The Missouri Basin Municipal Power Agency d/b/a Missouri River Energy Services applied Dec. 1 to FERC for a preliminary permit, good for up to three years of feasibility work on the 1,200-MW Gregory County Pump Storage Project in South Dakota.
This is an open loop pump storage project. The upper reservoir will cover approximately 1,200 acres and be constructed by an earthen embankment levee with an average height of 62 feet. The reservoir will receive water pumped from the existing Lake Francis Case reservoir created on the Missouri River by the Ft. Randall Dam.
Water will be pumped to the upper reservoir by a reversible Francis turbine-pump unit connected to a reversible synchronous generator-motor located in an underground powerhouse that is connected to Lake Francis Case through an underground tailrace tunnel. There will be a total of eight units in the underground powerhouse. Four units will share a common penstock approximately 6,000 feet long. The penstock will be constructed of reinforced concrete. There will be a total of two penstocks constructed. One tailrace tunnel located downstream of the powerhouse is expected to be approximately 6,000 feet long. The tunnel will have a horse-shoe configuration and have an approximate area of 3,500 square feet.
Each unit will generate 150 MW during the turbine mode and consume 200 MW during the pumping mode. The total plant rating will be 1,200 MW.
The proposed new transmission line will be approximately 21 miles long and will extend from a substation located aboveground near or over the underground powerhouse, cross the Missouri River, and be routed to the existing Lake Platte substation. The substation above the underground powerhouse will increase the voltage from 13.8 kV to 345 kV.
The proposed equipment will be a reversible Francis turbine-pump unit connected to a reversible synchronous generator-motor. The design flow for the Francis turbine-pump unit is 2,925 cubic feet per second (cfs) per unit, and a total plant design flow of 23,400 cfs. The design head for the units will be between 700 to 742 feet depending upon the water level of the upper reservoir. Each unit will generate 150 MW during the turbine mode and consume 200 MW during the pumping mode. There will be a total of eight units operating in the turbine mode and six units operating in the pump mode at any one time to yield a total facility rating of 1,200 MW.
It is anticipated with the upper reservoir will be able to sustain enough water flow downhill for 26 hours of operation at 1,200 MW.
A preliminary permit, good for an initial three years, with a two-year extension available if needed, allows the developer exclusivity on project development during the permit term. FERC expects a company to develop a license application for the project during the permit term.