ABSTRACT
About 95% of the Earth’s mass is at a temperature greater than 500°C, and this heat energy constitutes a huge resource for helping satisfy the energy needs of society. Earth’s ow of heat from its interior to the surface is estimated at 47 TW (Davies and Davies, 2010), which is about 20 times the total world power generation in 2012 (EIA, 2013a). At the end of 2015, worldwide geothermal power production was a little more than 12 GWe, which represents just a tiny fraction (0.025%) of Earth’s heat ow, or about 0.5% of world power generation. If only 0.1% of Earth’s heat energy could be tapped and utilized, it would amount to about 10% of the planet’s power generation. Thus, harnessing geothermal energy for the benet of society has tremendous potential to move from what is more or less a cottage industry at present for most regions of the planet toward becoming a major source of clean, baseload energy. In their U.S. Geological Survey assessment of domestic geothermal resources, Williams et al. (2008) indicated that an additional ~6000 MWe could be obtained from identied conventional geothermal systems and an estimated 30,000 MWe from undiscovered conventional geothermal resources. If realized, these sources would represent about a tenfold increase in the current U.S. installed geothermal power capacity of about 3500 MWe. In addition, these same researchers indicated that if engineered geothermal systems (EGSs) are included then the geothermal power potential could grow to 345,000 MWe (at 95% probability), which would represent about 35% of the total installed U.S. power generation (EIA, 2013b).
