Carnot battery

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A simplified scheme of a typical Carnot battery system

A Carnot battery is a type of energy storage system that stores electricity in thermal energy storage. During the charging process, electricity is converted into heat and kept in heat storage. During the discharging process, the stored heat is converted back into electricity.[1][2]

Moreover, “Marguerre” patented the concept of this technology 100 years ago[3] but the development of this concept has only recently been revitalized for increasing the shares of energy delivered by renewable sources. On the other hand, “Andre Thess” invented the term of Carnot battery in 2018, before the first International Workshop on Carnot Batteries.[4]

The name "Carnot battery" comes from Carnot's theorem, which describes the maximum efficiency of converting heat into mechanical energy. The word "battery" indicates that the purpose of this technology is to store electricity. The discharge efficiency of Carnot batteries is limited by the Carnot efficiency.

The German Aerospace Center (DLR) and University of Stuttgart have been working on the concept of Carnot batteries that store electricity in high-temperature heat storage since 2014.[5] In 2018, the name "Carnot battery" was used in Hannover Messe,[6] one of the world's largest trade fairs, by DLR.[5] However, the concept of Carnot batteries covers the technologies that have been developed for years,[7] such as pumped thermal energy storage[8][9] and liquid air energy storage.


In the transition to low-carbon energy systems, the penetration of variable renewable energy in electrical energy systems increases, and this also increases the need for energy storage. Currently, most of the new installed energy storage capacity comes from electrochemical batteries, such as lithium-ion batteries. This type of battery is suitable for short-term storage but may not be economical for longer durations due to its high energy capacity costs.[7] Thermal energy storage can store energy in inexpensive materials, such as water, rocks, and salts. Therefore, the cost for large-scale systems (e.g. gigawatt hours) can be lower than electrochemical batteries.[5]

Energy Storage Annex 36 - Carnot Batteries is a working group under the Energy Conservation and Energy Storage (ECES) programme, which is part of a Technology Collaboration Programme (TCP) under the International Energy Agency (IEA).[10]

System configuration[edit]

Possible energy conversion and storage technologies

A Carnot battery system can be divided into three parts: Power to Thermal (P2T), Thermal Energy Storage (TES), and Thermal to Power (T2P).

Electricity to heat technology[edit]

Electricity can be converted into heat through the use of various technologies.[1]

  • Resistive heating
  • Heat pump is the technology to pump heat from a lower temperature reservoir to a higher temperature. It can be divided into two groups: reverse Rankine cycle and reverse Brayton cycle.
    • The reverse Rankine cycle has been widely used in conventional heat pumps.
    • The concept of using the Brayton cycle for charging and discharging thermal energy was proposed by Prof. Robert B. Laughlin in 2017.[11]
  • Others: In liquid air energy storage systems, the Claude Cycle is utilised to liquify air. The Lamm–Honigmann process uses thermochemical cycles to covert power to heat.[12]

Thermal energy storage[edit]

According to the mechanism to store heat, thermal energy storage can be divided into three types: sensible heat storage, latent heat storage, and thermochemical storage. The storage materials that have been used for Carnot batteries are:

Heat to electricity[edit]

Heat can be converted into power through thermodynamic cycles, such as the Rankine cycle or Brayton cycle. Some technologies use the property of semiconductor materials to convert heat into electricity, and those are not considered a Carnot battery because there are no thermodynamic cycles involved in the conversion process, such as thermoelectric materials and the "Sun in a box".[14] The typical technologies are:

Advantages and disadvantages[edit]

The Carnot battery has been known by several other names such as “Pumped Thermal Electricity Storage’’ (PTES) or “Pumped Heat Electricity Storage” (PHES). This relatively new technology has become one of the most promising large-scale energy storage technology.

The main advantages of the Carnot battery are:[16]

  • Free choice of site;
  • Small environmental footprint;
  • Life expectancies of 20–30 years;
  • Optional low-cost backup capacity;
  • The components of an underutilized fossil-fueled power plant can be partially reused to build the Carnot batteries unit ;

The major drawback of this technology is:[17]

  • The limited roundtrip efficiency 𝜂𝑟𝑜𝑢𝑛𝑑, which relates the electricity 𝑾𝒅𝒊𝒔 delivered, during discharge, to the electricity 𝑾𝒄𝒉𝒂𝒓, needed to charge the system. Carnot batteries generally aim for 40-70% efficiency, significantly lower than pumped-storage hydroelectricity (65-85%).[18]


Carnot batteries can be used as grid energy storage to store excess power from variable renewable energy sources and to produce electricity when it is needed.

Some Carnot battery systems can use the stored heat or cold for other applications, such as district heating and cooling for data centers.

