Arizona Public Service (APS) said it plans to convert two closed coal-fired units at its Cholla Power Plant to burn natural gas. The utility this month said construction on the conversion would begin in 2028, with the new units—designed to generate 380 MW of electricity—coming online the following year.
The power station at Cholla, located in Joseph City in northeastern Arizona, stopped burning coal at its last two operating units in March 2025. The power plant entered commercial operation in 1962. State regulators still need to approve the plan to convert the facility to burn natural gas.
APS on its website wrote, “This project is about making sure customers have reliable, affordable energy they can count on. Converting coal units at Cholla to run on natural gas would make the most of existing infrastructure, helping meet growing energy needs with a cost-effective, around-the-clock resource that can come online in just a few years.
“As demand for energy in Arizona grows, natural gas is critical to deliver reliable service for all customers. It provides flexible, on-demand energy [including during the late afternoon and evening hours when customer energy use is highest] and supports around-the-clock energy needs.”
The utility noted, “Overall, a diverse energy mix—including nuclear, natural gas, solar, wind, battery energy storage, coal and customer demand response programs—supports reliability while keeping energy bills as low as possible for our customers.”
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The Cholla Power Plant historically operated as a 1.02-GW coal-fired facility jointly owned by APS and PacifiCorp. Units 2 and 4 at the site were retired in 2015 and 2020, respectively, while Units 1 and 3 were shut down in 2025.
The utility said the coal-burning equipment at the Cholla site will be removed. APS noted, “Because this project would be located at an existing power plant site, very little new transmission infrastructure would be needed, which would help meet growing energy needs in a cost-effective way. Most of the work would involve upgrading existing equipment rather than building new transmission lines.” APS said the plant will requite a lateral line, which is a smaller diameter pipeline, to bring natural gas to the facility. The lateral line will connect to an existing natural gas pipeline system.
APS said it stopped burning coal at Cholla due to federal regulations under the Regional Haze Program, which required the utility to cease burning coal in Cholla Units 1 and 3 by no later than April 30, 2025. The utility said that while there was an option to convert the plant to burn natural gas, the utility chose to wait on a conversion until it could be proved gas-fired generation would benefit customers. The utility said the need for more electricity across its service territory due to increased demand for power drove the decision to move forward with converting the former coal-burning units.
—Darrell Proctor is a senior editor for POWER.
