Compagnie Parisienne de Chauffage Urbain , this renewable heat will displace enough gas, coal and oil to avoid 14,000 tons of CO2 emissions annually.The 130-ton rig erected by French drilling contractor Cofor marks a strange sight for the world’s most visited travel destination: Paris. Yet there it was this April, its 37-meter-high boom drilling away beside the juncture of the Canal St. Denis and the Boulevard PÌ©riphÌ©rique – the freeway that rings France’s capitol. Such rigs and their wells usually bring up petroleum and natural gas, but in this case reducing the use of such fossil fuels is the order of the day. The two 1800-meter-deep wells installed by Cofor this spring in northern Paris will serve as the source and return feeds for a geothermal energy system accessing a deep 57C aquifer to provide both heating and air conditioning to over 1 million square meters of residential and commercial space. According to the district heating company that will operate the geothermal wells, the
Geothermal district heating is hardly a new concept but it is enjoying a renaissance after two decades of inactivity. Some 30 operations installed in the 1970s and 1980s draw upon the Dogger aquifer underlying the Paris region to heat a total of 150,000 dwellings. “Oil and gas exploration created many wells in the Paris basin. They found a bit of oil and a lot of hot water. When there was the oil shock in 1973 the French government had the idea of exploiting the hot water,” explains Fabrice Boissier, director of the geothermal department at France’s Geological and Mineral Research Bureau. Boissier says that after low energy prices halted developments in the mid-80s and 1990s, rising energy costs and climate change concerns have pushed geothermal energy back on the front-burner. He predicts that further installations tapping the Dogger may triple the number of geothermally-heated homes in the Paris-region by 2020.
The rejuvenation of geothermal energy production in and around Paris is one small part of a much larger global movement according to William Glassley, executive director of the California Geothermal Energy Collaborative, a nonprofit consortium identifying research needs of academic and commercial researchers. “The geothermal world is going through a remarkable renaissance right now,” says Glassley. Most investment worldwide is focused on using geothermal heat to produce steam and generate electricity, rather than for district heating. The scale is impressive. Geothermal projects slated for installation worldwide over just the next five years will, if completed, add over nine gigawatts of power generating capacity, according to a March 2009 report by Cambridge, MA-based consultancy Emerging Energy Research. That’s roughly the equivalent of six large coal or nuclear-fired power stations and close to the 10.5 GW of geothermal generating capacity installed worldwide over the past 30 years.
Investment bank Credit Suisse helped explain this projected geothermal speed-up in a January 2009 report which identified geothermal as the cheapest source of electricity available. Credit Suisse estimated that generating one kilowatt-hour of power from geothermal cost, on average, just 3.6 cents, versus 4.3 cents/kwh from wind farms and 5.5 cents/kwh from coal.
Earth observation could play an important role in realizing geothermal’s potential, according to geothermal developers and researchers such as Boissier and Glassley. Existing geothermal operations rely on easily-accessed hot water identified during oil exploration or where hot water literally bubbles out of the ground, such as the turbines that tap Northern California’s Geysers steam field to generate enough power for all the homes in San Francisco, San Jose and Oakland, combined. In contrast, developing new geothermal resource means drilling exploratory wells on the scale of the Paris operation. With teams of half-a-dozen roughnecks working round-the-clock, consuming about 3,000 liters of diesel fuel per day, Boissier pegs the price of each well at $4-5 million ÛÒ a hefty up-front charge that does not factor into Credit Suisse’s optimistic cost estimate for geothermal power. “You always have to do exploratory drilling,” says Boissier. “It’s very risky, but if you want to be certain, you have to pay.”
How much renewable energy lies hidden behind geothermal energy’s exploration barrier? Plenty according to the first national reassessment of U.S. geothermal resources in three decades, which the United States Geological Survey is in the process of completing. In an overview of preliminary results released last fall, USGS estimates that power generation from 241 geothermal systems in the U.S. known to contain hot water that can be readily pumped to the surface could be more than tripled to 9 GW. Adding in undiscovered systems increases that potential by an estimated 30-73 GW. USGS predicts that the latter figure will expand towards 518 GW (equal to half of the current power generating capacity of the U.S.) as geoscientists and developers learn how to access water trapped in hot but relatively impermeable strata, creating engineered geothermal systems by artificially inducing water flow through the hot rocks.
Sniffing the surface
Novel techniques are in development to minimize the amount of drilling required to exploit geothermal’s hidden resources. These include remote spectral imaging by satellite or airplane, exquisitely sensitive isotopic sampling techniques, and data-sharing via virtual observatories to make better use of existing geochemical data on, for example, the mineral composition of groundwater. One of the most promising prospects is remote sensing via multispectral analysis to identify the mineral fingerprint of places where thermal hotsprings once burst on to the Earth’s surface. “The main role of remote sensing in geothermal exploration would be to point at sites of interest for further exploration using the more expensive ground-based methods,” explains Mariana Eneva, principal with San Diego-based Imageair, an independent research firm.
