National Renewable Energy Laboratory

Large-scale geothermal energy relies on the heat and water that exists below the surface of the earth, but not everywhere has accessible naturally occurring hot water. A fairly recent technique called enhanced geothermal energy or hot dry rock geothermal energy makes it possible generate electricity from the earth’s heat in more places.

Getting off fossil fuels to generate electricity requires using renewable energy, but renewable energy has downsides, for example, intermittency. The sun doesn’t always shine and the wind doesn’t always blow. Battery backup overcomes intermittency, but it has its own environmental problems.

Enhanced geothermal energy can play an important role in the energy mix, but, of course, nothing is perfect. What is enhanced geothermal energy and what are possible problems?

An overview of enhanced geothermal energy

Geothermal energy does not have to be built on a massive scale. Heat pumps are applications of geothermal energy for home use. Even the deepest heat pump installations require digging only a few hundred feet. Geothermal energy to supply electricity to the grid requires not only much deeper digging but specific geological features.

Utility scale geothermal energy uses naturally occurring underground reservoirs of hot water and steam to power turbines. They require underground rock formations to be permeable to the water. Enhanced geothermal systema (EGS) are human-made reservoirs that accomplish the same thing.

The largest geothermal energy power plant in the world, called The Geysers, is located near Santa Rosa, California. It produces 20% of California’s renewable energy and emits no greenhouse gases. It is built in an area with a natural reservoir of hot water and steam. Not many other places in the world have such a geological advantage.

Almost anywhere in the world has hot, dry rock available deep beneath the surface, but it provides only the heat. A technique similar to fracking for oil and natural gas drilling makes it possible to pump water down there to make an artificial reservoir of hot water and steam. Injecting water into rock fractures it, providing both fluid and permeability.

It is then possible to pump the hot water up closer to the surface to power turbines and generate electricity, then return the water to the deeper level to reheat it. That is, with EGS, it is theoretically possible to provide cheap, abundant, predictable, and clean energy everywhere.

Some problems with enhanced geothermal energy

Wikimedia Commons

Of course, for all the advantages of enhanced geothermal energy, it is not a magic solution to all our energy problems. It has a big problem of its own: earthquakes.

For a long time, researchers knew that small earthquakes frequently occur near EGS sites. They assumed that the technique could only cause small quakes. Then, an enhanced geothermal power plant in Korea apparently touched off a 5.5 magnitude earthquake, which caused $75 million worth of damages in the area.

The fact is that no one really knows the risk of causing a large quake. Especially, no one knows if EGS could cause a magnitude 7 or 8 quake, which would be catastrophic. That consideration did not keep a company from developing the Salton Sea Geothermal field right at the southern end of the San Andreas fault in Southern California.

Safe EGS requires both careful risk analysis and procedures to keep the reservoirs at a steady state by injecting water evenly throughout the site. Humans do not seem to be very good at risk analysis. The location of the Salton Sea field neatly demonstrates our utter incompetence of careful planning.

How many of the bright ideas in this generation will prove to be very bad ideas a few decades from now? After all, burning coal once seemed like a good way to save trees!

Two new enhanced geothermal systems in Utah

On September 25, 2023, Texas-based Fervo Energy broke ground at Cape Station in Beaver County, Utah on what will become the world’s largest enhanced geothermal project. It will start to produce electricity in 2026. When it reaches full-scale production in 2028, it will produce more than 400 megawatts of electricity around the clock. Researchers estimate that southwestern Utah has more than 10 gigawatts of geothermal reserves.

The Cape Station project benefits from research and data collection from the Department of Energy’s Frontier Observatory for Research in Geothermal Energy (FORGE).

Another new project near Milford, Utah, the Rodatherm Geothermal Test Bed, is trying out a different approach. Instead of water, it will use the Organic Rankine Cycle, which converts organic fluids with a lower boiling point than water directly into electricity. It does not require injecting fluids.

The Utah Bureau of Land Management (BLM) approved it in September 2023. In partnership with the Southern Utah Wilderness Alliance, Utah-based Rodatherm will operate it for twelve months to assess its commercial viability. After that, if it wants to continue to operate the wells, it must receive additional analysis of its environmental impact according to the National Environmental Policy Act.

The alliance opposed three earlier geothermal lease sales, but it approves of the site Rodatherm selected. The BLM conducted a nine-month environmental assessment starting on December 12, 2022. It estimated impact on soil erosion and bird species during construction to be low and made recommendations for mitigating possible long-term impacts.

The description of this project that I read does not mention earthquake risk. The project apparently doesn’t require fracking, which seems to be the culprit in causing seismic activity. It will be worth keeping track of this technology.

Sources:

Assessing geothermal energy: How could a new project impact Southwest Utah? / Alysha Lundgren, St George News. October 20, 2023 [Link no longer works.]
Enhanced geothermal systems / Office of Energy Efficiency & Renewable Energy
Fervo Energy breaks ground on next-gen geothermal project / Renewable Energy World. September 25, 2023
Fervo Energy Cape Station groundbreaking / The Western Way. September 28, 2023
The pros and cons of enhanced geothermal energy systems / Will McCarthy, Yale Climate Connections. February 6, 2020