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This photo shows a view of the surface structure of salt cavern air storage inside the 300 MW compressed air energy storage station in Yingcheng City, central China's Hubei Province, Jan. 9, 2025. (Xinhua/Pan Zhiwei)

WUHAN, Jan. 9 (Xinhua) -- A compressed air energy storage (CAES) power station utilizing two underground salt caverns in Yingcheng City, central China's Hubei Province, was successfully connected to the grid at full capacity on Thursday, marking the official commencement of commercial operations for the power station.

The project utilizes the caverns of an abandoned salt mine, about 500 meters deep, as its gas storage facility. This approach creates a super "power bank" with a single unit power output of up to 300 MW and a storage capacity of 1,500 MWh. The system conversion efficiency is about 70 percent, according to China Energy Digital Technology Group Co., Ltd., one of the project's major investors.

The single unit power, energy storage capacity and conversion efficiency of this project rank first globally among similar salt cavern CAES power plants, the company said.

This power station can store energy for eight hours and release energy for five hours every day. It generates an annual average of approximately 500 million kilowatt-hours of electricity, which can meet the annual power demand of 750,000 residents, according to the company.

The Institute of Rock and Soil Mechanics (IRSM) of the Chinese Academy of Sciences (CAS) provided technical support for the underground energy storage system of the project.

"We will experience an era of energy transformation in the coming two decades. Large-scale energy storage technology is the key to renewable clean energy becoming a dominant energy source," said Ma Hongling, a researcher with the IRSM.

"However, renewable energy is intermittent and unpredictable. For instance, the annual amount of hydroelectric, wind and solar power generation wasted in 2017 alone exceeded the yearly electricity output of the Three Gorges Hydroelectric Power Station," Ma said.

The construction of salt cavern CAES power plants can effectively address the volatility, intermittency and randomness of renewable energy generation, Ma said.

The principle of CAES in salt caverns is similar to that of conventional pumped storage power plants. During periods of low electricity demand, electrical energy is used to compress air and store it in underground salt caverns. The compressed air can then be released during periods of peak demand to generate electricity, experts explained.

Deep underground gas storage is the key to CAES projects. However, China's most salt mines have a high content of impurities, with sediment occupying significant underground space. For instance, in the case of the Yingcheng project, the geological conditions of its salt cavern gas storage facility are quite complex, said Yang Chunhe, an academician of the Chinese Academy of Engineering and head of a research team with the IRSM.

The research team, collaborating with other companies and organizations, conducted technological research and experiments, continuously optimizing the utilization of salt caverns and the drilling engineering system.

The team has realized gas storage by utilizing the salt cavern sediment voids, significantly enhancing the utilization rate of salt cavern space while reducing project costs and shortening construction periods.

Enhancing the capacity of energy reserves is a significant strategic requirement to ensure China's energy security. With abundant salt mine resources, China has many underground mined-out areas. Utilizing these existing cavities not only mitigates geological hazards such as land subsidence and collapse in the salt mines but also transforms the mined-out areas into valuable underground resources. This achievement of resource utilization effectively turns waste into treasure, Yang said.

The technological research achievement lays a foundation and will provide support for the construction and operation of more salt cavern CAES facilities in China. It will be applied to the CAES power plants currently under construction or planned in provinces including Hunan, Henan, Jiangsu, Jiangxi, Yunnan, Shaanxi and Shandong, with a cumulative power output of 1,950 MW, according to IRSM.

This photo shows a corner of the 300 MW compressed air energy storage station in Yingcheng City, central China's Hubei Province, Dec. 24, 2024. (Xinhua/Xiao Yijiu)

A staff member from the Institute of Rock and Soil Mechanics of the Chinese Academy of Sciences partols at the 300 MW compressed air energy storage station in Yingcheng City, central China's Hubei Province, Dec. 24, 2024. (Xinhua/Xiao Yijiu)