Could the residual heat of hot rocks deep within the Earth power Vermont's electric utility industry by the year 2050? Maybe, according to a MIT study and if a U.S. Department of Energy (DOE) drilling program proves cost efficient. With some government incentives, utility and drilling companies would have to make the investment to make a Vermont geothermal power plant possible.
A U.S. News & World Report last year cited the MIT study and also indicates that geothermal energy might be tapped in untried places such as Vermont. "The limiting factor is the cost," according to the story.
DOE's Enhanced Geothermal Systems (EGS), also called engineered geothermal systems, offers the greatest potential for dramatically expanding the use of Earth's inner heat into previously unlikely geothermal locales.
Present geothermal power generation comes from hydrothermal reservoirs and is limited to the western U.S. But deep-drilling EGS technology offers the chance to extend geothermal resources into new areas of the U.S. such as the northeast.
More than 100,000 MWe of economically viable capacity may be available in the continental United States, representing a 40-fold increase over present geothermal power generating capacity. This potential is about 10 percent of the overall U.S. electric capacity today, and represents a domestic energy source that is clean, reliable, and proven.
In the case of Vermont, the EGS concept would extract residual heat from deep hot rocks-in excess of three miles below the surface-by creating a subsurface fracture system to which water is added via ultra-deep injection wells. Starting at 3.7 miles down, Vermont's rocks are a steamy 302 degrees Fahrenheit.
Creating an engineered geothermal system requires improving the natural permeability of rock. Rocks are permeable due to minute fractures and pore spaces between mineral grains. Injected water is heated by contact with the rock and returns to the surface through production wells, as in naturally occurring hydrothermal systems.
The MIT-led study of the potential for geothermal energy within the northeastern U.S. has found that mining the huge amounts of heat that reside as stored thermal energy in the Earth's hard rock crust could supply a substantial portion of Vermont's electricity-at competitive prices and with minimal environmental impact.
An 18-member panel led by MIT prepared the 400-plus page study, titled "The Future of Geothermal Energy." Sponsored by the U.S. Department of Energy, it is the first study in 30 years to take a new look at geothermal, a natural energy resource that has been largely ignored by planners and environmentalists.
"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 Dr. Jefferson W. Tester of MIT.
The new assessment of geothermal energy by energy experts, geologists, drilling specialists and others is important for several key reasons, Tester said: Geothermal is an ideal zero greenhouse energy source and a compliment to a new generation of ultra-safe, peaceful nuclear power plants planned for the post-carbon future.
Unlike conventional fossil-fuel power plants that burn coal, natural gas or oil, no fuel is needed. And unlike wind and solar systems, a geothermal plant works night and day offering a non-interruptible source of electric power.
Resources of geothermal energy range from the shallow ground to hot water and hot rock found a few miles beneath the Earth's surface, and down even deeper to the extremely high temperatures of molten rock called magma (magma is lava before it reaches the surface). Almost everywhere, the shallow ground or upper ten feet of the Earth's surface maintains a nearly constant temperature between 50 and 60 F (10 and 16 C).
The MIT panel said drilling must reach depths in excess of three miles in places such as New England. Still, the possibility of drilling into Vermont's ultra deep subsurface rocks-fracturing them and pumping water in to produce steam-has already been shown to be feasible.