|Fig. 1: Depiction of a standard geothermal binary system.  (Source: Wikimedia Commons)|
Efforts to find energy alternatives to fossil fuels in the United States have grown exponentially over the past decade. While the renewable energy industry has expanded greatly in recent years, the majority of U.S. energy consumption continues to come from fossil fuels. The biggest challenge that faces the renewable energy industry is finding a form of energy production that can compete with fossil fuels economically and quantitatively, as renewable energy producers do not currently have the means or ability to meet national energy demands. While solar, wind, nuclear, and hydropower energy currently hold the top spots for non-fossil fuel energy sources, excitement around geothermal energy is growing due to recent technological advances that could help geothermal become one of the key renewable energy sources in the 21st century.
Geothermal energy is a form of renewable energy production that takes advantage of the extremely hot temperatures underneath Earth's crust. Earth's molten core is about as hot as the surface of the sun, which is around 6,000°C. Only a few miles below the surface of the earth, rock temperatures are around the 100°C mark, increasing in temperature as depth increases. Geothermal power plants utilize this naturally produced heat by injecting water into the cracks of this rock through injection wells, and then collecting the steam that is produced as a result of evaporation through production wells. The steam travels back up to the surface where it turns a steam turbine to produce electricity. See Fig. 1. There is so much heat underneath earth's surface that human civilization could theoretically be powered for eons if humans were able to capture it effectively.
Capturing geothermal energy gets tricky, however, when the rock underneath the earth has no cracks into which the water can be injected. This problem is what led to the use of Enhanced Geothermal Systems (EGS), geothermal production systems that inject water into the rocks at high pressure in order to manually create the cracks in the rock required, a process known as fracking. There are some important distinctions between this kind of fracking and the fracking that is well known in the natural gas industry, mainly that geothermal fracking uses fluid that is much less polluting and that the fractures they create are much smaller and more controlled than those created by natural gas plants. EGS utilize very similar technology to natural gas plants, but produce fewer of the undesired effects that are typically associated with the fossil fuel industry. [1,2] Geothermal energy is also one of the few base-load renewable energy sources, meaning that it can be produced and used all the time, unlike solar and wind energy.
While wind and solar are the fastest growing renewables, increasing globally by 1.4 × 1018 J and 1.2 × 1018 J respectively in 2019, geothermal energy took the third spot with 0.3 × 1018 J of growth.  Today, Geothermal energy only accounts for approximately 0.4% of energy consumption in the United States. The total geothermal energy capacity of the United States currently stands just higher than 2.5 GWe.  An analysis from 2007 conducted by researchers from MIT and commissioned by the U.S. Department of Energy concluded that an investment in geothermal infrastructure of $1 billion over a 15-year period could contribute up to 100 GWe of additional energy capacity by 2050, or around 10% of current energy capacity in the United States.  While geothermal would not be able to take on the entire burden of meeting U.S. demands, a relatively small investment in geothermal infrastructure could produce major energy returns for the U.S. in the next few decades.
Modern EGS companies are putting EGS back on the map with new technological developments that could help make geothermal an attractive alternative to fossil fuels in the near future. One such company is Fervo Energy, which uses patented distributed fiber optic sensing to increase the productivity and lifetime of geothermal wells, making geothermal energy a more economically viable source of energy. The similarities between geothermal wells and natural gas plants make geothermal energy one of the most attractive alternative energy sources for oil and gas companies looking to transition into more renewables.
Advancements in geothermal well design are also contributing to goethermals recent momentum. One of these advancements is the exploration of super-hot-rock geothermal, or Super Hot EGS. These systems are very similar to traditional EGS but seek to drill into much deeper, much hotter rock. While traditional EGS seek to drill into rock in the 200°C temperature range, Super Hot EGS seek to tap into rock that measures around 400°C. Each Super Hot EGS project can produce the same amount of energy of about 10 traditional EGS projects, and are much more cost effective per megawatt-hour. Closed-loop geothermal systems, known as Advanced Geothermal Systems (AGS) are also gaining traction in the industry. These systems use entirely closed systems (no water or steam is injected into the rock) of horizontal wells in shallower rock in order to produce the steam they desire. AGS have large potential because they only require temperatures of 66°C (150°F), which is available almost anywhere in the world, and can theoretically have zero surface footprint, meaning the entire system is underground and virtually hidden. 
This report explored the recent technological advancements in geothermal energy production. Geothermal energy is poised to be an attractive renewable energy alternative for oil and gas companies due to the similarities between geothermal fracking and natural gas fracking. There have also been many technological and system improvements in geothermal wells that have opened it up to be one of the most economically efficient renewable energy resources in existence. Geothermal energy production is likely to increase significantly in the next few decades as more companies and sovereign nations look to increase their renewable energy production.
© Daniel McColl. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
 "Geothermal Technologies Program," U.S. Office of Energy Efficiency and Renewable Energy, DOE/GO-102004-1958, August 2004.
 A. Wall and K. Young, "Doubling Geothermal Generation Capacity by 2020: A Strategic Analysis," U.S. National Renewable Energy Laboratory, NREL/TP-6A20-64925, January 2016.
 "BP Statistical Review of World Energy 2020", British Petroleum, June 2020.
 "Geothermal Energy Factsheet," Center for Sustainable Systems, University of Michigan, September 2020.
 "The Future of Geothermal Energy: Impact of Enhanced geothermal Systems (EGS) on the United States in the 21st Century," INL/EXT-06-11746, Idaho National Laboratory, November 2006.
 R. DiPippo, Geothermal Power Plants (Elsevier, 2005), Ch. 15, pp. 339.