The heat of the Earth is considered limitless; its use is only limited by technology and the associated costs. Technology development and further studies are expected to show even greater potential, but here we have cited the first part of a new assessment released in September 2008 by the U.S. Geological Survey (USGS). (1) The report focuses on 13 western states and breaks the geothermal estimate into three categories:
· Identified Geothermal Systems: The resource is either liquid or vapor dominated and has moderate to high temperature. The resource is either producing (the reservoir is currently generating electric power), confirmed (the reservoir has been evaluated with a successful commercial flow test of a production well), or potential (there are reliable estimates of temperature and volume for the reservoir but no successful well tests to date).
· Undiscovered Geothermal Resources: Geothermal resources were assessed for the same 13 states in which the identified resources are located. The assessment was based on mapping potential via regression analysis.
· Enhanced Geothermal Systems (EGS): Resource probability in regions characterized by high temperatures but low permeability and lack of water in rock formations.
The assessment estimates power generation potential as follows:
· Identified Geothermal Systems: 3,675 MWe (95% probability) to 16,457 MWe (5% probability)
· Undiscovered Geothermal Systems: 7,917 MWe (95% probability) to 73,286 MWe (5% probability)
· EGS: 345,100 MWe (95% probability) to 727,900 MWe (5% probability).
The USGS assessment evaluates geothermal resources in the states of Alaska, Arizona, California, Colorado, Hawaii, Idaho, Montana, Nevada, New Mexico, Oregon, Utah, Washington, and Wyoming. The assessment identified 241 moderate-temperature (90 to 150°C; 194 to 302°F) and high-temperature (greater than 150°C) geothermal systems located on private and public lands in these states. Geothermal systems located on public lands closed to development, such as national parks, were not included in the assessment. Electric-power generation potential was also determined for several low-temperature (less than 90°C) systems in Alaska for which local conditions make electric power generation feasible.
Although the assessment only accounted for large-scale geothermal power production, the USGS is also in the process of updating information about direct use, small power, oil and gas co-production and geopressured resources and the potential energy contribution of those portions of the geothermal resource base are not included in the estimates above.
The USGS assessment is the first new national geothermal resource assessment since 1979, when USGS released its last geothermal resource estimate, Circular 790. A new component of the 2008 assessment is the inclusion of production potential of EGS techniques. For more information on the USGS assessment, please visit http://www.usgs.gov/newsroom/article.asp?ID=2027&from=rss_home.
In 2006, Massachusetts Institute of Technology (MIT) prepared an analysis of the future geothermal potential in the U.S. The report estimated that geothermal systems could produce 100 GWe in the next 50 years with a reasonable investment in R&D. The report, The Future of Geothermal Energy, is available at http://geothermal.inel.gov/publications/future_of_geothermal_energy.pdfhttp://www1.eere.energy.gov/geothermal/future_geothermal.html
Are there other examples of how geothermal resources are utilized?
· Distributed generation: Distributed generation facilities such as those at Chena Hot Springs in Alaska, the Burgett greenhouse in New Mexico, and the Oregon Institute of Technology are examples of small-scale electricity produced to cover the electricity needs of each facility. Energy not being used by the facility is sold back to the grid.
