Systematic Concept Study of Brayton Batteries for Efficient Combined Electricity, Heat, and Cooling Production

Kurzfassung

Brayton batteries hold significant potential for enhancing energy storage efficiency, yet there are considerable gaps between theoretical and practically achievable efficiencies. These discrepancies stem primarily from the limitations of turbomachinery: current achievable compressor discharge temperatures are limited to 400-500 °C, and isentropic efficiencies for large units range between 80-90 %, resulting in energy losses as heat. Fully utilizing this heat for electricity generation alone is not feasible. Therefore, efficiency optimization requires not only suitable topology and parameter selection but also extending the plant's functionality beyond pure electricity generation. This systematic study analyzed over 200,000 Brayton battery concept configurations using Ebsilon Professional® simulations. The focus was on various operational modes: pure electricity generation, combined electricity and heat generation, combined electricity and cooling generation, and combined electricity, heat, and cooling generation - each with or without waste heat integration. The results indicate that efficiencies for pure electricity generation range from 20 % to 50 %. Higher compressor discharge temperatures of 625 °C resulted in better efficiencies compared to 450 °C. Co-generation of electricity and heat or cooling improved overall efficiency but at the expense of electrical efficiency. Simultaneous generation of electricity, heat, and cooling was not achievable under the investigated parameters. The study identified promising concepts, predominantly air-based systems with or without charging line recuperators and heat exchangers positioned at various points within the cycle. These concepts will undergo further dynamic simulations focused on thermal energy storage. A key finding is that optimal heat exchanger integration is critical for enhancing efficiency. Systematic analysis of all possible integration points for heat input and output revealed that only certain topologies and parameter combinations are viable. Compared to existing literature, this study stands out for its comprehensive and systematic approach, covering a large number of concepts and thus facilitating better identification of optimal solutions. The findings provide valuable insights for the development of Brayton batteries and their potential applications in the energy transition, especially when their use extends beyond pure electricity generation. In summary, the study demonstrates that a clever combination of topology, parameters, and multipurpose utilization can significantly enhance Brayton battery efficiency. Future advancements in turbomachinery and thermal energy storage could further advance this technology, making it a vital component in a sustainable energy system.