23 Oct 2008
Deep Geothermal: The Untapped Renewable Energy Source
Until now, geothermal technology has only been used on a small scale to produce power. But with major new projects now underway, deep geothermal systems may soon begin making a significant contribution to the world’s energy needs.
In April of 1861, members of the first expedition to cross the Australian continent from south to north and back again blazed the word DIG on an old eucalyptus tree near Cooper Creek. The message for their comrades indicated that stores of food had been buried there that would keep them alive after their arduous trek.
Little did they know that two miles beneath that same soil lay 455° F granite — conducting the Earth's core heat closer to the surface than in most places, but still insulating it with a thick layer of coal- and clay-rich sedimentary rock.
Now a new expedition is digging, or rather drilling, through this soil and rock in an attempt that just might help humanity survive
Pacific Gas & Electric Company
The Geysers geothermal power plant in California is the world's largest.
the twin perils of global warming and the energy crisis. Brisbane-based Geodynamics has drilled four wells — two test and now one injection and one production — in an attempt to prove that the heat trapped in granite can power Australia past climate change. The company is aiming for 40 megawatts of electricity production at the site by 2010, expanding to 500 megawatts by 2015 — the size of a typical large coal-fired power plant, but without the pollution.
Ultimately, thanks to unusually hot rock close to the surface and existing infrastructure from oil-and-gas production, the Cooper River basin alone could produce about 10,000 megawatts of electricity — enough to replace 20 large coal-fired power plants, says geologist Doone Wyborn, Geodynamic's chief scientist. That’s just a taste of the potential that this technology, known as enhanced geothermal systems, holds for Australia and the world, according to Wyborn.
"Geothermal in Australia,” says Wyborn, “could potentially provide all the country’s electricity needs for the next 100 years without any trouble."
As the world searches for energy sources that don't pump more greenhouse gases into the atmosphere, renewables such as wind and solar power have garnered the most attention. But deep geothermal power — water pumped down to the hot rock, heated, and then brought back to the surface to turn turbines for electricity — is increasingly being eyed as an enormous potential source of pollution-free energy. Already, small demonstration plants are operating in France and Germany, while Iceland and the United States have ambitious projects in the works.
As much as 5 percent of U.S. power could come from geothermal by 2050, according to government estimates. But some analysts and scientists say that deep geothermal power, accessed through so-called “enhanced geothermal systems” (EGS), could contribute far more to America’s — and the world’s — energy grid. The potential is certainly enormous: A recent report by researchers at the Massachusetts Institute of Technology estimated that by tapping into geothermal energy, more than 200,000 exajoules of energy could be captured in the U.S. alone, or "2,000 times the (total) annual consumption of . . . energy in the United States in 2005." Says chemical engineer Jefferson Tester of MIT, lead author of the report, "This is a very large resource that perhaps has been undervalued in terms of the impact it might have on supplying energy to the U.S."
But although EGS has many advantages — it produces no emissions of carbon dioxide, is available day and night (unlike sunshine or fickle winds), and can potentially be developed nearly anywhere in the world — much remains to be done before it can be put to use on a large scale. The main barriers are cost and developing sophisticated pumps that can move large volumes of water through fractures in the deep, hot rock.
At present, geothermal power delivers a kilowatt-hour of electricity for somewhere between 10 cents and one dollar, depending on the depth of the hot rock and the
As much as 5 percent of U.S. power could come from geothermal by 2050, according to government estimates.
terrain’s geologic structure. That is far higher than the 6 cents per kilowatt-hour for electricity from burning coal. But that gap could steadily shrink as governments worldwide adopt cap-and-trade regimes that tax carbon emissions. As the true cost of burning coal, oil, and natural gas is factored into the equation, and as engineers improve the technologies used by enhanced geothermal systems, the appeal of this form of alternative energy is expected to grow.
"The question is: can we do it better?" says Karl Gawell, executive director of the U.S. Geothermal Energy Association in Washington, D.C. "At what size? And how broadly can it be replicated?"
