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Cryogenic energy storage systems are sustainable, low-carbon,
asynchronous alternatives to existing large-scale energy storage
systems. They employ a cryogen, like liquid nitrogen or liquid air,
for energy storage. In periods of low energy demand, surplus
electricity is employed to liquefy the air or nitrogen which is then
preserved in a specially designed cryogenic container. Upon surging
energy requirements, the liquid is released to evaporate,
expeditiously expanding in volume to drive a turbine and subsequently
generate electricity. These systems proffer unparalleled energy
density and prolonged-duration power supply, sans reliance on scarce
or unsafe substances, thus exemplifying an innovative solution to the
contemporary energy storage challenge.

In 1977, the idea of energy storage using liquid air, a cryogen, was
proposed that involved liquefying air with the energy to be stored and
later re-gasifying and expanding the liquid air to generate power as
needed. Hitachi later developed and demonstrated this system. However,
this method required compressors to operate at extremely high
temperatures and store energy within a narrow temperature range. In
2006, UK-based HighView Power initiated research and development work
to develop a scalable, modular liquid air energy storage system that
could be located anywhere. Their CRYOBattery® system has come a long
way, with reported efficiency as high as 60% and at an affordable and
competitive price per MWh of electrical energy.

In a typical cryogenic energy storage system, there are three
subsystems — the charging system, storage, and discharging system.
The charging system involves an air liquefaction cycle that uses a
compressor to raise the air pressure to about 120 times the
atmospheric pressure. The excess power from the grid or stored power
is used to run the compressor. The compressed air is then cooled by
the return-air stream from the liquefier in a heat exchanger before
being expanded in a valve or turbine resulting in the production of a
mixture of vapor and liquid at about -195 Degree Celsius. The
liquefied portion is stored in an insulated vessel (storage), while
the vapor is used for cooling the incoming air in the heat exchanger
before exiting the system, as mentioned earlier. During the discharge
process for use of the stored energy, the stored liquid is regasified
(by contacting with atmospheric air) at a pressure of about 150 atm to
produce highly pressurized gas, which is expanded in turbine(s) to
generate power.

The energy storage efficiency of the above process is low for the
technology to be commercially viable and competitive with other
storage options. Present research and development efforts, globally,
are focused on addressing this challenge. The author is also engaged
in the identification of methods to raise the energy storage
efficiency to or beyond commercial acceptability. The author’s
university, Anant National University, is collaborating with various
institutes, including IIT Kharagpur, to conduct extensive theoretical
and experimental studies. Through this research, they have identified
scopes and methods for process improvement, resulting in the
development of a novel process configuration with the potential to
achieve a storage efficiency of approximately 90%. Their proposed
modifications involve four different processes within the overall
system, including liquefaction, charging-discharging, waste-heat
utilization, and power generation. Allow me to illustrate a few
examples of the proposed modifications. Traditionally, the process of
producing liquid air involves expanding low-temperature and
high-pressure air using valves. However, we suggest a two-step
expansion method by incorporating a valve in series with a turbine to
enhance the liquefaction rate. To improve efficiency, we suggested
integrating the charging and discharging processes by storing the cold
energy wasted during discharging and the heat wasted during air
compression for charging. Moreover, the heat generated during
compression can be used for electricity generation through a
commercially available heat-to-power cycle, such as the organic
Rankine cycle. These modifications would lead to a greatly efficient
large-scale energy storage system as we have proven using rigorous
process simulation. Further research is being conducted to gather
empirical data in support of this technology. At this crucial stage,
joint ventures and financial support from the government and other
organizations are essential to advance the technology from the
conceptualization phase to the prototype stage, allowing for a
demonstration of its potential capabilities.

Similar research efforts are being carried out by scientists
worldwide, and it is expected that cryogenic energy storage systems
will soon be at par with other technologies in terms of storage
efficiency, giving them a competitive advantage. With India’s diverse
energy sector, there is enormous potential for the country to benefit
from this technology. The next article in this series will delve
deeper into the specific applications and advantages of cryogenic
energy storage in India’s context.

Source: https://energy.economictimes.indiatimes.com/news/power/the-cryogenic-series-how-cryogenic-energy-storage-systems-work/99721802