By Emily Gertz
The planet’s internal heat is a powerful, constant force that’s available anywhere on Earth — and a potential energy source that we’ve barely begun to harness.
In 2010, renewables supplied a mere eight percent of total energy consumption in the United States, led by biomass and hydroelectric power. Geothermal power made up only three percent of that mix.
What projects we do have on line are limited to a handful of spots in the Western states, and they’ve come about mostly as a result of serendipity.
“Most of the geothermal that’s operating today is what we call the low-hanging fruit,” Steven Chalk, the U.S. Department of Energy’s deputy assistant secretary for renewable energy said in an interview with TPM. “It’s where you see the steam coming out of the ground, or you’ve got the geology where it’s in the ring of fire, or near volcanoes.” These conventional geothermal installations pump heated underground water up to power plants on the surface.
The Obama administration envisions an expanded role for geothermal, however, as one of the clean technologies that will help the U.S. slash oil imports by a third in the next decade. So DOE is actively funding geothermal power R&D.
Most recently, in late June the department split $11 million in grants between eight different geothermal projects.
Industry boosters say this and more government help — which essentially means creating the right mix of funding, regulations and tax breaks — is crucial to fostering the development of geothermal. Since drilling is so expensive, and the technologies are still emerging, it’s been hard to find funding in the private sector.
Currently, there are a couple of bills in the House and the Senate that address some of these issues, and they enjoy bipartisan support. But it’s an open question if we’ll see any significant movement on them this year.
Some companies, like Google, do see enormous potential in geothermal power, due to the successful development of “enhanced geothermal systems” or EGS.
These technologies, also called “hot dry rock” geothermal systems, involve the creation of artificial fluid reservoirs in rock formations roughly 2.5-4 miles beneath the earth’s surface, where the temperature can exceed 360 deg. F.
According to a 2007 report from the Massachusetts Institute of Technology, sponsored by DOE, “[W]ith a reasonable investment in R&D, EGS could provide 100 [gigawatts] or more of cost-competitive generating capacity in the next 50 years.”
Among the projects in the DOE’s current slate of funding, a couple intend to explore an especially juicy piece of high-hanging EGS fruit: Injecting hot dry rock with carbon dioxide, the greenhouse gas that is the primary driver of human-propelled climate change.
One tantalizing possibility is that we could siphon off the greenhouse gas for EGS from existing pollution sources, which would help to reduce the USA’s ongoing, massive contributions to the climate change crisis.
“This would be a double win,” says Chalk. “We’d be creating electricity with a renewable power source-essentially, the heat of the earth-and also sequestering CO2, [perhaps] captured from industrial plants or coal plants.”
Among its June grants, DOE awarded $5 million–almost half of the total available–to a project that combines the potential for CO2 sequestration with conventional and enhanced geothermal techniques. Led by mechanical engineer Barry Freifeld of Lawrence Berkeley National Laboratory, the project’s goal is to design and build a small demonstration system that would use CO2 under high pressure, called “supercritical” CO2, instead of water, as the geothermal working fluid.
Supercritical CO2 has big advantages over water as a working fluid in geothermal energy generation, says Freifeld.
The density of supercritical CO2 is similar to that of water, which might mean that existing equipment can be adapted to use it, rather than building from scratch.
Supercritical CO2 is more efficient than water, as well: it retains heat much more capably than water, and has a much lower viscosity, so less energy would be needed to move the same amount of heat from below ground to the surface.
In most EGS scenarios, CO2 injections would be used to break up underground rock, toward creating the artificial reservoirs, says Freifeld. This project will utilize underground rock that is dry, but already broken up, or permeable. This will save a complex step on the way toward a fully realized geothermal technology.
Freifeld says that the plant design will be based upon the “Thermafficient Heat Recovery System,” a power-generation technology developed by the Ohio-based firm Echogen that uses supercritical CO2 to capture waste heat from industrial facilities. The University of Texas Bureau of Economic Geology is also collaborating on the project.
The demo plant will likely be the size of one or two shipping containers, Freifeld says, so that if it works, it will be easy to truck off for field-testing at the Cranfileld, Mississippi oil field that’s already home to of the Southeast Regional Carbon Sequestation Partnership (SECARB).
DOE has spent tens of millions co-financing SECARB, a multi-year underground CO2 storage demonstration project, which according to the project’s web site had injected over 3 million metric tons of CO2 underground as of November, 2010.
“We’re going to leverage that,” says Freifeld, referring to both Energy’s investment and the stored CO2.
Ultimately, if his novel approach can be scaled up to commercial use, it could involve transporting waste CO2 from industrial facilities, via pipelines, to geothermal energy plants sited above good rock formations for carbon storage.
One of the major pitfalls with underground CO2 storage is that it takes a whole lot of potentially expensive energy to push that gas into a subterranean rock formation.
If that energy is coming from a CO2-emitting energy source, such as a coal-fired power plant, what’s the point?
Freifeld hopes that the technologies he and his co-investigators develop will help offset some of that “energy penalty.”
The project will also seek to answer how much total energy this combined geothermal-carbon storage technology will be able to produce.
Emily Gertz is a freelance journalist and editor based in New York City. She is the co-author, with Patrick Di Justo of Wired magazine, of the forthcoming O’Reilly book Environmental Monitoring With Arduino. She’s also a contributor to Worldchanging: A User’s Guide to the 21st Century. You can follow her on Twitter at @ejgertz.
