Energy transition: TU Ilmenau researches batteries of the future

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In a joint research project, TU Ilmenau is designing innovative batteries for fu
In a joint research project, TU Ilmenau is designing innovative batteries for future energy supply systems
In a large-scale collaborative research project, 13 German universities, including the Technische Universität Ilmenau and the German Aerospace Center, are designing innovative battery storage systems for integrating renewable energy sources into future energy supply systems. In the context of the energy transition, the so-called Carnot batteries, which temporarily store electricity in the form of heat, are considered to be a promising storage technology of the future, providing a permanent power supply. The Group of Engineering Thermodynamics at TU Ilmenau is now researching how the efficiency of thermal energy storage, a key component of Carnot batteries, can be increased. The work is based on highly regarded basic research by the team led by Prof. Christian Cierpka, the results of which have just been published in the American Physical Society’s prestigious physics journal PRX Energy.

The worldwide demand for energy is constantly increasing. It is to be increasingly covered by renewable energy sources in order to reduce environmental pollution and dependence on fossil fuels. However, energy sources such as sunlight and wind power are not constantly available and not always in the same strength. In order to keep the energy supply stable, the energy must therefore be stored temporarily. However, there is still a lack of efficient technologies for storing as many gigawatt hours as are consumed daily in a large city in a location-independent, environmentally friendly and at the same time cost-effective manner. Carnot batteries offer a possible solution.

A Carnot battery converts electricity into heat with the help of high-temperature heat pumps, stores the heat and converts it back into electricity when needed. The storage media used, water or molten salt, not only have a high heat capacity - they can absorb a lot of energy relative to their mass - they are also environmentally friendly and cost-effective. However, although the functional principle of Carnot batteries has been known for a long time, there has been little reliable data on energy storage efficiencies, costs or even the concrete application potential of such batteries in energy markets. In the priority program "Carnot batteries: Inverse Design from Market to Molecule" of the German Research Foundation, 13 German universities and the German Aerospace Center under the scientific leadership of the University of Duisburg-Essen are designing components for optimal Carnot batteries for future energy systems.

The efficiency of the systems’ thermal energy storage plays a central role. Researchers led by Prof. Christian Cierpka, head of the Group of Engineering Thermodynamics at the TU Ilmenau, together with DLR Cologne and Stuttgart, have investigated how flows in the storage units negatively influence their performance. The results, which they have published in the renowned physics journal PRX Energy of the American Physical Society (DOI:­y.2.043001 ), now form the basis of their work in the Carnot project. The aim is to scientifically describe so-called thermal stratified storage systems, in which liquid salt serves as a storage medium at temperatures of around 300 degrees Celsius, and to derive design rules for sustainable energy systems. For the first time, novel laser technologies are being used to measure velocity and temperature in these salts.

The joint project "Carnot Batteries" , funded by the German Research Foundation, will start in October with a kick-off meeting. With a duration of three years, it has a total volume of 6.5 million euros, of which the TU Ilmenau will receive 350,000 euros for its research work. In the project, an interdisciplinary team is working hand in hand: scientists from the fields of thermodynamics, energy system analysis, heat transfer, fluid energy machines, numerical optimization and physical chemistry. In doing so, they are turning the previous approach to energy research on its head: Whereas, in the past, it was attempted to determine efficiencies on the basis of known components and energy cycles and to optimize them for a specific field of application, the Carnot project takes the opposite approach: Based on market requirements, the components - machines, storage units and fluids - are optimized accordingly. Prof. Christian Cierpka’s expectations are high: "Heat storage systems are the key technology for S storage systems of the future. They ensure a permanent power supply while using existing infrastructure, such as steam power plants. New thermal storage systems will bring us closer to the climate protection targets we have set - and at moderate cost."