The U.S. Department of Energy (DOE) Advanced Research Projects Agency-Energy (ARPA-E) has announced $30 million to increase geothermal power production by unlocking “superhot” reservoirs deep within the Earth.

Currently, geothermal baseload production in the U.S. is limited to 4 gigawatts (GW). ARPA-E’s Stimulate Utilization of Plentiful Energy in Rocks through High-temperature Original Technologies (SUPERHOT) program aims to provide access to superhot reservoirs capable of producing 10-20 GW of reliable baseload power at a “competitive cost” of less than $30 per megawatt hour (MWh) by 2040. As the demand for power increases in the U.S., driven primarily by data centers and manufacturing, DOE argues that expanding geothermal power production could play an important role.

“Geothermal is a reliable and secure baseload power source, but today we are only able to access a fraction of the energy it can provide,” said ARPA-E Director Evelyn N. Wang. “SUPERHOT projects can change that and allow access to hotter reservoirs to create more domestic flow of energy onto America’s grid.”

The SUPERHOT program will explore modification of conventional well designs or completely novel designs, materials, and materials systems that satisfy requirements to survive superhot conditions. SUPERHOT’s goals are to develop geothermal well construction capable of a 15-year operational life and enable transfer of heat from the surrounding geologic formation to the well. Projects will seek to enable access to resources with temperatures greater than 375 °C and pressures greater than 22 megapascals.

The program will have two categories:

SUPERHOT builds on ARPA-E’s history of support for enhanced geothermal projects. ARPA-E’s work in this area includes supporting industry leaders Fervo Energy, AltaRock Energy, and Eden Geopower.

EGS and AGS technology create engineered geothermal systems wherever hot rock exists either by creating subsurface fracture networks or drilling long boreholes. However, the highest temperatures that can be accessed are about 220 °C due to the lack of commercial, off-the-shelf equipment capable of handling higher temperatures, DOE said. This relatively low temperature limits the power production for EGS to about 10 megawatts-electric (MWe) per well site. DOE maintains that the ability to access superhot reservoirs will increase the electrical power per well, potentially up to 30-50 MWe, as both available subsurface heat and thermal-to-power efficiency increase.

High temperature subsurface rocks exist everywhere but vary greatly in depth. In volcanic regions with a high geothermal gradient (e.g., parts of Hawaii, Alaska, and the West Coast) temperatures of 375 °C may be found at depths as shallow as 5 km. Elsewhere, it will be necessary to drill to depths of 10 km (or more). Drilling wells greater than 9 km has been possible for decades in areas with lower geothermal gradients, although none reached superhot temperatures.

Previous attempts have been made to produce geothermal power from superhot reservoirs. Roughly 20 vertical and near-vertical boreholes have been drilled to temperatures as hot as 500 °C and to depths up to 5 km, DOE said, but most wells failed rapidly, and none are currently producing power.

Several key factors make construction of superhot wells difficult: high-performance metal alloys and materials are expensive for the quantities needed for kilometers of geothermal casing; installation and deployment require well-vetted procedures; and superhot geothermal technology experiences extreme conditions including high temperatures, high-pressure corrosive fluids, and repeated thermal cycling.

Addressing these issues will require a combination of design, procedures, and advanced materials, DOE argues. The designs and materials must undergo extensive reliability testing and be validated for superhot conditions prior to deployment. This will require testing facilities capable of handling superhot temperatures, pressures, and potentially corrosive fluids both in a subcritical and supercritical state. Facilities for testing water at supercritical temperatures and pressures exist in other industries, but they typically do not include highly corrosive fluids. Most thermal-hydraulic-mechanical-chemical (THMC) numerical codes used in reservoir engineering do not include ductile rock behavior or equation-of-state for supercritical water as required to model superhot reservoir and well behavior.

Originally published in Renewable Energy World.