The temperature range of the reservoirs shall be below 500°C and working fluids, reservoirs, heat exchangers and machines shall be investigated generally as variables (and not as prescribed input) of the system analysis, configuration and optimisation.

Both theoretical and experimental studies should address fundamentals with sufficient depth and, at the same time, ensure the possibility of generalisation; the expected results of the projects should have the potential for enabling upscaling to industrial applications. Furthermore, 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 at the latest.

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, partial-load behaviour and fluctuations
• Fluid-tailored storage concepts
• Flexible fluid energy machines and their behaviour as a function of fluid, load range and pressure ratio
• Thermoeconomic analyses and scalability
• Thermal storage concepts, materials and configurations
• Modelling, optimisation and experimental validation
• Carnot battery concepts 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

The following topics are not subject 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)