Enhanced geothermal systems for clean firm energy generation

Geothermal energy provides clean, steady and renewable electricity and heat, but the use of geothermal energy has conventionally been constrained to locations with adequate subsurface heat and fluid flow. Enhanced geothermal systems (EGS) enable geothermal energy usage in unconventional areas by enhancing the subsurface permeability and increasing fluid flow, which is then extracted as a carrier of the thermal energy. In this Review, we discuss the development of EGS and its role in providing energy. Some EGS are operating commercially in Europe and provide heat and/or electricity, but technical issues and concerns over induced seismicity have historically hindered the broader expansion of EGS. Adaptation of advanced drilling techniques (including the use of polycrystalline diamond compact bits, multiwell drilling pads, horizontal drilling and multistage stimulation) is enabling an increase in scale and decrease in cost of EGS projects. As a result, in the USA, enhanced geothermal is expected to achieve plant capital costs (US$4,500 kW−1) and a levelized cost of electricity (US$80 MWh−1) that are competitive with market electricity prices by 2027. With further development of EGS to manage induced seismicity risk and increase system flexibility, EGS could provide stable baseload and potentially dispatchable electricity in clean energy systems. Enhanced geothermal systems can provide clean energy in areas where conventional geothermal systems are not viable. This Review discusses energy production through these systems and the technological developments that could enable its future expansion.