Tapping the Earth's heat for energy has a long history. Hot springs have been used for bathing and cleaning since ancient times, earning a mention everywhere from Roman annals to the Icelandic sagas. And using such steamy outposts for electricity generation dates as far back as the 1920s. It was then that The Geysers complex in northern California began operating, relying on nature to provide the perfect circumstances — fractured subsurface rock filled with water that is then heated and escapes to the surface.
Today, The Geysers, the largest geothermal power plant in the world, produces enough electricity for 725,000 homes. The more than 1 gigawatt of geothermal power currently produced globally — from California to Iceland to the Philippines — relies nearly exclusively on such natural outpourings of the earth's heat. Already, there are more than 3,000 megawatts of geothermal capacity in the United States – the bulk of it at the The Geysers – and as many as 100 new geothermal power plants are proposed for promising sites. This week, the U.S. Interior Department announced it would make more than 190 million acres of federal land available to lease for geothermal development.
But mimicking nature — drilling deep beneath the surface, fracturing the rock and pumping water through it to capture heat — could
Steam flows from Geodynamic Limited's Habanero 3 well in Australia.
unleash a torrent of geothermal power, according to the recent MIT report, "The Future of Geothermal Energy." Such a manmade geothermal system could harvest as much as 40 percent of the heat in the bedrock and convert 15 percent of it into electricity via simple low-temperature steam turbines at the surface, according to mechanical engineer Ron DiPippo at the University of Massachusetts, Dartmouth, a member of the MIT report team.
The researchers estimate that for just $1 billion invested over 40 years — the cost of one large coal-fired power plant and a fraction of the cost of a nuclear power plant — 100 gigawatts of clean, dependable geothermal power could be developed in the United States alone. That’s the energy equivalent of more than 200 coal-fired power plants or 100 new nuclear power plants.
The technology to develop EGS on a large scale is not there yet, but will be soon, many scientists say. "We can open up fractures, that's not a problem,” said Tester of MIT, noting that the basic technology already exists. “You can certainly drill wells even directionally. And you can convert the hot water into steam.”
A key benefit of enhanced geothermal systems is their stability. Once in place, geothermal power plants produce electricity nearly all the time, according to Dennis Gilles, senior vice president for geothermal at The Geyser's owner, Calpine. EGS systems outperform even coal-fired power plants, Gilles says.
But the only existing EGS power plants are in Soultz-sous-Forets, France and Landau, Germany, the latter generating 22 gigawatt-hours a year for the European grid. No one has proven that such advanced geothermal systems will work on a large scale. And an effort to develop another such geothermal power plant in Basel, Switzerland pointed up another potential problem: earthquakes.
In December 2006 and January 2007, three earthquakes measuring more than 3 on the Richter scale — too small to cause serious damage but large enough to be felt by residents — rattled Basel (which had been leveled by an earthquake in 1356). The cause turned out to be the injection of cold water deep beneath the earth in an attempt to fracture hot, unstable rock and create another advanced geothermal system. The project was brought to a shuddering halt as a result of the tremors.
Such induced seismicity is an integral part of any enhanced geothermal system, in essence revealing where fractures are being created in the subsurface rock. The Geysers, for example, produces more than 3,000 small earthquakes a year, or an average of 10 a day. Some of the tremors are naturally occurring, while others are caused by the limited amount of water The Geysers pumps underground to augment the natural steam created at the site.
Experts say tremors caused by EGS are not likely to be a major stumbling block to the technology, particularly if the plants are located away from large population centers. "Induced seismicity has not caused the type of damaging earthquakes that people think of," explains EGS expert Allen Jelacic of the U.S. Department of Energy's geothermal technologies program. "It's not going to cause your house to fall down or cause significant damage. People could learn to live with it."
