APS looking to develop geothermal energy in Clifton

By Greg Jones, staff writer

Water below Clifton is a potential hotbed of energy.

Arizona Public Service Co. (APS) is buzzing over the possibility of tapping into this subterranean power source to produce electricity.

The utility provider, in conjunction with Northern Arizona University, Arizona State University, New Mexico State University and the consulting Ormund Group, is exploring the possibility of producing as much as 20 megawatts (MW) of electricity using geothermal energy in the Clifton area.

APS representatives and consultant Amanda Ormund met with Greenlee County officials Friday, Feb. 18, to discuss the potential development of a geothermal electric power plant in Greenlee County.

Geothermal energy is heat generated in the Earth's core that flows toward the surface. Most of this energy cannot be used because it is too cool when it arrives at the surface.

In other places, however, like Limestone Gulch in Clifton and the Gillard Hot Springs near Guthrie, underground hot springs hold enough energy to produce electricity.

"You folks have a known geothermal resource here," Ormund said. "It's showing at the surface. You can stick your hand in the river and feel the warm water."

Depending on the temperature of the water, it has potential to be used to make steam, turn a turbine and produce electricity.

Dr. Peter Johnston, manager of technology development for APS, said early reports show there is enough energy in the Clifton area to produce as much as 20 MW of electricity, but that information has to be confirmed with a test well that APS hopes to drill by summer.

The 3,000-foot-deep test well will show whether there is enough geothermal energy in the area and also help APS locate the best place to drill and tap into this resource. If the test well suggests there is not enough energy to produce electricity, Johnston said the company will likely back out of the project.

Otherwise, it will proceed in designing a system to use this energy to produce electricity.

Johnston said there are two main systems designed for turning hot water into electricity.

The first is a flash-steam unit, in which water hotter than 300 F stored at great pressure underground is brought through deep wells to the surface where it explosively boils, turns to steam and spins a turbine.

The second system, for waters in the 250-300 F range, is a binary-cycle plant. This is the kind of plant APS would have to build in the Clifton area.

In binary-cycle plants, hot water is pumped from wells into a heat exchanger that is used to heat a second substance with a lower boiling point than water. The steam produced with the secondary substance boils and spins the turbine, while the heat-depleted water is returned into the ground.

The benefit of this system is that both the water and the secondary substance are in closed systems. The amount of water underground is not reduced, and emissions and smells are not released from the plant.

Johnston said an initial binary-cycle unit producing 2 MW of electricity will be constructed and subsequent 2 MW units will be added in increments.

"We'll build in increments to see what happens to the temperature," he said. "If the temperature goes down, it's an indication we need to back off, that we've maximized the resource at a sustainable level."

Johnston said as long as the power plant doesn't drain all the energy out of the water, it will provide a constant source of clean electrity.

"Treated with respect, these renewable resources will last indefinitely," he said.

Johnston said APS is interested in the program because the company will earn "green credits." He said the company is under a mandate to generate a certain amount of its electricity using renewable resources like wind, solar, biomass and geothermal energy.

He said the company has not decided what it will do with the produced electricity. It can be put into the grid and moved throughout the state, or it can be used locally for Phelps Dodge or municipal uses.

With an estimated maximum production capacity of 20 MW, the geothermal resources in the Clifton area can provide only enough electricity for about 40 residences, based on the average residential usage of 500 kilowatts (kW) per month.

APS is paying 20 percent of the exploration costs associated with this project. The U.S. Department of Energy (DOE), under its new initiative called "GeoPowering the West," is paying the other 80 percent of the costs.

Johnston said APS has spent about $100,000 thus far, with the DOE adding about $400,000.

While the main purpose of the DOE initiative -- and the main interest of APS -- is to produce electricity, there are alternative uses if the subsurface water is not hot enough to do so.

Ormund said geothermal energy can be used for production like aquaculture -- the cultivation of the water products, such as fish, shellfish and plants under control conditions -- and greenhouse heating.

"We know you have a resource here," she said. "It's a matter of whether the town wants to do anything with it."

Geothermal energy can also be used to heat buildings, and it can be used for recreational uses, not a new idea in Clifton.

In the 1920s, a bathhouse and public swimming pool, both heated by underwater springs, were promoted as tourist attractions. These projects were abandoned as the country wrestled with the Great Depression. Ormund said these previous efforts will make it easier to recapture the energy below the ground.