The fifth unit of the Changlongshan pumped storage hydropower station in east China's Zhejiang Province passed its 15-day tests and started operation on May 4, according to China Three Gorges Corporation (CTGC).

Unit 5 of the pumped power station has a rated capacity of 350,000 kilowatts (kW), or 350 milliwatts (mW), and a rated speed of 600 revolutions per minute – the world's fastest of its kind.

The station has six pumped storage power units designed and installed in the plant, with a total rate capacity of 2100 mW that can generate nearly 2.5 billion kilowatt hours (kWh) of electricity each year. 

Pumped storage hydropower (PSH) is a type of hydroelectric energy storage. It is a configuration of two water reservoirs at different elevations that can generate power as water moves down through a turbine from one to the other. 

The fact that it also requires power to pump water back into the upper reservoir means a PSH functions like a giant battery as it can store power and then release it when needed.

The Changlongshan PSH has generated 1.3 billion kWh of electricity for the national grid during peak period and used 1.7 billion kWh of electricity to "recharge" during the off season since entering operation on June 25, 2021.

The station further helps to improve the regulation capacity of east China's power grid, optimize the power supply structure and promote the development of clean energy, the company said.

China's PSH has reached a rated capacity of 32,490,000 kW as of 2021, with the majority of stations operated under the State Grid Corporation of China and China Southern Power Grid Company. 

The country aims to add enough new PSH plants to more than double its current PSH capacity during the 14th Five Year Plan from 2021 to 2025.

The final power unit of the Changlongshan station is undergoing final adjustments and is expected to become operational by May 15. The station will then be in full operation by the end of June.