Gas-based electricity-storage technologies have become more serious in terms of scale and implementation, but this has not settled the most important question: can they provide storage services at a competitive cost when projects are replicated, rather than only when a single demonstration facility is built? Michael Barnard’s analysis examines this question in light of recent projects in China, the United States, and Europe, and concludes that increased scale has not yet demonstrated a comparable improvement in economics.
Larger Projects, but the Evidence Remains Limited
Over the past two years, the sector has seen the commissioning of a 600-megawatt, 2.4-gigawatt-hour compressed-air energy-storage facility in Huai’an, China. The Hydrostor project known as Willow Rock, with a net capacity of 500 megawatts and a capacity of 4,000 megawatt-hours, has also advanced through the approval process in California. In other technologies, Highview Power’s 50-megawatt, 300-megawatt-hour liquid-air energy-storage facility has entered the construction phase, while Energy Dome has developed a 20-megawatt, 200-megawatt-hour carbon-dioxide-based facility in Sardinia.
These projects go far beyond the scope of laboratories and theoretical demonstrations, but they are not sufficient on their own to prove that the industry can scale. Building a huge machine demonstrates engineering feasibility, not that customers will choose the same technology for the second, tenth, or hundredth project.
Thermal and Engineering Complexity Remains at the Core of the Problem
Cheap gas alone is not enough to create a cheap storage system. Compressing gas generates heat, requiring thermal reservoirs, heat exchangers, pipes, and control systems to recover the energy before expansion. Liquid-air storage adds deep-cooling processes, insulated tanks, and heat and cold recovery, along with compressors and expanders.
Using carbon dioxide in Energy Dome’s design represents a significant thermodynamic improvement because it is condensed at temperatures and pressures that are more manageable than those of liquid air. However, this does not eliminate the need for a complete industrial plant that compresses, cools, condenses, and stores the gas, then reheats and expands it.
Efficiency Does Not Give These Technologies a Clear Advantage
Round-trip efficiency in mature pumped-hydropower storage systems starts at around 80%, while global battery-storage-system prices fell in 2025 to approximately one-third of their 2020 levels, according to International Energy Agency data. A critical review published in 2025 generally places the efficiency of standalone liquid-air energy-storage systems at 50% to 60%, with greater improvement when they use external heat or cold.
The California Energy Commission staff assessment of the Willow Rock project estimates round-trip efficiency at approximately 60%. The project requires four trains of compressors and turbines, shared thermal reservoirs, a mined rock cavern, and a 19-mile transmission line. This solution may make sense at sites that lack suitable conditions for pumped hydropower and need eight-hour storage, but it does not turn the technology into an industrial product that can be easily replicated; costs instead shift to excavation, geotechnical work, water management, and site-specific construction.
What Is Actually Changing?
Some projects benefit from specific local conditions, such as using available cold next to liquefied-natural-gas regasification facilities or making use of waste industrial heat. But feasibility in these cases depends on a neighboring site, its operating schedule, and the value of the heat or cold if it were not used for storage. A particular facility may therefore succeed without the technology becoming a general option that can be replicated across different markets.
Claims of long lifetimes face a similar challenge. Energy Dome claims net efficiency above 70%, a lifetime of more than 30 years, and no degradation in capacity or performance. However, the commercial facility has not operated for anything close to thirty years to prove this point. The fact that carbon-dioxide molecules do not chemically decompose does not mean that compressors, turbines, pumps, valves, bearings, seals, heat exchangers, and storage tanks will operate without maintenance or replacement.
From the First Demonstration to a Repeatable Market
Energy Dome’s Sardinia project is receiving support from the European Investment Bank as an initial project to develop utility-scale technology, which is a logical use of innovation funding. But it does not prove that mature projects will be commercially competitive without support.
The analysis emphasizes that the learning curve alone is insufficient to justify expectations of lower costs. Batteries benefit from large-scale manufacturing of cells, modules, and power electronics, while compressed-gas facilities remain tied to land, foundations, pressure vessels, thermal storage, piping, grid connection, and on-site operations. Excavation and underground work also do not automatically become a mass-manufactured product merely because another project is completed.
Editorial reading: The real change is that these technologies have moved from drawings and small prototypes to large demonstration facilities, an engineering advance worth following. But the standard for commercial maturity has not yet been met: projects must be replicated because their economics outperform batteries or pumped hydropower storage, not because a single project could be built. The outcome remains open for specific local applications, while the source provides no evidence of broad-scale competitiveness so far.