Carnot Battery development: A review on system performance, applications and commercial state-of-the-art

Energy storage is widely recognised as one of the key enablers for higher renewable energy penetration and future energy system decarbonisation. The term Carnot Battery refers to a set of storage technologies with electricity stored in the form of thermal energy, thus making them suitable not only for power balancing, but also for multi-vector energy management as a unique asset. With growing scientific literature on different Carnot Battery technologies and data from ongoing pilot and demonstration projects worldwide, this article aims to provide a review on the most recent developments in the area. More specifically, three complementary aspects are addressed: i) the collection and cross-comparison of quantitative techno-economic performance data of different Carnot Battery systems based on scientific literature findings; ii) the discussion of proposed applications for Carnot Batteries at the energy system scale, including power and thermal service provisions and retrofit opportunities; iii) the discussion of the most recent commercial developments in Carnot Battery technologies. Through this, we present the commonalities and discrepancies between scientific research and system implementation in ongoing projects. Our results show (a) a clear difference in the techno-economics of various Carnot Battery technologies; (b) a wide range of some performance metrics due to the absence of empirical evidence; and, interestingly, (c) a certain discrepancy between the systems and applications most addressed by the scientific community and the projects under development. The harmonisation of these discrepancies and the inclusion of location-specific integration considerations are proposed as a way forward for performance advancement and future deployment of Carnot Batteries.