subsection (c), the average annual quantity of electricity delivered by the retail electricity supplier to electric consumers, or quantity of natural gas delivered by the retail natural gas supplier to natural gas consumers, during the 3 calendar years immediately preceding the year that compliance is required under subsection (c)(1). (B) Exclusion The term base quantity , with respect to a retail natural gas supplier, does not include natural gas delivered for purposes of electricity generation. (4) CHP savings The term CHP savings means— (A) CHP system savings from a combined heat and power system that commences operation after the date of enactment of this section