An overlooked technology for
nearly 50 years, the first liquid air energy storage facility is finally set to
power up in 2026. It's hoping to compete with grid-scale lithium batteries and
hydro to store clean power, and reduce the need to fall back on fossil fuels.
As the world's use of renewable electricity soars, surpassing coal for the first
time, the need to store that energy when the Sun isn't shining and
the wind isn't blowing is growing in step. While some turn to grid-scale
lithium batteries and others to pumped hydro, a small but growing industry is
convinced there's a better solution still: batteries that rely on air.
Near the village of Carrington in north-west England, the
foundations are being laid for the world's first commercial-scale liquid air
energy storage facility. The site will eventually become an array of industrial
machinery and a number of large storage tanks, filled with air that has been
compressed and cooled so much it has become a liquid, using renewable energy
surplus to demand. The stored energy can be discharged later when demand
exceeds supply.
If the project succeeds, more will follow. The site's developers Highview Power are confident that liquid air energy storage will make it easier for countries to replace fossil fuels with clean renewable energy – though at present, the technology is expensive. But as the need for clean energy storage surges, they're betting the balance will tip in favour of liquid air.
The intermittency problem
Switching to renewable energy is essential if the world is to cut greenhouse gas emissions and avoid the worst impacts of climate change. But doing so poses challenges for electricity grids.
Power plants that burn fossil fuels like coal and gas can
be turned on and off largely at will, offering a predictable supply of
electricity that can be matched to demand. In contrast, renewables are
intermittent. This means there is sometimes there isn't enough electricity
being generated, risking power cuts, and sometimes there is too much – such as
on very windy days – which could damage the grid.
A big part of the solution is to store the surplus energy
so that it can be released when it's needed. This helps ensure a reliable
supply and minimises the risk of damage to the grid. As renewable use has
ramped up, it has become increasingly important to build up grid-scale storage
capacity, says Shaylin Cetegen, a chemical engineer at the Massachusetts
Institute of Technology (MIT), who studies energy storage systems.
Liquid air demonstration
plants have been built in several countries besides the UK, including here in
Qinghai Province, China (Credit: Getty Images)
For decades, the main form of energy storage
has been pumped hydro. Surplus electricity is used to pump water
uphill, where it sits behind a dam. When energy is needed, the water is allowed
to flow through turbines, generating electricity. In 2021, the world had 160
gigawatts of pumped hydro capacity.
More recently, as demand for energy storage has risen,
large-scale battery storage systems have been built. This is happening quickly,
and accelerating. According to the International Energy Agency, grid-scale
battery storage grew from 1GW in 2013 to over 85GW in 2023, with
over 40GW added in 2023 alone.
The liquid air solution
Liquid
air energy storage, by contrast, is a relatively new technology on
the block. The basic idea has been
around since 1977, but it received little attention until this
century.
The process works in three stages. First, air is taken in
from the surroundings and cleaned. Second, the air is repeatedly compressed
until it is at very high pressure. Third, the air is cooled until it becomes
liquid, using a multi-stream
heat exchanger: a device that includes multiple channels and tubes
carrying substances at different temperatures, allowing heat to be transferred
between them in a controlled way.
"The energy that we're pulling from the grid is
powering this charging process," says Cetegen.
When the grid needs extra energy, the liquid air is put
to work. It is pumped out of storage and evaporated, becoming a gas again. It
is then used to drive turbines, generating electricity for the grid.
Afterwards, the air is released back into the atmosphere.
There are a few neat energy-saving tricks along the way.
For instance, gases under high pressure get hotter, so the processing of compressing
the air generates heat. This heat can be used to help restore the liquid air in
the second half of the process. "Without these thermal recovery cycles,
the efficiency of the process is closer to 50%, but when we implement this, we
can get over 60%, approaching 70% efficiency," says Cetegen.
The challenge is to roll out enough liquid air energy storage to
meaningfully accelerate the green transition.
A grid-scale stop-gap
The new plant at Manchester is the first commercial-scale
endeavour in the world. It's being built by Highview Power, which has been developing
liquid air energy storage for 20 years. It follows a demonstration plant at
nearby Pilsbury. The
Carrington plant will be able to store 300 megawatt-hours of
electricity, enough to plug a short gap in power for as many as 480,000 homes.
