Geothermal Energy Still Hot

The pool at Hot Springs Lodge and Pool in Glenwood, Colo., is the world’s largest hot springs pool. Photograph is courtesy of Hot Springs Lodge and Pool.

“Biofuels” may be the alternative energy du jour, but geothermal energy enthusiasts want you to remember that corn- and soybean-based ethanols are still just parts of the buffet of alternative fuel options. Although overshadowed by recent federal enthusiasm for the crop-based fuels, U.S. researchers are still investigating wind, solar, hydrothermal and geothermal energy, and continue to puzzle over how to convert these resources into environmentally friendly — but still economically viable — alternatives to oil, gas and coal.

Two of those options, however, recently became victims of a budget squeeze. In March, the U.S. Department of Energy (DOE) announced that its fiscal year 2008 budget will nix funding for hydropower and geothermal power.

For proponents of geothermal energy, that decision is frustrating, if not new: DOE also cut geothermal program funding in past budgets, but Congress has restored it, at least in part. Considering the current energy concerns, however, those cuts are short-sighted, proponents say: Scientific studies suggest that geothermal resources in the United States can potentially supply as much as 20 percent of the country’s total energy needs — but fully developing the resource will require government support.

“We can triple capacity in 10 years if we have federal and state support,” says Karl Gawell, executive director of the Geothermal Energy Association. Despite geothermal proponents’ confidence that federal support for new technology is the most important ingredient, a spokeswoman for DOE stated that the department now considers geothermal technology to be “mature” — and it is time for private enterprise to take the lead in its development. “They’re giving up,” Gawell says. “They’re saying we just can’t do it, and they’re wrong.”

At a congressional hearing on geothermal energy in March, Roy Mink, the former director of DOE’s geothermal program, said that there is plenty that DOE could still do to drive geothermal energy forward. Mink, who left DOE in 2006 in frustration over its lack of support for the resource, said that in addition to facilitating existing production by updating permitting regulations, offering production tax incentives similar to what oil and gas companies receive and helping develop infrastructure to transmit the energy, the government could invest in new drilling and exploration technologies to locate vast, still-hidden geothermal resources.

Currently there are only about 60 geothermal plants in the United States, producing less than 1 percent of the country’s electric power, and producing about 2,800 megawatts of electricity, according to the Geothermal Energy Association. Substantial scientific evidence suggests that far more extensive geothermal resources exist in the United States, however, including a 1979 U.S. Geological Survey (USGS) study that estimated the potential resource.

But only a small fraction of that resource has actually been “located” to date. The rest is still “blind,” hidden by thick layers of sediment or shallow cold-water aquifers, Mink said. “This is where research is needed,” he said. “It’s the subsurface understanding that really needs some work.”

Earth naturally contains heat flowing through the crust. The heat is generated both by the decay of radioactive elements in the crust itself, and within Earth’s mantle and core, from which it is transported by convection and conduction. The shallowest heat sources, such as hydrothermal fluids, are already being harnessed in a variety of ways, but geothermal proponents suggest that much more heat is available deep underground, if researchers can find it.

Beneath the Western United States, temperatures are hot at relatively shallower depths, but geothermal resources exist across the country if drilled deep enough. Image is by David Blackwell.

“Basically Earth is a heat engine,” says David Blackwell, a geologist at Southern Methodist University. “No matter where you go, if you drill deep enough, it’s hot.”

In 2006, an MIT-led report built on the USGS study, assessing the potential for geothermal energy to become a major source of energy to the country. The report focused both on the currently existing, economically viable hydrothermal resources of Western states, and on the potential to find and access the deeper but widespread thermal resource spanning the country. According to the report, long-range hopes for large-scale geothermal power in the country will rest with that deep resource and with “enhanced geothermal systems” (EGS) — innovative technology that can increase rock permeability and create more economic hydrothermal reservoirs, increasing their productivity and lifetimes. With an investment of $1 billion in research and development for EGS over 15 years, the report states, the United States could affordably generate 100 gigawatts of electricity or more by 2050.

In the United States, heat flow can be categorized into “three general areas,” Blackwell says. For the MIT report, he constructed a series of heat flow maps that show how temperatures change with depth belowground across the country. In much of the Western United States, including Idaho, Nevada, California and Utah, temperatures are hot even at shallow depths. Hydrothermal power developed from this heat has long been in use in some places: In 1892, the world’s first district heating system went online in Boise, Idaho, when water from nearby hot springs was piped into town buildings. Hydro-thermal fluids in the Western United States tend to be at least 150 to 200 degrees Celsius at depths less than 100 meters, Blackwell says. Although considered relatively low-temperature, that is still hot enough to produce electrical energy using newer technology, such as “binary” geothermal plants.

Other Western states have also developed the resource to help supply power to their residents: Nevada, for example, currently has 14 geothermal power plants, and 24 new plants are under development. Geothermal energy also supplies 5 percent of California’s power needs, although development of new plants has been hampered in the past decade by permitting regulations and infrastructure issues, according to the Geothermal Energy Association.

In the middle of the country, however, sufficient geothermal temperatures are only found much deeper underground, at depths of around 3 to 6 kilometers, Blackwell says. Even farther east, “you’d have to drill to deeper depths than that,” he says, and in those regions EGS would become particularly important to make recovering the resource technologically and economically feasible.

Along the U.S. Gulf Coast, however, some wells have already been drilled to those depths. In that region, hot water is often buried at high pressure, and is also saturated with natural gas. Furthermore, the “geopressured” water in those wells is often artesian, rising naturally to the elevation of the land surface. “Basically, the Gulf Coast is floating,” Blackwell says. “In Texas there are hundreds of thousands of wells already drilled deeper than 3 kilometers, and thousands deeper than 6 kilometers and over 150 degrees [Celsius],” he says.

Beginning in 1989, DOE tested one such geopressured well in the region, which showed that the reservoir was viable, Blackwell says. But the historically low price of fossil fuels meant there was little financial incentive to develop those wells at the time. Now, however, the rising cost of fossil fuels may once again make geopressured wells more competitive, he says. In Texas, there is a specific need for that power “right now,” he adds. “It’s an energy-intensive state, due to its climate and industrial activities,” and Texas is currently using within 4 percent of its total installed power capacity — compared to the buffer of 10 to 15 percent that states prefer.

Geothermal’s supporters point to its array of current and future applications, and hope it will again survive this latest round of budget cuts. Fueled by growing concerns over climate change, Gawell says, “the public interest and support is there. And maybe Washington will catch up.”

Carolyn Gramling

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