The Illinois Commerce Commission last week ordered Ameren Illinois to study the costs and benefits of being a MISO member compared with joining the PJM Interconnection, the grid operator that serves the northern part of the state.

“The ICC feels it is appropriate to explore whether membership in MISO continues to provide net benefits to Ameren Illinois’ electricity customers,” ICC Chairman Carrie Zalewski said Friday.

The Prairie State is the only MISO state that fully deregulated its electric utility sector.

In MISO’s last planning resource auction, the clearing price soared to $236.66 MW-day across its North and Central regions. The auction is voluntary and not intended to spur new capacity needed to ensure resource adequacy, but instead is designed to complement state efforts to make sure they have enough power supply, ICC staff said in a report.

“In the case of Illinois, this means that MISO’s resource adequacy construct must complement Illinois’ reliance on competitive wholesale markets to discipline retail electricity prices,” staff said. “Given the most recent MISO [planning resources auction] results and the regulatory structure of its membership, it is not clear that MISO’s resource adequacy construct accomplishes this goal.”

The ICC directed Ameren to consider various factors in its study, including reliability, resource adequacy, resiliency, affordability, equity and environmental effects.

Ameren has a year to finish the analysis.