It will come online in two stages, says chief executive
officer Richard Butland.
In August 2026, the turbine is set to begin operating.
This will not generate electricity, but will help to stabilise the electricity
grid. At present, says Butland, the grid operators are sometimes turning on
gas-fired power plants to stabilise the grid. "It's a huge cost to the
system," he says. By offering an alternative means of stabilisation,
"we can stop them doing that".
Liquid air energy
storage could be a relatively cheap way to store renewable power to even out
intermittent supply (Credit: Getty Images)
Then in 2027 the liquid air storage is expected to begin
operating. Highview intends to make money by selling electricity to the grid
when it is most needed.
The bottom line
While energy storage is an essential technology, the
economics are challenging, says Cetegen. In a study published in March, she and
her colleagues assessed how feasible liquid air energy
storage would be in 18 regions of the US. They compared eight
different decarbonisation scenarios, with varying uptake of renewables. In all
cases, they estimated how much money a project could make by buying and selling
electricity over a 40-year lifespan.
Under the most aggressive decarbonisation scenario,
liquid air energy storage was viable in Florida and Texas, but nowhere else.
"We didn't observe any economically viable systems under the other
decarbonisation scenarios," says Cetegen.
While this could be naively seen as "a negative
result", says Cetegen, she emphasises it does not mean liquid air energy
storage is a bad idea. For starters, her methods were deliberately
conservative, and her study found other forms of energy storage like pumped hydro
and batteries were even less economically viable. More to the point, the
biggest issue was that storage facilities could not make much money in their
early years, because there weren't enough renewables on the US grid to drive up
price volatility. "The system wasn't getting used a lot in the early years
[of the model]," she says.
Large-scale energy
storage with lithium batteries is one way to store excess renewables, but
liquid air could be cheaper (Credit: Getty Images)
Providers of liquid air energy storage could wait a few
years until renewables drive up price volatility, but doing so would impede the
energy transition, says Cetegen.
Instead, she says governments could support the
technology. In her study, subsidising the initial capital costs to set up the
systems "could be a viable approach to achieve economic viability in the
short term", she says.
Furthermore, faster uptake of renewables would increase
energy price volatility, making energy storage more economically viable.
The plan for global roll-out
Highview Power don't seem concerned. "Manchester
will make very good returns," says Butland.
Two other planned plants by Highview Power, in
Hunterston, Scotland, and Killingholme in Lincolnshire, have been aided by
a UK
government policy called a "cap and floor", which
guarantees the company a minimum return on capital. This gave investors
confidence in those projects, Butland says. However, he adds it shouldn't cost
the government a penny. "They're expecting every project to make more than
the minimum," he says, "so the government doesn't expect to have to
pay out on it".
And the company has plans for two
additional UK plants, plus more in Japan and Australia. These will
be much bigger: while the Carrington plant will store 300MWh, the Scottish one
will be almost 10 times larger, capturing 2.5GWh. While compressors and cooling
machinery are expensive, storage tanks are cheap, so it's easy to scale up.
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Cetegen makes a final point in favour of liquid air energy storage: it's cheap. Energy storage technologies are often assessed using a metric called the "levelised cost of storage", which estimates how much each unit of stored energy costs over the lifespan of the project. For liquid air, this can be as low as $45 (£34) per megawatt-hour – compared to $120 (£89) for pumped hydro and $175 (£130) for lithium-ion batteries.
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"While none of these storage methods are likely
economically viable right now without policy support, liquid air energy storage
stands out as a particularly cost-effective option for large-scale
storage," Cotegen says.
Ultimately, Butland expects electricity grids to rely on
a mix of storage technologies. Pumped hydro is extremely effective and works
for decades, but it's location-dependent because it needs a water supply.
Meanwhile, batteries are highly efficient and can be placed anywhere, but need
to be replaced after about 10 years. Liquid air has the advantage that it can
store energy for longer than batteries, with minimal losses.
As any country enters the green transition, its
electricity grid needs to be remodelled to cope. "We're rebuilding all
grids globally, based on new generation," says Butland. And that could
well mean a lot of liquid air energy storage.
