Great Expectations for Geothermal to 2100 -- Messages for Now

Abstract

Geothermal energy systems: have a modest environmental footprint; will not be impacted by climate change; and have potential to become the world’s lowest cost source of sustainable renewable thermal fuel for zero-emission, base-load direct use and power generation. Displacement of more emissive fossil energy supplies with geothermal energy can also be expected to play a key role in advancing both energy security and climate change mitigation strategies. In this context, shared challenges on the road to a global portfolio of safe, secure, competitively priced energy supplies are drivers for international cooperation in research, exploration, pilot demonstration and pre-competitive development of geothermal energy resources and technologies. As for the here and now: • At year-end 2010, geothermal base-load power is used in 24 nations. The global installed capacity is ~11 GWelectric with an average 75% capacity factor and > 90% capacity factor in modern plants; • At year-end 2010, geothermal energy direct uses are deployed in 78 nations; amounting to ~ 50 GWthermal with an average 27.5% capacity factor; • In 2005-09, global geothermal energy use increased by ~4% pa for electricity and by ~10% pa for direct-use, while direct use from geothermal heat pump production increased by ~ 20% pa; • Flash power plants yield about 120g CO2/kWhelectric. Current binary cycle plants with total reinjection yield less than 1 g CO2/kWhelectric. Emissions from direct use applications are even lower; and • The extraction of geothermal energy can be fully or partially replenished over the long term by the continental terrestrial heat flow of 315 EJ/y at an average flux of 65 mW/m2 (Stefansson, 2005). • Hot rocks are everywhere, so enhanced (engineered) geothermal systems (EGS) pose great global promise for the future supply of emissions-free base-load power.