Updated by Leslie Blodgett GEA 2014
The heat of the Earth is considered infinite; its use is only limited by technology and the associated costs, but the potential is there to provide enough energy to meet the power needs of humankind many times over. Production is becoming viable in more states and areas of the world as research and development uncovers the possibilities.
3.1. What is the potential of using geothermal resources in the U.S.?
The temperature at a depth of 6.5 km is above boiling nearly everywhere in the U.S., so the potential for generating electrical power from geothermal resources could be realized in every state in the country.
The USGS has identified potential for geothermal energy production in 13 Western states of up to 16,457 MW from known geothermal systems; up to 73,286 MW from resources yet to be discovered; and up to 727,900 MW from the use of EGS (Table 1).
The Western Governors Association has stated that by 2025, around 13,000 MW of identified geothermal resources could be developed in Western states.
In 2013 the Imperial Irrigation District in California pledged to build 1,700 MW of additional geothermal power by the early 2030s.
Production is already happening beyond the Western states and will continue to expand. In recent years there are geothermal projects in development as far east as Texas and Louisiana.
Table 1. Geothermal Resource Potential in Western States
U.S. Geological Survey. The report assessed Alaska, Arizona, California, Colorado, Hawaii, Idaho, Montana, Nevada, New Mexico, Oregon, Utah, Washington, and Wyoming. Not included in the assessment: geothermal systems located on public lands closed to development, such as national parks; geothermal direct use, small power, oil and gas coproduction and geopressured resources
Western Governors Association
||Potential MWe (% probability)
|Identified Geothermal Systems
||3,675 (95%) to 16,457 (5%)
||The resource is either liquid or vapor dominated and has moderate to high temperature. The resource is either producing, confirmed, or potential.
|Undiscovered Geothermal Resources
||7,917 (95%) to 73,286 (5%)
||Based on mapping potential via regression analysis.
|Enhanced Geothermal Systems
||345,100 (95%) to 727,900 (5%)
||Resource probability in regions characterized by high temperatures but low permeability and lack of water in rock formations.
Separate studies by the National Renewable Energy Laboratory (NREL) and the Massachusetts Institute of Technology (MIT) concluded over 100,000 MWe could feasibly be reached in the next 15 to 50 years, respectively, with a reasonable, sustained investment in R&D. ,
In 2010, in a study funded by Google.org, Southern Methodist University (SMU) collected data that broadened the known geothermal potential for EGS technology across the U.S. to 2,980,295 MW—a near 40-fold increase compared to traditional geothermal technology potential. A major discovery within this study was that West Virginia, with temperatures of 392°F (200°C) at 5-km depths, places the state’s geothermal power potential at 18,890 MW: a significant increase over prior estimates and the largest known geothermal reserve in the Eastern U.S.
Massachusetts Institute of Technology
U.S. Department of Energy “Geothermal—The Energy.” This report does not include hidden or undiscovered geothermal systems, which the USGS report estimates have substantial energy potential; nor does it examine small power systems or distributed generation.
Google’s investment made it the top investor in geothermal energy in the U.S. at the time, outspending the federal government.
3.2. What technologies will expand geothermal energy uses in the short term?
This section covers mineral recovery, enhanced or engineered geothermal systems (EGS), coproduction of geothermal and oil/gas, geopressured resources, and supercritical cycles.
3.2.1. Mineral Recovery
Mineral recovery is the practice of extracting minerals from water at conventional geothermal sites, reducing the environmental impacts of mining. Known minerals found in geothermal fluids include: silica in many forms, strontium, zinc, rubidium, lithium, potassium, magnesium, lead, manganese, copper, boron, silver, tungsten, gold, cesium, and barium. Different geothermal sites contain different suites of minerals.
Simbol Materials is working to produce lithium from geothermal plants at a demonstration facility in Imperial Valley, California. Lithium has been called an energy-critical element, needed for high-performance battery materials and electrolyte solutions in electric vehicles and other clean-energy storage applications. Imperial Valley could be well-positioned strategically to competitively, sustainably, and reliably meet the world’s needs for high-performance battery materials for years to come.
3.2.2. Enhanced Geothermal Systems
Enhanced or engineered geothermal systems (EGS) refer to the creation of artificial conditions at a site where a reservoir has the potential to produce geothermal energy. A geothermal system requires heat, permeability, and water, so EGS techniques make up for reservoir deficiencies in any of these areas by enhancing existing fracture networks in rock, introducing water or another working fluid, or otherwise building on a geothermal reservoir.
At The Geysers, California, two pipelines bring treated sewage water from Lake County and Santa Rosa to improve the generation capacity of the wells.
In the Deschutes National Forest in Oregon, AltaRock Energy, Inc. is leading an EGS demonstration project.
The 260-MW Coso facility in southern California used EGS technology to extend capacity by 20 MW.
Desert Peak, Nevada, hosts an EGS expansion of an existing natural geothermal field.
For more information on the DOE effort visit: http://www1.eere.energy.gov/geothermal/enhanced_geothermal_systems.html.
See also the International Partnership for Geothermal Technology: http://internationalgeothermal.org.
