In 2023, Wyoming proposed a 972-megawatt renewable-energy battery beneath its mountains, with water pumped to a reservoir 1,000 feet higher. 3 years later, the project reached final federal environmental review, bringing the giant water battery closer

Renewable energy can produce enormous amounts of electricity, but generating power is only part of the challenge. The electricity also has to be available when people and businesses need it, creating a particular problem when strong wind arrives during periods of low demand.

Wyoming is pursuing an unusual answer at Seminoe Reservoir: store electricity by moving water uphill.

The proposed Seminoe Pumped Storage Project would combine an existing reservoir, a new elevated lake and an underground powerhouse. When excess wind electricity is available, the system would use it to pump water roughly 1,000 feet uphill; when demand increases, that stored water would flow back through underground turbines to produce electricity.


The concept is essentially a giant water-based battery. But building it would need major construction in a landscape containing wildlife habitat, pine stands and downstream trout fisheries.

A mountain reservoir with a new role

Seminoe Reservoir lies on the North Platte River in central Wyoming, about 35 miles east of Rawlins. The reservoir was built by the Bureau of Reclamation and forms a significant part of the region’s water management strategy.

The surrounding landscape includes steep granite cliffs and limber pine trees. The proposed energy project would introduce a large new utility installation across around 1,900 acres of federal and privately owned land around the reservoir.

Federal land would fall under the oversight of the Bureau of Land Management, while local conservation boards would monitor soil conditions and animal habitats.

The project would also join a region that already contains overhead transmission lines running through mountain passes to carry electricity to communities farther away.

The new facility is intended to address a different challenge: storing electricity that is generated when the grid does not immediately need it.

Wyoming's wind-power problem

Wyoming has extensive wind generation, generating substantial amounts of electricity from turbines across the state.

The difficulty comes when production and demand do not line up.

Wind can be strongest at night, when commercial and household electricity consumption is comparatively low. When turbines are producing large amounts of electricity but the grid has little demand for it, the surplus has limited immediate value.

Grid operators can reduce turbine output to prevent excess electricity from entering the system. Another option is dumping surplus energy at discounted rates, explained in the supplied material as a serious waste of power and a source of missed revenue.

The Seminoe project would offer another option: store that electricity rather than immediately curtailing or discounting it.

Building a lake above the lake

The project's most unusual physical feature would be its upper reservoir.

Engineers plan to create a new basin in a natural rock depression approximately 1,000 feet above Seminoe Reservoir and around 10,000 feet to the east.

Developing an elevated reservoir in granite needs a complex geological strategy. The upper basin would be connected to a powerhouse within the mountain by subterranean tunnels.

Instead of constructing a conventional hydroelectric station at the shoreline, the proposal would place the generating equipment underground.

Water could therefore travel between the two reservoirs through a hidden network beneath the mountain.

How the water battery would work

The Seminoe Pumped Storage Project is designed around a closed-loop system.

At night, when demand is low, cheap excess wind power will be used to pump water up the mountain into the upper reservoir.

When electricity demand increases in the day, the stored water would travel downhill through underground turbines. The movement of the water would generate electricity, with the project's expected output reaching 972 megawatts.

After passing through the turbines, the water would return to the lower reservoir.

The cycle can then started again.

The system is therefore not intended to consume a new supply of water every time it generates electricity. Instead, the same water would be circulated repeatedly between the two reservoirs.

How much water would it need?

The initial filling of the upper reservoir would require 10,000 acre-feet of water from the existing Seminoe Reservoir.

Once filled, however, most of that water would remain within the closed-loop system. Approximately 300 acre-feet of “makeup” water would be needed annually to replace water lost through evaporation from sun and wind.

That means the project's basic energy-storage process depends on repeatedly moving the same water rather than continually drawing a large fresh supply.

The water is efficiently the medium in which the system stores energy.

Electricity lifts it.

Gravity releases it.

Construction would change the landscape

Although much of the power-generating equipment would be underground, construction would still have a significant physical footprint.

The project would occupy about 1,900 acres of federal and private land. Building the upper reservoir and associated infrastructure would disturb soil and pine stands.

The surrounding area is also used by wildlife.

