Closed-Loop Geothermal Systems

Detailed overview of innovation with sample startups and prominent university research

What it is

Closed-loop geothermal systems, also known as advanced geothermal systems (AGS), are a type of geothermal energy technology that circulates a working fluid through a closed loop of underground pipes to extract heat from the Earth’s subsurface. Unlike traditional geothermal systems that rely on naturally occurring hydrothermal resources, closed-loop systems can access geothermal energy in a wider range of geological settings, making them a more versatile and sustainable option.

Impact on climate action

Closed-Loop Geothermal Systems in Geothermal Energy amplify climate action by providing renewable, low-emission heating and cooling solutions. By utilizing the Earth’s natural heat, these systems reduce reliance on fossil fuels, mitigate greenhouse gas emissions, and contribute to a sustainable energy future, combating climate change while ensuring energy efficiency and resilience.


  • Closed-Loop Circulation: A working fluid, typically water or a water-based solution, is circulated through a closed loop of underground pipes. The fluid absorbs heat from the surrounding rock formations and returns to the surface, where the heat is extracted for various applications.
  • Heat Exchangers: Heat exchangers transfer the heat from the working fluid to a secondary fluid, which can be used for electricity generation, space heating and cooling, or industrial process heat.
  • Wellbore Design and Drilling: Closed-loop systems require specialized wellbore designs and drilling techniques to ensure efficient heat transfer and minimize environmental impacts.
  • Reservoir Engineering: Understanding the thermal properties and flow characteristics of the subsurface rock formations is crucial for optimizing the design and operation of closed-loop geothermal systems.

TRL : 6-7

Prominent Innovation themes

  • Advanced Drilling Technologies: Innovations in drilling technologies, such as directional drilling and horizontal drilling, are enabling the development of more complex and efficient wellbore designs for closed-loop geothermal systems.
  • Enhanced Heat Transfer Fluids: Researchers are developing new heat transfer fluids with improved thermal properties and stability, enhancing the efficiency of heat extraction from the subsurface.
  • Coaxial Borehole Heat Exchangers: These innovative heat exchangers utilize a concentric pipe design to improve heat transfer efficiency and reduce the footprint of closed-loop geothermal systems.
  • Hybrid Closed-Loop Systems: Combining closed-loop geothermal systems with other renewable energy sources, such as solar PV or wind power, can create hybrid systems that offer increased energy generation consistency and improved grid stability.

Other Innovation Subthemes

  • Closed-Loop Circulation Efficiency
  • Advanced Drilling Techniques
  • Heat Exchanger Innovations
  • Reservoir Characterization and Optimization
  • Enhanced Heat Transfer Fluids
  • Horizontal Well Network Development
  • Advanced Stimulation Techniques
  • Minimizing Seismic Risk
  • Groundwater Contamination Prevention
  • Nanotechnology Applications

Sample Global Startups and Companies

  1. Eavor Technologies:
    • Technology Enhancement: Eavor Technologies has developed a novel closed-loop geothermal system called the “Eavor-Loop,” which utilizes a proprietary technology known as the “Eavor-STM” (Standing Column Well). This system involves drilling a pair of deep wells connected by a subsurface loop to circulate a working fluid (usually water) continuously through the underground reservoir. The heat from the Earth’s crust warms the fluid as it circulates, and the heat is then extracted at the surface to generate electricity or provide heating and cooling.
    • Uniqueness of the Startup: Eavor Technologies stands out for its innovative approach to geothermal energy extraction, which eliminates the need for hydraulic fracturing (fracking) or the use of aquifers, addressing common concerns associated with traditional geothermal systems. Their closed-loop system offers a scalable, low-impact, and cost-effective solution for harnessing geothermal energy on a commercial scale.
    • End-User Segments Addressing: Eavor Technologies targets utilities, developers, and governments seeking clean and reliable energy solutions. Their closed-loop geothermal systems can be deployed in various settings, including utility-scale power generation, industrial heating, district heating, and residential heating and cooling.
  2. Fervo Energy:
    • Technology Enhancement: Fervo Energy specializes in advanced drilling and reservoir engineering techniques to enhance the performance and efficiency of closed-loop geothermal systems. Their approach involves high-temperature drilling technologies, advanced reservoir modeling, and optimized well design to maximize heat extraction from deep geothermal reservoirs. Fervo Energy’s closed-loop systems enable the sustainable and cost-effective production of geothermal energy.
    • Uniqueness of the Startup: Fervo Energy stands out for its focus on innovation and optimization in closed-loop geothermal technology, leveraging expertise from the oil and gas industry to unlock the potential of geothermal resources. Their approach enables deeper and hotter geothermal reservoirs to be accessed economically, expanding the geographic reach and scalability of geothermal energy.
    • End-User Segments Addressing: Fervo Energy serves utilities, independent power producers (IPPs), and industrial customers seeking clean and reliable energy solutions. Their closed-loop geothermal systems can be deployed in areas with suitable geological conditions, providing baseload power, grid stability, and decarbonization benefits.
  3. GreenFire Energy:
    • Technology Enhancement: GreenFire Energy specializes in closed-loop geothermal systems utilizing supercritical carbon dioxide (sCO2) as the working fluid. Their proprietary technology, known as the “GreenLoop,” involves circulating sCO2 through the geothermal reservoir at high pressure and temperature to extract heat efficiently. The heated sCO2 is then expanded through turbines to generate electricity before being re-injected into the reservoir, creating a closed-loop cycle.
    • Uniqueness of the Startup: GreenFire Energy stands out for its innovative use of sCO2 technology in closed-loop geothermal systems, which offers several advantages over traditional water-based systems, including higher efficiency, lower environmental impact, and broader applicability to a range of geothermal resources. Their approach enables the cost-effective development of geothermal energy projects in diverse geological settings.
    • End-User Segments Addressing: GreenFire Energy serves utilities, developers, and investors seeking advanced geothermal energy solutions. Their closed-loop sCO2 systems can be deployed in areas with high-temperature geothermal reservoirs, providing dispatchable and renewable power generation, as well as opportunities for energy storage and grid balancing.

