Most powerful pumped hydroelectric energy storage station

The most powerful pumped storage station is the Fengning Pumped Storage Power Plant, located in Hebei Province, China. This facility, which was commissioned by the State Grid Corporation of China, has an installed capacity of 3,600 megawatts. It was completed on 30 December 2021.

Pumped storage power stations are used to balance electrical grids when there's a mismatch of supply and demand. The amount of electricity we use varies over the course of a typical day, rising to a peak in the evening before dropping to a very low level at night. Most methods of generating electricity, however, deliver power at a steady rate, making it difficult for grid operators to balance these pressures. This is particularly problematic for grids with lots of renewable sources – such as wind and solar – which generate power in a cyclical and often unpredictable way.

A pumped storage power station works by pumping water from a low-altitude reservoir to a high-altitude reservoir during periods when there's more supply than demand, and then letting the water flow back down through hydropower turbines when there's more demand than supply. It's essentially a gigantic, gravity-based battery. A lot of energy is lost in the process (it takes more power to pump water up than is released by letting it flow back down), but it's worth it as the energy would have been wasted anyway.

Fengning is connected to the Beijing-Tianjin-North Hebei grid, which connects some of the most densely populated and economically active regions of China with the massive solar and wind farms in the northern desert. The upper reservoir holds 40.61 million cubic metres of water 440 m (1,440 ft) above the lower reservoir. Releasing the entire contents of the upper reservoir would feed 40,000 megawatt-hours of power into the grid. Over the course of year, with regular cycles of filling and emptying, the facility is designed to take 8,716 gigawatt-hours of unused generating capacity out of the grid and feed 6,612 gigawatt hours of electricity back into the grid at times when it's needed.