Earth has an estimated 500,000 suitable sites for closed-loop pumped hydro storage, which can pair well with solar power.

In the United States, 24 pumped hydro storage units are in operation, totaling 18.4 GW of capacity. Most were authorized more than 30 years ago—attesting to the longevity of the technology—as reported by the Federal Energy Regulatory Commission (FERC).

The largest new project proposed in the United States would create 2 GW of closed-loop pumped hydro storage in Arizona. Project owner Big Chino Valley Pumped Storage LLC, which holds a preliminary permit from FERC, is owned by ITC Holdings Corp., the largest independent electricity transmission company in the U.S.—which is itself a division of Fortis. The project has a website.

A project report and update describe a 2,000 MW closed-loop pumped storage hydro facility, with two water reservoirs covering 420 acres, one powerhouse with reversible hydropower turbines, and a daily operational schedule of 10 hours generating and 12 -14 hours pumping. FERC considers a hydro system to be closed-loop if it is not continuously connected to a river.

While the project is not paired with solar power, its arid location and the attractive cost of solar generation in such regions make pairing with solar likely.

The proposed project would be located five miles southeast of Seligman, Arizona, and ITC Holdings is conducting ongoing feasibility and environmental studies. A project timeline shows that a final FERC decision is expected by early 2021; the preliminary permit’s expiration date is November 30, 2020. If approved by FERC, ITC Holdings projects a commercial online date of 2025-2028.

ITC Holdings is considering three potential transmission interconnections:

A 500 kV tie to the Western Area Power Administration at a future Peacock Substation in Mohave County, Arizona A 500 kV tie to Southern California Edison at the Eldorado Substation in Clark County, Nevada A 500 kV tie to Arizona Public Service at the Yavapai Substation in Yavapai County, Arizona.

At times of low electricity demand or high renewable generation, electricity could be used to pump water from the lower to the upper reservoir using reversible turbines. At times of high electricity demand or low renewable generation, water could flow from the upper to the lower reservoir, through the turbines, to generate electricity.

Stakeholder comments on the proposed project have been summarized by ITC Holdings.

FERC says it has recently seen an increase in the number of preliminary permit and license applications filed for pumped storage projects, and has issued licenses for several new projects in recent years.

Editorial note: Thanks to Hans Hyde for this story tip.