Page 64 - Energize March 2022

TECHNICAL

Liquified air electricity storage

The growing need for bulk electricity storage has resulted in the development of several

advanced storage systems. Bulk energy storage is usually used to store “surplus” electricity,
available either during periods of reduced demand or more recently, overproduction by
renewable energy systems.

ENERGIZE STAFF WRITER

tored energy can then be used to translates to significantly lower storage volumes (in the order of 700 times smaller) and
balance production and demand, thus offers higher flexibility. 1
Sduring increased demand and
underproduction periods. Very large Principle of operation
storage systems are required to The system works by compressing and liquefying air, storing the air at a low (cryogenic)
achieve this. temperature, and then using ambient heat – or other heat source – to expand the air in a
turbine-based electricity generator.
Types of storage The LAES system decouples the liquefaction and expansion cycles of the air into two
In addition to chemical storage, there separate processes. Separating the compression, storage and expansion components
are systems which use gravity and allows a disconnect between the power rating and the energy storage capacity and allows
gaseous pressure as storage mediums. a flexible difference in storage and discharge rates.
Pumped water storage is a well-known Figure 1 shows the basic components of a LAES
and well-developed technology, while
compressed air energy storage and gas LAES involves three core processes
storage in caverns is used at several • Charging the system: The charging system is an air liquefier, which consists of a
sites around the world. Both of these multistage compressor with cooling between the stages. The electrical energy which
however, need suitable geographic is to be stored is used to draw air from the surrounding environment, clean it and
features and involve large plant and long then compress and cool the air to sub-zero temperatures until it liquefies (-195°C
construction times. at atmospheric pressure). Seven hundred litres of ambient air produces one litre of
The recent development of small, liquid air.
compressed air storage systems (CAES), • Energy storage: Liquid air is stored in an insulated tank at low pressure, and this
which can be located anywhere, has functions as the energy store. Cryogenic gas storage is globally deployed for bulk storage
found application, but are limited in of liquid nitrogen, oxygen and natural gas. The storage tanks used within industry have
capacity. the potential to hold many GWh of stored energy.

New development
A new development sees the use of
liquefied air as a storage medium,
which takes the compressed air storage
concept to a new level. Liquid air
energy storage (LAES), also referred to
as cryogenic energy storage (CES), is a
long duration, large-scale energy storage
technology which can be located at the
point of demand. The working fluid is
liquefied air or liquid nitrogen (about
78% of air).
The storage of energy in liquid form
(rather than as a high-pressure gas as in
CAES systems) results in a higher energy
density for liquid air systems, and Figure 1: Basic liquid air electricity storage system (O’Callagan )
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