Superhot Rock Geothermal

What is superhot rock geothermal and what are its benefits?

Superhot rock geothermal is a transformative new zero-carbon, always-available energy source that could be used for power, heat, hydrogen production, and industrial process energy. It has the potential to be economically competitive with most other zero-carbon energy sources and could be deployed rapidly in much of the world. It could potentially repower or replace many existing fossil fuel energy facilities and strengthen energy security by providing a local energy source – all with a relatively small environmental footprint.

Superhot rock energy is a form of geothermal energy; a consistent, dispatchable “baseload” source. Unlike other renewable energy resources, geothermal energy is consistently available and doesn’t require the use of battery storage, nor does it need to be backed up by a baseload power source such as fossil fuels. Using deep drilling technology, we could access superhot rock geothermal worldwide – increasing energy access, energy equity, and energy security.

What is geothermal energy and how does it work?

Geothermal energy taps into the energy beneath our feet. Our planet’s interior contains naturally occurring heat, which spreads through conduction and convection up to the Earth’s surface. In “shallow heat” regions where concentrated heat is available near the surface, such as Italy, Turkey, or the Western U.S., conventional, or hydrothermal, geothermal energy works by drilling into reservoirs of heated groundwater and bringing steam to the surface to provide hot water to heat buildings, and to turn turbines to produce electricity. Where heat is deep, accessing hot water requires drilling farther into the Earth’s crust. In many areas, heat exists without a source of water. In those regions, water can be sent down to circulate through hot rock. The heat turns the water into steam, which is then brought to the surface. There are many emerging innovations that are looking to tap into these regions for heating, cooling, and the production of electricity.

How is superhot rock geothermal different from conventional geothermal energy?

Conventional geothermal power is produced from naturally heated groundwater close to the surface and generally at temperatures of 150-200°C. Superhot rock geothermal will be produced by drilling into hotter rock at deeper depths (>400°C), injecting and circulating water through the rock to heat it to very high temperatures, and then pumping it back to the surface to a generation plant. With successful deep drilling innovation, superhot rock geothermal could be produced anywhere in the world and will not be limited to regions with shallow heat and groundwater.

Water above 400°C is in the “superhot” (supercritical) state, which is much more energy-dense and can circulate more efficiently than lower-temperature water. These properties will allow superhot rock geothermal systems to produce an estimated 5-10x the energy of conventional geothermal systems – giving it the potential to be competitive with today’s costs for power. This high energy potential has been demonstrated in Iceland, where the Iceland Deep Drilling Project’s Krafla borehole produced superhot water at 452°C and an estimated 36 megawatts of energy (MWe) production potential. In comparison, a conventional geothermal project produces about 7-8 MWe per well.

Though humans have been using geothermal energy for over 100 years, (starting in Tuscany, Italy, in 1904) it’s only recently that technological advancements have made superhot rock geothermal a possibility. As of 2018, there were only 15 GW of conventional geothermal power in the world and geothermal accounted for less than 0.5% of total global electricity production. Because of its dramatically higher energy capacity and “geothermal everywhere” potential, superhot rock geothermal can be a much larger source of power, potentially on a terawatt scale.

Where can superhot rock geothermal be developed?

The temperatures required to create superhot rock geothermal have already been accessed in regions where the earth’s heat is near the surface, such as Iceland, Italy, Turkey, or the Western U.S. These shallow-heat regions will likely be the first regions where superhot rock geothermal will be developed. However, superhot rock has the potential to be deployed on a global scale, almost anywhere in the world. Achieving “geothermal everywhere” will require innovative drilling technologies that can cost-effectively reach superhot resources at depths of up to 15 km/~9 mi (compared to depths of 7 km/~4 mi accessible through current drilling methods). There are several companies currently working to push the limits of today’s drilling, and the innovations needed are engineering innovations rather than major scientific breakthroughs.

View the superhot rock project map.

How much will it cost to generate superhot rock geothermal?

Clean Air Task Force commissioned Hot Rock Energy Research Organization (HERO) and LucidCatalyst to estimate the levelized cost of energy for future mature (“nth of a kind”) superhot rock power plants. Levelized cost of energy (LCOE) is a standard measurement in the energy industry that is used to compare the cost of energy sources and is calculated by dividing the lifetime cost of a power plant by the total energy produced by that plant. Results suggest that mature superhot rock will be competitive at $20-35 per MWh, compared to $40 per MWh, the current U.S. market price for electricity.

Does superhot rock geothermal produce CO₂?

The Earth’s heat is a carbon-free energy source. Unlike fossil fuel power, no direct carbon dioxide (CO₂) will be emitted in the process of generating power in dry rock. Superhot rock also represents an advantage over commercial hydrothermal geothermal systems, which harvest hydrothermal fluids that sometimes contain carbon dioxide. Because superhot rock geothermal will work in hot dry rock, which is highly unlikely to contain free CO₂, it’s envisioned as an entirely carbon-free form of energy.

Is superhot rock geothermal renewable, or does it risk depleting the Earth’s heat?