Beyond earthquakes, enhanced geothermal systems face the barrier of drilling costs: For the oil-and-gas industry, those costs amount to more than $500 a foot for wells deeper than 18,500 feet, with costs increasing every day. Tapping the geothermal heat in regions like the northeastern U.S. would require drilling nearly twice that deep, and geothermal wells need to be wider and more permanent—read more expensive—than their oil-and-gas counterparts.
Finally, enabling the steady flow of water through fractured hot rock will require pumps that can withstand temperatures in excess of 392° F, pressures of more than 5,000 pounds-per-square inch,
Currently, nearly 100 new geothermal power plants are being planned for development at promising sites.
and corrosive brines. "You have to improve the efficiency of the pumps so that you don't lose too much electricity pumping water around," says Lucien Bronicki, co-founder of geothermal developer, Ormat, in Reno, Nevada. The list of other needs is long: faster drilling techniques, subsurface mapping and an understanding of subsurface fluid flow, high temperature logging tools and sensors, as well as better tracers and tracer interpretation techniques.
But the potential for stable, secure and, perhaps most importantly, carbon-free electricity has drawn investment. The U.S. government has renewed its interest, committing $20 million in 2008 and promising an additional $43 million over the next four years, pending Congressional approval. The U.S. government also wants to collaborate with Australia and Iceland to help develop the technology. The Australian government, for its part, has pledged 43.5 million Australian dollars for such renewable power, and the 39 private companies rushing to take advantage of this program have also been able to raise capital from investors in the stock market. Geodynamics, for example, has raised 319 million Australian dollars from more than 13,000 investors.
And Google.org — the philanthropic arm of the electricity-hungry Internet giant — has committed $11 million in funding for two start-up geothermal companies, including one that is developing a new drilling technique that would melt rock rather than fracturing it, as well as improved subsurface mapping.
"Geothermal is a resource that can be looked at to supply power throughout the U.S.," says geothermal program manager Ed Wall of the U.S. Department of Energy. The Western U.S. is particularly promising as geology conspires to bring the Earth's heat even closer to the surface. California and Nevada host many promising sites. But, assuming that deep drilling and the basic technology can be improved, geothermal resources are available throughout the country. "It's clean, renewable, baseload power," Wall adds.
Ultimately, the techniques and technologies that deliver the promise of such enhanced geothermal systems may first be developed at existing natural sites that have proven disappointing in terms of heat or water flow. Already, The Geysers has shown that reinjecting water can improve power production — pumping in wastewater from surrounding California communities boosted electricity output to six million megawatt-hours annually without affecting the temperature of the rock below. The oil-and-gas business has laid the groundwork for much of a potential EGS business — injecting water or other liquids, fracturing rock, manipulating drills and improving drill bits.
"It's not here but it's not 40 years away," Gawell, of the U.S. Geothermal Energy Association adds. "The real challenge isn't the power plant, it's the subsurface."
An Australian outback outpost known as Innamincka will soon become the first completely geothermally powered town in the world using EGS. Geodynamics is in the process of constructing a 1 megawatt pilot plant in the Cooper Basin that should be operational next year and provide power to the town of 15 hardy souls.
Everything needed for the power plant is ready and just needs to be assembled, says civil engineer and Geodynamic's technical advisor, Adrian Williams. "In Australia, there's no shortage of energy,” says Williams. “Clearly the lowest-cost way of generating power is conventional coal. But it's the acceptance of the reality of climate change and the commitment to cut emissions that have provided the economic basis for the investments."
Once the power plant is completed, a conventional transmission line that crosses the 7 miles of outback will turn Innamincka into an electricity oasis. The one-megawatt plant "will satisfy our site needs but more importantly it will enable us to power Innamincka" free of charge, Williams says, adding, “This will be the first powering of a whole township in the world, a township which is currently dependent on diesel generators."
And that will make the Dig Tree and the Cooper Creek basin more than a point of local interest.
ABOUT THE AUTHOR
has been covering energy and the environment for nearly a decade, the last three years as an associate editor at Scientific American
. He also hosts 60-Second Earth
, a Scientific American
podcast covering environmental news.