Seneca, Pennsylvania, CLUI photo

CLUI photo

OFF-STREAM: On the Trail of Pumped Storage

Deep in the hills across the country are massive reservoirs of potential energy—pumped storage hydropower. Water is lifted hundreds of feet up by the largest pumps in the land into isolated off-stream holding ponds, only to have it fall back down, a few hours later, day after day. Spending energy to make energy, and leveling out the supply and demand of the grid.

In pumped storage hydroelectric plants, the turbines that generate electricity from water flowing into them can be reversed to function as pumps, lifting the water back up to the reservoir. Pumping water up typically occurs at night, when demand for power is low, while generating power occurs during the day, when demand is greater. Of course this consumes more energy than it produces, but since energy is more valuable when it is in higher demand during the day, the costs can be offset.

Pumped storage was developed starting in the 1960s, as a way to capture the excess energy produced by other types of large-scale power plants, especially nuclear power plants, being built around the nation, and to serve as back up energy sources, in case a major plant suddenly shut down. There are now around 40 pumped storage hydroelectric facilities around the nation, 25 or so of which have an isolated “off-stream” upper storage reservoir.

Though there hasn’t been a major pumped storage project built in the USA since 1995, there are currently several dozen proposals being considered to build more, spurred on by the shift to intermittent renewable energy sources like solar and wind, which need to store energy on a large scale, even for a few hours, when the sun sets, and the wind stops blowing. Pumped storage projects tend to be large and expensive to construct though, and few of these proposals have passed the permit process, so far.
In the meantime, these few dozen pumped storage facilities, many of which have been around for half a century, constitute 95% of the storage capacity of the electrical grid, nationwide. They continue to operate, in the background, like infrastructural leviathans, breathing in and out.

2022 CLUI Research Project


Visiting Pumped Storage Across the USA
Visiting pumped storage sites is like going on a safari to see immobile land beasts in their native habitat. The genre is monolithic and simple, and in a way uniform and redundant. However each site is unique, and expressive, in its way.

The earliest pumped storage facilities in the country, as well as some of the largest, can be found in the northeastern states. Some are owned by private utility companies, others by the New York State Power Authority.

The largest pumped storage plant in the nation is in the south, as are a number of other major pumped storage projects connected to wide regional hydrological projects, like the Tennessee Valley Authority.

Pumped storage projects are scattered across the country, from New Jersey to Colorado, wherever politics and resources converged to permit them. Some are isolated, and others are part of larger regional water projects, but all are part of the national grid. 

California is the most hydraulically transformed state in the country, with large-scale waterworks moving water from one end of the state to the other. It’s not surprising then, that within this engineered statewide water network is the most pumped storage capacity in the USA.