Enhanced geothermal system

An enhanced geothermal system (EGS) generates geothermal electricity without needing natural hot water or open rock spaces. Traditional geothermal power only works in special places where hot rocks, water, and open spaces occur naturally. But most of the heat under the ground is trapped in dry, solid rock that normal methods cannot use.

EGS uses special techniques to make it possible to get energy from these dry rocks. One common method is called 'hydraulic stimulation,' which helps create spaces in the rock so water can flow and carry heat to the surface. This means we can access more geothermal energy than ever before, opening up new places where clean power can be produced.

Overview

In many rocks, water can’t flow easily because the cracks and holes are too small. To fix this, we can pump water deep into the rock at high pressure through a special well. This pressure makes the tiny cracks grow bigger, letting more water flow.

The water moves through these cracks, heating up, and then comes back up to the surface. We can use this hot water to make electricity. The water goes back underground to heat up again and start the cycle.

These kinds of plants can run all the time and might work almost anywhere if we dig deep enough. They are being tested in places like Australia, France, Germany, Japan, Switzerland, and the United States. The biggest one so far is in Australia, and it could make a lot of power for many years.

Research and development

EGS technologies use different methods to create pathways for water to flow through hot rocks. These methods include using water pressure, chemicals, heat, carbon materials, and even explosions. Some EGS projects are located near natural geothermal areas but in rocks that don’t let water flow easily. By using these methods, scientists make it easier for water to move through the rocks and carry heat to the surface. The table below shows EGS projects around the world.

Australia

Main article: Geothermal power in Australia

The government of Australia has supported research to develop Hot Dry Rock technology. Projects include Hunter Valley in 1999, Cooper Basin: Habanero and Jolokia 1 in 2002, and Olympic Dam in 2005.

European Union

The EU’s EGS research project at Soultz-sous-Forêts, France, connects a small power plant to the electricity grid. This project tested linking several areas and using three wells—one to inject water and two to produce it. Soultz is located in Alsace.

South Korea

The Pohang EGS project began in December 2010 with the aim of producing 1 MW of power. Research activities stopped in 2018 after an earthquake in Pohang in 2017 that may have been related to the project.

United Kingdom

United States

Early days — Fenton Hill

The first EGS project, called Hot Dry Rock, took place at Fenton Hill, New Mexico. Run by Los Alamos Laboratory, it was the first attempt to create a deep EGS reservoir. The reservoir was completed in 1977 at a depth of about 2.6 km, using rocks heated to 185°C. After expanding the reservoir in 1979, it was tested for about a year. In 1986, a second reservoir was prepared for testing, and during a 30-day test, the temperature rose steadily to about 190°C.

2000-2010

In 2009, the US Department of Energy (USDOE) announced funding opportunities for EGS projects, offering up to $84 million over six years.

FORGE

Cornell University — Ithaca, NY

Cornell University plans to develop EGS as part of their campus heating system. The project started in 2018 to check if it’s possible, get funding, and monitor earthquakes. In 2022, a deep well was drilled to reach rocks hotter than 85°C. This project aims to provide 20% of the campus heating needs. Possible locations for the reservoir include the Trenton-Black River formation and basement crystalline rock.

EGS "earthshot"

In September 2022, the Department of Energy announced an “Enhanced Geothermal Shot” to lower the cost of EGS to $45 per megawatt hour by 2035.

Other federal funding and support

The Infrastructure Investment and Jobs Act provided $84 million for EGS development through four projects. The Inflation Reduction Act extended tax credits for renewable energy, including geothermal, until 2024.

Induced seismicity

Main article: Induced seismicity

Induced seismicity refers to earth tremors caused by human actions. In enhanced geothermal systems (EGS), these tremors often happen because of the high pressures used. For example, at the Geysers geothermal field in California, shaking events are linked to injection activities.

In some places, like Basel, such activity caused concerns, leading the city to stop its project. However, experts say the risks from these human-caused tremors are usually smaller than natural earthquakes and can be managed with careful planning and monitoring. Each location is different, so these risks should be checked before starting big projects that involve injecting fluids underground.

EGS potential

United States

A report from 2006 by MIT, supported by the U.S. Department of Energy, studied EGS in detail. It found that the United States has a huge amount of energy stored in hot rocks deep underground—more than enough to meet the country’s energy needs many times over.

The report suggested that with enough research and development, the U.S. could produce a lot of electricity from these resources by 2050. It also noted that the cost of this energy could be very affordable, depending on factors like how hot the rocks are and how well we can bring the heat to the surface.