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Hot rocks may be new power source

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.

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