A Carnot battery is a type of

energy storage Energy storage is the capture of energy produced at one time for use at a later time to reduce imbalances between energy demand and energy production. A device that stores energy is generally called an accumulator or battery. Energy comes in ...

system that stores

electricity Electricity is the set of physical phenomena associated with the presence and motion of matter that has a property of electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as describe ...

in thermal energy storage. During the charging process, electricity is converted into

heat In thermodynamics, heat is defined as the form of energy crossing the boundary of a thermodynamic system by virtue of a temperature difference across the boundary. A thermodynamic system does not ''contain'' heat. Nevertheless, the term is ...

and kept in heat storage. During the discharging process, the stored heat is converted back into electricity. Moreover, “Marguerre” patented the concept of this technology 100 years ago 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. The name "Carnot battery" comes from Carnot's theorem, which describes the maximum efficiency of converting heat into

mechanical energy In physical sciences, mechanical energy is the sum of potential energy and kinetic energy. The principle of conservation of mechanical energy states that if an isolated system is subject only to conservative forces, then the mechanical energy is ...

. 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 A Carnot cycle is an ideal thermodynamic cycle proposed by French physicist Sadi Carnot in 1824 and expanded upon by others in the 1830s and 1840s. By Carnot's theorem, it provides an upper limit on the efficiency of any classical thermodynam ...

. The German Aerospace Center (DLR) and

University of Stuttgart The University of Stuttgart (german: Universität Stuttgart) is a leading research university located in Stuttgart, Germany. It was founded in 1829 and is organized into 10 faculties. It is one of the oldest technical universities in Germany wi ...

have been working on the concept of Carnot batteries that store electricity in high-temperature heat storage since 2014. In 2018, the name "Carnot battery" was used in Hannover Messe, one of the world's largest trade fairs, by DLR. However, the concept of Carnot batteries covers the technologies that have been developed for years, such as pumped thermal energy storage and liquid air energy storage.

Background

In the transition to low-carbon energy systems, the penetration of

variable renewable energy Variable renewable energy (VRE) or intermittent renewable energy sources (IRES) are renewable energy sources that are not dispatchable due to their fluctuating nature, such as wind power and solar power, as opposed to controllable renewable ener ...

in electrical energy systems increases, and this also increases the need for

. Currently, most of the new installed energy storage capacity comes from electrochemical

batteries Battery most often refers to: * Electric battery, a device that provides electrical power * Battery (crime), a crime involving unlawful physical contact Battery may also refer to: Energy source *Automotive battery, a device to provide power t ...

, 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. 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.
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).

System configuration

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

Electricity can be converted into heat through the use of various technologies. *

Resistive heating Joule heating, also known as resistive, resistance, or Ohmic heating, is the process by which the passage of an electric current through a conductor produces heat. Joule's first law (also just Joule's law), also known in countries of former ...

Heat pump A heat pump is a device that can heat a building (or part of a building) by transferring thermal energy from the outside using a refrigeration cycle. Many heat pumps can also operate in the opposite direction, cooling the building by removing ...

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 The Rankine cycle is an idealized thermodynamic cycle describing the process by which certain heat engines, such as steam turbines or reciprocating steam engines, allow mechanical work to be extracted from a fluid as it moves between a heat sourc ...

and reverse

Brayton cycle The Brayton cycle is a thermodynamic cycle that describes the operation of certain heat engines that have air or some other gas as their working fluid. The original Brayton engines used a piston compressor and piston expander, but modern gas tu ...

. ** 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 Robert Betts Laughlin (born November 1, 1950) is the Anne T. and Robert M. Bass Professor of Physics and Applied Physics at Stanford University. Along with Horst L. Störmer of Columbia University and Daniel C. Tsui of Princeton Universi ...

in 2017. * Others: In liquid air energy storage systems, the Claude Cycle is utilised to liquify air. The Lamm–Honigmann process uses thermochemical cycles to convert power to heat.

Thermal energy storage

According to the mechanism to store heat, thermal energy storage can be divided into three types:

sensible heat Sensible heat is heat exchanged by a body or thermodynamic system in which the exchange of heat changes the temperature of the body or system, and some macroscopic variables of the body or system, but leaves unchanged certain other macroscopic vari ...

storage,

latent heat Latent heat (also known as latent energy or heat of transformation) is energy released or absorbed, by a body or a thermodynamic system, during a constant-temperature process — usually a first-order phase transition. Latent heat can be underst ...

storage, and thermochemical storage. The storage materials that have been used for Carnot batteries are: * Hot water *

Molten salt Molten salt is salt which is solid at standard temperature and pressure but enters the liquid phase due to elevated temperature. Regular table salt has a melting point of 801 °C (1474°F) and a heat of fusion of 520 J/g.Journal of Chemical T ...

