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.

Courtesy of the General Theological Seminary
Members of the General Theological Seminary in New York gather for snapshot in 2007 before drilling began on their geothermal heating and cooling system.

Could hot rocks miles below the earth’s surface be the “killer app” of the energy industry?

Google thinks so. It’s investing more than $10 million to develop new technology that would make this subterranean resource a widespread, economically viable competitor to fossil fuels.

Geothermal heat could meet 10 percent of America’s energy needs by mid-century, according to the US Department of Energy. What’s more, it would not generate the climate-warming carbon emissions associated with fossil fuels.

Once tapped, a geothermal system would stay online for centuries. Unlike wind and solar, it would be a “base load” energy source, available 24 hours a day, 365 days a year.

That all sounds great – but of course there’s a catch. A geothermal well costs millions of dollars to drill and drilling is the only way to determine if a location has the right kind of hot rock. The result: With only a trickle of federal aid allotted to developing the resource, geothermal is growing slowly.

That may change under the Obama administration, which has pledged strong support for renewable energy.

“If sufficient [research and development] funding were invested in the next 20 years or so, as much as 10 or 20 percent of the electricity in the United States could come from geothermal,” says Robert Neilson, who manages the Renewable Energy and Power Technologies Department at the US Department of Energy’s Idaho National Laboratory.

The US already produces more geothermal electricity than any country in the world. In California, it accounts for nearly 5 percent of total electrical capacity. But these traditional geothermal plants require three things: hot rock formations near the surface, water to take the heat out of the rock and bring it to the surface, and fractures in the rock to allow the hot water to circulate.

Most known locations with all these qualities are found in the western US and are already being tapped.
The possibility of enhanced geothermal systems (EGS), however, have reenergized the movement. These systems would use technology to either fracture the rock or inject needed water. If EGS can surmount the technical and cost hurdles, many more places, including the eastern and central US, suddenly would be candidates for geothermal plants.

“EGS could be the ‘killer app’ of the energy world,” said Dan Reicher, director of climate and energy initiatives for, announcing Google funding for EGS research last August. “It has the potential to deliver vast quantities of power 24/7 and be captured nearly anywhere on the planet. And it would be a perfect complement to intermittent sources like solar and wind.”

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.

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.

A few other EGS efforts are under way around the world, including one in Soltz, France, and another expected to come online in Australia next spring.

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.”

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