Illinois may have to provide subsidies to more of Exelon Corp’s nuclear plants if it wants the carbon-free power those reactors produce to help the state transition from dirty fossil fuels to cleaner forms of energy, according to a study.

Illinois hired Synapse Energy Economics, a consulting firm, to conduct the study in January after Exelon in August 2020 said it would retire "uneconomic" nuclear reactors at Byron in September 2021 and Dresden in November 2021.