IEEE Electrification - December 2021 - 84

VIEWPOINT
Scaling up to Long-Duration
Storage
By Eric Hsieh
T
ODAY'S LITHIUM (LI)based
battery has ushered
in an era of cost-effective,
gigawatt-hour-scale storage resources.
However, the future of Li as the dominant
or even preferred technology is
uncertain. History is replete with
examples of pioneering technologies
being displaced by subsequent innovations,
including lighting, computation,
and power generation. Given the
fundamental properties of candidate
technologies and target markets, this
article identifies a diverse technology
portfolio as the most likely future for
the storage industry.
The Winding Path of
Large-Scale Storage
Pumped storage was the first megawatt-scale
storage technology on the
early U.S. grid, with a 31-MW plant in
Connecticut that began operations
between 1928 and 1930. The combination
of high efficiency and low cost
allowed the technology to become
widespread in a few decades. Of the
21.9-GW, operational pumped-storage
capacity today, 14.5 GW, or roughly twothirds,
was built between 1960 and
1980. Today, pumped storage still occupies
the top of the charts in all storagedeployment
metrics, except for growth.
Before turning to the new fastest-growing
storage technology, it's
Digital Object Identifier 10.1109/MELE.2021.3115546
Date of current version: 1 December 2021
84
worth examining the other technologies
encountered on the storageadoption
path. Sodium sulfide
(Na2S) and lead acid were examples
of early second-generation pioneers.
Some selected initial projects demonstrated
the technology's feasibility,
such as the 20-MW, 14-MWh
lead-acid battery installed in 1994
by the Puerto Rico Electric Power
Authority. An early Na2S battery was
installed by American Electric Power
(AEP) Ohio in 2002. However, the
maintenance or operations requirements
of these battery technologies
relegated further deployments to
niche applications.
The AEP site also tested a flywheel-based
storage system. Subsequent
demonstrations showed that
flywheels were particularly suited to
short-duration, high-power applications,
like frequency regulation. With
the potential for a full charge-discharge
cycle every hour, a storage
resource providing frequency regulation
might have to undergo thousands
of cycles every year. The
accurate performance and long lifetime
indicated a potentially viable
commercial business case for flywheels.
The test results convinced
regional markets and federal regulators
to revise compensation rules in
such a way that would recognize the
incremental value of fast-responding
devices, like flywheels and batteries.
Unfortunately for champions of
IEEE Electrification Magazine / DECEMBER 2021
flywheels, a lower-cost competitor
was already on deck.
In many ways, Li-ion batteries
were the beneficiaries of doubly
lucky timing. Although flywheels
were demonstrating how new storage
technologies could provide grid
benefits, Li-battery manufacturing
benefited from investments in electric
vehicle manufacturing. With cost
reductions exceeding analyst projections
every year, Li-based energy
storage systems quickly displaced
flywheels as the least-expensive
technology for frequency regulation,
even after accounting for the longer
lifetimes of flywheels. As Li-ion prices
continued their nearly 90% price
decline through the 2010s, the technology
not only displaced other storage
technologies but also began to
displace peaking and midmerit thermal
units. According to IHS Markit
(formerly known as Information Handling
Services), the United States saw
1.7 GW and 3.8 GWh of new battery
storage capacity installed in 2020. Of
this amount, all but 30 MWh were Li
ion. The expectations for 2021 installations
exceed 5 GW and 14 GWh,
with more than 99% based on Li.
Given the overwhelming market
share of Li-ion batteries, a keen
observer may ask how long this
dominance may endure. Supplychain
constraints and underlying
(continued on page 78)
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