Salt River Project announced its intention Wednesday to build three new natural gas-fired power plants in Pinal County to meet the growing demand for electricity in the northern part of the county.
The utility said it has identified three sites for the plants, and SRP plans to hold open houses in June to explain the power projects to interested residents.
SRP said it will need up to 2,500 megawatts of new generating capacity by 2020 to meet the anticipated growth in Pinal County. That would be enough power to meet the needs of more than 500,000 homes.
Earlier this year SRP reached an agreement with TransCanada Corp. to purchase 500 megawatts from a natural gas power plant that TransCanada plans to build near Coolidge by 2011. But SRP said more plants will be necessary to meet the peak demand for electricity during hot summer afternoons.
"We are trying to get out ahead of the development," said Karen Smith, manager of the Pinal Energy Projects. All three of the SRP plants are proposed near a new high-voltage transmission line the utility is building to connect the Palo Verde hub west of Phoenix with the Browning substation in east Mesa. That line, which runs in a loop through Pinal County, is scheduled to be completed in 2011.
No schedule has been decided for construction of the three plants, but the soonest they could be completed is 2012, Smith said.
Nor has the cost been determined or even if SRP will own the plants or if a third-party developer like TransCanada would build them and sell the power to SRP.
Also additional renewable energy from solar, wind or geothermal plants could provide a portion of the 2,500 megawatts, Smith said. Details of the Pinal projects will be determined this summer as part of a public planning process that will include three open houses, she said. The locations are at the planned Abel Substation north of Florence, the planned Pinal Central Substation south of Coolidge and near the Eloy Detention Center north of Eloy.SRP has options to purchase the first two sites from private owners, and also has an agreement with the city of Mesa, which owns the Eloy site. Mesa acquired the property in 1985 for its water rights but later determined the water wasn't needed.
Smith said the natural gas plants will help to ensure the reliability of electric service within SRP's service territory, which includes areas of Pinal County north of Arizona Farms Road. That area includes the 275-square-mile Superstition Vistas project proposed on state land south of Apache Junction, which is going through a planning process. The development is expected to have a million residents by mid-century.
Natural gas was chosen as the fuel for the new plants because it been meets the operating needs of the plants, which will be used primarily to meet peak demand during summer afternoons, said John Coggins, SRP's manager of resource planning and development.
"We need resources that are highly flexible and can start up and shut down quickly," he said. "Also we need backups for renewables. For that type of resource, natural gas is the best choice."
Natural gas is relatively clean burning, but it does release carbon dioxide, a greenhouse gas blamed for global warming. Coggins said the fuel still is the best choice, even if carbon dioxide comes under increased government regulation.
"When you look at the carbon issue, the most uncertainty exists with coal," he said. "And we do not plan to run these plants a lot, so the total emissions will be low."
The plants also will use relatively little water, Smith said.
Before the plants can be built, they must be reviewed by the Arizona Power Plant and Transmission Line Siting Committee, which makes a recommendation to the Arizona Corporation Commission, which makes the final decision on whether to approve their construction. Also they must receive an air permit from Pinal County.