In March 2022, the Senate of the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) established the Priority Programme “Carnot Batteries: Inverse Design from Markets to Molecules” (SPP 2403)(externer Link). The programme is designed to run for six years. The present call invites proposals for the second three-year funding period.

The affordable, site-independent and resource-saving storage of electrical energy in the societally relevant order of magnitude of gigawatt hours (GWh) is the central unsolved problem in the transition to fluctuating renewable energy sources. One possible solution could involve the Carnot battery technology, which converts electrical energy into heat by means of high-temperature heat pumps, heat being stored in cheap materials as internal energy and then converted back into electrical energy when required, e.g. by means of steam turbines. The underlying thermodynamic principle has been known for a long time, however, there are still no general methods for designing or analysing Carnot batteries based on their fundamental properties and objectives. Carnot batteries are complex, coupled, time-varying systems with a large number of components and degrees of freedom. Published efficiencies and costs are poorly verified or apply only to specific systems; the integration into future energy markets is unexplored.

The intrinsically new approach proposed by the SPP is a comprehensive inverse top-down design methodology, starting from the target variables (market) all the way down to the individual components (machines, storages and fluids, i.e. molecules) and their coupling, aiming at their optimal design and operation.

This approach sets a completely new course with respect to today's design methodology, which – based on known components and circuits – seeks to determine target operation parameters, e.g. efficiencies, and implements the optimal case identified in a very limited parameter space.

The working hypothesis of the Priority Programme is: “Through a paradigm shift towards an inverse design methodology, it is possible for the first time to test the feasibility of storage efficiencies above 70 percent and market-compliant storage costs using thermodynamic principles and to assess their compatibility with energy markets”. This hypothesis is to be assessed by an interdisciplinary team representing the fields of energy system analysis, thermodynamics, heat transfer, fluid energy machines, numerical optimisation and physical chemistry in close cooperation between universities and research centres (DLR). This is to be done in the inversely arranged research areas:

A – Carnot batteries in energy markets
B – Design of Carnot batteries and
C – Components for Carnot batteries  

In the first period, the focus lay on the development of steady-state fluid-dependent models for Carnot batteries, machines and storages and the implementation of inverse design approaches, including a proof of concept. In the second period, it is planned to use these models in cooperations and to refine them with respect to the ability of predicting transient behaviour and the inclusion of sub-models or multiple objectives from the other research areas.

Project proposals in these areas are expected to show a close connection with at least one of the projects from the other research areas in order to establish an inverse and transferable top-down design methodology with quality and assessment criteria defined by the energy system analysis.

Subject Area A investigates and specifies quality criteria with inverse energy system modelling methods. Such criteria may include, among others, overall efficiencies, storage periods, costs, material supply risks or robustness under uncertain future developments, e.g. varying market conditions and dynamics, where the simultaneous consideration of multiple criteria is desirable. Besides country-wide energy systems, behind-the-meter applications are also of interest.

In Subject Area B, the thermodynamic and thermoeconomic inverse design of Carnot battery concepts will be pursued, which can fulfil the combinations of quality criteria selected in Area A and, in doing so, also uncover the need for new research in Area C with respect to the most relevant properties of the components. In Area B, entire Carnot batteries are investigated theoretically or experimentally as a function of components and fluids taken as variables. In addition to considering actual working fluids and their mixtures, approaches adopting optimal fluids or fluids defined abstractly by model parameters are desirable.

In Subject Area C, fluids, storages, heat exchangers and fluid energy machines are investigated according to the specifications of the criteria and required properties derived in Area B. Component models as well as new methods of analysis and design are developed, which, in addition to good predictive power, also allow their implementation in optimisation procedures employed in Area B.

The temperature range of the reservoirs is to be below 500°C, and working fluids (and their mixture compositions), reservoirs, heat exchangers and machines are to be investigated generally as variables (rather than prescribed input) of the system analysis, configuration and optimisation. Both theoretical and experimental studies should address fundamentals in sufficient depth and at the same time ensure the possibility of generalisation; the expected results of the projects should have the potential to enable upscaling to industrial applications. The models developed during the first phase should provide the basis for a time-dependent analysis and control of the Carnot battery in the second funding period.

