(a) To mitigate capacity and energy costs for all customers, the department shall ensure that, subject to subsection (c) of section 19, electric and natural gas resource needs shall first be met through all available energy efficiency and demand reduction resources that are cost effective or less expensive than supply; provided, however, that when determining cost-effectiveness, the calculation of benefits shall include calculations of the social value of greenhouse gas emissions reductions. The cost of supply shall be determined by the department with consideration of the average cost of generation to all customer classes over the previous 24 months.

[Paragraphs (1) and (2) of subsection (b) applicable to energy efficiency plans beginning with the 2025 to 2027 plan. See 2022, 179, Sec. 94.]