As a green energy source, geothermal heat is tough to beat, but until recently, it was believed to be economically feasible only in areas with shallow tectonic (volcanic) activity. Now, with a generous grant from Google.org, the search engine giant's philanthropic arm, two scientists from Southern Methodist University (SMU) have pooled together the results from more than 35,000 data sites to paint a very different, almost rosy, energy picture for the United States and, indeed, the world.

For over one hundred years, traditional geothermal plants have exploited natural steam reservoirs fairly close to the surface of the earth's crust. The superheated steam is captured by wells which channel it to drive turbines in adjacent power plants. Calpine Corporation's Geysers Field, situated north of San Francisco in the craggy Mayacamas Mountains, is the world's largest earth-powered electrical generation complex and provides a good example of this green technology at work.

Currently, more than 2700 MWh of electricity are generated geothermally in the U.S. each year- roughly equivalent to 60 million barrels of oil - and sufficient to power 3.5 million homes, all while eliminating 22 million tons of carbon dioxide, 200,000 tons of sulfur dioxide, 80,000 tons of nitrogen oxide and 110,000 tons of particulate matter. Clean, indeed.

SMU Geothermal Lab Coordinator Maria Richards and Geophysics professor David Blackwell's research has revealed, however, that a much larger portion of the earth's crust can yield usable energy than was previously thought, especially in the eastern U.S. The project's findings indicate that, with advanced technology already available, the continental U.S. harbors a staggering 2,980,000 MW of potential energy! That's especially impressive considering the current global geothermal generating capacity is only 9,000MW.

The SMU team's research meshes nicely with new technology coming online, collectively dubbed Enhanced Geothermal Systems (EGS), that promises to expand the yield of geothermal energy by several orders of magnitude. Whereas traditional plants exploit naturally existing steam, the EGS technique involves injecting water into wells drilled deep into hot rock. The resultant steam is then captured to drive turbines and generators, similar to those powered by natural steam.

To date, Google.org has made over US$10 million in grants to foster EGS development. Other plants will use a lower temperature approach, such as this facility we covered a few years back, which can generate power with much less heat.

"This assessment of geothermal potential will only improve with time," said Blackwell. "Our study assumes that we tap only a small fraction of the available stored heat in the Earth's crust, and our capabilities to capture that heat are expected to grow substantially as we improve upon the energy conversion and exploitation factors through technological advances and improved techniques."

We now know that potentially exploitable EGS resources can be found in all 50 U.S. states and countless regions around the globe as well, so it's only a matter of time before abundant clean energy begins to flow from tapping into that massive molten furnace churning below our feet.

"Both Google and the SMU researchers are fundamentally changing the way we look at how we can use the heat of the Earth to meet our energy needs, and by doing so are making significant contributions to enhancing our national security and environmental quality," said Karl Gawell, executive director of the Geothermal Energy Association.

To view the new Enhanced Geothermal Systems maps constructed with SMU's data , go here to get the latest version of Google Earth, then download and open the file here.

Check out the videos below for more info on EGS systems. The second video, a Google.org animation of the Habanero EGS facility currently under development in Australia, has no sound.