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So-called “pumped storage hydropower” is increasingly in the news as private, for-profit companies submit applications to the Federal Energy Regulatory Commission (FERC) in the U.S. to make money in the electric utility market.

Pumped storage tends to seem complicated, but it’s really not. First, we will explain what pumped storage hydropower is, and then explain why we never support it.

What is pumped storage hydropower?

There are generally two types of pumped storage hydropower – 1) Open Loop, and 2) Closed Loop (see Figure 1 below, courtesy U.S. Dept of Energy).

  • Open Loop pumped storage hydropower uses a river or a lake or a reservoir as the lower source of water, and then builds a reservoir on top of a nearby hill or plateau.
  • Closed loop pumped storage does not use an existing river/lake/reservoir, but instead builds both the upper and lower reservoirs independently of local water sources.

Both open loop and closed loop use the same technique to store water and generate electricity. Water is pumped uphill (using electricity) through a penstock or tunnel, then the water is stored in the upper reservoir. To generate electricity, the water is run back downhill in the same penstock or tunnel where that water passes through a powerhouse containing hydroelectric turbines.

Further, in an open loop system, the river/lake/reservoir at the bottom is a constant source of water for the “initial fill” of the upper reservoir as well as the ongoing refilling needed for evaporation that occurs from all reservoirs. In a closed loop system, which does not use a lake/river/reservoir for the lower reservoir, the water for the initial fill and ongoing replacement of evaporated water has to come from local sources. Often, the local source is groundwater, which generally comes from pumping water from beneath the surface of the Earth up into both reservoirs. The amount of water needed for the initial fill and evaporation, and the electricity required for pumping to fill both, completely depends on the size of the reservoirs which determines the size of the hydropower plant and the amount of electricity it can generate.

Pumped storage hydropower projects are increasingly proposed by private companies which are seeking to make money off of the difference in the cost of electricity between when the water is pumped uphill versus when the water runs downhill to generate electricity. For example, at night, electricity rates are often lower because of decreased demand for heating and cooling by people in cities, while rates are higher during the daytime due to increased demand for heating and cooling when people are awake and working in offices or at home. It’s possible that night-time electricity rates could be 4 cents per kilowatt hour (kwh) while daytime rates could be 8 cents/kwh. Thus, most of the projects we see are from private companies that are simply trying to make money off of the difference in those two rates.

Why we never support pumped storage hydropower

First and foremost, we are an environmental river-protection organization, not an electricity supply or a clean energy organization. We only get involved in water projects that either protect and restore, or conversely dam and drain, rivers. Similar to how we don’t engage in debates around nuclear power (unless a river issue is related), or lithium mining for batteries (unless a river issue is related), and wind and solar projects, we don’t engage in pumped storage hydropower debates unless it involves the increased destruction of, or protection of, a river. Because we are a river-protection organization, we never support pumped storage hydropower because it never helps protect or restore a river. Likewise, we only engage in pumped storage hydropower debates and permit processes when the project would further dam and drain a river, during which we oppose it.

Second, all pumped storage hydropower projects consume more electricity than they generate. Note that all pumped storage hydropower projects pump water uphill, store that water in an upper reservoir, and then run the water downhill through a powerplant. Every project, no matter what, uses more electricity to pump the water uphill than is generated when the water runs downhill through the powerplant. Across the spectrum of all pumped storage hydropower projects, they consume about 25% more electricity than they generate[1]. Stated differently, as an electricity storage device, pumped storage hydropower is only ~75% efficient.

As such, pumped storage hydropower drains the grid of electricity, and further, the more pumped storage gets built, the more electricity gets consumed for the purpose of storing electricity. For example, if a solar farm is built and the electricity is stored in a pumped storage facility, the project would automatically consume ~25% of the solar farm’s electricity just by storing it.

As such, pumped storage hydropower is often referred to as a type of “battery” that has energy stored in it (as water on top of a hill) which can be ran downhill to produce electricity. We point out that “pumped storage hydropower” should be thought of as an energy “storage” technology, not as “hydropower electricity generation” technology. Further, it is true that there is a need for energy storage on many grids in the U.S., as storage can help balance increasing amounts of intermittent solar and wind resources.  Pumped storage hydropower (and other forms of storage) is often promoted as this type of battery. However, it’s important to repeat that pumped storage hydropower is not a resource for generating electricity.

Third, members of the public occasionally ask us to help them oppose closed loop pumped storage hydropower projects. In such a case, we take a hard look at the project to see if it has any impact on nearby creeks and rivers. One such example was in Western Colorado where Xcel Energy proposed the Unaweep Canyon Pumped Storage Hydropower Project[2]. After a thorough examination, we determined that the project would have ~zero impact on flows of water in nearby East Creek and the Gunnison River. Although Xcel was proposing to get the water for the initial fill, and ongoing evaporation, from groundwater wells near the river, and it was true that the groundwater depletion could have impacted the river, the water was going to have to be bought from nearby farmers who were already diverting the water out of the Gunnison River. As such, there would be no net impact on flows in the river, and so we neither opposed or supported the project.

Fourth, in open loop systems, a pumped storage project can place increased demands on a river or a reservoir which we could potentially oppose. As one example, a large-scale $4 billion project called the “Navajo Pumped Storage Project”[3] proposes to build a large reservoir on the mesa above Lake Powell near Page, AZ, and use Lake Powell (which was created by damming the Colorado River with Glen Canyon Dam) as the lower reservoir. We oppose this project because the $4 billion of infrastructure would place increased water demands on the Colorado River while also cementing a larger financial commitment to the long-term existence of Lake Powell. Our organization advocates for the decommissioning of Glen Canyon Dam and the draining of Lake Powell, and as such we don’t want to see more infrastructure built the requires the Lake’s existence. We intervened in the FERC permitting process against the project, which is still active.

Additionally as another example, we’ve intervened against the “Big Canyon Project” in which a private company proposes to build an open loop pumped storage hydropower project, including new dam in Big Canyon, on a tributary of the Little Colorado River near the Grand Canyon, plus a new reservoir on top of the nearby mesa. This is a ridiculous project that would irrevocably harm a pristine canyon watershed beside the Grand Canyon and the Little Colorado River. Our intervention against it is still active[4].

Fifth, we are sometimes asked to oppose open loop projects that could have an impact on a river, although we may not actively engage in opposition. One example is the proposed pumped hydropower project utilizing Seminoe Reservoir on the North Platte River, Wyoming[5]. We looked at the project closely, and it does not rise to a level of concern for our organization. The dam and reservoir are already built, and there is zero chance of the dam being removed anytime in the next 50 years. The initial fill and ongoing water use by the project would have a minimal impact on the North Platte River. As such, we would never support such this project, but we won’t oppose it either. That said, other environmental groups may oppose this project due to its negative environmental impact on surrounding landscapes.

Finally, there are many reasons why members of the public and environmental groups oppose pumped storage hydropower projects, both open and closed loop. These projects often have significant impacts to local landscapes, to wildlife habitat and migration, to private property, and to natural and scenic vistas. The Unaweep Canyon Project mentioned above would have large-scale environmental impacts on publicly owned land, on private land, and would have marred a significant natural and recreational resource in the local area. While we did not oppose the project (other environmental groups did) because the project would not impact East Creek or the Gunnison River, we had absolutely no reason to support it.

We encourage river-protection groups to learn more about pumped storage hydropower projects and engage in permitting process against projects when it seems appropriate. We don’t, however, see any reason for a river-protection group to support pumped storage hydropower.







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