HOLYOKE, Mass. (AP) - Energy efficiency will help ensure enough electricity is available in New England even during an extended heat wave, the region's electric grid operator said Tuesday.

If the temperature hits 90 degrees, electricity demand is expected to peak at about 26,660 megawatts as customers crank up air conditioners, ISO-New England said. In an extended heat wave of about 95 degrees, demand could peak at about 28,965 megawatts.

If all the generators in New England operate at maximum ability, about 30,900 megawatts would be available. Vamsi Chadalavada, ISO's chief operating officer, said widespread energy-efficiency in the region has reduced the peak demand forecast for electricity.

Beginning June 1, the remaining units of the Salem Harbor power station in the Boston area will shut, representing a reduction of 585 megawatts of generating capacity in the region.

ISO expects to be able to meet consumer demand this summer, but the plant closing is the first in a series of expected "large resource retirements" in the coming years that will reduce available generating capacity in New England, Chadalavada said.

Without efficiency measures, the peak forecasts would be about 1,500 megawatts more, which is enough to power more than 1,000 homes. Measures include compact fluorescent bulbs, energy-efficient appliances and upgraded heating and cooling systems.

Holyoke, Mass.-based ISO said electricity imports and potential demand reductions could deliver even more power.

Last summer, electricity use peaked on July 19 at 27,379 megawatts. The record for peak demand was set on Aug. 2, 2006, when demand reached 28,130 megawatts.

Consumer demand for electricity peaks in the summer, due largely to a spike in air conditioning. Concerns about the supply of fuel to natural-gas-fired generators are more significant during the winter because pipelines have been at or near full-capacity.

But ISO said difficulties also are reported in the summer because of pipeline maintenance.