Closed-loop geothermal, a new type of geothermal energy system
Closed-loop geothermal systems (also known as “advanced geothermal systems” or “AGS”) are a type of engineered geothermal energy system containing subsurface working fluid that is heated in a hot rock reservoir without direct contact with rock pores and fractures.: Instead, the subsurface working fluid stays inside a closed loop of deeply buried pipes that conduct Earth’s heat. Closed-loop geothermal systems are one of the prominent categories of next-generation geothermal systems in development today.
Like all geothermal systems, closed-loop geothermal systems provide renewable energy, and primarily operate as baseload resources that produce energy at a constant rate. Unlike conventional geothermal energy plants, closed-loop geothermal plants can be placed anywhere in the world, depending only on the depth of the hot rock resource.
Closed-loop geothermal projects are under development in the United States, Canada, Japan, and Germany.
Technology.
Closed-loop geothermal companies use a wide variety of engineered systems to produce geothermal energy. These systems primarily vary based on the length and geometry of the closed-loop wells placed subsurface, but can also vary in the materials used in well construction and the working fluid used.
Two commons designs of closed-loop geothermal systems are the U-tube and the tube-in-tube:
Research and development.
Several closed-loop geothermal systems have been demonstrated globally. One commercial closed-loop geothermal project is under construction in Geretsried, Germany.
Advantages.
The advantages of a deep, closed-loop geothermal circuit include
These advantages mean closed-loop geothermal systems can be placed anywhere in the world as a source of carbon-free, baseload energy, with no impact to natural water resources and significantly reduced risk of induced seismicity.
Related terminology.
Hot dry rock.
Hot dry rock (HDR) is an abundant source of geothermal energy, but it is typically difficult to access. Hot, dry crystalline basement rocks are found almost everywhere sufficiently far beneath the surface.
Multiple deep hot dry rock wells have been drilled around the world, including the US, Japan, Australia, France, and the UK. Whereas hydrothermal energy production can exploit already present hot fluids, HDR recovers heat from dry rock via the circulation of an artificially introduced working fluid. Ongoing efforts are underway to further develop and test technologies that can produce geothermal energy from hot dry rock, including Enhanced Geothermal Systems and Closed-Loop Geothermal Systems.
Closed-loop geothermal systems vs. ground source heat pumps.
Closed-loop geothermal systems are not to be confused with the ground source heat pumps used for small-scale, largely residential heating and cooling. While both systems use underground closed-loop circuits of working fluid, there are important differences in the depth, temperature, scale, and applications for each system:
See the glossary of geothermal heating and cooling page for further clarification.
References.
 ;templatestyles src="Reflist/styles.css" / ;