(a) Definitions. As used in this section:
(1) “Average four-year generation” is computed by dividing by four the sum of a generating units net generation, expressed in kilowatt hours, for calendar years 1991, 1992, 1993, and 1994. For any generating unit which was newly installed and placed into commercial operation after January 1, 1991, and prior to the effective date of this section, “average four-year generation” is computed by dividing the units net generation for the period beginning with the month in which the unit was placed into commercial operation and ending with the month preceding the effective date of this section by the number of months in the period and multiplying the resulting amount by twelve with the result being a representative 12-month average of the units net generation while in an operational status.