Sample Research At Top-Tier Universities

  1. Stanford University:
    • Research Focus: Stanford University is a leader in research on Closed-Loop Geothermal Systems, focusing on developing advanced technologies and modeling approaches for efficient and sustainable geothermal energy extraction.
    • Uniqueness: Their research involves the design and optimization of closed-loop geothermal systems, which utilize heat exchange fluids circulated through a network of underground pipes to extract heat from the Earth’s subsurface. They explore novel materials, drilling techniques, and reservoir engineering strategies to enhance heat transfer, minimize environmental impact, and improve system performance.
    • End-use Applications: The outcomes of their work have applications in district heating and cooling, industrial process heat, and greenhouse operations. By harnessing the Earth’s thermal energy resources, Stanford’s research contributes to decarbonizing heating and cooling systems, reducing energy costs, and enhancing energy resilience in urban and rural communities.
  2. Massachusetts Institute of Technology (MIT):
    • Research Focus: MIT conducts pioneering research on Closed-Loop Geothermal Systems, leveraging its expertise in geosciences, fluid dynamics, and renewable energy technologies to develop innovative solutions for geothermal heat extraction and utilization.
    • Uniqueness: Their research encompasses the development of advanced modeling tools, numerical simulations, and experimental techniques for characterizing subsurface reservoirs, predicting fluid behavior, and optimizing geothermal system performance. They also explore hybrid geothermal-electric systems, enhanced geothermal systems (EGS), and geothermal heat pumps for various applications.
    • End-use Applications: The outcomes of their work find applications in building heating and cooling, industrial processes, and electricity generation. By advancing closed-loop geothermal technologies, MIT’s research supports the transition to low-carbon energy systems, enhances energy security, and mitigates climate change impacts.
  3. University of California, Berkeley:
    • Research Focus: UC Berkeley is engaged in innovative research on Closed-Loop Geothermal Systems, leveraging its expertise in geophysics, reservoir engineering, and environmental sustainability to address challenges related to geothermal resource exploration, development, and utilization.
    • Uniqueness: Their research involves interdisciplinary collaborations, field experiments, and numerical modeling studies to characterize geothermal reservoirs, optimize well placement, and mitigate induced seismicity risks associated with geothermal operations. They also investigate the integration of geothermal energy with other renewable energy sources, grid management technologies, and energy storage systems.
    • End-use Applications: The outcomes of their work have applications in sustainable urban development, geothermal power generation, and carbon-neutral heating and cooling solutions. By advancing closed-loop geothermal systems, UC Berkeley’s research contributes to reducing greenhouse gas emissions, promoting energy equity, and fostering regional economic development.

commercial_img Commercial Implementation

Closed-loop geothermal systems are being implemented in various applications around the world, including residential and commercial building heating and cooling, district heating systems, and industrial process heat. For example, Eavor Technologies has deployed its closed-loop EGS technology in a pilot project in Canada, demonstrating the feasibility and potential of this technology.