Photo: Soultz, France, 1.5-MW EGS Power Plant
3.2.3 Coproduction of Geothermal and Oil/Gas
Heated water is a natural byproduct of oilfield production processes that has long been considered unusable. But much of the “wastewater” produced at oil wells each year in the U.S. is hot enough to produce electricity through geothermal coproduction.
Many of these wells are estimated to have clean energy capacities of up to 1 MW. A 1-MW power generator is small in conventional power generation terms, but the potential for hundreds of these to be brought on line within a short period of time is promising.
“According to reports by Massachusetts Institute of Technology and the National Renewable Energy Laboratory, there are 823,000 oil and gas wells in the U.S. that co-produce hot water concurrent to the oil and gas production,” states the white paper for the six-month demonstration at the Denbury, Mississippi oil field in 2011. “This equates to approximately 25 billion barrels annually of water which could be used as fuel to produce up to 3 GW of clean power.”
At the DOE’s Rocky Mountain Oil Test Center (RMOTC), Wyoming, geothermal company Ormat Technologies built a successful 0.25 MW coproduction demo unit which first ran in 2008.
A DOE-funded coproduction demonstration projects is underway by the University of North Dakota.
American Physical Society Panel on Public Affairs and the Materials Research Society
Figure 13 provides a perspective of the known estimated coproduced geothermal potential as of the 2006 report from MIT. (Note: Chad Augustine and Dave Falkenstern’s 2012 paper “An Estimate of the Near-Term Electricity Generation Potential of Co-Produced Water from Active Oil and Gas Wells” provides some updates; for example, new geothermal potential was recently discovered in West Virginia.)
Figure 13: SMU Estimated Co-Produced Geothermal Potential
3.2.4. Geopressured Resources
Geopressured resources are reservoirs of naturally high-pressured hot water. Figure 14 shows major oil-producing basins in the U.S. The most significant of these located in Texas, Louisiana, and the Gulf of Mexico. (Note: The major oil-producing basins (of all types) in the U.S. are highlighted. The gray stippling indicates the parts of those basins where geopressured strata have been encountered.)
Figure 14: Geopressured Basins in the United States
A demonstration plant in Texas produced electricity from geopressured resources as part of a DOE research program from 1979-1983. In 2012, DOE funded a Geopressured Demonstration Project by Louisiana Tank in Louisiana.
Photo: Geopressured Demonstration Plant in Texas
3.2.5. Supercritical Cycles
Supercritical fluids are in a physical state in which the temperature and pressure are above the critical point for that compound, meaning there is no distinction between liquid and vapor. Carbon dioxide is an example of a fluid that, when used in a supercritical state, can be pumped into an underground geological formation where it will heat up and expand, enhancing the fracture system in the rock as needed for geothermal production. It is then pumped out of the reservoir to transfer the heat to a surface power plant or other application and then returned to the reservoir.
A demonstration plant is underway by GreenFire Energy at the Arizona-New Mexico border region. The project would compress and reinject naturally occurring CO2 to carry heat to the plant. It has the potential not only to utilize natural carbon dioxide, but also to sequester human-made CO2 from nearby power, resulting in net negative emissions.
The Iceland Deep Drilling Project (IDDP), a supercritical geothermal project, unexpectedly drilled into magma in 2009. IDDP has been able to fund continuing studies. The superheated high-pressure steam exceeded 842°F (450°C), a record for geothermal heat.
U.S. Department of Energy “Innovative Geothermal”
3.3. What is the international potential of geothermal energy?
Table 2. World Continental Geothermal Resources
Based on industry announcements and feedback, in early 2014, GEA estimated about 12,000 MW of geothermal planned capacity additions, and about 30,000 MW of geothermal resources, under development worldwide. Since geothermal sources are considered essentially limitless, estimates of its potential focus on commercial possibilities using quantifiers such as available lands and technology limits. Geothermal resources were estimated to potentially support between 35,448 MW and 72,392 MW of worldwide electrical generation capacity using technology available at the time of a 1999 GEA study. Table 2 shows University of Utah estimates of world geothermal resources for four different geologic regimes.
||bbl oil equivalent
||15 × 1024 J
||2,400,000 × 109
||490 × 1024 J
||79,000,000 × 109
||810 × 1018 J
||130 × 109
||2.5 × 1024 J
||410,000 × 109
|Total Oil Reserves (for comparison)*
||5,300 × 109 J
*Includes crude oil, heavy oil, tar sands, and oil shale
National Academy of Sciences
Indonesia is the country holding the highest percentage of known geothermal resources, estimated at 28 GW, or 40% of the world total. Of this, about 5% has been developed.
Even more information. . .
Photo: Chena Hot Springs, Alaska, Distributed Generation
Image: United States Heat Flow Map at 6 km Depth
Image: Hydrothermal Areas in the Western United States; dots identify geothermal reservoirs
Image: Location of Geothermal Projects and Resources
Image: Geothermal Heat Pump Installations in 2006; states in darker green have the higher number of installations.
The USGS assessment is available at http://www.usgs.gov/newsroom/article.asp?ID=2027&from=rss_home.
The MIT report, The Future of Geothermal Energy, is available at
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