Brayton batteries for combined electricity and heat and cooling production: Systematic concept and parameter study

Abstract

Carnot batteries are considered a promising technology to contribute to the implementation of the energy transition in the power sector because of their potentially very high power-to-power efficiency. However, with regard to Brayton batteries, the gap between theoretically and realistically achievable efficiency is quite high. This has several causes, especially on the part of the required turbomachinery. On the one hand, the maximum achievable compressor discharge temperatures are limited to 400-500 °C on the machine side, and their significant increase requires intensive development efforts. Secondly, the isentropic efficiencies of the turbomachinery are high at 80 to 90 % for large units, but not 100 %. As a result, a considerable amount of energy is converted into heat during both the charging and discharging cycles, which cannot be fully utilized in the electricity generation alone. On the conceptual side, in addition to an advantageous topology and parameter selection, optimization of energy efficiency is also required. The latter can be achieved in particular by extending the benefits of the plant beyond pure electricity generation to other purposes: Electricity generation with heat integration as well as coupled generation of electricity/heat, electricity/cold, electricity/heat/cold and electricity/cold with heat integration. For these different purposes, the paper presents a concept study in which all theoretically possible integration points for the necessary heat exchangers for the input or output of heat into the plant are systematically investigated by system simulations. Another focus is an extensive sensitivity analysis with respect to the relevant parameters. Both are carried out with a universal model created in the simulation software Ebsilon Professional®, which is able to cover all theoretically possible topologies with regard to heat exchanger integration. As a result, out of hundreds of possible concepts for Brayton batteries, those are found that are physically possible and have the highest degree of efficiency or utilization.