As ancient as the earth itself, unharnessed geothermal energy most often bubbles to the surface in geological hot spots long known for geysers and naturally-boiling mud pots.
Although such conventional shallow geothermal power has heretofore been harnessed with varying degrees of success, EGS (Enhanced Geothermal Systems) is capable of engineering a circulating energy-producing reservoir of hot water and steam as much as 10,000 feet beneath the surface. In fact, EGS could eventually be used on a global scale to tap into an almost endless energy supply from which to generate electricity.
By some projections, the world’s total reliance upon geothermal energy could, within a decade, climb from its present production low of 1 percent to 25 percent. But like all energy technologies, geothermal will need to be price competitive to become commercially viable.
The key to making it practical, regardless of the above ground landscape, entails new deep-drilling technology capable of hitting depths of some 10 kilometers. EGS involves deep drilling to hit hot rock, then hundreds of thousands of gallons of cold water from shallow ground water wells is pumped at high pressure to fracture the hot rock.
Once the cold water has been injected, the fractures it creates are mapped using a micro-seismic monitoring network. This network literally listens for the popping and snapping sounds that accompany fracturing rock. It’s at these intersections of fractured rock that production wells are then drilled. Having absorbed heat of a couple of hundred degrees Celcius, the injected water emerges from the production well, spewing hot water and steam at rates of 50 to 100 kgs per second. This steam is then used to generate electricity via steam turbine. Once it exits the turbine, it is then cooled using a heat condenser and re-injected back into the ground to complete a closed-loop system.
Although EGS technology was proven in the 1980s at Los Alamos National Lab, the technology remains a commercial fledgling with start up companies worldwide trying to make EGS practical on commercial scales.
Part of geothermal’s problem is the lack of a public profile.
“Solar and wind energy are easily understood,” said Colorado-based geologist Gerard Huttrer and president of Geothermal Management. “Even someone with a high school education can stand out in a field and feel the wind blow and realize there’s energy there. Geothermal energy is an arcane thing to most people. But if you drill deep enough you will hit high temperatures.”
Australia has several thousand square miles of high heat producing radiogenic granite within 3 to 5 kms of the surface. Geodynamics has drilled six wells in South Australia’s Cooper Basin where they are planning a 25-MW EGS project.
“We hope to be able to develop 1000 sq. kms for EGS,” said Doone Wyborn, Geodynamics’ chief scientist. “We’re producing hot water in a circulation test and we’re building a small demonstration 1-MW power station that should be in the commissioning stage by December 2012.”
Wyborn says the company’s first commercial power station will generate 25 MW; requiring up to nine wells at a cost of about $300 million. Due in part to a few technical setbacks, however, geodynamics refuses to say when the 25-MW plant will come online. But the company hopes to ultimately generate 5,000 to 10,000 MW of power, or about a third of Australia’s present electricity budget.
“But we need to get up to 200-300 megawatts to justify transmission to the grid and that could cost $1 billion,” said Wyborn. “Hopefully, by the time we have our second 50 MW power module running, we’ll be under the costs of all other baseload power generation systems, including coal.”
Meanwhile, here in the US, Davenport Newberry Holdings and Altarock Energy have a $43.5 million EGS demonstration project on Deschutes National Forest lands some 30 miles south of Bend, Oregon. Newberry has already drilled two 10,000 ft. wells, one of which is ready for injection with cold water.
“We’re the only company in the US aimed at commercial-scale EGS production,” said Susan Petty, Altarock’s president and chief technology officer. She says the biggest risk with such a project is not technical, but financial.
“Suppose you design your project for 250 degrees Celcius at a depth of 4 kms,” said Petty. “But then you don’t hit it there, so you have to go deeper.” Petty notes that such difficulties won’t necessarily cause a project to ultimately fail, but they will drive up its final production costs. For EGS, the big hurdle right now is being able to create a reservoir with sufficient flow rates from its production wells.
“You can model this to death,” said Jeff Tester, a Cornell University chemical engineer. “But Cooper Basin and Altarock are generating operating data in real reservoirs. What’s not clear however is a given well’s fluid production rate over years instead of weeks and months. The higher the rate of flow per well, the fewer number of wells you need.”
Huttrer estimates current EGS production costs at $10 to $12 million a well. With a minimum of 10 wells needed to reach commercial power, that makes wholesale costs of the system’s geothermal electricity some $10,000 a kW. But Huttrer says with advanced drilling and better fracturing techniques the costs will come down.
Petty says they hope to have their production wells drilled and tested by the end of 2013 with potential commercial production by 2015.
A 2006 geothermal study panel led by Tester, then at MIT, found that with enough investment in research and development geothermal energy could make up as much as 10 percent of the US electricity budget within the next half century at prices competitive with fossil-fuel.
Petty is even more optimistic: “With technology improvement based on very modest research over the next 25 years, you could get 100,000 MWs of [geothermal] online, or about a quarter of the US’ [present electricity needs.]”
