Pinnacle West is a holding company whose principal subsidiary is Arizona Public Service, a vertically integrated electric utility serving approximately 1.4 million customers across a 35,000-square-mile territory in central Arizona, including the Phoenix area. APS owns or leases 6.5 gigawatts of power generation capacity, including a 29% ownership stake in one of the largest nuclear plants in the US, Palo Verde. Half of the electricity that APS supplies to customers comes from clean energy sources, including nuclear.