Majority
Proceeding pursuant to CPLR article 78 (transferred to this court by order of the Supreme Court at Special Term, entered in Albany County) to review a determination of the Public Service Commission imposing a differential between the rate charged for electricity to general primary service (SC-3) customers in the summer and winter. Petitioners, which together form the Industrial Energy Users Association (IEUA), operate industrial facilities in either Orange or Rockland County. Each of them purchases electric power from Orange & Rockland Utilities, Inc. (O & R), and is a member of O & R’s SG3 class of customers. On November 10, 1976, O & R filed with the Public Service Commission (commission) tariff revisions designed to produce additional revenues from the sale of electricity. The commission determined that O & R was entitled to additional electric revenues of $10,826,000, and also approved imposition of a rate differential of $2.25 per kilowatt (the differential) higher in the summer than winter on SC-3 customers. In this transferred CPLR article 78 proceeding, petitioners seek to annul only that part of the commission’s order which approved the differential. Petitioners first contend that imposition of the differential is not supported by substantial evidence in the record. In support, they argue that a marginal cost study prepared by O & R was not probative of the difference in seasonal costs, and that the testimony of the two supporting witnesses was insufficient to justify the differential. We cannot agree. The purpose of the differential was to reflect in the rates the higher summer capacity O & R concededly experiences as a summer peaking utility, and to assess costs on those customers who contribute to the system peaks. Contrary to petitioners’ contention, testimony by a witness for O & R and by a staff witness supported imposition of the differential. Both witnesses clearly relied on the marginal cost study which showed that O & R’s marginal costs were six times higher in the summer than in the winter. Although the company’s study was not used by it to design its time-of-day rates, it did provide evidence demonstrating a difference in summer and winter capacity costs. Regardless of how the difference in cost is measured (i.e., on an embedded or marginal basis), imposition of a summer/winter differential was therefore justified. Moreover, it cannot be said that the differential is without a rational basis. Although, as argued by petitioners, the differential may have no impact on O & R’s plans for future capacity additions or produce short-term cost savings, it imposes the cost of facilities already built to meet peak demands upon those customers whose highest demand occurs during the summer