Pumped storage is an essential solution for grid reliability, providing one of the few large-scale, affordable means of storing and deploying electricity. Pumped storage projects store and generate energy by moving water between two reservoirs at different elevations. Essentially, this low tech concept creates a simple land and water based battery.
This info from Australia explains the concept in detail and elaborates on both new and existing pumped storage projects and their potential to balance out fluctuations between supply and demand.
Source: Pumped Hydro Energy Storage Archives – Australian Renewable Energy Agency
Visit the US National Hydropower Association’s webpage for an overview of the state of pumped hydro here at home. According to the NHA, pumped storage today makes up 97 percent of utility-scale energy storage in the United States.