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Contents Introduction/History Geothermal Heat Pumps Geothermal Plants Economics Conclusion: Comparative Renewables

An array of renewable energy sources-geothermal, solar, water, and wind-have the theoretical potential to deliver all the energy humanity needs thousands of times over in a clean, renewable way, if only that energy could be collected. Doing so efficiently would mean using a combination of resources depending upon local conditions and developing technology. Expensive to implement, once in place these technologies could provide energy on a long-term basis for very little cost. The four articles in this Discovery Guide series on renewable energy explain many of the advantages and drawbacks of wind, solar, biofuels, and geothermal.

Many kinds of renewable energy, notably solar and wind, are intermittent, which means that, until the problem of storage is solved, they can only provide a portion of energy needs. Two resources, geothermal and solar thermal (when used with a molten salt medium) are capable of providing baseline power, that is, a steady stream of power 24 hours a day. Beyond the start-up costs, the other major hurdle to these two energy sources is location: they are not viable in many areas. In the United States, these resources are abundant in the Southwest and scant elsewhere, meaning that, to be widely implemented, the electrical grid would require a major upgrade at great expense.

Another factor to consider is electricity usage versus transportation usage. Regarding transportation only biofuels, in the form of ethanol or biodiesel, can be directly used for transportation. Other forms of renewables, which generate power in the form of electricity, must be collected and stored in battery form to be used for transportation, and current technology to do so is cumbersome and expensive (the exception is subway and trolley systems, which can use electricity through direct transmission). The chart below summarizes many of the pluses and minuses of different types of renewable energy:

Renewable Energy Comparison Chart

	Types	Economic	Environmental Impact	Key Characteristics
Hydro	Dams	Extremely competitive when suitable water is available; by far the most widely used renewable energy	Building dams alters hydrology resulting in population displacement and environmental costs	Provides dependable baseline power
Solar	Photovoltaic, Solar Thermal	High start-up costs, then virtually free	Could occupy large land area	Intermittent; solar thermal may provide baseline power
Wind	Turbines	High start-up costs, then virtually free	May harm birds and bats. Visual impact	Intermittent only
Biofuels	Ethanol, Biodiesel, Algal, Biomass	Continuing costs to produce	Takes energy input to create. Displaces land that can be used for food or wilderness	Used primarily for transportation; Biomass may provide electricity
Geothermal	Heat Pumps, Plants, EGS (experimental only)	Extremely high start-up costs, then virtually free		Provides baseline power
Wave & Tidal	Hydraulic ram Turbine generator	High initial cost. Only beginning development	Can disrupt fishing grounds and navigation	Still experimental. Intermittent (but more predictable than wind)

Ocean Power One energy source not discussed at length in this Discovery Guide series is wave and tidal power from the oceans. Currently far less developed than other renewables, wave and tidal have the potential to become a major power source. According to one estimate, "just 2 one-thousandths of the oceans' untapped energy could provide power equal to current worldwide demand" (von Jouanne). Tidal Turbine Tidal energy relies on undersea propellers driven by the tides. Similar to windmills, the energy is potentially much greater, as water is some 800 times denser than air. This means, however, that tidal turbines need to be extremely tough to withstand the power of the ocean. Currently only two commercial tidal plants are in operation, in France and Canada (US DOE Ocean). Wave power depends on focusing waves into a narrow channel to capture their energy. However, no commercial wave power plants currently exist. Because ocean cycles are relatively consistent, wave and tidal energy, although intermittent, is more predictable than wind or photovoltaic power. Potential effects on marine ecosystems are unknown, however, particularly since harnessing ocean energy on a large scale will require huge and unprecedented turbine arrays, or other possibly disruptive technology. Furthermore, with ocean power technology still experimental, commercial deployment is estimated to be at least five years away (Clayton), while wave energy is about as developed as wind turbines were 15 or 20 years ago (von Jouanne). Still, the potential is great. According to the Electric Power Research Institute, "Waves alone could produce 10,000 megawatts of power, about 6.5 percent of US electricity demand" (Clayton).

While all alternative energy sources should be considered, compared to solar, wind, and biofuels, geothermal has been overlooked in much of the media. Although geothermal technology is well developed, its potential has barely been tapped. With an accelerating global environmental crisis, with fossil fuels increasingly difficult to find and extract, clean, natural, geothermal and other renewable energy sources are undergoing intensive research and development to solve our environmental problems and provide our energy needs.

Special thanks to the Geothermal Energy Association for their help with this Discovery Guide

Other Discovery Guides in the Renewable Energy Series:

• Biofuels: What Place in Our Energy Future?
• Why Not the Sun? Advantages of and Problems with Solar Energy
• Capturing the Wind: Power for the 21st Century

List of Visuals

1. Drilling crew performing tests, geothermal demonstration project, Nevada
   http://www.nrel.gov/geothermal/projects.html
   National Renewable Energy Laboratory (NREL)

2. First geothermal power plant, 1904, Lardarello, Italy
   http://www1.eere.energy.gov/
   geothermal/history.html
   U.S. Department of Energy, Energy Efficiency and Renewable Energy

3. The Nesjavellir Geothermal Power Plant in Iceland
   http://en.wikipedia.org/wiki/Geothermal_power
   Wikipedia

4. Geothermal Heat Pumps
   http://www1.eere.energy.gov/tribalenergy/
   guide/geothermal_heat_pumps.html
   Department of Energy, Energy Efficiency and Renewable Energy

5. Dry steam power plants at The Geysers,n California
   http://www1.eere.energy.gov/geothermal/powerplants.html
   Department of Energy, Energy Efficiency and Renewable Energy

