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Estimating greenhouse gas emissions from geothermal technologies

September 26, 2025

Geothermal energy — energy harnessed from the earth’s internal heat — is considered one of the most consistent and reliable sources of renewable energy.

The land use required to harness geothermal energy is minimal, and the heat below the earth’s surface is constant. However, estimates of greenhouse gas emissions from geothermal plants vary widely, depending on the types of geothermal technologies used.

ACEP summer intern Sidney Hackett wanted to find trends in the global impacts of different geothermal technologies throughout the phases of their lifetime. Working under the mentorship of Magnus de Witt, he developed a report aggregating the many studies and publications on the topic.

Hackett sought to establish cohesive estimates of emissions from geothermal technologies based on a systematic review of current data. He focused on three different geothermal systems: 1) hydrothermal binary, 2) hydrothermal flash and 3) enhanced geothermal systems, or EGS, binary.

Hydrothermal binary is a geothermal electricity production technology that uses natural reservoirs with temperatures below 182 C (360 F) in earth’s interior, making use of a binary cycle (two separate fluid cycles) with a heat exchanger to generate electricity. Hydrothermal flash is a technology that uses natural reservoirs with temperatures above 182 C (360 F) to generate electricity. EGS binary also makes use of a binary cycle but requires hydraulic stimulation in the creation of an artificial reservoir.

Hackett found that of these three geothermal technologies, hydrothermal flash plants reported the highest lifetime greenhouse gas emissions, followed by EGS binary, then hydrothermal binary.

In developing the report, Hackett discovered how Alaska could best make use of geothermal energy as a means to support the state’s unique energy needs, taking inspiration from other electrical grids in the Arctic.

“Alaska has the high potential for geothermal energy and a unique energy landscape. Harnessing geothermal energy for electricity and heat could lead to a future of more affordable and more reliable energy,” he said.

This internship, Hackett’s first experience with formal academic research, gave him a new perspective on what it means to be a researcher.

“Not only have I gained skills in data analysis and navigating academic literature, but I have also learned what it’s like to be a part of a research team and community,” said Hackett, who is a mechanical engineering student at Harvard College.

“Being able to engage not only with ACEP researchers but also with scientists throughout the university and even throughout the state has opened up new doors and given me a greater appreciation for the research ecosystem as a whole,” he said.

This internship was funded by the U.S. through ACEP’s Research Experiences for Undergraduates program. View the on ACEP’s YouTube channel. For more information on this project, contact Magnus de Witt at mdewitt9@alaska.edu.