MISO said Tuesday that it will likely be forced to renew a Missouri coal plant’s operating extension for almost two more years.

Ameren Missouri’s (NYSE: AEE) 1.2-GW Rush Island Energy Center has been operating under a system support resource (SSR) designation since September, when FERC approved a one-year SSR agreement. (See FERC: Rush Island Plant’s Extension Essential to MISO Reliability.)

During a Central Subregional Planning meeting Tuesday, MISO’s Grant Larson said staff reanalyzed the system without Rush Island’s assistance and again found transient voltage recovery and steady state voltage violations if it is allowed to suspend operations. Larson said Rush Island’s SSR status will have to be renewed for another year Sept. 1 unless stakeholders can suggest generation or transmission alternatives by June 20.

“MISO likes to consider SSRs a last resort,” Larson told attendees, but he said the RTO has “unfortunately” not found any reconfiguration, redispatch or demand-response alternatives to avert another extension.

“Transient voltage recovery violations, that result in cascading outages and instability, cannot be mitigated,” he told stakeholders. He said more than 1,000 MW of load is at risk due to the violations.

MISO restudies system conditions annually to assess the need for SSR agreements.

Larson said transmission upgrades in the area that negate the SSR won’t come online until mid-2024 and 2025. He said the wind, solar and battery storage projects proposed in Illinois and Missouri won’t be available in time either.

While some system upgrades that will be completed by September have improved reliability performance and mitigated a few of the issues since 2022, Larson said, it won’t be enough to allow Rush Island to suspend operations. He also said the SSR’s cost allocation to load won’t be “drastically” different, though some elemental pricing nodes will change.