Geothermal literally means "Heat (thermal) from the Earth(geo)". Perhaps the best-known geothermal phenomenon is "Old Faithful" in the Yellowstone National Park. While Old Faithful displays its energy through regular eruptions, thermal energy for human use is typically accessed by drilling water or steam wells in a process similar to drilling for oil. Geothermal energy is clean, but has great limitations.

CARE'S POSITION

Geothermal power is potentially another renewable resource for the future. Small-scale applications are problematic and large-scale applications are currently not technologically feasible. Geothermal power will be an extremely small contributor to America's energy needs over the next several decades and may never become a viable, large-scale energy recourse.

CARE supports continued research and development of geothermal power, however only in small amounts. Currently it is more responsible to utilize our limited financial resources on energy sources that have greater near and long-term potential.

WHAT IT IS

Geothermal energy is the heat from the Earth. Resources of geothermal energy range from the shallow ground to hot water and hot rock found a few miles beneath the Earth's surface, and down even deeper to the extremely high temperatures of molten rock called magma.

HOW IT WORKS

• Power plants generate electricity from geothermal reservoirs. Mile-or-more-deep wells can be drilled into underground reservoirs to tap steam and very hot water that drive turbines that drive electricity generators.
• Three types of power plants are operating today:
  Dry steam plants, which directly use geothermal steam to turn turbines;
  Flash steam plants, which pull deep, high-pressure hot water into lower-pressure tanks and use the resulting flashed steam to drive turbines; and
  Binary-cycle plants, which pass moderately hot geothermal water by a secondary fluid with a much lower boiling point than water. This causes the secondary fluid to flash to vapor, which then drives the turbines.
• Geothermal heat pumps can tap into the resource to heat (and actually cool) buildings. A geothermal system consists of a heat pump, ductwork to deliver the heated air and a heat exchanger-a system of pipes buried in the shallow ground near the building. During winter months the heat pump removes heat from the heat exchanger and pumps it into the indoor air delivery system. In the summer, the process is reversed. The pump sucks indoor air into the heat exchanger. The heat removed from the indoor air during the summer can also be used to provide a free source of hot water.
• Some geothermal plants use reservoir steam to power turbines or generators. Others use the hot water indirectly to boil a working fluid that vaporizes and then turns a turbine.Hot water near the surface can also be used as a direct heat source for heating buildings, growing plants in greenhouses, drying crops, heating water at fish farms, and several industrial processes such as pasteurizing milk.
• Hot dry rock resources are found in the upper crust of the Earth's surface, typically at depths of 3 to 5 miles. Retrieving this resource involves injecting cold water down one well, circulating it through hot fractured rock, and drawing off the heated water from another well. Unfortunately, there are currently no commercial applications of this technology. Nor have scientists figured out how to practically use heat from magma, the very deep and most powerful resource of geothermal energy.

PROS

• Geothermal energy is clean, requiring no burning of fossil fuels.
• It is always available. Geothermal power plants have average availabilities of 90% or higher, compared to about 75% for coal plants.

CONS

• It has limited availability, existing in only a few western states, Alaska and Hawaii
• Many of the best geothermal sites are located in environmentally sensitive areas such as national parks
• Geothermal sites have a tendency to cool down with use, greatly limiting their long-term potential, and therefore economic viability

THE FUTURE

• Worldwide geothermal production is very small. The United States by far the greatest producer of the resource.
• The three technologies discussed above use only a tiny fraction of the total geothermal resource. Several miles everywhere beneath Earth's surface is hot, dry rock being heated by the molten magma directly below it. Technology is being developed to drill into this rock, inject cold water down one well, circulate it through the hot, fractured rock, and draw off the heated water from another well. One day, we might also be able to recover heat directly from the magma.