Ameren Missouri is planning to build a new natural gas plant at the location of the former coal plant in south St. Louis County.

The proposed Castle Bluff Energy Center would only be used as a backup power source during peak demand, said Ameren’s director of combustion turbine generators, Jeff Moore, and is part of the company’s transition toward renewable energy.

“With renewable energy, sometimes there’s cloud cover that may limit solar production, or there may not be wind at all times, so you need a plant like Castle Bluff that will provide the backup at all times,” Moore said.

Ameren is targeting net-zero carbon emissions by 2045, with 37% of its energy coming from renewable sources, 27% from other zero-carbon sources and 23% from nuclear, with roughly 14% of energy coming from natural gas with offset or captured emissions.

“We have big plans out there to add more and more renewable energy sources … and as we do that, we have to have on-demand, reliable resources like Castle Bluff,” Moore said. “In order for us to make progress toward our net zero goals … we have to have these types of plants to provide backup power reliably.”

The new energy center will be built at the former location of the Meramec Power Plant, a coal-fired power plant that closed at the end of 2022. The Castle Bluff center is projected to cost $800 million. Moore said on-site construction is expected to start in the summer of 2025, with the plant ready to go into service by the end of 2027. Since Ameren already owns the property and the necessary infrastructure is there, Moore said building Castle Bluff at the old Meramec Power Plant site is more cost-effective.

The proposed energy center is expected to generate new employment opportunities, in addition to reducing carbon dioxide emissions by 40% compared to the coal site it replaces. Additionally, the facility is designed to lower nitrogen oxide and sulfur dioxide emissions by 80% and 99%, respectively.

“It’s not going to run all the time. It’s only going to run whenever it’s needed,” Moore said. “The emissions from this plant are going to be a lot less than its predecessor, the old coal plant. So the other thing you have to remember is it’s going to run a lot less of the time than the old plant did, so there’s going to be fewer emissions just from the fact that it’s not going to be in operation on a continuous basis.”

The project must still be submitted to the Missouri Public Service Commission for approval before construction can begin.