What is it?
The Gregory County Pumped Storage Project is an energy project that would start with a 1,439 acre (2.25 square miles) upper reservoir in Gregory County, three miles south of the Platte-Winner bridge.
Upper Reservoir berm height will average 90 feet with a maximum height of 114 feet. It will hold 25 billion gallons of water, that would then run down through two 30-45 foot dia. tunnels. These tunnels will transfer water in and out of Lake Francis Case. The storage volume is equivalent to draining up to 2.6 miles of Lake Francis Case and equals 2.5% of all the water in the lake.
Twenty-two miles of transmission line and substations would be built. These lines are considered primary distribution lines. A high voltage direct current transmission line would be constructed in the future.
An approximately 150 acre substation (equal to 110 football fields in size) would be located 7 miles east of Platte, South Dakota.
Function
The function of this pumped storage project is to work as a hydroelectric source of power. The maximum output for this dam would be 2,100 megawatts- equivalent to 120% of all power produced by hydroelectric dams in South Dakota.
The project is being touted to produce up to 3,500 GWh annually. However, the project consumes more energy than it produces. Based on an estimated energy efficiency of 75%, the project will consume up to 4,667 GWh which is slightly higher than all of the electricity produced annually by Fort Randall and Oahe dams combined.
Supposedly, wind power would be used to fill the reservoir. However, this is doubtful as it would require up to 50% of all of the wind energy currently produced in South Dakota. Water would be pumped up and released for up to 53% of the year—equivalent to emptying and filling Lake Francis Case twice annually—to generate energy to eastern power grids.
Although being sold as a "Green Energy" project, there is no evidence that it will lower carbon emissions, stabilize the grid, or lower energy bills.
The energy companies have offered estimates on tax revenue increases for Gregory County and the Burke School District. However, the South Dakota Department of Revenue has stated that they will not be able to determine the tax value of the project until construction has begun (projected 2030), nor can they confirm the applicant’s projected tax revenue estimates.
This project will be funded by MidAmerican Energy, Missouri River Energy Services, and the American taxpayers through the Federal Government.