Use of underground formations for cost-competitive compressed air energy storage systems, image courtesy of Pacific Northwest National Laboratory.

New Energy Storage Systems From Thin (Compressed) Air Can Compete With Li-Ion Batteries

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Compressed air energy storage systems were practically non-existent just a few years ago. Now energy planners are beginning to take notice, attracted by the ability of compressed air to provide the kind of scaled-up, long duration storage capacity needed for a global economy saturated with wind and solar energy. The sticky wicket is cost, but a new analysis indicates that issue has already begun to fade from view.

Compressed Air Energy Storage Competes With Lithium-Ion Batteries, Says BNEF

Lithium-ion batteries have been doing the hero’s work of energy storage, as grid planners seek to balance electricity supply with demand while intermittent resources — namely, wind turbines and solar panels — replace fossil power plants.

So far so good, but Li-ion batteries face supply chain issues and technology limitations, motivating energy storage innovators to seek alternatives. The US Department of Energy, for one, has set a goal of at least 10 hours of storage for long duration system, with full days, weeks, or whole seasons as additional targets (see more long duration storage news here).

Innovations in the long duration storage field have been coming thick and fast, but cost has been a stumbling block. Among other issues, long duration systems are case-specific, which suppresses opportunities to cut supply chain costs. In contrast, Li-ion batteries are widely used in electric vehicles and other applications, in addition to stationary energy storage.

Well, that was then. Last week, BloombergNEF presented its first-ever comparative capex (capital expenditure) analysis of long duration storage systems that hit the mark of 8 hours or more, against 4-hour Li-ion battery arrays.

BNEF came up with an average capex of $293 per kilowatt-hour for compressed air, compared to $304 for Li-ion arrays in the 4-hour category.

Don’t get too excited just yet. No single storage solution can be applied universally, so BNEF is not suggesting that fans of Li-ion technology should pack up and go home. Still, the analysis does indicate that cost-competitive alternatives are beginning to emerge.

The BNEF analysis covers six other technologies in addition to compressed air. That includes thermal energy storage systems of 8 hours or more, which outpaced both compressed air and Li-ion with a capex of $232 per kilowatt-hour.

Compressed Air Vs. Fossil Energy, Salt Cavern Edition

We’ll get to those other technologies in another post, but for now let’s focus on the emerging compressed air storage industry because it could go head-to-head with fossil energy in the matter of access to underground storage sites for natural gas.

In particular, underground salt domes are commonly used around the world for storing large quantities of natural gas and oil. The cost savings is considerable compared to storing fossil energy in hard-rock mines or above-ground tanks, partly due to the natural sealing qualities of salt.

Salt dome failure is rare, but it can still happen. In particular, the rush to develop new LNG (liquid natural gas) facilities in Louisiana has put a spotlight on the underground storage issue, with signs of leakage spotted at salt dome facility in Calcasieu Parish last fall.

Compressed air energy storage could provide a competing use for salt caverns without the environmental baggage.  The global chemical firm Solvay, for example, is already laying plans for salt cavern compressed air storage in Germany.

The Ireland-listed, Netherlands-headquartered firm Corre Energy is also dipping a toe in US market, having acquired a compressed air energy storage sight leveraging three salt caverns in Texas.

Then there’s the Canadian firm Hydrostor, which deploys water as a weight to balance the pressure in underground rock formations. On May 30, the company announced the formation of a new US headquarters in Colorado, upping the ante on its commitment to the long duration energy storage field.

Other Options For Compressed Air

Underground caverns may the the least costly option for compressed air storage. However, they are geo-specific. Storage innovators have also been scouting for cost-competitive alternatives that open up new sites.

Storing compressed air in above-ground tanks is not a new thing. The issue is scale-up and cost. One solution that recently surfaced on the CleanTechnica radar is a tank-based storage system developed by the Israeli startup BaroMar. As a cost-cutting measure, the tanks are submerged in the ocean to offset the internal pressure.

A different approach to compression-based technology is represented by the Italian startup Energy Dome. Instead of leveraging plain air, Energy Dome deploys a closed loop carbon dioxide system in an above-ground facility that looks like an oversized Quonset Hut.

More Than One Energy Storage Option For Air

Both compressed air and fossil energy stakeholders will have to compete with green hydrogen for underground storage space, so it will be interesting to see how that shakes out in relation to above-ground and ocean-based systems.

In the meantime, researchers have also been exploring ways to deploy the buoyancy of air-filled objects in water as a platform for energy storage.

Back in 2022 CleanTechnica took note of a pumped hydropower energy storage system designed to be deployed in the ocean. A similar (but different) approach applies to buoyancy.

The buoyancy idea is a perfect fit for offshore wind turbines. At night or during other periods when excess wind energy is available, a spool-tethered, air-filled buoy is pushed below the surface. When electricity demand rises, the buoy is allowed to rise towards the surface.

A research team in the United Arab Emirates is among those exploring buoyancy based systems. They reported an initial study in 2022. Earlier this year they followed up with some additional refinements under the title, “Performance assessment of buoyancy work energy storage system with various buoy materials, coatings, and gasses” in the Journal of Energy Storage.

“Buoyancy energy storage system is a type of mechanical energy storage system that utilizes the density difference between a fluid and an immersed body to store energy,” they explained. “Buoyancy force is produced when a body is submerged in a fluid, and its magnitude is dependent on the immersion volume.”

“The buoyancy energy storage system offers various advantages, including its simple design, high energy density, and high efficiency, especially for large-scale offshore system such as maritime wind turbine arrays,” the research team observes.

That sounds simple enough, though the devil is in the details.

In an interesting twist, the researchers also suggest that an offshore buoyancy energy storage system could be deployed to compress green hydrogen produced at offshore wind sites, so stay tuned for more on that.

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Image (cropped): Use of underground formations for cost-competitive compressed air energy storage systems, courtesy of Pacific Northwest National Laboratory.


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Tina Casey

Tina specializes in advanced energy technology, military sustainability, emerging materials, biofuels, ESG and related policy and political matters. Views expressed are her own. Follow her on LinkedIn, Threads, or Bluesky.

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