Efficient Brayton Batteries: Powering Integrated Electricity, Heat, and Cooling Solutions

Kurzfassung

Carnot batteries show promise in advancing the energy transition in the power sector due to their potentially high power-to-power efficiency. However, Brayton batteries face a significant efficiency gap between theoretical and practical limits. This is primarily due to limitations in the turbomachinery. The maximum achievable compressor discharge temperatures are restricted to 400-500°C, necessitating substantial development efforts for higher temperatures. Additionally, although the isentropic efficiencies of turbomachinery typically range from 80-90% for large units, they do not reach 100%. Consequently, a notable portion of energy is lost as heat, which cannot be fully harnessed for electricity generation alone. A pragmatic approach to increased efficiency therefore not only optimizes the parameters and configurations of the systems, but also attempts to generate additional benefits beyond electricity generation. This includes, for example, combined heat, power and cold (CHPC) concepts and/or the uptake of waste heat streams. In order to quantify the benefits of such an approach, a concept study has systematically examined a variety of system configurations to identify concepts with above-average efficiency. The focus was on air-operated systems at low pressure (<13 bar), with or without a recuperator, and with heat supply or removal at different integration points, considering compressor outlet temperatures of 450°C or 625°C. Dynamic system simulations confirmed the high efficiencies for coupled power and heat generation, with values exceeding 85% for round-trip utilisation (accounting for both useful electricity and heat). Integration of waste heat can further increase these values, albeit at the expense of the electricity share in the output. For combined heat and power generation, electrical round-trip efficiencies of up to 60% were achieved. Finally, investment costs and dynamic subsystem requirements were estimated for the identified concepts.