A Study of the Potential for geothermal energy within the United States, led by the Massachusetts Institute of Technology (MIT), has found mining the heat in the Earth’s hard rock crust could supply a substantial portion of electricity to the United States. In addition, the study predicts the energy source could do so at competitive prices and with minimal environmental impact.
The study, “The Future of Geothermal Energy”, was sponsored by the U.S. Department of Energy and is the first in 30 years to take a new look at geothermal.
“We’ve determined that heat mining can be economical in the short term, based on a global analysis of existing geothermal systems, an assessment of the total U.S. resource and continuing improvements in deep-drilling and reservoir stimulation technology,” said panel head Jefferson W. Tester, the H. P. Meissner Professor of Chemical Engineering at MIT.
According to Tester, the new assessment of geothermal energy by energy experts, geologists, drilling specialists and others is important for several key reasons.
First, fossil fuels are increasingly expensive and consumed in ever-increasing amounts. Second, oil and gas imports from foreign sources raise concerns over long-term energy security. Third, burning fossil fuels releases carbon dioxide and other pollutants into the atmosphere. Finally, heat mining has the potential to supply a significant amount of the country’s electricity currently being generated by conventional fossil fuel, hydroelectric and nuclear plants.
The study shows drilling several wells to reach hot rock and connecting them to a fractured rock region that has been stimulated to let water flow through it creates a heat exchanger that can produce large amounts of hot water or steam to run electric generators at the surface. Unlike conventional fossil fuel power plants that burn coal, natural gas or oil, no fuel would be required. In addition, a geothermal plant works night and day, offering a uninterruptible source of electric power.
Tester and panel member David Blackwell, professor of geophysics at Southern Methodist University in Dallas, also pointed out that geothermal resources are available nationwide, although the highest grade sites are in western states, where hot rocks are closer to the surface, requiring less drilling and thus lowering costs.
One drawback is that meeting water requirements for geothermal plants may be an issue, particularly in arid regions. Further, the seismic risk potential needs to be monitored and managed, the report said.
According to panel member M. Nafi Toksöz, professor of geophysics at MIT, the electricity produced annually by geothermal energy systems now in use in the United States at sites in California, Hawaii, Utah and Nevada is comparable to that produced by solar and wind power combined with a much higher potential.
Tester and his colleagues emphasize that federally funded engineering research and development must still be done to lower risks and encourage investment by early adopters. Of particular importance is to demonstrate that enhanced geothermal systems technology is scalable and transferable to sites in different geologic settings. So contractors won’t see an immediate shift toward this source, but it could become a large part of the alternative energy market in the coming years. For more information on this topic, see “Beneath Our Feet.” EC