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rPlus Hydro is seeking approval to develop a 900 MW pumped storage project to address energy storage needs in the western U.S.

The Seminoe Pumped Storage Project would about 30 miles outside Rawlins, Wyoming. It would be the state’s first pumped hydro storage project. Construction costs are estimated at $2.5 billion.

rPlus Hydro submitted a license application to state and federal authorities, it said June 6. The application opens a multi-year study and approval process which includes engineering designs, environmental assessments and community engagement.

After a 90-day review, rPlus Hydro would then submit a final license application to the Federal Energy Regulatory Commission (FERC). That submission would include additional data collection, impact analysis and opportunities for public input.

The proposed project could include one new reservoir, underground tunnels and underground powerhouse, an intake-outlet structure in the Seminoe Reservoir, and a new transmission line. The reservoir will be located some 1,000 feet above the Seminoe Reservoir, and around two miles east of the Seminoe Dam.

Energy for pumping, and power generated by the project, would be delivered through a 30-mile transmission line connecting with PacifiCorp’s existing Aeolus Substation near Medicine Bow. 

Construction could be underway as early as 2025, pending FERC and other approvals, and would take approximately four years. 

In October 2021 our partner publication Hydro Review reported that rPlus Hydro chose the engineering firm Stantec to conduct a detailed feasibility study for the Seminoe project.

Stantec would identify and analyze the alternative intake and outlet structure types and identify the location and type of upper reservoir to complete the pumped storage scheme.

Additionally, the firm would plan and perform a geotechnical investigation to support the feasibility design of the underground facilities, identify pump-generating equipment, identify routing for a transmission line to a nearby grid interconnection, evaluate project constructability, and provide an opinion on probable construction cost.

Pumped storage is currently the largest form of energy storage on the U.S. grid today, accounting for about 95% of the country’s utility-scale energy storage capacity.

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