What is Pumped-storage hydropower (PSH)?

"Pumped storage is a method of keeping water in reserve for peak period power demands by pumping water that has already flowed through the turbines back up a storage pool above the power plant at a time when customer demand for energy is low, such as during the middle of the night."
https://www.usgs.gov/special-topic/water-science-school/science/hydroelectric-power-how-it-works?qt-science_center_objects=0#qt-science_center_objects

"Currently, there is over 90 GW of pumped storage in operation world wide, which is about 3 % of global generation capacity (CPUC, 2010). The main applications of pumped hydro are for energy management, frequency controal and provision of reserve (CPUC, 2010). Pumped storage plants are characterized by long construction times and high capital expenditure."
https://www.ctc-n.org/technologies/pumped-hydroelectric-energy-storage

"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 (discharge) as water moves down through a turbine; this draws power as it pumps water (recharge) to the upper reservoir.

PSH capabilities can be characterized as open loop—where there is an ongoing hydrologic connection to a natural body of water—or closed loop, where the reservoirs are not connected to an outside body of water."
https://www.energy.gov/eere/water/pumped-storage-hydropower

"Pumped-storage hydropower (PSH) is the most developed energy storage technology in the world today. The IEA estimates that PSH installations account for 99% of the energy storage capacity worldwide [24]. In the United States, the PSH fleet consists of 42 plants accounting for 21.6 GW of capacity, or 97% of the total utility-scale electricity storage in the United States at the end of 2015"
https://www.sciencedirect.com/topics/engineering/storage-hydropower

"Pumped storage hydropower is the world's largest battery technology, accounting for over 94 per cent of installed energy storage capacity, well ahead of lithium-ion and other battery types.

IHA estimates that pumped storage hydropower (PSH) projects now store up to 9,000 gigawatt hours (GWh) of electricity globally."
https://www.hydropower.org/resources/factsheets/pumped-storage

Pumped Hydropower
https://energystorage.org/why-energy-storage/technologies/pumped-hydropower/