Enhanced Geothermal Systems

Matthew Potter
October 24, 2010

Submitted as coursework for Physics 240, Stanford University, Fall 2010

Introduction

In the first half of 2009, Geodynamics Limited, an Australian geothermal exploration and development company, announced that it had successfully proved its strategy for extracting energy from the hot granite beneath the Earth's surface, perhaps marking a new era in geothermal energy technology. [1]

Traditional Geothermal Generation

Geothermal generation - using steam escaping from within the Earth's crust to power turbines that produce electricity - has been commercially viable since 1913, when the world's first commercial-grade geothermal power plant opened in Larderello, Italy. [2] Today, there are scores of wells and plants in Larderello, providing a combined 562.5 MW of capacity. [3]

Limitations of Traditional Geothermal Generation

Worldwide, traditional geothermal plants like Larderello - those that rely on naturally occurring steam venting from the crust to power its turbines - provide 10,715 MW of capacity, accounting for just 0.2% of the world's energy production. [4,5] Beyond this humble contribution, traditional plants are limited to locations where there are existing, easily accessible hydrothermal vents. [6] Furthermore, steam pressure at these locations diminishes over time as the magma is cooled by water, as at Larderello, where pressure is down 30% from its peak in the 1950s. [2]

Enhanced Geothermal Systems (EGS)

To overcome the limitations of conventional plants, Geodynamics and a handful of other companies around the world hope to use a new method of geothermal generation: Enhanced Geothermal Systems (EGS). With EGS, wells are drilled deep into the Earth's surface and cold water is injected to induce fracturing of the rock, creating a reservoir similar to those found naturally. Following the creation of the artificial reservoir, cold water injected into the space is heated and the resulting steam is used to power a turbine to generate electricity. As the heat from the steam is exchanged with the turbine, the water is returned to the reservoir and the process begins anew. Thus, EGS is completely clean and always on, making it more attractive than other renewable energy sources like solar and wind. [7]

The promise of EGS has attracted investors such as Google, Kleiner Perkins Caufield & Byer, and the United States and Australian governments. The American Recovery and Reinvestment Act of 2008 includes over $100M in funding for EGS research and implementation, while Google has invested over $10M. [8]

Current Limitations of EGS

Despite this enthusiasm, EGS methods remain extremely expensive compared to conventional geothermal; and, more dramatically, drilling deep wells and inducing fractures beneath the surface causes earthquakes in surrounding regions. [9] In Basel, Switzerland, an EGS project was terminated after microseismic activity damaged nearby buildings and alarmed residents. [10] Shortly thereafter, another project, at the Geysers, north of San Francisco, also closed, after protests from area inhabitants. [11]

Moving Forward

Over the next ten years, whether EGS methods can succeed in bringing untapped geothermal energy to market economically should be revealed. In the Cooper Basin of Australia, Geodynamics is hoping to construct a 1 MW pilot plant by 2012, the success of which will determine whether to invest in and construct a 25 MW commercial demonstration plant. [8] With scientists around the world working to develop the technologies required to implement Enhanced Geothermal systems, and with the attention of the world's governments and private investors, the future looks bright.

© 2010 Matthew Potter. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.

References

[1] "Geothermal Projects Heat Up," Ecogeneration, May/June 09.

[2] J. Israely, "Steaming Forward," Time, 8 Jun 03.

[3] G. Cappetti, P. Romagnoli and F. Sabatelli, "Geothermal Power Generation in Italy 2005-2009 Update Report," Proceedings of World Geothermal Congress 2010, Bali, Indonesia, 25-29 Apr 10.

[4] I.B. Fridleifsson et al., "The Possible Role and Contribution of Geothermal Energy to the Mitigation of Climate Change," Proceedings of IPCC Scoping Meeting on Renewable Energy Resources, Luebeck, Germany, 20-25 Jan 08.

[5] "Renewables Global Status Report 2009 Update," REN21, 09.

[6] T. Zeller, "Enhanced Geothermal: The Next Killer App?," The New York Times, 20 Aug 08.

[7] A. Revkin, "Study Says Tapping of Granite Could Unleash Energy Source," The New York Times, 23 Jan 07.

[8] "Hot Rocks and High Hopes," The Economist, 2 Sep 10.

[9] J. Tester et al., "The Future of Geothermal Energy: Impact of Enhanced Geothermal Systems (EGS) on the United States in the 21st Century" MIT, 06.

[10] J. Glanz, "Deep in Bedrock, Clean Energy and Quake Fears", The New York Times, 23 Jun 09.

[11] J. Glanz, "Geothermal Project in California is Shut Down," The New York Times, 11 Dec 09.