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Cryogenic energy storage (CES) is the use of low temperature (
cryogenic In physics, cryogenics is the production and behaviour of materials at very low temperatures. The 13th IIR International Congress of Refrigeration (held in Washington DC in 1971) endorsed a universal definition of “cryogenics” and “cr ...
) liquids such as
liquid air Liquid air is air that has been cooled to very low temperatures ( cryogenic temperatures), so that it has condensed into a pale blue mobile liquid. To thermally insulate it from room temperature, it is stored in specialized containers ( vacuum in ...
or
liquid nitrogen Liquid nitrogen—LN2—is nitrogen in a liquid state at low temperature. Liquid nitrogen has a boiling point of about . It is produced industrially by fractional distillation of liquid air. It is a colorless, low viscosity liquid that is wide ...
to store energy. The technology is primarily used for the large-scale storage of electricity. Following grid-scale demonstrator plants, a 250 MWh commercial plant is now under construction in the UK, and a 400 MWh store is planned in the USA.


Grid energy storage


Process

When it is cheaper (usually at night), electricity is used to cool air from the atmosphere to -195 °C using the Claude Cycle to the point where it liquefies. The liquid air, which takes up one-thousandth of the volume of the gas, can be kept for a long time in a large vacuum flask at
atmospheric pressure Atmospheric pressure, also known as barometric pressure (after the barometer), is the pressure within the atmosphere of Earth. The standard atmosphere (symbol: atm) is a unit of pressure defined as , which is equivalent to 1013.25 millibars, ...
. At times of high demand for electricity, the liquid air is pumped at high pressure into a
heat exchanger A heat exchanger is a system used to transfer heat between a source and a working fluid. Heat exchangers are used in both cooling and heating processes. The fluids may be separated by a solid wall to prevent mixing or they may be in direct contac ...
, which acts as a boiler. Air from the atmosphere at ambient temperature, or hot water from an industrial heat source, is used to heat the liquid and turn it back into a gas. The massive increase in volume and pressure from this is used to drive a
turbine A turbine ( or ) (from the Greek , ''tyrbē'', or Latin ''turbo'', meaning vortex) is a rotary mechanical device that extracts energy from a fluid flow and converts it into useful work. The work produced by a turbine can be used for generating e ...
to generate electricity.


Efficiency

In isolation the process is only 25% efficient, but this is increased to around 50% when used with a low-grade cold store, such as a large gravel bed, to capture the cold generated by evaporating the cryogen. The cold is re-used during the next refrigeration cycle. Efficiency is further increased when used in conjunction with a
power plant A power station, also referred to as a power plant and sometimes generating station or generating plant, is an industrial facility for the generation of electric power. Power stations are generally connected to an electrical grid. Many ...
or other source of low-grade heat that would otherwise be lost to the atmosphere. Highview Power claims an AC to AC round-trip efficiency of 70%, by using an otherwise
waste heat Waste heat is heat that is produced by a machine, or other process that uses energy, as a byproduct of doing work. All such processes give off some waste heat as a fundamental result of the laws of thermodynamics. Waste heat has lower utility ( ...
source at 115 °C. The
IMechE The Institution of Mechanical Engineers (IMechE) is an independent professional association and learned society headquartered in London, United Kingdom, that represents mechanical engineers and the engineering profession. With over 120,000 membe ...
(Institution of Mechanical Engineers) agrees that these estimates for a commercial-scale plant are realistic. However this number was not checked or confirmed by independent professional institutions.


Advantages

The system is based on proven technology, used safely in many industrial processes, and does not require any particularly rare elements or expensive components to manufacture. Dr Tim Fox, the head of Energy at the IMechE says "It uses standard industrial components - which reduces commercial risk; it will last for decades and it can be fixed with a spanner."


Applications


Economics

The technology is only economic where there is large variation in the wholesale price of electricity over time. Typically this will be where it is difficult to vary generation in response to changing demand. The technology thus complements growing energy sources like wind and solar, and allows a greater penetration of such renewables into the energy mix. It is less useful where electricity is mostly provided by dispatchable generation, like coal or gas-fired thermal plants, or hydro-electricity. Cryogenic plants can also provide grid services, including grid balancing, voltage support,
frequency response In signal processing and electronics, the frequency response of a system is the quantitative measure of the magnitude and phase of the output as a function of input frequency. The frequency response is widely used in the design and analysis of s ...
and synchronous inertia.


