A national laboratory of the U.S. Department of Energy Office of Energy Efficiency & Renewable Energy National Renewable Energy Laboratory Innovation for Our Energy Future Geothermal— Technical Report NREL/TP-840-40665 The Energy Under Our Feet November 2006 Geothermal Resource Estimates for the United States Bruce D. Green and R. Gerald Nix, National Renewable Energy Laboratory NREL is operated by Midwest Research Institute • Battelle Contract No. DE-AC36-99-GO10337 Geothermal— Technical Report NREL/TP-840-40665 The Energy Under Our Feet November 2006 Geothermal Resource Estimates for the United States Bruce D. Green and R. Gerald Nix, National Renewable Energy Laboratory National Renewable Energy Laboratory 1617 Cole Boulevard, Golden, Colorado 80401-3393 303-275-3000 • www.nrel.gov Operated for the U.S. Department of Energy Office of Energy Efficiency and Renewable Energy by Midwest Research Institute • Battelle Contract No. DE-AC36-99-GO10337 Executive Summary he Earth houses a vast energy supply or application: (1) Hydrothermal, (2) Deep in the form of geothermal resources. Geothermal Systems, (3) Direct Use, T Domestic resources are equivalent (4) Geothermal Heat Pumps (GHPs), to a 30,000-year energy supply at our and (5) Co-Produced and Geopressured. current rate for the United States! In fact, geothermal energy is used in all 50 Geothermal resources are categorized in U.S. states today. But geothermal energy several layers of accessibility and feasibility, has not reached its full potential as a clean, from broadest criteria (i.e., total physically secure energy alternative because of issues available), to criteria that includes with resources, technology, historically low technical and economic considerations. natural gas prices, and public policies. These The total resource base is scaled downward issues affect the economic competitiveness to accessible resource, and finally to a of geothermal energy category called developable resource (see p. 4 for explanation). On May 16, 2006, the National Renewable Energy Laboratory (NREL) in Golden, The table below shows estimates for the Colorado hosted a geothermal resources different geothermal resource categories, as workshop with experts from the geothermal compiled by the workshop experts. These community. The purpose of the workshop estimates show the enormous potential was to re-examine domestic geothermal of the U. S. geothermal energy resource. resource estimates. The participating experts New low-temperature electric generation were organized into five working groups technology may greatly expand the based on their primary area of expertise in geothermal resources that can be developed the following types of geothermal resource economically today. Findings by Resource Category Estimated Developable Resource* Estimated 2006 205 2025 2050 Accessible (Actual MWe) (MWe) (MWe) (MWe) Resource (MWe) Shallow Hydrothermal 30,000 2,800 10,000 20,000 30,000 (Identified) >90˚C/94˚F Shallow Hydrothermal 120,000 TBD TBD TBD (Unidentified) >50˚C/302˚F Co-Produced & >100,000 23 10,000 to 70,000 >100,000 Geopressured2 15,000 Deep Geothermal4 1,300,000 to 0 1000 10,000 130,000 13,000,000 Thermal Uses (MWt) (MWt) (MWt) (MWt) Direct Uses5 >60,000 620 1600 4,200 45,000 Geothermal Heat Pumps6 >1,000,000 7,385 18,400 66,400 >1,000,000 GHP6 Avoided Power 120,000 880 2,100 8,000 120,000 * Please note that these resource estimates represent a consensus of a group of experts who considered existing resource assessments (referenced on next page). There is considerable uncertainty in the estimates as many resources are hidden and exploration to date has been relatively limited. The figures shown above are not a resource assessment, but, even with uncertainty, clearly show that the U.S. geothermal resource is a very large and important domestic energy source. References 1. Assessment of Geothermal Resources of the United States – 1978, USGS Circular 790 (p. 41 and 157). Includes identified and unidentified resources; 2015 and later estimates are a consensus of the experts at the workshop. Estimated accessible figure includes identified (~30,000 MW) and unidentified (~120,000 MW) (i.e., hidden or showing no surface manifestations) PIX 14846 NREL, Bruce Green, hydrothermal resources. 2. “Geothermal Electric Power Supply Possible from Gulf Coast, Midcontinent Oil Field Waters,” Oil and Gas Journal, September 5, 2005, and SMU Geothermal Laboratory Geothermal Energy Generation in Oil and Gas Settings Conference Dr. Roy Mink, DOE Geothermal Technologies Program findings, March 13 – 14, 2006, and USGS manager, making opening comments. Circular 790. 3. Based on Mafi Trench Unit on offshore platform now in operation. 4. Energy Recovery from Enhanced/Engineered Geothermal Systems (EGS), Massachusetts Institute of Technology (MIT), September 2006. 