Is waste heat recovery a promising avenue for the Carnot battery? Techno-economic optimisation of an electric booster-assisted Carnot battery integrated into different data centres

The transition to intermittent renewable energies will necessitate the integration of storage. An interesting technology is the Carnot battery (CB), a novel power-to-heat-to-power system, capable of harnessing waste energy streams. While initial studies have indicated that, under ideal conditions, CB can be competitive with conventional technologies such as chemical batteries, their economic viability in real-world applications remains uncertain. To fill this gap, this work explores the techno-economic potential of electric booster-assisted CB integrated within data centres. Motivation for this case study is the recovery of waste heat, leading to an improved electrical storage efficiency. To maximise the energy self-sufficiency and the internal rate of return, we have applied multi-criteria optimisation to the system design, under three different thermal integration scenarios and for two sets of climatic conditions, using a thermodynamic model and time series from a real data centre. Our analyses suggest that current projections for electricity prices and CB costs yield payback periods exceeding a decade, but that these could fall below ten years if the CB capital costs were halved. Furthermore, it turns out that the choice of optimum charging system (i.e. right balance between heat pump and electrical heater) is contingent on the heat source temperature and availability. For higher temperatures (e.g. 60 C), heat pumps emerge as the financially most attractive option, thanks to their superior coefficient of performance, whereas for lower temperatures (< 25 C), resistive heaters are preferable. Results also show that when the aim is to increase the energy self-sufficiency, there exist an efficiency/charging capacity trade-off, which causes a dilemma for the system design. On the one hand, heat pumps are vital to increase the efficiency of the CB, but on the other hand, as the amount of thermal energy available at its source is limited by the data centre operations, electrical boosters are indispensable to increase the charging capacity. To soften this dilemma and enhance the techno-economic performance of thermally integrated CB, future research should explore more efficient booster configurations, such as dual heat source heat pumps.