Carnot batteries are a quickly developing group of technologies for medium and long duration electricity storage. It covers a large range of concepts which share processes of a conversion of power to heat, thermal energy storage (i.e., storing thermal exergy) and in times of need conversion of the heat back to (electric) power. Even though these systems were already proposed in the 19th century, it is only in the recent years that this field experiences a rapid development, which is associated mostly with the increasing penetration of intermittent cheap renewables in power grids and the requirement of electricity storage in unprecedented capacities. Compared to the more established storage options, such as pumped hydro and electrochemical batteries, the efficiency is generally much lower, but the low cost of thermal energy storage in large scale and long lifespans comparable with thermal power plants make this technology especially feasible for storing surpluses of cheap renewable electricity over typically dozens of hours and up to days. Within the increasingly extensive scientific research of the Carnot Battery technologies, commercial development plays the major role in technology implementation. This review addresses the gap between academia and industry in the mapping of the technologies under commercial development and puts them in the perspective of related scientific works. Technologies ranging from kW to hundreds of MW scale are at various levels of development. Some are still in the stage of concepts, whilst others are in the experimental and pilot operations, up to a few commercial installations. As a comprehensive technology review, this paper addresses the needs of both academics and industry practitioners.

Carbon dioxide (CO2) captured in carbon dioxide capture and storage (CCS) processes is transported and stored in a supercritical state. Heat exchangers, especially recuperators, with CO2 on both the hot and the cold side are often impacted by the occurrence of a pinch point, that is, area of closest approach between hot and cold temperature curves. CO2 in CCS systems is not pure, and even small amount of admixtures can have a significant effect on the location and impact of the pinch point, on heat transfer properties and exchanger sizing. This work investigates the effects of several admixtures on these parameters. It is found that these admixtures may have a slightly positive effect on recuperative heat exchangers. However, these admixtures also result in a significant size increase of CO2 coolers