During the hottest July and August temperatures ever recorded, Phoenix-based Arizona Public Service (APS) relied on its fossil fuel generation fleet, along with nuclear and customer conservation, to avoid a power emergency, the CEO of parent company Pinnacle West Capital Corp. said last week.

“Our fossil fleets equivalent availability factor, or the percentage of time a plant is available, was 95.3% from June through September,” said CEO Jeff Guldner. The Palo Verde Nuclear Generating Plant’s factor was 100.2% during the same four-month time frame.

“We relied heavily on our baseload and fast-ramping assets, including the Four Corners,” a coal-fired unit, along with the natural gas-fired Ocotillo plant and Palo Verde. “Those plants were all available when we needed...