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). The programme is designed to run for six years. 

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 be represented by the Carnot battery-technology, whereby electrical energy is converted 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 fundamentals 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 % and market-compliant storage costs using thermodynamic principles and to assess their compatibility with energy markets". This hypothesis is 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).