For the first time in its history, state-owned utility Santee Cooper will shutter four power-generating units at two electric plants on Dec. 31.

Powering down

State-owned utility Santee Cooper is closing the six electric generating units at its two oldest fossil-fuel power plants: Jefferies StationLocation: Moncks CornerPlan: Four units to be retired. Two are coal-fired, two use oil (to be closed later). Jefferies Hydroelectric Generating Station remains in operation.History: The oldest two units being closed date to 1954; the others followed in 1970.Output: The four units have a combined capacity of 394 megawatts.Grainger StationLocation: ConwayPlan: To be permanently closed. It has been idle for most of 2012 as Santee Cooper evaluated the potential effects of the EPA’s new Mercury and Air Toxics Standard.Output: Capacity of 170 megawatts.Santee Cooper

The closings, approved by the utility’s board in October without specifying a date, represent 10 percent of the Moncks Corner-based power provider’s electric-generating capacity.

They affect both coal-fired units at Grainger Generating Station in Conway and all four units at Jefferies Generating Station in Moncks Corner.

The two coal-fired units at Jefferies will stop producing power at year’s end. The two other Jefferies units are oil-fired, little-used and will be closed eventually. No date has been set, Santee Cooper spokeswoman Mollie Gore said.

The decision to mothball the power plants is in response to changing generation needs and expensive new environmental regulations that would require significant upgrades at the power plants, Gore said.

They are among Santee Cooper’s oldest and smallest generating stations.

The Conway plant generates 166 megawatts and was built in 1966. The Jefferies coal units in Moncks Corner produce 302 megawatts and were constructed in 1970. The two oil-fired units at Jefferies generate 92 megawatts and were built in 1954.

Santee Cooper has the capacity to produce roughly 5,700 megawatts. When the oil-fired units go cold as well, the company will have trimmed 552 megawatts.

One megawatt can power about 500 homes, Gore said.

The Jefferies hydroelectric units, the first to start producing electricity for the Berkeley County-based utility in 1942 during World War II, will not be affected by the shut down. The hydro units generate 128 megawatts.

About 80 Jefferies employees affected by the plant’s demise will be relocated to other positions made available through retirements and employee departures, Gore said.

The Grainger plant, which had about 45 workers before it was idled in the spring, has just five or six employees remaining on site. They, too, will be transferred to other positions.

“Nobody has been laid off because of this,” Gore said.

In October, Santee Cooper CEO Lonnie Carter said the shutdowns would be a multi-year process that will require permits, engineering work and public input.

On Monday, Gore said the utility has never shut down power plants before and, on closer inspection, decided to do everything at one time.

“We are not using them on a daily basis,” she said.

After the electric plants are closed, the utility will still have to monitor ash ponds, transfer coal to other sites and determine how to dispose of the facilities, Gore added.

“This is the first step,” she said. “We will continue to work with regulators to determine what is required to close down the rest of the facilities.”

Santee Cooper is not the only utility abandoning coal-fired plants.

Earlier this year, South Carolina Electric & Gas Co. said it would retire six coal-fired units in three of its facilities by 2018, including its Canadys plant on the Edisto River. In October, Progress Energy, a subsidiary of Duke Energy, announced it would shut down its coal plant in Hartsville.

The shift away from coal-fired energy production also comes amid a flood of new natural gas production in the United States and Canada. The increasing supply has driven down prices for that fuel, making it less expensive than coal.

Santee Cooper has long been dependent on coal to generate between 70 percent and 80 percent of its electricity, but the plant closings mark a significant shift away from that fuel source.

Santee Cooper and SCE&G are also building a $10 billion expansion of the V.C. Summer Nuclear Generating Station north of Columbia. The two new reactors are expected to start delivering power in 2017 and 2018.

Reach Warren L. Wise at 937-5524 or