The Seminoe Pumped Storage project is a planned reservoir-based energy storage project that will be located in Wyoming, the US. The project will be the first pumped hydro storage project in the state.

Currently, the project is in design and permitting phase.

Black Canyon Hydro, a subsidiary of project developer rPlus Hydro, is the licence applicant for the Seminoe Pumped Storage project.

According to the Final License Application, construction works may start in October 2026, after securing the licence and completion of land lease/ purchase agreements.

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Commercial operations are expected to begin in 2031. The cost of construction is estimated to be $2.5bn.

Once complete, the project will with a generating capacity of up to 900MW.

Seminoe Project location and infrastructure

The Seminoe Pumped Storage project will be located in Carbon County, Wyoming.

The site, around 35miles northeast of Rawlins in Wyoming, was selected as it meets all requirements for a pumped storage project.

A typical pumped hydro energy storage project has two water reservoirs at different elevations. Such facilities generate and store electricity by moving water between the two reservoirs.

The Seminoe project will have two such reservoirs, three variable pump-turbine units in an underground powerhouse, groundwater wells and a connection to the existing electric transmission grid.

The project’s facilities will create an ‘open loop’ hydraulic arrangement.

Seminoe Pumped Storage Project details

The existing Seminoe Reservoir, which has a water storage capacity of nearly one million acre-ft, will be used as the lower reservoir for the project.

Key construction works will involve building the above-ground reservoir and a nearly 30-mile transmission line for the project.

The above-ground reservoir will be located in the Bennet Mountains around 1.7 miles east of the Seminoe Dam around 1,000ft higher than the Seminoe Reservoir.

The upper reservoir will be constructed as a roller-compacted concrete (RCC) water-retaining perimeter structure. The crest of the RCC water-retaining structure will be at an elevation 7,455ft.

The two reservoirs will be joined by underground tunnels, while underground powerhouse will host the pump-turbine units to generate power from water flow.

The same equipment in the powerhouse will also pump water from the lower reservoir back to the upper reservoir to restart the cycle.

The machine hall will also have three generator-motors, and unit spherical shut-off valves upstream of the pump-turbines, control room, stores and other systems for the general functioning of the plant.

When the process will start with a full upper reservoir, the plant would be capable of providing full power output for ten hours before recharge.

The project is expected to create up to 500 high-skilled construction jobs over three to five years.  Once operational, the project will employ 35 people in full-time skilled positions.

Power Evacuation

The power generated by the project will be delivered through a new 30-mile transmission line that will connect the project to electric power company PacifiCorp’s existing Aeolus Substation.

Two 500kV circuits from the underground gas insulated switchgear will transfer power through the low-level cable tunnel up the cable shaft to a take-off structure at the surface.

Subsequently, two separate 500kV overhead primary transmission lines will evacuate power to Aeolus Substation, located 30miles to the southeast of the project.

The overhead transmission system will transverse through Bureau of Land Management (BLM) and private lands.

Regulatory process

In April 2020, Black Canyon Hydro filed a Notice of Intent to File License Application, Pre-Application Document (PAD) and Request to Use the Traditional Licensing Process (TLP) with the Federal Energy Regulatory Commission (FERC), the agency for non-federal hydropower projects in the US.

The use of the TLP was approved in June 2020.

Study plans were developed and distributed to stakeholders for comment in March 2021.

According to rPlus Hydro, detailed engineering and environmental studies will continue through approximately 2024.

rPlus Hydro announced the submission of the Draft License Application for the project in June 2022 to Wyoming and Federal agencies.

This was followed by the submission of the Final License Application to the Federal Energy Regulatory Commission (FERC) in January 2023.

Contractors involved

In October 2021, rPlus Hydro selected Stantec to conduct a detailed feasibility study for the Seminoe Pumped Storage project.

The scope of work included identifying the alternative intake and outlet structure types; location and type of upper reservoir to complete the pumped storage scheme.

Stantec also performed a geotechnical investigation to support the feasibility design of the underground facilities, identified pump-generating equipment and transmission line route, assessed project constructability and offered an opinion on probable construction cost.

Engineering company HDR is also serving as a project partner.