220 ILCS 5/9-215
The Commission shall have power to consider, on a case by case basis, the status of a utility's capacity and to determine whether or not such utility's capacity is in excess of that reasonably necessary to provide adequate and reliable electric service. Excess capacity for purposes of this Section shall mean capacity in excess of that reasonably necessary to provide adequate and reliable electric service. Such consideration shall be related to the utility's historic and projected peak.
The Commission is empowered to make appropriate and equitable adjustments to rates for utility service upon a finding of excess capacity.
With respect to generating capacity existing or under construction on the effective date of this amendatory Act of 1985, any such determination and adjustment to rates, and any determination as to whether such capacity is used and useful for any purpose under this Act, shall be limited to the determination and adjustment, if any, appropriate under the law in effect prior to such effective date.
220 ILCS 5/9-215