5. OIT Geo-Heat Center, using analysis based on USGS Circulars 790 and 892. 6. Geothermal Heat Pump Consortium, based on Energy Information Administration data and projections. The ‘avoided power’ figure represents the peak power not required or offset through use of GHPs. Thus, GHPs act as a proven demand and growth management option for utilities. Bruce Green, NREL PIX 14843 Bruce Green, The geothermal heat pump working-group during their resource deliberations. John Geyer (l), Wael El-Sharif (c), and Jack DiEnna (r) made up this working group. 2 Introduction he United States possesses vast underground work in partnership with U.S. industry to establish Tstores of heat whose full potential has yet geothermal energy as an economically competitive to be realized. The Earth’s interior reaches contributor to the nation’s energy supply. temperatures greater than 4,000°C (>7,200°F), and this geothermal energy flows continuously to the The purpose of the workshop was to re-examine surface. The energy content of domestic geothermal domestic geothermal resource estimates. There resources to a depth of 3 km (~2 mile) is estimated were two guiding questions: what is the total to be 3 million quads, equivalent to a 30,000-year potential accessible resource in the United States, supply of energy at our current rate for the and, given favorable circumstances and using United States! While the entire resource base existing practices with improved technology, and cannot be recovered, the recovery of even a very with institutional issues solved, how much of small percentage of this heat would make a large the resource is developable by 2015, 2025, and difference to the nation’s energy supplies. New low- 2050? Resource types include hydrothermal, deep temperature electric generation technology may geothermal systems, co-produced, geopressured, greatly expand the geothermal resources that can be direct use, and GHPs. developed economically today. The goal of the workshop was to gather and Geothermal resources could meet a substantial summarize expert opinions about the potential portion of the nation’s energy needs in the 21st of various geothermal resources for generation century. In fact, when including geothermal heat of electricity and utilization of heat energy. The pumps (GHPs), geothermal energy is used in workshop was not a formal assessment, but a all 50 U.S. states today. The U.S. Department recorded discussion by a group of experts who of Energy’s (DOE) Geothermal Technologies collectively state their opinions based on their Program seeks to make geothermal energy the experiences, knowledge, and interpretations nation’s environmentally preferred baseload of various detailed assessments (e.g., USGS energy alternative. The Program’s mission is to Circular 790). Figure 1. U.S. Energy and Geothermal Resources Note: U.S. Total Resource Base from Characterization of U.S. Energy Resources and Reserves, December 1989, U.S. Department of Energy, DOE/CE-0279. Data for “Estimated Accessible Geothermal Resource” and “Estimated Developable Resource” are from Table 4 of this report. 3 Resource Definitions Energy resources are traditionally classified according The total resource base in the United States, to the degree of certainty and the economic feasibility both renewable and non-renewable, is very of exploiting the particular resource. The U.S. Geological large, with an energy content of over 657,000 Survey (USGS) and the U.S. Department of Energy billion barrels of oil equivalent (BBOE), or (DOE) have used such identifying terms for resource nearly 50,000 times the annual current rate of classification. Following are simple definitions of these classification terms: national energy consumption. Figure 1 shows graphically what the total resource base looks U.S. Total Resource Base – Resource base is all of a like, and in descending order, the values for the given material in the Earth’s crust, whether its existence is estimated accessible geothermal resource and known or unknown and regardless of cost considerationsa. estimated developable resource. Estimated Accessible Geothermal Resource– The accessible resource base for geothermal energy is that part of the resource base shallow enough to be reached by production drilling in the foreseeable futurea. Estimated Developable Resource – This category is the subset of the accessible resource base that the workshop experts believe likely to be developed in future years. aSource: Assessment of Geothermal Resources of the United States – 1978, USGS Circular 790 (p. 4). NREL, PIX03698 NREL, Geothermal resources are available throughout the entire U.S. 4 Description of Geothermal Resource Categories Hydrothermal Deep Geothermal