The proposed installation would require it to operate in a landscape containing pronghorn herds, wintering elk and nesting raptors. Downstream trout fisheries add another environmental consideration.

Federal environmental reviews therefore analyzed the potential impact on the wildlife against the physical requirements of the proposed energy project.

The objective is to carry out the construction while causing the absolute minimum disturbance to the surrounding environment.

Protecting wildlife corridors

The project's environmental requirements extend beyond the immediate construction site.

Federal licensing from the Federal Energy Regulatory Commission includes mandatory mitigation measures intended to protect the movement of big game through long-established migration corridors.

Those measures are important because wildlife in the region depends on established movement routes.

Construction also has to account for nearby trout streams and downstream fisheries. According to the supplied material, those resources would have to be protected before workers are allowed to break ground.

The environmental review consequently becomes a balancing exercise between the proposed energy system and the landscape in which it would be built.

A four- to five-year construction effort

The project would not be a quick installation.

The supplied project information estimates that construction would take between four and five years. During that period, workers would have to develop the elevated reservoir, underground facilities and supporting infrastructure.

Soil and pine stands would be disturbed as construction progresses.

The challenge is particularly unusual because the facility requires both substantial excavation and a carefully engineered upper basin. The new reservoir has to hold enough water to support the energy-storage cycle while remaining connected to the underground powerhouse below.

Why the 24-hour cycle matters

The project's repeated daily cycle is directly connected to Wyoming's electricity pattern.

At night, wind generation can remain strong while electricity consumption falls. That creates surplus electricity at precisely the time when demand is weakest.

Instead of enabling that energy to go unused, the proposed system would direct it toward the pumps.

The pumps would raise water into the upper reservoir.

During periods of higher daytime demand, gravity would reverse the process. Water would descend through the turbines and produce electricity.

The system therefore moves energy from one part of the day to another.

It does not create energy from nothing. It stores energy that is already available and makes it accessible later.

A giant battery made from water

The Seminoe concept features a different way of thinking about renewable-energy storage.

A conventional battery stores electricity through chemical reactions. This project would store it by lifting a large quantity of water against gravity.

The upper reservoir would represent stored energy.

The underground turbines would release that energy when electricity is needed.

The lower Seminoe Reservoir would then receive the water and complete the cycle.

That arrangement allows the project to function as a giant closed-loop battery while reducing ongoing water consumption.

The environmental trade-off

The proposal ultimately comes down to a difficult question.

How much environmental disturbance is acceptable when building infrastructure intended to make renewable electricity more useful?

The Seminoe project would provide a way to store surplus wind power, potentially allowing electricity produced at night to be used later when demand is higher.

At the same time, construction would alter a large area, disturb soil and pine stands, and require careful consideration of wildlife and aquatic resources.

The project's environmental review therefore has to regard both sides of the equation.

The benefit is an energy-storage system capable of producing 972 megawatts when needed.

The cost is the physical infrastructure required to build that system in a mountain landscape.

From surplus wind to stored water

The underlying oncept is simple even though the engineering is complex.

When electricity is plentiful, pumps use some of that power to move water uphill.

The water waits in the elevated reservoir.

When electricity demand rises, the water comes back down.

Underground turbines convert its movement into electricity.

Then the water returns to the lower reservoir and can begin the journey again.

At Seminoe, that cycle would connect Wyoming's wind resources with a form of large-scale energy storage.

The proposed project would place a new lake approximately 1,000 feet above the existing reservoir and connect the two through underground infrastructure.

It would turn elevation into stored energy.

And it would attempt to solve a modern grid problem using one of the oldest forces available: gravity.

For Wyoming, the challenge is not simply building a hydroelectric facility. It is creating a large energy-storage system while limiting the consequences for the wildlife, vegetation and waterways surrounding it.

That balance will determine whether the proposed water battery can move from an ambitious engineering plan to a working part of the state's renewable-energy infrastructure.

Source: THE PULSE

FAQs:

Q1. What is the Seminoe Pumped Storage Project?

It is a proposed energy-storage project in Wyoming that would use two reservoirs at different elevations. Water would move between them to store and generate electricity.

Q2. Where would the project be located?

The project is planned at Seminoe Reservoir in central Wyoming. The site is about 35 miles east of Rawlins.