Furthermore, says Robertson-Tait, “there is ignored geothermal potential deep beneath the Great Basin.” Deep underneath eastern Nevada and western Utah, underlying limestone-and-dolomite formations “represent a significant geothermal target,” she said; they are susceptible to the kind of permeability needed for a successful geothermal reservoir, and there is a significant body of knowledge related to permeability enhancement. Additionally, oil and gas drilling in the area means that there are already wells for gathering data.
This concept of high-temperature geothermal resources beneath young sedimentary basins was the topic of a project and a 2012 Geothermal Resources Council paper by Rick Allis of the Utah Geological Survey and several co-authors: “Stratigraphic Reservoirs in the Great Basin – The Bridge to Development of Enhanced Geothermal Systems.”
Conventional Hydrothermal Projects Continue to Lead Geothermal Development
Technology innovations complement the addition of geothermal MW to the grid in recent years, mostly via conventional hydrothermal facilities. The GEA’s springtime survey of projects-under-development showed that of the 147 projects surveyed, 116 projects (about 80%) were developing conventional hydrothermal resources in areas where the geothermal resource had not previously been developed for power generation; 18 were developing conventional projects in areas already proven for production; and five were expansions to existing conventional plants.
There were also five coproduction and three EGS projects. These are both rather different than conventional hydrothermal, and are exciting, relatively new technology developments that are bringing geothermal energy to more regions of the U.S. than ever before. Efforts in Nevada, California, and throughout the West are undoubtedly an inspiring example, particularly as state leaders and communities across the U.S. are becoming more aware of geothermal technology as a reliable and renewable resource.
While a 2006 estimate by the Western Governors Association (WGA) considered 13,000 MW could be developed by 2025 in Western states, there was no equivalent study in the Eastern states. Four years later, Southern Methodist University (SMU) brought to light 18,890 MW of geothermal power potential in West Virginia – a discovery representing the largest known geothermal reserve in the Eastern U.S. The future successful production of EGS technologies, many of which are being tested now, could ultimately mean geothermal energy in parts of the U.S. where it hasn’t previously been viable.
EGS a Substantial Resource that Merits Further R&D
The data from the SMU study supports estimates that EGS could widen geothermal potential across the U.S. to 2,980,295 MW -- a near 40-fold increase compared to traditional geothermal technology potential. It is considerable both in terms of the potential, and in the work that still needs to be done.
“How can we stimulate large volumes of rock and create these heat exchangers? What conditions are best for that? What stress conditions, what rock types? Is it realistic to think we can do this in the Eastern U.S. at depths of 15,000 or 20,000 feet?” said Robertson-Tait, laying out the kinds of problems EGS scientists are dealing with.
Still, in order to get to something like 10% of the U.S. electricity supply – considered realistic by many experts – it “will probably require an EGS component,” she reasons.
A report from the Massachusetts Institute of Technology (MIT) conducted in 2006, the same year as the WGA estimate, concluded over 100,000 MWe could feasibly be reached in the next 50 years with a reasonable, sustained investment in R&D. “As the MIT report showed very well, [EGS] is a substantial resource. As a long-term strategic resource that is still not viable, it merits research.”
The U.S. DOE helps the industry do just that through its Geothermal Technologies Program of the Office of Energy Efficiency and Renewable Energy. Their work to demonstrate the technical feasibility of EGS includes seven demonstration projects in five Western states. Seventeen other currently-funded projects comprise a mix of coproduction, geopressure, and low-temperature projects.
“A DOE program to fund exploratory drilling would be very successful, as was done in the late 1970s with a U.S. industry drilling program which drilled many wells across the West,” Robertson-Tait said. Iovenitti, Faulds, and others noted the industry’s need for improvements in drilling and data analysis; DOE has also recognized this.
DOE has set targets to reduce the levelized cost of electricity from EGS to 6 cents/kWh by 2030 and the LCOE from coproduction, geopressure, and low-temperature technologies to 6 cents/kWh by 2020. GEA’s next feature article, “Geothermal Innovations, Part 2” will follow up with a look at DOE’s hand in some of the most creative geothermal innovations happening today.
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