Facebook icon YouTube icon Pinterest icon RSS icon Flickr icon

Geothermal Energy

What is Geothermal Energy?

Thermal springs can be harnessed for heat and energy.




Geothermal Uses

The geothermal resource potential map.




Arizona’s Geothermal Development










Tucson Geoexchange

Geoexchange uses a geothermal heat pump.

Geoexchange uses a geothermal heat pump.Geoexchange uses a geothermal heat pump.

Geoexchange uses a geothermal heat pump.


Tucson site information provided by Blaine Miller (AZ Gov).


U.S. DOE Energy Efficiency and Renewable Energy (EERE)

A Hot Idea for Power

Extensive development of the warm-water systems in direct use applications can significantly improve the energy balance of a nation. For example, the use of geothermal water for space heating and other direct-use applications in Iceland substantially benefits the economy of that nation. Great potential exists for additional direct use of geothermal energy in the Western United States.

The U.S. leads the world in geothermal capacity, but its potential is just beginning to be tapped. Since the earth’s heat is permanently present, waiting to be harnessed, this form of renewable energy is highly cost effective—once a system is installed. The U.S. Department of Energy (DOE) initiative, “GeoPowering the West,” is exploring geothermal opportunities to answer the rising costs of energy.

The Philippines, Indonesia, and several countries in Central America already benefit greatly from geothermally generated electricity; additional projects are underway and planned. Of course, the use of geothermal energy already contributes to the economies of industrialized nations along the circum-Pacific Ring of Fire, such as the United States, Japan, New Zealand, and Mexico.

Who Can Use Geothermal Energy?

Geothermal energy is present everywhere beneath the earth’s surface, although the highest temperature, and thus the most desirable, resources are concentrated near active or geologically young volcanoes. Large quantities of heat that are economically extractable tend to be found in places where hot or even molten rock (magma) exists at relatively shallow depths in the earth’s outermost layer (the crust). Such “hot” zones generally are near the boundaries of the tectonic plates that form the earth’s crust.

Most volcanic eruptions and earthquakes occur near plate boundaries. Frequent earthquakes produce fractures in bedrock, thus allowing water to circulate at depth and to transport heat toward the earth’s surface. Regions of stretched and fault-broken rocks (rift valleys) within plates, like those in East Africa and along the Rio Grande River in Colorado and New Mexico, also are favorable target areas for high concentrations of the earth’s heat at relatively shallow depths.

Electrical-Grade Systems: Power Generation

Visualize geothermal electricity with this simple interactive plant tour.

High temperature hydrothermal systems of about 392° F or more (200°C) are able to produce steam at pressures sufficient to drive turbine generators. These systems are developed in porous rock saturated with water, which partly boils to steam when it rises up in production wells. This steam rotates a turbine generator to produce electricity. Prime examples of hot-water systems are the geothermal fields at Coso and the Geysers in California. At both Coso and the Geysers, fractures in rocks beneath a large area are filled with steam at depths that can easily be reached using today’s drilling methods. With a generating capacity of about 1,000 megawatts electric, the Geysers is presently the largest group of geothermally powered electrical plants in the world.

Moderate temperature hydrothermal systems are unable to produce steam at high enough pressure to directly drive a turbine generator. They are, however, hot enough to produce a high-pressure vapor through heat transfer to a sec­ond “working” fluid, which in turn drives a turbine generator. The power-generation technique that transfers the geothermal heat to another fluid (for example, isobutane), whose boiling temperature is lower than that of water, is called a binary-cycle, or simply, a binary system. A binary system that produces geo­thermal electricity is in operation near Mammoth Lakes, east of the Sierra Nevada in central California.


The Clifton area boasts some of Arizona’s highest geothermal potential.

Geothermal resource potential map.