Pumped storage could help firm wind generation in Wyoming.Pumped storage could help firm wind generation in Wyoming.

Developer Gridflex Energy LLC is proposing to build up to 700 megawatts of pumped hydroelectric energy storage for a site near the proposed Transwest Express DC line in Wyoming.

Seminoe Pumped Storage, which could be developed in phases of 400 and 300 MW each, would pair new upper reservoirs with Seminoe Reservoir as the lower reservoir to create an energy storage plant that could be matched to Wyoming's wind energy resource.

The project site is 30 miles from both the planned origin terminal of the Transwest Express DC line and Rocky Mountain Power's Aeolus substation. If built, Transwest Express would deliver up to 3,000 MW of wind energy from the Chokecherry and Sierra Madre projects.

Gridflex says it has been considering the Seminoe site for a number of years. It says the timing for advancing the Seminoe Pumped Storage may be improved due to market interest in Wyoming wind and progress in new transmission to western markets.

Gridflex says that Seminoe Pumped Storage could help to create a more reliable resource and create savings on new transmission through more efficient use. Pairing Wyoming wind with Seminoe Pumped Storage could also help utilities in the region such as Pacificorp reduce their reliance on coal.

Gridflex says that Seminoe Pumped Storage ranked high in Pacificorp's 2017 Integrated Resource Plan when compared with other regional pumped storage options. Project value is estimated at approximately $1.6 billion for full build-out of the project, which Gridflex says could be online by 2026.