Ameren Missouri Utility to Build a Gas Plant with Energy Storage

Ameren Missouri, a subsidiary of Ameren Corp., has announced plans to build a new 800-MW natural gas-fired power plant coupled with the utility’s first large-scale battery energy storage system. The proposed Big Hollow Energy Center, to be located in Jefferson County near St. Louis, marks a significant step in the utility’s long-term strategy to strengthen grid reliability and support growing energy demand.

The company filed an application for the project with the Missouri Public Service Commission in late June. If approved, the facility is expected to come online by 2028.

A Modern Energy Solution for Peak Demand

Designed as a simple-cycle natural gas plant, Big Hollow will operate similarly to the upcoming Castle Bluff Energy Center, also planned near St. Louis. Simple-cycle plants are often deployed to meet peak energy demand, providing rapid-response power during extreme temperature periods when electricity usage spikes and intermittent renewable sources like wind or solar are insufficient.

Big Hollow will be constructed on land already owned by Ameren Missouri, allowing the company to reduce construction timelines and project costs by leveraging existing infrastructure.

“Our strategy is to invest in energy infrastructure that benefits customers while creating a balanced generation portfolio,” said Mark Birk, Chairman and President of Ameren Missouri. “As we transition our generation fleet, we remain committed to delivering reliable energy and preparing for rising demand.”

Battery Storage to Boost Grid Flexibility

In addition to the gas plant, Big Hollow will include Ameren Missouri’s first large-scale lithium-ion battery energy storage facility, with an initial capacity of 400 MW. This marks a critical advancement in the company’s broader commitment to deploy 1,000 MW of battery storage by 2030, and 1,800 MW by 2042.

The utility said the batteries will store excess electricity—often produced during off-peak periods or from renewables—and then discharge it during high-demand times, regardless of weather conditions. The planned system can power thousands of homes for hours, reinforcing grid stability and increasing energy reliability during emergencies or peak events.

“This is a fast-acting asset,” Ameren said in a statement. “It’s ready in moments to support customers’ energy needs and plays a vital role in supporting a cleaner, more flexible grid.”

Supporting the Energy Transition

Ameren Missouri has been gradually phasing out coal-fired generation. In 2022, the utility shut down the Meramec Energy Center, and in 2023, it closed the Rush Island coal plant. The Sioux Energy Center is scheduled for retirement by 2032. The company’s largest coal facility, the 2,400-MW Labadie plant, remains operational for now.

Meanwhile, Castle Bluff—like Big Hollow—will be built on the former Meramec site, utilizing existing infrastructure and repurposing legacy energy sites for cleaner alternatives.

Ajay Arora, Ameren Missouri’s Senior Vice President and Chief Development Officer, emphasized the strategic siting of these new assets: “A balanced mix of generation technologies—strategically located—ensures we can maximize output and support the region’s energy needs reliably.”

Economic Impact for Jefferson County

Local officials have welcomed the Big Hollow Energy Center as a major economic opportunity for the region.

“This is more than just an energy project—it’s a commitment to the future of Jefferson County,” said Dennis Gannon, Jefferson County Executive. “We’ve worked closely with Ameren Missouri, and this forward-thinking investment will strengthen our economy for generations. It will bring jobs, support our schools, first responders, and the community at large.”

Rob Dixon, Ameren’s Senior Director of Economic and Community Development, added: “We’re proud to continue investing in Jefferson County. The Big Hollow Energy Center reflects years of collaboration with local leaders and will help power progress for the entire region.”