SRP to Convert Unit 4 of SGS Station in Arizona to Use Gas

Three of the four units at the coal-fired Springerville Generation Station (SGS) in Arizona will shift to natural gas in the early 2030s.

This week Salt River Project’s (SRP) board approved the conversion of Unit 4. Earlier this year Tucson Electric Power (TEP), which operates all four units, said it will convert Units 1 and 2. Unit 3, owned by the Tri-State Generation and Transmission Association, is set to be retired.

“Today’s decision is the lowest-cost option to preserve the plant’s 400-megawatt (MW) generating capacity, enough to serve 90,000 homes, which is important to meeting the Valley’s growing power need in the early 2030s”, SRP said in a statement on its website.

“Converting SGS Unit 4 to run on natural gas is expected to save SRP customers about $45 million compared to building a new natural gas facility and about $826 million relative to adding new long-duration lithium-ion batteries over the same period”, the public power utility added.

“The decision also provides a bridge to the mid-2040s, when other generating technology options, including advanced nuclear, are mature”.

Gas for the converted Unit 4 will come from a new pipeline that SRP will build. The pipeline will also supply gas to the Coronado Generating Station (CGS). On June 24 SRP announced board approval for the conversion of CGS from coal to gas.

“SRP is working to more than double the capacity of its power system in the next 10 years while maintaining reliability and affordability and making continued progress toward our sustainability goals”, SRP said. “SRP will accomplish this through an all-of-the-above approach that plans to add renewables in addition to natural gas and storage resources”. 

SRP currently supplies 3,000 MW of “carbon-free energy” including over 1,500 MW of solar, with nearly 1,300 MW of battery and pumped hydro storage supporting its grid, according to the utility.

In July TEP said it will convert Units 1 and 2 to run on gas by 2030.

“The conversion will provide comparable capacity to the coal-fired units while costing less than building new resources such as a new combined cycle natural gas-fired facility or solar plus long-term energy storage systems that provide comparable reliability”, TEP, owned by Canada’s Fortis, said in an online statement.

TEP had planned to retire Units 1 and 2 in 2027 and 2032 respectively “due to rising fuel costs, increasing delivery risks, anticipated mine closures and environmental considerations and regulation”, the statement said. “Although current federal policy is supportive of coal-fired generation, those long-term risks remain.

“Natural gas-fired generators provide advantages over coal-fired power plants on today’s energy grid, as they can better accommodate and support increasing levels of intermittent wind and solar power. Coal plants are designed to operate at steady levels and cannot easily ramp up or down in response to customer needs and renewable energy output”.

TEP expects the conversion to cut the two units’ carbon dioxide emissions by 40 percent, helping the company achieve its goal of net-zero direct greenhouse gas emissions by 2050.

Meanwhile Unit 3 is scheduled to be permanently shut down 2031, as part of the Tri-State Generation and Transmission Association’s energy transition plan announced 2023.

SGS has been producing electricity since 1985 as one of several coal power plants built during the 1970s and 1980s in the Four Corners area to support growing population in the southwest United States, according to TEP. The station sits about 175 miles northeast of Tucson, near the Arizona-New Mexico border.

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