Key Findings
China Huadian has completed the first grid connection of a 100 MW/1,000 MWh compressed CO2 energy storage plant on September 30. Located in the Gobi Desert of Changji Prefecture, Mulei County, the facility is integrated with a renewable energy hub consisting of 600 MW of wind and 400 MW of solar capacity. Once fully operational, the plant is expected to generate approximately 200 GWh annually, potentially reducing standard coal consumption by 50,000 metric tons and CO2 emissions by 170,000 metric tons per year.
Technical Details
The plant occupies 565,000 square meters and utilizes a closed thermodynamic cycle with CO2 as the working fluid. The infrastructure includes five gas storage enclosures, 141 liquid CO2 storage units, and 97 thermal storage units, providing a nominal discharge duration of 10 hours. The process operates as follows:
- Charging: Surplus electricity powers compressors to pressurize gaseous CO2. Generated heat is recovered and stored, while the gas is cooled and liquefied for storage in pressure vessels.
- Discharging: Liquid CO2 is evaporated, reheated using stored thermal energy, and expanded through a turbine to generate electricity.
The CO2 turbine features a design efficiency exceeding 92%. The system is designed for a 30-year operational life, supporting over 20,000 start-stop cycles with a startup-to-full-load time of under 20 minutes. However, system-level round-trip efficiency and levelized storage costs have not been disclosed.
Background and Context
The technology was developed by Professor Xie Yonghui’s team at Xi’an Jiaotong University and commercialized by Exax Energy (Bairang New Energy), with Dongfang Electric serving as the EPC contractor. This 100 MW project follows smaller Chinese demonstrations, including a 10 MW/20 MWh system in 2022 and a 10 MW/80 MWh plant in Anhui province in December 2023. Internationally, Italy’s Energy Dome has deployed a similar 20 MW/200 MWh facility in Sardinia.
Significance and Outlook
By using CO2, which liquefies at moderate pressures, the system allows for more compact storage than conventional compressed air energy storage (CAES) and eliminates the requirement for underground salt caverns. While it still requires significant above-ground infrastructure and specialized turbomachinery, the Mulei project demonstrates the engineering integration of this technology at a utility scale.
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