APS hits peak demand, solar contribution varies

August 21, 2015

As Arizona residents endured sweltering temperatures a week ago, demand for power to keep their homes and businesses cool rose to the highest level APS has seen so far in 2015.

APS reached peak demand of 7,031 megawatts (MW) at 4:45 p.m. on Saturday, Aug. 15. The same day, Phoenix Sky Harbor International Airport recorded a high temperature of 115 degrees, the second consecutive day of record heat in the Valley. The mercury hit 117 degrees on Friday, Aug. 14.

Despite the record temperatures and high demand for electricity, APS is prepared to satisfy customers’ needs during our busiest season. Between our own generating facilities and power-supply contracts, APS has 9,095 MW of resources available to meet summer demand reliably.

The resources include 904 MW of utility-scale and rooftop solar energy on the system statewide. On the record-setting Saturday, solar achieved its peak production in late morning, well before demand soared later. Residential rooftop systems hit a combined peak shortly after 11 a.m., while the large-scale plants in APS's AZ Sun Program topped out at 11:30 a.m.

Solar’s contribution to powering customers’ homes and businesses during the peak period varied widely. The eight AZ Sun plants with solar panels that track the sun’s movement maintained strong generation with 141 MW of electricity, 89 percent of maximum output. The lone plant with fixed-axis panels, Paloma, added 8.2 MW, half of its maximum output.

The contribution from residential rooftop panels was an estimated 46 MW, or 31 percent of the combined maximum output. Because rooftop systems are typically south-facing and fixed in place, panels do not produce as much electricity late in the day – when demand is highest – as they do when the sun is overhead around noon.

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