Design, component selection and critical considerations for the development of a 50 kWe Carnot Battery coupled to waste heat

Carnot Batteries (CB) integrate two conversion cycles: a power-to-heat cycle via a Heat Pump (HP) and a heat-to-power cycle using an Organic Rankine Cycle (ORC). HPs are widely available and highly efficient due to their Coefficient of Performance, while ORCs, though commercially established, exhibit low efficiency at temperatures below 120°C and require further advancements. CBs have been extensively studied in various applications. The primary barriers include high initial investment and operational complexity. Systems capable of sharing key components between HP and ORC emerge as a suitable and scalable solution, as they can significantly reduce investment costs. This paper presents the design, component selection, and key considerations for a 50 kWe and 600 kWth CB, utilising waste heat from abandoned underground caverns in southern Belgium. The system is built from off-the-shelf components, including twin-screw machines (compressor and expander), brazed plate heat exchangers, a low Net Positive Suction Head (NPSH) centrifugal pump, a liquid receiver, an expansion valve, piping, and auxiliary elements. The study addresses 3D design, structural considerations, expected efficiency, and integration challenges. Through numerical simulation, it is estimated that under operating conditions, the ORC can achieve a maximum efficiency of 7.6%, and the HP a maximum Coefficient Of Performance (COP) of 6.6. Additionally, it provides critical insights into the integration of HP and ORC, highlighting control variables for optimisation. Finally, a conceptual design of the proposed machine is outlined, offering a foundation for further research and development.