The world's biggest pumped-storage hydroelectric power plant was put into operation on Dec 30, said its operator State Grid Corp of China, the country's largest State-owned utility company.

The 3.6-gigawatt Fengning pumped storage power station, consisting of 12 reversible pump-turbine units of 300-megawatt capacity each, is located in Hebei province, some 180 kilometers from the nation's capital, host of the 2022 Winter Olympics.

With a designed annual power generation capacity of 6.612 billion kilowatt-hours and annual power pumped-storage capacity of 8.716 billion hours, it also has the largest pumping storage underground plant, State Grid said.

Pumped storage hydropower is the most common type of energy storage in use today. Such plants save excess power by pumping water from a lower to an upper reservoir at night when electricity demand is low and release water to generate power during daytime when demand is high.

Increasing pumped storage hydropower capacity is vital for promoting the green energy transition in China. The country aims to have 62 GW of storage facilities operating by 2025 and 120 GW by 2030, the National Energy Administration said.

The operation of the pumped-storage hydroelectric power plant will be responsible for all Beijing venues of the 2022 Winter Olympics, a move to help fulfill China's green pledge of hosting the games with clean energy, said Xin Baoan, chairman of State Grid.

The Fengning pumped storage facility will operate as a peaking power plant for the safe and stable operation of the Beijing-Tianjin-North Hebei grid while balancing intermittent power supply from large wind and solar parks in northern Hebei and Inner Mongolia, it said.

When operating at full capacity, the plant is capable of storing power generated by renewable energy of up to 40 million kWh, which not only helps ensure the stable and steady operation of the power grid in North China but also pushes forward the clean transition of the country's energy mix, facilitating the country's efforts in realizing carbon peak by 2030 and carbon neutrality by 2060, it said.

State Grid said this is also the first time that a pumped-storage hydroelectric power plant was connected to a flexible DC network.

Wei Hanyang, a power market analyst at research firm BloombergNEF, said as the world's largest power storage unit that can last for 10.8 hours, the Fengning pumped hydro station has a good location to support key regions including Beijing and Tianjin.

This area is also dense with renewable energy, whose intermittence requires a robust output stabilizer, he said.

Construction on the first phase of the project has been underway since May 2013, while phase two started construction in September 2015, the company said.