How underground 'hot rocks' could power America’s future
With enough investment, geothermal power could satisfy 10 percent of the US energy diet, energy experts say.
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A study led by the Massachusetts Institute of Technology released in early 2007 estimated that a public and private investment in EGS of $800 million to $1 billion over 15 years could yield 100,000 MWe (Megawatts electrical) of electrical capacity by mid-century. The US currently has about 1 million MWe of capacity, or about 10 times that amount. Geothermal sources today generate just under 3,000 MWe of capacity.Skip to next paragraph
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The development of geothermal energy is paralleling the history of oil and gas exploration “except we’re about 100 years behind them,” says Karl Gawell, executive director of the Geothermal Energy Association, an industry group.
A century ago, oil companies could only find oil where it was already coming out of the ground, he says. That’s akin to finding geothermal by looking for hot springs or geysers today.
But later in the 20th century, oil companies found “you could fracture [the rock], you could add water, add gases,” and employ other techniques to create new wells or extend the life of existing ones, he says. “The oil industry essentially learned to engineer oil fields to get a lot more production out of them.”
That’s exactly what EGS proponents hope to do with geothermal sources. At The Geysers, a geothermal plant north of San Francisco, 4 billion gallons of treated sewer water from the city of Santa Rosa is being injected into the ground each year to replenish the system and maintain the flow of heated water to the surface. That represents a kind of EGS already at work.
But more research is needed if the effort is going to take off.
“I think it’s going to really require the federal government to stimulate activity by coming in and trying to support demonstration projects and things like that for it to get started in a big way,” says David Blackwell, a professor of geophysics at Southern Methodist University, one of the 18 members of MIT’s EGS study panel. “There are some places in the central and eastern United States that are quite hot at reasonable depths that could probably be developed in the relatively near future.”
Shale gas wells in West Virginia and Pennsylvania provide an intriguing possibility. After the gas has been extracted, they’d “make wonderful heat exchangers” using the 250 to 350 degree F. water found in them, Dr. Blackwell says.
The potential for EGS is “vast,” he says. “I think that the MIT report is conservative if we really start to develop it.”
The big unknown is going to be cost. “And until we actually have a number of [EGS] systems operating,” he says, “we don’t know what the cost will be.”