ISE Topical Meeting was attended by several hundred participants from a variety of different countries around the world.

SONAR attended the 31st ISE Topical Meeting in Aachen

May 2022, Aachen / Germany

The 31st Topical Meeting of the International Society of Electrochemistry was held in Aachen, Germany from May 15 – 19, 2022. Among the participants and as presenters were Dr. Astrid Maaß from the Fraunhofer Institute for Algorithms and Scientific Computing (Fraunhofer SCAI) and AA/Prof. Dr. Jens Noack (Fraunhofer ICT / University of New South Wales), project coordinator of SONAR. Astrid presented results from High-Throughput Screening to find new organic active materials for redox flow batteries during a talk and Jens gave an overview talk on the results achieved so far in SONAR.

SONAR is an international collaborative project of several outstanding research institutes and universities to develop a model-based tool to find new organic active materials for future redox flow batteries.

The International Society of Electrochemistry is one of the two leading electrochemical societies worldwide and organizes different conferences in the field of electrochemistry every year. The 31st ISE Topical Meeting was attended by over 150 participants from a variety of different countries around the world.

Tent City of Science & Science Night

May 2022, Bonn / Germany

© Michael Krapp, Fraunhofer SCAI

Over two days, school classes and interested citizens were able to learn about the current state of research in the Bonn region in Germany. To explain the screening process to be developed in SONAR, Fraunhofer SCAI challenged visitors to find the best combination of active materials to build a complete redox flow battery cell. In general the topic of energy storage and in particular flow batteries received a lot of attention and encouragement.

Smart Energy Expo, Sydney/Australia

May 2022

SMART Energy is one of the largest renewable energy events in Australia.
Among other things, a technology demonstrator for the High-Throughput screening process, which is being developed in the international SONAR project, was presented. The software for the search for new active materials for aqueous organic redox flow batteries could be tested on a laptop. In addition, materials of cells, electrodes and a small demonstration redox flow battery were shown. The booth was supervised especially with the support of UNSW students from UNSW Challenge program NextGEN.

SONAR attended the 18th ModVal in Germany

March 2022

During March 14 – 16, 2022, the 18th Symposium on Modelling and Experimental Validation of Electrochemical Energy Technologies (ModVal) was held at Schloss Hohenkammer, Germany. Among the participants and as speakers were Dr. Roman Schärer from the University of Applied Sciences Zurich and AA/Prof. Dr. Jens Noack (Fraunhofer ICT / University New South Wales), project coordinator of SONAR. Roman was present with a poster on the results obtained in SONAR in the field of 0D modelling of redox flow batteries and Jens gave an overview talk on the results obtained so far in SONAR.

ModVal is one of the most important conferences on modelling and simulation of electrochemical devices. This year's conference was held with over 200 attendees from all over the world despite the severe constraints of the COVID pandemic.

Animation of RFB half-cell compartment during discharge operation

March 2022

© Amadeus Wolf, KIT, Germany

CFD simulations based on the Finite Volume Method for an electrolyte passing through a section of carbon felt: watch the behaviour of several (normalized) quantities 

  1. Velocity profile (arrows) of flow coming from the bottom to the top,
  2. Quasi steady-state TEMPO+ concentration profile within the electrolyte and during normalized time (constant inlet concentration assumed),
  3. Butler-Volmer current at the surface of the fiber domain, and
  4. Electrolyte potential distribution and ionic current (arrows).

New Paper about a physics-based 0D-U-I-SoC Cell Performance Model

March 2022

WP4 and co-workers present a physics-based dimensionality reduced model for the performance prediction of aqueous organic redox flow batteries. The model allows for fast evaluations of the cell voltage and power density, which are expressed explicitly in terms of the electric current density and state of charge. The model takes into consideration important phenomena, such as the activation and concentration overpotentials in the electrodes as well as the non-negligible electro-osmotic drag of water through the membrane. A sensitivity analysis of the model indicates the influence of various model parameters at different current densities on the predicted cell voltage. In this work we found the formal potentials and ohmic cell resistance to be the most critical parameters for performance prediction. Experimental parameterization and validation on cycling and polarization experiments revealed good agreement with the experiments within a predicted range of validity due to the different simplifying assumptions.