One instrument used for such studies is the Japanese-built Advanced Spaceborne Thermal Emission and Reflection Radiometer or ASTER carried by the U.S. Terra satellite. Eneva says her colleague Mark Coolbaugh, a geologist at the University of Nevada’s Great Basin Geothermal Center in Reno, has successfully applied ASTER imaging to identify the presence of borates leached out of sediments and rocks by geothermal activity. Both Eneva and Coolbaugh are seeking to extend remote sensing by using ASTER’s infrared sensing channels to directly identify regions with elevated surface temperatures. The challenge is identifying true surface temperature anomalies amidst an ever-shifting background complicated by such variables as the daily heating from above by sun and weather, topographical effects on air and heat flows, and the rates at which different materials and vegetation release heat. “This is very much breaking into new ground,” says Eneva.
Of course, remote sensing cannot help if the water or heat from a geothermal system never reaches the top, which is likely to be the case for many promising targets for engineered geothermal systems. One novel method that could help here is a helium-sniffing concept proposed by geochemists Mack Kennedy, a senior scientist at Lawrence Berkeley National Laboratory, and Matthijs van Soest, an associate research professional at Arizona State University’s School of Earth and Space Exploration. They have shown that traces of helium isotopes at the surface provide a proxy for regions deep underground likely to have both heat and at least some permeability—the starting point for an engineering geothermal system.
Kennedy and van Soest’s method is a twist on longstanding practice. Elevated levels of bulk helium in soil have long pointed geologists toward regions of enhanced permeability, as helium produced in the Earth’s crust from the radioactive decay of uranium and thorium migrates upward more rapidly in such regions. Kennedy and van Soest have shown that exquisitely sensitive detection of helium isotopes via mass spectroscopy can identify areas where permeability reaches all the way to the Earth’s superheated mantle, even in areas where no lava is flowing up. The key is the ratio of common helium-4 and its rarefied cousin, helium-3: Earth’s crust contains, on average, just one helium-3 atom for every 100 million atoms of helium-4, while helium-3 is a thousand times more common in the Earth’s mantle.
Kennedy and van Soest correlated elevated helium-3 with geothermal potential by measuring it in the water pumped through a geothermal power plant in Nevada’s Dixie Valley–an area that has not seen volcanic activity in 30 million years. Kennedy says their isotope method, published first in the journal Science in December 2007, has since generated considerable interest. “We have been approached to apply the technique in new areas and to extend our study,” he says.
However, in what is definitely a theme amongst geothermal researchers, Kennedy reports that funding limits have stalled further work on the technique. “The Department of Energy’s geothermal program was zeroed out of the federal budget in 2007,” says Kennedy. “Since then we have been just trying to hold on and help DOE keep the program alive.”
Federal funding of DOE’s geothermal program has now been restored and DOE has issued several calls for research proposals on engineered geothermal systems from the private sector, academia and the national labs. “Hopefully, with the return of DOE’s geothermal program and with anticipated increases in the level of program funding, the geothermal exploration component of the program will be reborn,” says Kennedy.
USGS researchers are similarly looking forward to a funding boost. Cost constraints limited the USGS reassessment, for example, to using mostly existing data, according to Colin Williams, the USGS geophysicist who led the study. Williams says he was “minimally satisfied” with the quantity and quality of the data available: “There was enough to complete the assessment and characterize our overall uncertainties, but we could reduce the uncertainties significantly with some additional data.” One example is their estimate of the potential for engineered geothermal systems, which is based primarily on the availability of hot strata with little attention to their permeability. “Understanding the role of rock type and the presence or absence of preexisting permeability on the resource estimate is a major focus of our ongoing research,” says Williams.
Geothermal researchers say that much can be done in the short term to aid exploration simply by making existing observational data more accessible. “For most of the developed world we have a tremendous amount of information but it’s not put together in a way that makes it readily useful for geothermal mapping and resource development,” says Glassley at the California Geothermal Cooperative. He points to data from oil and gas exploration wells, which are often filed away as paper reports in state data repositories, making access “a real slog.” Even more data on geothermal potential is potentially accessible from the millions of water wells in operation around the world. “Water contains a tremendous amount of information about its experience moving through the crust. If that kind of thing could be put together in a smart way that could be a tremendous boon,” says Glassley.
Glassley says DOE has put out solicitations for the creation of a center to undertake data collection for geothermal research, which he calls a good first step. “It’s a huge task,” says Glassley. But it is one that he predicts will be well worth the trouble: “What’s going to come out of this is recognition of geothermal systems not imagined before.”
Boissier agrees, and says there are hopeful signs of movement on a global scale. He points to OneGeology, an ambitious international effort launched in 2007 to create a global map of water resources. The final objective will be a GIS-based data system akin to Google Earth. “Geothermal energy could be a layer in this system,” says Boissier. “But first we need to have this infrastructure.”