EXPLOITING THE MAGMA
Extracting energy from accessible magma plumes that have formed within Earth’s outer crust is the most difficult way of obtaining geothermal energy, but it is also the most exciting because of the enormous quantities of heat avail- able. A single plume can contain between 100,000 MW-centuries and 300,000 MW-centuries of energy.
Drilling into, or close to, such hot regions is difficult because the equipment can easily fail at the elevated temperatures to which it will be subject. As an additional hazard, if a drill causes a sudden release of pressure, the result can be explosive. Further, ways have yet to be found to tap the heat. Research continues but exploiting magma for power generation is a long-term project with no immediate prospect of exploitation.
LOCATION OF GEOTHERMAL RESOURCES
The easiest geothermal resources to exploit are those that can provide water or steam with a temperature above 200 oC. Resources of this type are located almost exclusively along the boundaries between Earth’s crustal plates, in regions where there is significant plate movement. These areas are found around the Pacific Ocean in New Zealand, Japan, Indonesia, the Philippines, the western coasts of North and South America, the central and eastern parts of the Mediterranean, east Africa, the Azores, and Iceland.
Lower-temperature underground reservoirs exist in many other parts of the world and though these contain less energy they can be used to generate electricity too. A project installed in Austria in 2001, for example, generates electricity from 106 oC water, which is also used for district heating. However, these reservoirs can be more difficult to locate in the absence of hot surface springs. Nevertheless, there were around 60 countries using geothermal energy at the beginning of the 21st century for either heating, generating electricity, or both.
SIZE OF THE RESOURCE
Today it is difficult to estimate the size of this energy resource but as survey techniques improve, more accurate data will become available. Based on data available at the beginning of the 21st century, reservoirs located in the United States, for example, might provide 10% of U.S. electricity.
According to figures published by the World Energy Council in its 2010 Survey of Energy Resources the global geothermal generating potential could be between 35 GW and 140 GW, while the technical potential could be 210 GW. However, if hot dry–rock techniques could be exploited, the total potential could be 5–10 times higher than this. A reasonable estimate, again from the World Energy Council, suggests that 8.3% of global electricity generation could be provided by geothermal sources.