China’s superpower bank: World’s largest hybrid pumped hydro plant

High on the Western Sichuan plateau, construction crews have completed excavation of the underground “power heart” of what is set to become the world’s largest hybrid pumped hydro storage facility — a project designed to anchor China’s rapidly expanding renewable energy capacity.

The milestone was reached at the Lianghekou Dam site, where the hybrid pumped storage project is being built at an elevation of 3,000 metres. According to media reports, excavation of the underground powerhouse has now been completed, while construction of the downstream reservoir has also begun, Interesting Engineering writes.

As renewable energy generation from wind and solar plants continues to grow, countries are intensifying efforts to develop efficient storage systems capable of holding surplus electricity produced during periods of low demand. While lithium-ion batteries offer high energy density, their large-scale deployment remains costly, prompting exploration of alternative technologies.

Pumped hydro storage has increasingly emerged as a preferred solution.

Why pumped hydro storage works

Pumped hydro storage converts excess renewable energy into potential energy by pumping water from a lower reservoir to a higher one. When demand rises, water is released back downhill through turbines to generate electricity.

Unlike conventional hydropower plants — where water flows only in one direction and generation can halt during periods of scarcity — pumped hydro systems are designed for reuse. Water is cycled between reservoirs, allowing year-round operation and enabling facilities to act like large-scale batteries that can be charged and discharged as needed.

However, such projects require years of planning and complex construction before they become operational.

World’s largest hybrid system

The Lianghekou hybrid pumped storage facility will consist of four 300-megawatt units. It integrates with the existing Lianghekou Reservoir, which hosts a conventional hydropower plant and will serve as the upper reservoir for the pumped storage system.

The lower reservoir is being constructed near the Yagen Level-1 Hydropower Station.

At the core of the project is the underground powerhouse — referred to as the “power heart” — built nearly 500 metres beneath the mountain. The cavernous structure stretches roughly 200 metres in length and nearly 60 metres  in height, with a burial depth exceeding 650 metres.

Over the weekend, excavation of this underground powerhouse was completed, while concrete pouring for the lower reservoir began.

Once operational, the pumped hydro facility combined with the conventional 3,000 MW Lianghekou hydropower project will deliver a total capacity of 4.2 gigawatts, making it the world’s largest hybrid pumped hydro storage system. The integrated setup will allow the site to provide both runoff and bidirectional power generation.

Designed to absorb green energy from 7 GW of renewable energy plants being developed on the plateau, the facility is expected to serve as a “super power bank” for the region.

By Sabina Mammadli