【Frontiers in HaiChuan Chemical Technology】The Institute of Engineering Thermophysics, Chinese Academy of Sciences, completed the world’s first experiment with a megawatt-class constant-pressure compressed air energy storage system

Thread Content

Offshore wind power faces a long-standing problem: there is excess electricity when the wind is strong, but not enough electricity when there is no wind. If there were an energy storage system built directly offshore, living side by side with the wind turbines, wouldn’t that perfectly solve this problem? The Institute of Engineering Thermophysics at the Chinese Academy of Sciences has just provided the answer. They carried out the world’s first experiment with a megawatt-class constant-pressure compressed air energy storage system, achieving an efficiency of 88.28% for the centrifugal expander. Frontline Jun noticed that this technology has been applied in a very specific location—underwater. 01 Why “constant pressure underwater”? Let’s first discuss the technical principles of an overlooked energy storage sector. Traditional compressed air energy storage requires a huge volume for gas storage – this can be either abandoned salt caverns or artificially created chambers. In either case, the gas storage pressure will decrease as air is released, causing the expander to deviate from its optimal operating conditions and resulting in reduced efficiency. The approach to underwater constant-pressure compressed air energy storage is completely different. It places the gas storage device underwater, using a constant hydrostatic pressure to achieve constant-pressure energy storage and release. No matter how much air remains inside the cabin, the external water pressure remains constant. This means that the compressor can operate under constant conditions, while the expander always operates within the optimal efficiency range. No need for a base layer; the system structure is simpler, with an energy efficiency of up to 80%. See it? This is not a mere “patchwork” of traditional compressed air energy storage; it is a fundamental reconstruction at the principle level. By the end of 2025, the global cumulative installed capacity for offshore wind power was approximately 89.2 gigawatts, with China ranking first in the world with a cumulative installed capacity of 52 gigawatts. Offshore wind power exhibits typical \"anti-peak\" characteristics – strong winds do not necessarily coincide with peak electricity demand, and there may be no wind during peak demand periods. To ensure the stable grid integration of this green electricity, energy storage is an indispensable component. Underwater constant-pressure compressed air energy storage can form a perfect match with offshore wind power: there is wind at sea and space underwater, so no additional land is required; energy storage and power generation can take place within the same marine area, creating a closed loop. 02 Behind the 88.28%: The “hardcore” configuration of the experimental platform. Now, let’s delve into the technical details of this breakthrough. The R&D team developed China’s first megawatt-class constant-pressure compressed air energy storage experimental platform, which is capable of simulating an environment at a water depth of 700 meters and supporting experimental research on key components as well as the entire system. What can this platform do? Frontline Jun has summarized that there are mainly three levels of breakthroughs: First, verification of dynamic characteristics under all operating conditions. The study revealed the dynamic regulation characteristics of power and rotational speed throughout the entire process, including system startup, steady-state operation, and shutdown. It also accurately described the variations in temperature/pressure at the inlet and outlet of each stage of the expander, the pressure loss in the heat exchanger, and the patterns of temperature/pressure changes within the constant-pressure tank. Second, verification of rapid regulation capability. The experimental system verified the real-time absorption capacity of renewable energy during the energy storage process. During power generation, the expander exhibits minimal vibration; the cold start time is no more than 5 minutes, and shutdown can be completed within 2 minutes. Third, fill research gaps. Previously, there was a severe lack of research on the dynamic characteristics of constant-pressure compressed air energy storage, which remains a key bottleneck for its large-scale engineering applications. This experiment fills the gap in research on the dynamic characteristics of energy release under all operating conditions for megawatt-class constant-pressure compressed air energy storage systems. Frontline Jun summarizes it in one sentence: It’s not just that it was “made,” but that it was also “thoroughly studied.” 03 A broader perspective: Compressed air energy storage is moving toward \"diversification.\" This breakthrough is just a glimpse of the development of compressed air energy storage technology. In February 2026, the Institute of Engineering Thermophysics of the Chinese Academy of Sciences, in collaboration with ESNL, successfully developed the world’s first compressed air energy storage compressor with the highest single-unit power output; it has passed third-party testing. This compressor can achieve a maximum exhaust pressure of 10.1 MPa, a maximum power output of 101 MW, and an efficiency of 88.1%. Its operating range spans from 38.7% to 118.4%, which is at the international leading level. On the ground, the “Nengchu No. 1”, the world’s first 300-megawatt compressed air energy storage power plant built by China Energy Engineering Group in Yingcheng, Hubei Province, has achieved full-capacity power generation and been connected to the Hubei power grid. This super “air battery” charges for 8 hours and discharges for 5 hours each day. Its power conversion efficiency is approximately 70%, and it is designed to generate up to 500 million kWh of electricity per year. Beneath the ground, abandoned salt caverns are being transformed into “power banks”. Thanks to its abundant underground rock salt resources, Yingcheng has salt cavern cavities with a total volume of over 40 million cubic meters. “\"Neng Chu Yi Hao\" makes use of salt caverns located 500 meters underground, with a storage capacity of over 800,000 cubic meters, and employs \"non-reburning\" technology to achieve zero-carbon emissions. Underwater, this breakthrough in efficiency of 88.28% opens up new possibilities for energy storage systems used in offshore wind power. Frontline Jun has noticed a clear trend: compressed air energy storage is shifting from a \"single technical approach\" to a more diversified approach tailored to different applications – there are ways to utilize salt caves for this purpose, ways to use artificial chambers, and ways to apply this technology in underwater environments with constant pressure. Different resource endowments and geographical conditions each have their own optimal solutions. 04 When lithium batteries meet compressed air energy storage: It’s not “substitution” but “complementation”. Finally, let’s discuss a topic that cannot be ignored: the relationship between lithium-based and non-lithium energy storage systems. Over the past few years, lithium-ion battery energy storage has taken a dominant position in the new energy storage market, thanks to its advantages such as rapid response and flexible deployment. However, lithium batteries also have their own “ceiling”—the cost of long-duration energy storage for over 4 hours is relatively high, and there are concerns regarding resource security. The advantages of compressed air energy storage complement each other well: low costs for long-term energy storage, long service life (over 30 years), few resource constraints, and high safety. Underwater constant-pressure compressed air energy storage further addresses the site-selection constraints of traditional compressed air energy storage – it can be implemented wherever there is sea water. Frontline Jun believes that the new power systems of the future will not be \"one technology solving everything.\" Lithium-ion batteries address short-term frequency regulation and intra-day peak shaving; compressed air energy storage meets long-duration energy storage needs spanning multiple days, weeks, or even seasons. Technologies such as sodium batteries and flow batteries fill the gaps in specific application scenarios – this is an era of “combined solutions”. Conclusion: Returning to the initial question: What does an efficiency improvement of 88.28% mean? Frontline Jun believes that the answer lies in three dimensions: First, technically, it has demonstrated that underwater constant-pressure compressed air energy storage already has the experimental foundation for large-scale application. Moving from “can it be done?” to “how can it be done better?”, the research team provided answers based on data. Secondly, in terms of applications, it provides a new pathway for coastal regions to address the issue of integrating offshore wind power into the grid. China’s 52 GW of installed offshore wind capacity requires an energy storage solution that is capable of handling and stabilizing such volumes. Third, in the industrial sector, it enhances the completeness of the technological landscape for compressed air energy storage. From salt caves to artificial chambers, and then to constant-pressure underwater environments, each scenario has its own \"optimal solution\". So the question arises: as lithium-ion energy storage develops side by side with technologies such as compressed air energy storage and sodium-ion energy storage, what kind of \"golden age\" will the regulation resources of new power systems experience?