6. The three basic types of geothermal plants: Dry Steam, Flash Steam, & Binary
   http://www1.eere.energy.gov/geothermal/powerplants.html
   Department of Energy, Energy Efficiency and Renewable Energy

7. EGS Development Sequence
   http://www1.eere.energy.gov/geothermal/enhanced_systems.html
   Department of Energy, Energy Efficiency and Renewable Energy

8. The Earth's heat-called geothermal energy-escapes as steam at a hot springs in Nevada
   http://www.nrel.gov/learning/re_geothermal.html
   National Renewable Energy Laboratory (NREL)

9. Interactive Geothermal Projects and Resources Map
   http://geoheat.oit.edu/dusys.htm
   Geo-Heat Center, Oregon Institute of Technology

10. Tidal Turbine
    http://www.eia.doe.gov/kids/energyfacts/sources/renewable/ocean.html
    Energy Information Administration (EIA)

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1. Air Conditioning, Heating & Refrigeration News. It's a "Perfect Storm" for Geo Systems. July 24, 2006

2. Blair, Pam. Tapping into Nature for Power. Bulletin, Northwest Public Power Association, June 1, 2005

3. Blodgett, Leslie & Kara Slack. Geothermal 101: Basics of Geothermal Energy Production and Use. Geothermal Energy Association, February 15, 2009

4. Blodgett, Leslie. Unsubstantiated Claims Draw Response from Reykjavik Energy. RenewableEnergyWorld.com. http://www.renewableenergyworld.com/rea/news/article/2009/06/unsubstantiated-claims-draw-response-from-reykjavik-energy

5. Bryson, George. Geothermal Technology: A Smart Way to Lower Energy Bills. Anchorage Daily News, November 3, 2008

6. Calahan, Scott. Geothermal Technology: A Smart Way to Lower Energy Bills. Tech Directions, February 1, 2007

7. California Energy Commission. Geothermal or Ground Source Heat Pumps, 2006. http://www.consumerenergycenter.org/home/heating_cooling/geothermal.html

8. Clayton, Mark. Ocean Power Surges Forward. The Christian Science Monitor, April 28, 2009

9. Dorreen Yellow Bird. Geothermal Power. Grand Forks Herald, N.D., February 1, 2009

10. The Economist. Science and Technology: Blowing Hot and Cold; Geothermal energy, September 16, 2006

11. Encyclopædia Britannica Online. Geothermal Energy. http://www.britannica.com/EBchecked/topic/230403/geothermal-energy

12. Europe Information Environment. Renewable Energy: Geothermal Barometer Points to Growing Sector in Europe. December 16, 2005

13. Gawell, Karl, Executive Director of the Geothermal Energy Association. Personal Interview, July 24, 2009

14. Gawell, Karl & Griffin Greenberg. 2007 Interim Report, Update on World Geothermal Development. Geothermal Energy Association, May 1, 2007

15. Hughes, Patrick. Geothermal (Ground-Source) Heat Pumps: Market Status, Barriers to Adoption, and Actions to Overcome Barriers. Oak Ridge National Library, December 2008.

16. Jennejohn, Daniel; Leslie Blodgett & Karl Gawell. Geothermal Energy and Induced Seismicity. Geothermal Energy Association Issue Brief, July 31, 2009

17. Kozlowski, David. Simple, Reliable and Efficient: Geothermal Heat Pump Systems. Building Operating Management, August 1, 2007

18. Mims, Christopher. Can Geothermal Power Compete with Coal on Price? Scientific American, March 2, 2009 http://www.scientificamerican.com/article.cfm?id=can-geothermal-power-compete-with-coal-on-price

19. Rupar, Terri. Heat-Pump Systems Get Down To Earth: Geothermal Efficient, Though Costly to Install. The Washington Post, January 10, 2009

20. Sanford, Kathleen. Geoexchange. New York State Conservationist, June 1, 2007

21. Slack, Kara. U.S. Geothermal Power Production and Development Update. Geothermal Energy Association, March, 2009.

22. Hayden, Gary. Understanding Geothermal Opportunities. Plumbing & Mechanical, September 1, 2008

23. Smith, Julian; Ben Crystall; Colin Barras & Helen Knight. Going Underground. New Scientist, October 11, 2008

24. Sunteq Geo Distributors. Geothermal Heat Pump Energy. How It Works! http://geothermalheatpump.com/how.htm

25. U.S. Department of Energy, Energy Efficiency and Renewable Energy. Geothermal FAQs http://www1.eere.energy.gov/geothermal/printable_versions/faqs.html

26. U.S. Department of Energy, Energy Efficiency and Renewable Energy. Hydrothermal Power Systems http://www1.eere.energy.gov/geothermal/powerplants.html

27. U.S. Department of Energy, Energy Efficiency and Renewable Energy. Ocean Energy http://www.eia.doe.gov/kids/energyfacts/sources/renewable/ocean.html

28. Vastyan, John. Direct-Exchange Geothermal Systems Coming Into Their Own. Reeves Journal, February 1, 2005

29. Veal, Lowana. Geothermal Is Not So Clean. Inter Press Service News Agency, May 26, 2009.
    http://www.ipsnews.net/news.asp?idnews=46969

30. von Jouanne, Annette. Harvesting the Waves. Mechanical Engineering, December 1, 2006

31. Watson, Stephanie. How Geothermal Energy Works. HowStuffWorks http://science.howstuffworks.com/geothermal-energy.htm

32. Whittington, Jane. Energy from the Earth. Greater Lansing Business Monthly, August 1, 2006