Two Arizona utilities received approval to convert coal-fired power plants to run on natural gas, projects they say will enhance grid reliability, reduce emissions and preserve jobs.
The Arizona Corporation Commission voted 5-0 on March 4 to approve an application from Tucson Electric Power to convert units 1 and 2 of Springerville Generating Station to natural gas. In a separate 5-0 vote, the commission approved Salt River Project’s application to convert two units to gas at the Coronado Generating Station. The applications sought modifications to certificates of environmental compatibility (CEC) for the facilities.
The Springerville and Coronado stations are about 30 miles apart in Apache County, Ariz.
Of the four coal-fired units at Springerville, TEP owns units 1 and 2, which have a combined capacity of about 800 MW. Unit 1 was slated for retirement in 2027, with Unit 2 to follow in 2032 “due to rising fuel costs, increasing delivery risks, anticipated mine closures, and environmental considerations and regulations,” TEP said previously.
Terry Nay, TEP’s vice president of energy resources, noted that the company did not propose repowering Springerville in its 2023 integrated resource plan (IRP) because “the prospect of a [gas] pipeline was not feasible.”
But since the IRP was filed, “we learned that a pipeline is feasible, making repowering Springerville the most economical choice for replacement gas generation,” Nay told the commission.
In August 2025, TEP and SRP were among Arizona utilities that announced commitment plans for Transwestern Pipeline’s Desert Southwest expansion project. The pipeline will transport natural gas from the Permian Basin in west Texas to Arizona. Construction is expected to be finished in late 2029.
Nay said gas conversion of the Springerville units would cost about $200 million. That would be less expensive than keeping the units running on coal at a cost of about $450 million, building a new combined cycle gas facility, or building new renewables with battery storage.
TEP expects to complete conversion of units 1 and 2 in 2030.
SRP expects the Coronado conversion to be finished in 2029. While the Coronado coal plant has provided baseload generation, SRP plans to use it as a peaking resource after the gas conversion.
“We think that converting to natural gas is a good long-term durable decision that will allow us to operate well into the 2040s, when other technologies will become available,” said Bill McClellan, SRP’s director of resource planning and development.
A new natural gas pipeline lateral is expected to serve Springerville and Coronado. An SRP spokesperson told RTO Insider that SRP has not finalized an agreement for the lateral to serve Coronado.
‘Economic Backbone’
Proponents cited multiple benefits of converting coal-fired units at Springerville and Coronado to gas fuel. The converted gas plants will emit fewer greenhouse gases and other pollutants. Many of the power plant workers will be able to keep their jobs.
“These plants are the economic backbone of our area,” said St. Johns Mayor Spence Udall, who works at the Coronado plant.
Representatives of the Sierra Club and Western Resource Advocates asked the commission to send the applications to the Arizona Power Plant and Transmission Line Siting Committee to better examine potential impacts and evaluate alternatives.
“Regulatory prudence points to the need for a new hearing for a CEC that has not been revisited since 1977,” said Alex Routhier, a senior policy adviser at WRA.
Meghan Grabel, an attorney representing TEP, said the commission is “fully authorized” to rule on the applications. She said going to the line-siting committee for an evidentiary hearing would cost ratepayers hundreds of thousands of dollars. The committee would be required to hold the hearing near Springerville.
“It’s logistically difficult, and it’s expensive,” she said.
Matt Derstine, an attorney representing SRP, said the commission has an evidentiary record in sworn declarations from the utility. The project is not a substantial change, he said, and it would provide a net environmental benefit.
Commission Support
Commission Chair Nick Myers said he saw “absolutely no reason to require another half a million dollars’ worth of studies and process just to do something that’s better than what’s currently happening.”
“This is a great opportunity for us to show the rest of the world what it’s like for government to just get out of the way,” Myers said.
Myers’ comments came before the Springerville vote, but he reiterated them before voting to approve the Coronado conversion.
Commissioner Kevin Thompson said the Coronado power plant supplies about 10% of SRP’s peak demand. The estimated cost to convert Coronado to gas and run it through 2045 would be $1.1 billion, he said, about $300 million less than replacing Coronado with a new natural gas plant for the same time frame.
“These plants are cornerstones of their local communities and, once converted to natural gas, will become a key pillar of long-term grid reliability versus being seasonally operated generating stations,” Thompson said in a statement after the meeting.
Of the remaining two units at Springerville, SRP owns Unit 4. The SRP board of directors in November approved the conversion of the unit to run on natural gas.
Springerville Unit 3 is owned by Tri-State Generation and Transmission Association. It is slated for retirement in 2031.