More info

SONAR attended the autumn school of the Nordic Flow Battery Network

November 2021

Prof. Dr. Piotr de Silva at the autumn school in Turku, Finland.

At the end of November 2021, the autumn school of the "Nordic Flow Battery Network" took place in Turku, Finland. It was hosted by the University of Turku under the leadership of the EU-funded COMPBAT project. Similar to SONAR, COMPBAT is concerned with the development of a high-throughput screening process to search for new organic active materials for redox flow batteries.

Over the three-day event, a variety of speakers reported on different topics in the research and development of redox flow batteries. PhD students were given the opportunity to present posters on their work, give talks or exchange information. The last day of the autumn school was entirely organised by the PhD students in Turku. The speakers were from a mixture of academic and commercial backgrounds, so that application-related content was also presented beside basic research.

Among the invited speakers were Prof. Dr. Piotr de Silva from the Technical University of Denmark and Prof. Dr. Jens Noack from Fraunhofer ICT, who are both involved in SONAR. Piotr gave a talk on DFT calculations (DFT - density functional theory) in general and specifically in relation to flow batteries. Jens gave a short overview of the development of flow batteries over the last 15 years at Fraunhofer ICT.

SONAR will present a first functional demonstrator for the simulation-based screening of organic active materials for novel redox flow batteries.

March 2023

Screenshot of interface for entering compounds and search criteria

This year SONAR will share a booth with the German-Australian Alliance for Electrochemical Storage for Renewable Energy (CENELEST) at Smart Energy 2022 in Sydney, Australia. For the first time, a functional demonstrator will be presented for the high-throughput screening method to be developed in SONAR. The demonstrator allows the calculation of parameters such as redox potentials and cell voltages on the basis of optimised scale models. The user can enter structural formulae of organic chemical compounds and obtain the results within a few seconds. The high-throughput screening will later be able to select, from hundreds of thousands of organic compounds, those with the highest potential for application as active materials for novel redox flow batteries, and also calculate their properties.
The Smart Energy Council Conference and Exhibition is the largest meeting place for renewable energy topics in Australia, and will take place this year on 4 – 5 May at the ICC in Sydney, Australia.

SONAR successfully completes phase I of the project

November 2021

Flow battery test cell at the Fraunhofer ICT for simulation results validation

After a project duration of 18 months, the SONAR project was evaluated by INEA, the project executive agency of the European Commission (EC), as planned. Within the framework of a report and a special review meeting, the EC project officers and an external reviewer were presented with the results of the project so far. The main focus was on the status of the development of the high-throughput screening method to search for new organic active materials, as well as the sub-aspects based on atomistic, Kinetic Monte Carlo (meso-scale) and continuum modelling and simulation. SONAR successfully passed the peer review and secured funding for the next phase, which will also focus on the stack, system, costs and behavior in the network.

ZHAW publishes open source 0D cell model and program to calculate flow battery characteristics

November 11, 2021

Screenshot of GUI for interactive manipulation

As part of the EU-Australian SONAR project, the University of Applied Sciences Zurich, Switzerland, has published an open-source program for calculating the characteristics of organic redox flow batteries. The program is based on the popular mathematical application "Mathematica" and allows the evaluation of polarization curves as predicted by the 0D-U-I-SoC model for user-specified model parameters. Especially for small and medium current densities, which are not in the range of mass transport limitations, the results of the software are very accurate and can be adapted to the specific battery chemistry by adjusting the input parameters. This allows statements to be made about the expected voltages and currents, as well as capacities and energy densities at different states of charge for an almost infinite number of battery chemistries.
In the SONAR project, ZHAW is responsible for the development of optimized cell models for automated high-throughput screening of organic active materials for future, novel redox-flow batteries to store renewable energy.
The open source simulation software and a user discussion forum are available on GitHub.

