Underground plant of State Grid Xinyuan Fengning Power Station | Image: State Grid Corporation of China

The Fengning Pumped Storage Power Station, the world’s largest facility of its kind, has commenced full operations with the commissioning of its final variable-speed unit on December 31. Located in Fengning County, Hebei Province, near Beijing and Tianjin, the plant is a key part of China’s renewable energy infrastructure, supporting a nearby 10 GW wind and solar base in nearby Zhangjiakou.

Developed by State Grid Xinyuan Group Co., Ltd., a subsidiary of the State Grid Corporation of China, the project represents a total investment of CNY 19.24 billion ($2.6 billion). Construction began in May 2013 and took more than 11 years to complete. The plant features 12 reversible pump-turbine units, each with a capacity of 300 MW, including two variable-speed units, bringing the total installed capacity to 3.6 GW. It is designed to generate 6.61 TWh annually while consuming 8.71 TWh of electricity for pumping, and it connects to the North China power grid via four 500 kV transmission lines.

Fengning’s advanced design includes an upper reservoir with a capacity of 45.04 million cubic meters and a lower reservoir holding 71.56 million cubic meters. When fully charged, the upper reservoir can store enough energy to power the plant at full capacity for 10.8 hours, equivalent to nearly 40 GWh. This makes Fengning the most significant pumped storage facility in North China in terms of balancing renewable energy output.

One of the plant’s standout features is its underground powerhouse, the largest of its kind globally. The facility spans 414 meters in length, 54.5 meters in height, and 25 meters in width. Additionally, the supporting infrastructure includes 190 underground tunnels stretching over 50 kilometers.

The plant employs cutting-edge variable-speed pump-turbine technology, enabling flexible load adjustments during pumping operations and faster frequency response. These advancements enhance the plant’s ability to manage the intermittency of renewable energy sources like wind and solar. According to the developers, the station integrates its output with a flexible direct current (DC) grid and supports multi-energy complementarity, reducing the impact of fluctuating renewable energy supplies on the broader grid.

China has emerged as a global leader in pumped storage technology, which is the most mature solution for large-scale, long-duration energy storage. By the end of 2024, the State Grid Corporation of China had 40.56 GW of operational pumped storage capacity, with an additional 53.48 GW under construction. As China continues to expand its renewable energy capacity, pumped storage projects like Fengning are expected to play a crucial role in stabilizing the grid and maximizing the use of clean energy.