Enhanced Geothermal Systems - The "Killer App" of the Energy World
Google surprised the audience at the National Clean Energy Summit in August by pronouncing that “enhanced” geothermal energy could be the “killer app” of the energy world. In September, Google and General Electric jointly announced an effort to more fully develop this potentially unlimited resource.
What exactly is “enhanced” geothermal energy? Why has it excited such giants as General Electric and Google? And, will it live up to expectations?
Traditional geothermal energy relies on naturally occurring pockets of steam and hot water beneath the earth. Geothermal power plants on the surface use the steam from 1 to 2 miles below the surface to run turbines and generate electricity. In order to be economic, large geothermal plants are usually built where the heat is relatively near the surface and where the temperatures of the hydrothermal resources are generally warm (between 300 and 700 degrees Fahrenheit). These plants produce, on average, for about 30 years and, depending on their location, are competitive with the prices from traditional fossil fuels plants. However, large scale geothermal resources seem quite hard to come by or the resources are located at uneconomic depths. Consequently, traditional geothermal power plants produce less than .0035 of total electric generation in the US and less than 1 percent world-wide.
“Enhanced” geothermal however, taps into the earth’s unlimited hot rock. Those rocks are then fractured, water is circulated through the system, and the resulting steam is used to produce electricity in a conventional turbine.
A 2006 report on Enhanced Geothermal Systems (EGS) by MIT (sited by Idaho National Laboratory and Wikipedia) concluded that it would be affordable to generate 100 GWe (gigawatts of electricity) or more by 2050 in the United States alone, for a maximum investment of 1 billion US dollars in research and development over 15 years.
The MIT report calculated the world's total EGS resources to be over 13,000 ZJ. Of these, over 200 ZJ would be extractable, with the potential to increase this to over 2,000 ZJ with technology improvements - sufficient to provide all the world's present energy needs for several millennia. The key characteristic of an EGS (also called a Hot Dry Rock system), is that it reaches at least 10 km down into hard rock. At a typical site two holes would be bored and the deep rock between them fractured. Water would be pumped down one and steam would come up the other. The MIT report estimated that there was enough energy in hard rocks 10 km below the United States to supply all the world's current needs for 30,000 years.
What then are the impediments to this seemingly unlimited resource? First, the depth of these holes are daunting. There are technological challenges involved in drilling wide bore holes to depths of 4,500 meters (about 2.8 miles) as well as the difficulty involved with breaking (fracturing) rock over large volumes. Second, drilling to such depths is currently very expensive. Conventional oil and gas wells drilled to 15,000 feet generally cost tens of millions of dollars. Each enhanced geothermal plant would require two holes.
Google is relying on several potential breakthroughs to advance EGS. On the cost side, Google expects that the economies of scale will bring project costs down in line with coal-fired plants. On the technology side, Google has invested in new hard rock drilling technologies and in companies involved in EGS research and development.
Certainly, the injection of GE as a participant in enhanced geothermal lends tremendous credibility to Google’s efforts. The only question in my mind is whether any one approach is truly the “killer app” in the energy world.
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