Carnot batteries have been proposed as a solution to convert existing coal-fired power plants into a fossil fuel-free generation system by replacing the coal fueled boiler.[19][20] The existing facilities in power plants such as power generation systems and transmission systems can be used.

List of Carnot battery projects[edit]

Although the term Carnot battery is new, many existing technologies can be classified as Carnot batteries.[7]

See also[edit]


  1. ^ a b Dumont, Olivier; Frate, Guido Francesco; Pillai, Aditya; Lecompte, Steven; De paepe, Michel; Lemort, Vincent (2020). "Carnot battery technology: A state-of-the-art review". Journal of Energy Storage. 32: 101756. doi:10.1016/j.est.2020.101756. ISSN 2352-152X. S2CID 225019981.
  2. ^ "IEA Energy Storage Annex 36 - Carnot Batteries". Technology Collaboration Programme Energy Storage, International Energy Agency. Retrieved 28 October 2020.
  3. ^ Marguerre F., « Ueber ein neues Verfahren zur Aufspeicherung elektrischer Energie. Mitteilungen der Vereinigung der Elektrizitätswerke 1924;354(55):27e35.
  4. ^ "International Workshop on Carnot Batteries".
  5. ^ a b c "Carnot batteries: Low-cost and location-independent energy storage in the gigawatt hour range". German Aerospace Centre (DLR). 2018.
  6. ^ "HANNOVER MESSE (industrial trade fairs), 23-27 APril, 2018".
  7. ^ a b c Josh McTigue (4 December 2019). "'Carnot Batteries' for electricity storage" (PDF). Retrieved 29 October 2020.
  8. ^ "Carnot Battery Energy Storage: A more cost-effective and flexible solution for grid-scale energy storage". Rushlight Events. 30 January 2019. Retrieved 29 October 2020.
  9. ^ Steinmann, Wolf-Dieter; Jockenhöfer, Henning; Bauer, Dan (2019). "Thermodynamic Analysis of High‐Temperature Carnot Battery Concepts". Energy Technology. 8 (3): 1900895. doi:10.1002/ente.201900895. ISSN 2194-4288.
  10. ^ "Energy Convervation and Energy Storage (ECES)". Retrieved 28 October 2020.
  11. ^ Laughlin, Robert B. (2017). "Pumped thermal grid storage with heat exchange". Journal of Renewable and Sustainable Energy. 9 (4): 044103. doi:10.1063/1.4994054. ISSN 1941-7012.
  12. ^ a b c Thiele, Elisabeth; Jahnke, Anna; Ziegler, Felix (2020). "Efficiency of the Lamm–Honigmann thermochemical energy storage". Thermal Science and Engineering Progress. 19: 100606. doi:10.1016/j.tsep.2020.100606. ISSN 2451-9049. S2CID 225010799.
  13. ^ "World's first Carnot battery stores electricity in heat". German Energy Solutions Initiative. 20 September 2020. Retrieved 29 Oct 2020.
  14. ^ Jennifer Chu (5 December 2018). "'Sun in a box' would store renewable energy for the grid". MIT News Office. Retrieved 30 October 2020.
  15. ^ Holy, Felix; Textor, Michel; Lechner, Stefan (2021-12-01). "Gas turbine cogeneration concepts for the pressureless discharge of high temperature thermal energy storage units". Journal of Energy Storage. 44: 103283. doi:10.1016/j.est.2021.103283. ISSN 2352-152X.
  16. ^ W.-D. Steinmann, D. Bauer, H. Jockenhöfer, et M. Johnson, « Pumped thermal energy storage (PTES) as smart sector-coupling technology for heat and electricity », Energy, vol. 183, p. 185‑190, sept. 2019, doi: 10.1016/
  17. ^ W. D. Steinmann, « The CHEST (Compressed Heat Energy STorage) concept for facility scale thermo mechanical energy storage », Energy, vol. 69, p. 543‑552, mai 2014, doi: 10.1016/
  18. ^ A. Koen et P. F. Antunez, « How heat can be used to store renewable energy », The Conversation. (consulté le févr. 27, 2020).
  19. ^ Susan Kraemer (16 April 2019). "Make Carnot Batteries with Molten Salt Thermal Energy Storage in ex-Coal Plants". SolarPACES.
  20. ^ "Webinar on Carnot Batteries" (PDF). ATA insights. April 2019. Retrieved 29 October 2020.
  21. ^ Olivier Dumont; Vincent Lemort (September 2020). "First Experimental Results of a Thermally Integrated Carnot Battery Using a Reversible Heat Pump / Organic Rankine Cycle". Conference: 2nd International Workshop on Carnot Batteries 2020. Retrieved 29 October 2020.
  22. ^ "project website". TU Berlin. Retrieved 15 April 2021.

External links[edit]