Historically, geothermal energy has been recovered from limited, yet abundant “hot-spots” consisting of natural thermal geysers and tectonic plate boundaries or fault lines.
Using traditional geothermal methods of dry steam plants and flash steam plants, subsurface temperatures of 150°C to 180°C are required. However, a binary cycle power plant can generate power at temperatures as low as 57°C. The binary cycle power essentially removes the restriction of hot-spots. Although efficiency is about 10%, this energy source is unlimited.
A 2006 report by MIT sponsored by the US Department of Energy http://geothermal.inel.gov/publications/future_of_geothermal_energy.pdf estimated over 200 ZJ of energy could be extracted from the Earth, with the potential to increase this to over 2,000 ZJ with technology improvements.
In 2007, the California Energy Commission published that geo-thermal energy plants were at parity or less than traditional fossil fuel plants. Given that Geothermal energy supplies more than 10 GW to 24 countries worldwide and now produces enough electricity to meet the needs of 60 million people. According to the International Geothermal Association (IGA) in IGA News 72 (April–June 2008), total global geothermal capacity is expected to rise to 11 GW by 2010. As of August 2008, almost 4,000 MW of new geothermal power plant capacity was under development in the U.S. Those states with projects currently under consideration or development are: Alaska, Arizona, California, Colorado, Florida, Hawaii, Idaho, Nevada, New Mexico, Oregon, Utah, Washington, and Wyoming.
If geothermal energy is truly at parity with fossil fuels with over 200 ZJ of energy to be extracted, what’s needed to massively scale this renewable resource?