Arizona Public Service (APS) recently said its customers are reaching peak summer energy usage 45 minutes later on average than they did in 2012.

In 2012, the average peak time during June through August was at 4:30 p.m. In 2014, the peak time was 5 p.m. and now it is at 5:15, with high energy use for several more hours beyond this time.

The shift is significant, but not surprising. The number of solar panels installed on customer rooftops has doubled or tripled each year. The demand for electricity hasn't changed, but customers with solar panels do not need to rely on APS until later in the day when the sun descends.

“With customers using more energy later in the evening, the more than 10-year-old on-peak hours of noon to 7 p.m. are outdated,” Stacy Derstine, APS vice president of customer service and chief customer officer, said. “We recently requested to change on-peak hours to 3 to 8 p.m. in order to align with the actual periods of highest demand. This would send a better price signal to customers to reduce their energy use at the times when resources are most expensive, providing them more savings – especially to those customers on a demand rate.”

APS, like all utilities, must plan and build its system to meet the annual peak usage, or the greatest amount of energy customers require at any given moment. APS tracks energy trends to ensure reliable energy and expects that peak use times will continue to move later in the day.