* Packed-bed rocks * Liquid air * Latent heat thermal energy storage * Thermochemical materials (pairs of chemicals), such as LiBr/H2O and H2O/NH3

Heat to electricity

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 Thermoelectric materials show the thermoelectric effect in a strong or convenient form. The ''thermoelectric effect'' refers to phenomena by which either a temperature difference creates an electric potential or an electric current creates a t ...

and the "Sun in a box". The typical technologies are: *

Heat engine In thermodynamics and engineering, a heat engine is a system that converts heat to mechanical energy, which can then be used to do mechanical work. It does this by bringing a working substance from a higher state temperature to a lower stat ...

Steam turbine A steam turbine is a machine that extracts thermal energy from pressurized steam and uses it to do mechanical work on a rotating output shaft. Its modern manifestation was invented by Charles Parsons in 1884. Fabrication of a modern steam tu ...

Gas turbine A gas turbine, also called a combustion turbine, is a type of continuous flow internal combustion engine. The main parts common to all gas turbine engines form the power-producing part (known as the gas generator or core) and are, in the directio ...

* Organic Rankine cycle machines * Lamm-Honigmann process can convert the stored energy in thermochemical storage into electricity.

Advantages and disadvantages

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: * 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: *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%).

Application

Carnot batteries can be used as

grid energy storage Grid energy storage (also called large-scale energy storage) is a collection of methods used for energy storage on a large scale within an electrical power grid. Electrical energy is stored during times when electricity is plentiful and inex ...

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 District heating (also known as heat networks or teleheating) is a system for distributing heat generated in a centralized location through a system of insulated pipes for residential and commercial heating requirements such as space heating ...

and cooling for

data centers A data center (American English) or data centre (British English)See spelling differences. is a building, a dedicated space within a building, or a group of buildings used to house computer systems and associated components, such as telecommun ...

. Carnot batteries have been proposed as a solution to convert existing

coal-fired power plants Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal is formed when dead ...

into a

fossil fuel A fossil fuel is a hydrocarbon-containing material formed naturally in the Earth's crust from the remains of dead plants and animals that is extracted and burned as a fuel. The main fossil fuels are coal, oil, and natural gas. Fossil fuels ma ...

-free generation system by replacing the coal fueled boiler. The existing facilities in power plants such as power generation systems and transmission systems can be used.

List of Carnot battery projects

Although the term ''Carnot battery'' is new, many existing technologies can be classified as Carnot batteries. * Liquid air energy storage: Highview Power,

University of Birmingham , mottoeng = Through efforts to heights , established = 1825 – Birmingham School of Medicine and Surgery1836 – Birmingham Royal School of Medicine and Surgery1843 – Queen's College1875 – Mason Science College1898 – Mason Univers ...

* Pumped thermal energy storage: Malta Inc.,

University of Durham , mottoeng = Her foundations are upon the holy hills ( Psalm 87:1) , established = (university status) , type = Public , academic_staff = 1,830 (2020) , administrative_staff = 2,640 (2018/19) , chancellor = Sir Thomas Allen , vice_cha ...

* Electric thermal energy storage: Siemens Gamesa,

National Renewable Energy Laboratory The National Renewable Energy Laboratory (NREL) in the US specializes in the research and development of renewable energy, energy efficiency, energy systems integration, and sustainable transportation. NREL is a federally funded research an ...

* Reversible heat pump / ORC:

University of Liège The University of Liège (french: Université de Liège), or ULiège, is a major public university of the French Community of Belgium based in Liège, Wallonia, Belgium. Its official language is French. As of 2020, ULiège is ranked in the ...

* Lamm-Honigmann energy storage:

Technical University of Berlin The Technical University of Berlin (official name both in English and german: link=no, Technische Universität Berlin, also known as TU Berlin and Berlin Institute of Technology) is a public research university located in Berlin, Germany. It was ...

