I'm no Oakey, but I can give you a very quick summary of geothermal, which I believe is fairly objective:
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Geothermal is stable and relatively clean. It releases some greenhouse gasses. It's often inexpensive, but available only in a very limited area, certain parts of the "ring of fire" that circles the Pacific Ocean. Half of the ring is at the bottom of the ocean, so geothermal is available in spots along the west coast of the Americas and northern Asia. Geothermal wells are often very, very deep, and therefore risky - you could spend several million dollars, then hit a section that can't be drilled through, so you're out a few million dollars with nothing to show for it.
Overall, geothermal is, in my opinion, very attractive for the people in those few places where it's available.
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Here's a bit more detail, with references:
The United States produces over 1 billion kilowatt hours of geothermal energy each year, more than any other country (EIA 2012). As calculated by Bertani & Thain (2002), greenhouse gas emissions from geothermal energy are 75% lower than natural gas and 87% lower than coal. From the earliest research into modern geothermal, it has been known that energy can be retrieved only from specific areas with appropriate tectonic activity (Elder 1965). John W. Elder found that areas where geothermal energy can be found within one kilometer of the surface are stable sources of energy at a reasonable cost and identified those areas as being primarily along the Pacific Rim and in Iceland. The areas identified as viable represent less than 1% of the earth. In all other areas, geothermal energy is not viable, primarily because forcing fluid against the high pressure at great depths would require more energy than could be retrieved.
The 2,566 megawatts of installed capacity in California and other parts of the country are certainly of benefit in those areas. The energy cannot be efficiently transported throughout the rest of the country, meaning the potential of geothermal is limited to those specific areas. Geothermal projects involve a considerable degree of risk because the energy source is buried under thousands of feet of rock, where engineers can see neither the potential energy reservoir nor the thousands of feet of rock that must be drilled to reach it. Therefore, it cannot be known ahead of time how long a geothermal well will produce, or if the intervening material is likely to cause the project to fail. Southton (2005) documented many failure modes which can stop a project after millions of dollars have already been invested. Lap leaks, compression failure, and casing cracks can ruin a geothermal well before any energy is produced (Southton 2005). Pruess (1990) considered various models for predicting when a well might stop producing, but those are only predictions. A geothermal well may stop producing at any time.
The U.S. Geological Survey presented a procedure currently in use to extend the life of existing wells and allow geothermal wells to be drilled in new locations (Pierce 2010). The Pierce presentation of this method, known as hydraulic fracturing, also referenced the possibility that hydraulic fracturing, or “fracking”, might increase the risk of earthquakes. The potential danger of hydraulic fracturing was identified in 1994 by Bruhn, Parry, and Thompson, and the issue has received attention in the press lately. Guidelines for safe use of hydraulic fracturing may be developed by engineers and geologists, however issues of public opinion and politics exist in this area. Some proponents of renewable energy argue against the use of inexpensive natural gas by pointing out the potential risk of using hydraulic fracturing for natural gas production. It is therefore difficult for the same groups to argue for geothermal energy, which is also produced by hydraulic fracturing. Although the geothermal fields in California are the largest source of geothermal in the world, they provide less than 0.001% of energy needs, according to EIA data (2012). If it were possible to increase hydrothermal production by 1000%, this would fulfill 0.1% of U.S. energy needs.