Arizona Has Untapped Geothermal Potential

The U.S. Department of Energy recently announced a new initiative “GeoPowering the West,” an effort to promote the development and use of geothermal power in the western states. According to DOE, all of Arizona’s neighboring states have good geothermal resources, with California, Nevada and Utah listed as the top three states with electrical generation potential and New Mexico considered a high potential state. Arizona does not make the rankings.

Arizona’s no-show raises question about the state’s geothermal potential. What potential does the state have, and what purposes could its geothermal reserves serve?

In Arizona, water as a source of energy mostly means hydroelectric power. Glen Canyon and Hoover dams come to mind, where surging water turns turbines to generate electricity. Geothermal power puts groundwater to work. Extreme heat deep within the earth rises near the surface and heats groundwater that then becomes naturally occurring hot water and steam, and a source of geothermal energy.

The uses of geothermal energy are determined by temperature, with the hottest reserves (greater than 150·C or 302·F) generally used for electric power generation. The process involves boring deep into the earth’s crust, to tap into the hot, briny reservoirs of water. The water is pumped to the surface and converted to steam that spins turbine engines to generate electricity. Geothermal energy for electrical production is the main goal of the DOE initiative. Arizona, however, lacks the thermal capacity to generate electricity, although the state has other geothermal potential.

Water temperatures lower than what is needed to generate electricity also have geothermal uses. Low temperature (less than 90·C or 194·F) and moderate temperature (90·C - 150·C or 194·F - 302·F) geothermal water can be used for direct use and ground-source heat pumps. Direct use means using the water directly, without heat pump or power plant, for such applications as heating of buildings and use in industrial processes, greenhouses, aquaculture and resorts. Direct use projects generally involve resource temperatures between 38·C (100·F) to 149·C (300·F).

Arizona geothermal potential has been evaluated to some extent. During 1977-82, the Geothermal Assessment team within the Arizona Bureau of Geology and Mineral Technology (now known as the Arizona Geological Survey) conducted a reconnaissance of the state’s geothermal resources, with attention focused mainly on the southern part of the state. The agency issued reports evaluating Arizona’s geothermal potential. Drilling would have been the next step, but neither federal nor state funds were available to support the project. This work was part of a national effort at that time, with federal funds provided to states to research their geothermal potential to reduce the nation’s reliance on foreign oil.

Various reports resulted that showed Arizona has many areas with low-to-moderate-temperature fluids at depths sufficiently shallow to tap and use for energy. Areas of geothermal activity in Arizona are mostly located in the basin and range providence, mainly in the southern part of the state. Nine counties were identified as having such geothermal reserves including the metropolitan Phoenix and Tucson areas. Reports also were done to determine the geothermal potential for various cities, including Clifton, Scottsdale-Paradise Valley, Tucson, Willcox and Yuma.

White areas shown on the map have potential for geothermal resources.

In the 1970s, the Geothermal Commercialization Team within the University of Arizona’s Department of Chemical Engineering studied possible uses of geothermal resources. The team completed geothermal development plans for Cochise, Graham, Greenlee, Maricopa, Pima, Pinal, Santa Cruz and Yuma counties. These reports are available from the Arizona Geological Survey. (See the summer issue of the Arizona Geological Survey’s publication, “Arizona Geology,” for a list of available AZGS geothermal publications.)

A recent geothermal database for Arizona indicates 1,251 discrete thermal wells or springs in the state. The thermal fluids, however, are put to traditional water resource uses; i.e., irrigation of field crops, municipal water supply and industrial uses, with little advantage taken of the heat carried by the waters. At present, geothermal aquaculture is the only major direct-use application in the state. In fact, Arizona leads the nation in the aquacultural use of geothermal fluids.

The summer issue of “Arizona Geology” identifies a wide range of possible uses of geothermal energy within various sectors, including domestic, industrial and especially agriculture. According to the publication the low-to- moderate-temperature geothermal fluids found in the state can be used to heat homes and businesses. Agriculture uses include controlled-environment agriculture, such as greenhouses and nurseries, aquaculture, grain and vegetable drying, and soil warming for mushroom growing and earthworm farms.

The evidence points to an obvious discrepancy between current and potential geothermal applications in the state. Geothermal energy would seem to represent an untapped potential in Arizona, presenting opportunities yet to be developed.