Locations

Unlike other grid-scale energy storage technologies which require specific geographies such as mountain reservoirs (
pumped-storage hydropower Pumped-storage hydroelectricity (PSH), or pumped hydroelectric energy storage (PHES), is a type of hydroelectric energy storage used by electric power systems for load balancing. The method stores energy in the form of gravitational potent ...
) or underground salt caverns ( compressed-air energy storage), a cryogenic energy storage plant can be located just about anywhere. To achieve the greatest efficiencies, a cryogenic plant should be located near a source of low-grade heat which would otherwise be lost to the atmosphere. Often this would be a thermal power station that could be expected to be also generating electricity at times of peak demand and the highest prices. Colocation with a source of unused cold, such as an LNG
regasification Regasification is a process of converting liquefied natural gas (LNG) at −162 °C (−260 °F) temperature back to natural gas at atmospheric temperature. LNG gasification plants can be located on land as well as on floating barges, i.e. a Float ...
facility is also an advantage.


Grid-scale demonstrators


United Kingdom

In April 2014, the UK government announced it had given £8 million to
Viridor Viridor Ltd (from the Latin 'to become green') is a recycling, renewable energy and waste management company in the United Kingdom, owned by KKR (previously owned by Pennon Group). History The company was formed in 1956 as Harrison Western Lt ...
and Highview Power to fund the next stage of the demonstration. The resulting grid-scale demonstrator plant at Pilsworth Landfill facility in
Bury, Greater Manchester Bury ( ) is a market town on the River Irwell in Greater Manchester, England. Metropolitan Borough of Bury is administered from the town, which had an estimated population of 78,723 in 2015. The town is within the historic county boundaries ...
, UK, started operation in April 2018. The design was based on research by the Birmingham Centre for Cryogenic Energy Storage (BCCES) associated with the University of Birmingham, and has storage for up to 15 MWh, and can generate a peak supply of 5 MW (so when fully charged lasts for three hours at maximum output) and is designed for an operational life of 40 years.


United States

In 2019, the Washington State Department of Commerce's Clean Energy Fund announced it would provide a grant to help Tacoma Power partner with
Praxair Praxair, Inc. was an American worldwide industrial gases company. Founded in 1907, Praxair was the largest industrial gases company in North and South America, and the third-largest worldwide by revenue. In 2018 it merged with Linde AG to form ...
to build a 15 MW / 450 MWh liquid air energy storage plant. It will store up to 850,000 gallons of liquid nitrogen to help balance power loads.


Commercial plants


United Kingdom

In October 2019, Highview Power announced that it planned to build a 50 MW / 250 MWh commercial plant in Carrington, Greater Manchester. Construction began in November 2020, with commercial operation planned for 2022. At 250 MWh, the plant would match the storage capacity of the world's largest existing lithium-ion battery, the Gateway Energy Storage facility in California. In November 2022 Highview Power stated that they were still trying to raise money "to construct a storage plant in Carrington that has a 30 megawatts capacity and can store 300 megawatt hours of electricity" with commissioning planned for "the end of 2024."


United States

In December 2019, Highview announced plans to build a 50 MW plant in northern Vermont, with the proposed facility able to store eight hours of energy, for a 400 MWh storage capacity.


Chile

In June 2021, Highview announced that it was developing a 50MW / 500MWh storage plant in the Atacama region of Chile.


History


Transport

Both liquid air and liquid nitrogen have been used experimentally to power cars. A liquid air powered car called
Liquid Air Liquid air is air that has been cooled to very low temperatures ( cryogenic temperatures), so that it has condensed into a pale blue mobile liquid. To thermally insulate it from room temperature, it is stored in specialized containers ( vacuum in ...
was built between 1899 and 1902 but it couldn't at the time compete in terms of efficiency with other engines. More recently, a liquid nitrogen vehicle was built. Peter Dearman, a garage inventor in Hertfordshire, UK who had initially developed a liquid air powered car, then put the technology to use 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 inexp ...
The Dearman engine differs from former nitrogen engine designs in that the nitrogen is heated by combining it with the heat exchange fluid inside the cylinder of the engine.


Electricity storage pilots

In 2010, the technology was piloted at a UK power station. A 300 kW, 2.5 MWh storage capacity pilot cryogenic energy system developed by researchers at the
University of Leeds , mottoeng = And knowledge will be increased , established = 1831 – Leeds School of Medicine1874 – Yorkshire College of Science1884 - Yorkshire College1887 – affiliated to the federal Victoria University1904 – University of Leeds , t ...
and Highview Power that uses liquid air (with the and water removed as they would turn solid at the storage temperature) as the energy store, and low-grade waste heat to boost the thermal re-expansion of the air, operated at an 80 MW biomass power station in
Slough Slough () is a town and unparished area in the unitary authority of the same name in Berkshire, England, bordering west London. It lies in the Thames Valley, west of central London and north-east of Reading, at the intersection of the M4, ...
, UK, from 2010 until 2014 when it was relocated to the university of Birmingham. The efficiency is less than 15% because of low efficiency hardware components used, but the engineers are targeting an efficiency of about 60 percent for the next generation of CES based on operation experiences of this system.


See also

* United States Department of Energy International Energy Storage Database


References

{{reflist, 30em Grid energy storage Cryogenics