References

{{reflist, 30em, refs= {{cite web , title = Webinar on Carnot Batteries , date = April 2019 , publisher = ATA insights , url=https://atainsights.com/wp-content/uploads/2019/04/190404-_Michael-Geyer-Sebastian-Freund-Webinar-Carnot-Batteries-distr.pdf , accessdate = 29 October 2020 {{cite web , title = IEA Energy Storage Annex 36 - Carnot Batteries , url=https://www.eces-a36.org/ , publisher = Technology Collaboration Programme Energy Storage, International Energy Agency , accessdate = 28 October 2020 {{cite web , title = Carnot batteries: Low-cost and location-independent energy storage in the gigawatt hour range , date = 2018 , publisher = German Aerospace Centre (DLR) , url=https://event.dlr.de/en/hmi2018/carnot-batterien/ {{cite web , title = World's first Carnot battery stores electricity in heat , date = 20 September 2020 , publisher = German Energy Solutions Initiative , url=https://www.german-energy-solutions.de/GES/Redaktion/EN/News/2020/20200930-carnot-battery.html , accessdate = 29 Oct 2020 {{cite web , title = First Experimental Results of a Thermally Integrated Carnot Battery Using a Reversible Heat Pump / Organic Rankine Cycle , author1 = Olivier Dumont , author2 = Vincent Lemort , url=https://www.researchgate.net/publication/344252650 , date = September 2020 , publisher = Conference: 2nd International Workshop on Carnot Batteries 2020 , accessdate = 29 October 2020 {{cite journal , last1=Dumont , first1=Olivier , last2=Frate , first2=Guido Francesco , last3=Pillai , first3=Aditya , last4=Lecompte , first4=Steven , last5=De paepe , first5=Michel , last6=Lemort, first6=Vincent , title=Carnot battery technology: A state-of-the-art review , journal=Journal of Energy Storage, volume=32, year=2020, pages=101756 , issn=2352-152X, doi=10.1016/j.est.2020.101756, s2cid=225019981 {{cite web , title = HANNOVER MESSE (industrial trade fairs), 23-27 APril, 2018 , url=https://event.dlr.de/en/hannover-messe-2018/ {{cite web , title = Energy Convervation and Energy Storage (ECES) , url=https://iea-eces.org/ , accessdate = 28 October 2020 {{cite web , title = Make Carnot Batteries with Molten Salt Thermal Energy Storage in ex-Coal Plants , url=https://www.solarpaces.org/make-carnot-batteries-with-molten-salt-thermal-energy-storage-from-ex-coal-plants/ , date = 16 April 2019 , author = Susan Kraemer , publisher = SolarPACES {{cite journal , last1=Laughlin, first1=Robert B. , title=Pumped thermal grid storage with heat exchange , journal=Journal of Renewable and Sustainable Energy , volume=9, issue=4, year=2017, pages=044103, issn=1941-7012, doi=10.1063/1.4994054 , doi-access=free {{cite web , title = Carnot Battery Energy Storage: A more cost-effective and flexible solution for grid-scale energy storage , date = 30 January 2019 , url=https://www.rushlightevents.com/wp-content/uploads/2019/02/RUSHLIGHT-SHOW-2019-CLEANTECH-CONF-PANEL-1-NEWCASTLE-UNIV.pd , publisher = Rushlight Events , accessdate = 29 October 2020 {{cite web , title = 'Carnot Batteries' for electricity storage , author = Josh McTigue , date = 4 December 2019 , url=https://www.nrel.gov/docs/fy20osti/75559.pdf , accessdate = 29 October 2020 {{cite journal , last1=Steinmann , first1=Wolf-Dieter , last2=Jockenhöfer , first2=Henning , last3=Bauer , first3=Dan , title = Thermodynamic Analysis of High‐Temperature Carnot Battery Concepts, journal=Energy Technology , volume=8 , issue=3 , year=2019 , pages=1900895 , issn=2194-4288 , doi=10.1002/ente.201900895 , doi-access=free {{cite web , title = 'Sun in a box' would store renewable energy for the grid , author = Jennifer Chu , publisher = MIT News Office , date = 5 December 2018 , url=https://news.mit.edu/2018/liquid-silicon-store-renewable-energy-1206 , accessdate = 30 October 2020 {{cite journal, last1=Thiele, first1=Elisabeth, last2=Jahnke, first2=Anna, last3=Ziegler, first3=Felix, title=Efficiency of the Lamm–Honigmann thermochemical energy storage, journal=Thermal Science and Engineering Progress, volume=19, year=2020, pages=100606, issn=2451-9049, doi=10.1016/j.tsep.2020.100606, s2cid=225010799

External links

2nd International Workshop on Carnot Batteries, University Stuttgart, September 15-16, 2020

International Workshop on Carnot Batteries, Stuttgart, Germany, October 9-10, 2018
Energy storage