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 imple-mentation 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 sci-entific community and the projects under development. The harmonisation of these discrepancies and the in-clusion of location-specific integration considerations are proposed as a way forward for performance advancement and future deployment of Carnot Batteries.