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 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 ways to make paths for water to flow through hot rocks. These ways include using water pressure, chemicals, heat, carbon materials, and even explosions. Some EGS projects are close to natural geothermal areas but in rocks that don’t let water flow easily. By using these ways, scientists help water 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 helped 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 put in water and two to get it out. Soultz is in Alsace.

South Korea

The Pohang EGS project began in December 2010 with the goal of making 1 MW of power. Research stopped in 2018 after an earthquake in Pohang in 2017 that might have been linked to the project.

United Kingdom

United States

Early days — Fenton Hill

The first EGS project, called Hot Dry Rock, happened at Fenton Hill, New Mexico. Run by Los Alamos Laboratory, it was the first try to make a deep EGS reservoir. The reservoir was finished in 1977 at a depth of about 2.6 km, using rocks heated to 185°C. After making the reservoir bigger in 1979, it was tested for about a year. In 1986, a second reservoir was ready for testing, and during a 30-day test, the temperature went up steadily to about 190°C.

2000-2010

In 2009, the US Department of Energy (USDOE) said it would give money 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 see if it’s possible, get money, and watch for earthquakes. In 2022, a deep well was drilled to reach rocks hotter than 85°C. This project wants to provide 20% of the campus heating needs. Possible places for the reservoir include the Trenton-Black River formation and basement crystalline rock.

EGS "earthshot"

In September 2022, the Department of Energy said it would start an “Enhanced Geothermal Shot” to make the cost of EGS $45 per megawatt hour by 2035.

Other federal funding and support

The Infrastructure Investment and Jobs Act gave $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 means earth shaking caused by people. In enhanced geothermal systems (EGS), this shaking often happens 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, this activity caused worries, so the city stopped its project. But experts say the risks from these shakes are usually smaller than natural earthquakes and can be managed with careful planning and watching. Each place is different, so these risks should be checked before starting big projects that put fluids underground.

EGS potential

United States

A report from 2006 by MIT, supported by the U.S. Department of Energy, looked at EGS closely. It found that the United States has lots 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 make a lot of electricity from these resources by 2050. It also said that the cost of this energy could be very affordable, depending on things like how hot the rocks are and how well we can bring the heat to the surface.