A geothermal resource requires fluid, heat and permeability in order to generate electricity: Fluid—Sufficient fluid must exist naturally or be pumped into the reservoir. Heat—The earth's temperature naturally increases with depth and varies based on geographic location. Permeability—In order to access heat, the fluid must come into contact with the heated rock, either via natural fractures or through stimulating the rock. Conventional hydrothermal resources contain all three elements naturally. Increasingly, however, geothermal systems where subsurface fluid and permeability are lacking are being engineered or enhanced to access the earth's heat by adding fluid to these hot subsurface resources. Known as enhanced geothermal systems (EGS), this technology could be a game-changer in the geothermal sector, tapping 100+ gigawatts of geothermal energy, roughly ten percent of domestic energy demand. In addition, low-temperature and coproduced technologies are being explored for near-term power solutions.