Possible topics are defined by the following keywords, where a focus on the Carnot battery (CB) and the inverse design methodology is compulsory:
•    Inverse energy system optimisation with the required CB parameter combinations as model outputs
•    Size dependence, dynamic behaviour, fluctuations and control
•    Fluid-tailored storage concepts
•    Flexible fluid energy machines and their behaviour as a function of fluid (composition), load range and pressure ratio 
•    Thermoeconomic analyses and scalability
•    Thermal storage concepts, materials and configurations
•    Modelling, optimisation and experimental validation
•    Carnot battery concept configurations and modes of operation
•    Fluid properties of pure substances and zeotropic mixtures with low GWP (thermodynamic and transport properties)
•    Heat exchanger concepts and properties under variable load conditions and temporal variations

The following topics are not subjects of research in the SPP:
•    Processes using ideal gases and pure water
•    Thermo-chemical energy storage or adsorption/absorption storage
•    Synthesis of new fluids or storage materials
•    Classical energy system optimisation with extensive parameter variation
•    Use of additional energy sources (e.g. waste heat above 40°C), while the use of the rejected heat, resulting from roundtrip efficiencies below one, is not excluded, provided the focus remains on the electrical energy output. Also, the use of abundant low-exergy waste heat up to temperatures of approximately 40°C is not excluded.

It is planned that the work of the SPP will be systematised and validated in a shared flexible small-scale Carnot battery laboratory. Participants are invited to use the Carnot battery laboratory in their own work packages. If the Carnot battery laboratory gets funded, storages, machines, fluid (mixtures) and the working load conditions can be selected by the participants to validate models or investigate the influence of process parameters. A researcher from the coordination project will support the experiments. For further information and planning, it is recommended to contact the coordinator (see below) prior to writing the proposals.

If interested applicants need support in finding project partners or need further information, they are invited to contact the coordinator.

Proposals must be written in English and submitted to the DFG by 3 February 2026. 
Proposals are to be submitted solely via the elan portal(externer Link), the DFG’s electronic proposal processing system, in order to ensure proposal-related data is recorded and documents are securely transmitted.

If this is the first time you are submitting a proposal to the DFG, please note that you must register in the elan portal before you can submit your proposal. You must do so by 27 January 2026 to submit a proposal under this call; registration requests received after this time cannot be considered. You will normally receive confirmation of your registration by the next working day. Note that you will be asked to select the appropriate Priority Programme call during both the registration and the proposal process.

If you wish to submit a proposal for a new project within the existing Priority Programme, please go to Proposal Submission – New Project – Priority Programmes and select “SPP 2403” from the current list of calls. Previous applicants can submit a proposal for the renewal of an existing project under Proposal Submission – Proposal Overview/Renewal Proposal.

When preparing your proposal, please refer to the programme guidelines (DFG form 50.05(interner Link), section B) and follow the proposal preparation instructions (DFG form 54.01(interner Link)). These forms can either be downloaded from our website or accessed through the elan portal.

The review colloquium for the Priority Programme will be held on 20 May 2026 in Duisburg.

Equity and Diversity

The DFG strongly welcomes proposals from researchers of all genders and sexual identities, from different ethnic, cultural, religious, ideological or social backgrounds, from different career stages, types of universities and research institutions, and with disabilities or chronic illness. With regard to the subject-specific focus of this call, the DFG encourages female researchers in particular to submit proposals.

Good Research Practice

According to a resolution of the DFG General Assembly, DFG funding may only be awarded to research institutions that have implemented the guidelines laid down in the Code of Conduct for Safeguarding Good Research Practice in their own regulations. The management of your institution is responsible for implementing the guidelines in a legally binding manner. In order to avoid delays in the disbursement of funding, please verify implementation within your institution in good time. For information regarding the implementation, please refer to the Research Integrity Portal. If you have any questions on this subject, please contact the Research Integrity team at the DFG Head Office.

Further Information

More information on the Priority Programme(externer Link) can be found here.

Here you can access the elan system(externer Link).

Please also refer to the DFG forms 50.05(interner Link) and 54.01(interner Link).

For scientific enquiries please contact the Priority Programme coordinator:
Professor Dr. Burak Atakan, Chair for Thermodynamics, Institute for Energy and Materials Processes, Faculty of Engineering, University Duisburg-Essen, Lotharstraße 1, 47057 Duisburg, phone +49 203 379-3355, b.atakan@uni-due.de(externer Link)

Contact Persons at the DFG Head Office

Programme contact: Dr. Simon Jörres, phone +49 228 885-2971, simon.joerres@dfg.de(externer Link)

Administrative contact: Anja Kleefuß, phone +49 228 885-2293, anja.kleefuss@dfg.de(externer Link)

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