Superhot rock geothermal does not risk depleting the Earth’s heat. On human timescales, superhot rock geothermal is endless, the ultimate renewable resource. One estimate suggests that 0.1% of the Earth’s heat could meet our world’s energy needs for 2 million years. Scientists predict that the Earth will continue to produce geothermal heat for billions of years, and the amount of energy needed by humans is tiny compared to the energy produced. Human geothermal use will not affect the Earth’s heat in any meaningful way.

How can superhot rock geothermal help produce hydrogen?

Superhot rock geothermal is well-suited to generate low-carbon hydrogen, which can be used to decarbonize hard-to-abate sectors such as heavy transport and industry. There are multiple factors that make superhot rock geothermal and hydrogen production a good match.

First, the intense heat and power that superhot rock generates could be used for hydrogen production. Superhot rock geothermal generates electricity, which can be used for hydrogen generation via high temperature electrolysis. The superheated steam could increase the efficiency of electrolytic hydrogen production in solid oxide electrolyzers.

Additionally, superhot rock geothermal is a source of inexhaustible, firm energy, operating around the clock regardless of weather or other external factors. This energy production profile is what hydrogen plants need to operate 24 hours a day.

A forthcoming Lucid Catalyst analysis produced for Clean Air Task Force estimates that superhot rock energy could produce hydrogen cost-competitively, though hydrogen production from superhot rock geothermal still needs to be demonstrated.

Is superhot rock geothermal the same thing as supercritical geothermal energy?

“Supercritical” is a technical term that refers to water that has heat at or above 400°C and pressure at or above 22 MPa. “Superhot” is a less technical term that refers to water at or above about 400°C, regardless of pressure, as well as to other very hot fluids.

What are engineered geothermal systems (EGS) and hot dry rock systems, and how do they relate to superhot rock geothermal?

Geothermal energy typically requires a heat source (rock), water, and permeable rock so that the water can circulate through it and absorb the heat. In geothermal systems where hot rock does not contain a natural source of water and permeability, permeability must be created. Engineered geothermal systems (EGS) are geothermal systems that do not use natural hydrothermal water. They have also been referred to as “hot dry rock systems.”

Superhot rock geothermal is a subset of EGS that accesses much hotter temperatures (above 400°C) than EGS has historically accessed. “Direct-contact” superhot rock works by pumping water down one pipe into hot rock, where it circulates through tiny fractures in the rock to absorb heat, and then rises up a second pipe to the surface. An alternative to circulating water through fractures may be closed-loop injection systems, which heat water inside deep drilled conduits or pipes through the hot rock at depth.

What’s needed to speed the development of superhot rock geothermal?

Key innovations are needed to unlock the widespread deployment of superhot rock geothermal. These include developing tools that work in the extreme conditions of superhot rock, new well construction materials, new methods designed to function in deep heat, new ultra-deep drilling methods, and new methods for creating reservoirs. While technically challenging, these advancements are achievable, and could be developed relatively quickly with aggressive funding—as has been the case for many other energy technologies.

An intensive drilling and resource development program by well-funded consortia could provide the knowledge and innovation needed to develop and rapidly commercialize superhot rock around the world. Using the subsurface expertise and capital resources from the oil and gas industry could speed up the rapid development of superhot rock geothermal systems.

Global regulatory needs and agency technical staffing need to be anticipated early on to provide a roadmap for superhot rock geothermal developers while generating confidence among policymakers and the public that these projects will be safe and environmentally-friendly.

What advanced drilling technologies are being developed?

Drilling deep into hard rock causes drill bits to wear out quickly. Emerging innovations like hammer drilling, hybrid PDC/particle drilling, and contactless energy drilling solve this problem by finding other ways to drill.

• Plasma drilling, such as the Plasmabit drill under development by GA Drilling, works by emitting a stream of plasma—extreme heat energy formed as electrons are stripped from atoms using a high-voltage electric current.
• Millimeter wave drilling vaporizes rock and is under development by Quaise in Houston, TX, in collaboration with Oak Ridge National Laboratory.
• The PDC bit has been proven to increase rate of penetration and reduce drill times significantly in the crystalline rock at FORGE.
• Other developing technologies include hybrid PDC/particle drilling, projectile drilling, hybrid laser drilling, and mudhammer drilling.

What are the next steps toward commercialization of superhot rock technologies?

Numerous drilling projects have drilled into superhot rock. Iceland and Italy have both hosted international R&D projects and more pilot demonstrations are in planning stages in regions around the world where superhot conditions are near-surface. Once these pilot demonstrations successfully produce energy-dense superhot water at the surface, and ultimately create electricity, the next step is to demonstrate superhot rock geothermal at commercial scale (e.g., 100+ MW) in locations with a wide range of geologies and depths to heat. In the final stage, superhot rock geothermal will expand to full global-scale commercialization.

Each of these steps will involve tremendous learning-by-doing and will also rely on laboratory research into reservoir creation, drilling, and surface infrastructure. Public and private investments will be needed in the early stages of commercialization to provide drilling campaign incentives and to enhance cross-pollination among international projects. Ultimately, commercializing superhot rock geothermal will require resources from the geothermal industry, governments, national laboratories, academic institutions, and the existing energy industry.