Flow battery systems and their future in stationary energy storage – Policy brief

November 2, 2021

On 9th July 2021, at the Summer Symposium of the International Flow Battery Forum, the FLORES Network of Flow-Battery Research Initiatives held a workshop to identify research
needs, barriers, potential markets and impacts of flow batteries. The outcomes, including resulting policy recommendations, are provided here.

Work on system modelling and cost analysis started in SONAR

September 2021

Current distribution of the 2D single cell of VRFB under different constant flow rates, left) flowrate = 30 mL/min right) flow rate = 5 mL/min

The University of New South Wales and Fraunhofer ICT started their work on stack and system modeling and cost analysis for organic flow batteries, with one new PhD student at each of the two institutions. The system modeling will be carried out using a multiphysics approach, where first the hydraulic, electrochemical and thermal properties of a single cell, then a stack and finally a whole flow battery system are modeled and simulated. The results will lead to a better understanding of systems and thus to cheaper and more reliable systems, and also form the basis for the cost analysis.

In the cost analysis of flow battery systems, Fraunhofer ICT is concerned with linking technical parameters with costs using mathematical functions. The objective is to map a cost structure for the investment costs of flow batteries in order to determine cost proportions and for sensitivity analyses. Based on the calculated costs, batteries can be compared on the basis of investment costs (CAPEX). A much more substantiated comparison is possible based on levelized cost of storage (LCOS), where lifetime costs are calculated in relation to energy throughput. In the future, it will be possible to calculate the LCOS of a large number of new organic flow battery chemistries automatically, in order to be able to develop low-cost candidates for new, safe and environmentally friendly organic flow batteries for the storage of renewable energy.

New Paper about predicting pH-dependent Redox Potentials

June 29, 2021

In the Special Issue Computational Design and Modelling of Organic Materials for Energy Applications of Molecules Rocco Fornari and Piotr de Silva present a computational protocol combining DFT and Cheminformatics for pH-Dependent Redox Potentials:
more Info

Animation of RFB discharge simulation with constant inlet concentration

June, 2021

© Amadeus Wolf, KIT, Germany

The image shows a pore scale 2D slice that is coloured according to the [4-OH-TEMPO]+ concentration in mol/m³.  Wholes represent cylindrical electrode fibres and arrows represent the steady-state velocity profile in m/s with Reynolds-Number of 0.0005. Note the depletion of [4-OH-TEMPO]+  at the electrode-electrolyte interface over time: The concentration profile evolves according to the velocity field and reaches a steady state after several milliseconds.

New paper on a graph convolutional network for rapid prescreening of organic compounds

May 31, 2021

A paper on machine learning for predicting formal potentials appears in a Special Collection on Artificial Intelligence in Electrochemical Energy Storage in Batteries & Supercaps by Laura Berg et al:

Interview of Maria Skyllas-Kazacos by QEM’s managing director Gavin Loyden

May 27, 2021

Find the full interview here.

Flow Batteries Europe: Long-Term Strategy for Flow Battery Technology

April 28, 2021

In order to create more awareness for RFB technology, and to combine the interests of industry and research in the field, the association “Flow Batteries Europe” was founded on 28.04.2021. Flow Batteries Europe will try to increase knowledge about redox flow batteries through dissemination and policy briefing.

The German/Australian Alliance for Electrochemical Technologies for Renewable Energy Storage (CENELEST) is a founding member of Flow Batteries Europe. CENELEST member and FlowCamp coordinator Dr. Peter Fischer (Fraunhofer ICT) was elected to the Executive Board and will represent Fraunhofer ICT (Germany) and the University of New South Wales (Australia) in Flow Batteries Europe.

For more information about the association, please contact Peter Fischer or visit the website.