Topical Article: Storing Electricity with Industrial Heat Pumps: Carnot Batteries for Grid-Level Energy Storage

This article discusses the need for efficient electricity storage systems to mitigate environmental impacts, especially in the context of the electrification of energy-intensive processes. Pumped Hydro Energy Storage (PHES) is the predominant grid-scale electricity storage technology, but alternative electricity storage solutions must be investigated and brought to market to fully exploit the electrification potential. One such option is Carnot Batteries (CB), which combine heat engines with thermal energy storage systems to store and recover electricity as thermal exergy. The article defines and characterizes CBs, providing an overview of the charging and discharging processes, and highlights the importance of an integrated design approach for large-scale heat pumps as a key component. 

The article discusses the requirements for grid-scale electricity storage systems, such as high storage capacities, low discharge times, and low unit costs. The need for unit costs to be as cheap as possible rules out concepts based on lithium-ion batteries. The article highlights the potential of CBs, which are based on a concept originally proposed in 1922 and comprise a low technology readiness level. The charging process of CBs can be performed with a large-scale heat pump, and the discharge process is performed with an Organic-Rankine-Cycle (ORC) heat engine. The overall efficiency of CBs depends on the coefficient of performance (COP) of the heat pump, efficiencies of the storage system, and the ORC. 

The article concludes that to push CBs to the market, it is promising to focus on commercially available equipment. An integrated design approach for large-scale heat pumps can provide optimal use of electricity from renewable energy sources. Additionally, using waste heat as an additional heat source can reduce the temperature gradient, improving heat pump efficiencies. While CBs may not be as efficient as lithium-ion batteries, they offer a promising alternative for grid-scale electricity storage systems. Further research is needed to improve the efficiency and feasibility of CBs. 

Hannah Romberg, Sebastian Ostlender, Christian Vering and Dirk Müller, Germany

This text has been shortened by the HPC team 

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Heat Pumping Technologies MAGAZINE, Vol.41 No. 1/2023

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