High temperature sensible thermal energy storage as a crucial element of Carnot Batteries: Overall classification and technical review based on parameters and key figures
Alexej Paul, Felix Holy, Michel Textor, Stefan Lechner
Abstract
Electricity storage is a key component in the transition to a (100%) CO2-neutral energy system and a way to maximize the efficiency of power grids. Carnot Batteries offer an important alternative to other electricity storage systems due to the possible use of low-cost storage materials in their thermal energy storage units. The use of sensible storage material at high temperatures is of particular interest in order to achieve higher storage densities. A high number of research projects are currently being carried out in this field, and an increasing number of industrial players are also pushing the development of systems to market maturity, which results in a large variety of concepts. This work offers new approaches to the classification of Carnot Batteries and thermal energy storage systems. It gives an overview of the current state of the art in the field of thermal energy storage above 500 °C and compares the systems and concepts on the basis of key figures. The large number of concepts will inevitably be selected based on technical and environmental considerations. It is shown that solid and sensible thermal energy storage units can be represented as an efficient component of a Carnot Battery in the high temperature range. Total cycle energy efficiencies of ≥ 95% have been shown in literature. The ‘fixed structure’ design as a differentiation to the ‘packed bed’ is particularly well suited as it allows internal charging at temperatures greater than 1000 °C while minimizing charging losses.