Underground Energy, Now in Real Time

AltaRock and Fervo deploy fiber-optic sensing to improve subsurface visibility, speeding development and reducing geothermal project risk

21 Feb 2025

Geothermal developers in the US have begun using fiber-optic sensing to monitor underground energy flows in real time, a step they say will make geothermal projects faster, cheaper, and more reliable.

The technology, known as distributed acoustic sensing (DAS), converts standard fiber-optic cables into thousands of underground sensors. When installed in geothermal wells, these cables allow engineers to observe how heat, steam, and water move through deep rock layers. Until now, such data was either unavailable or delayed.

“It’s like switching from a map to a live GPS,” said one engineer involved in a June field test. “We can now see exactly how the subsurface behaves as we operate, without pausing the system.”

Companies including AltaRock Energy and Fervo Energy are integrating the system into their new-generation geothermal sites. These sites also feature advanced drilling methods, such as horizontal wells and multi-stage stimulation, aimed at improving output and lowering costs.

The approach has attracted attention from government agencies and large technology firms seeking round-the-clock renewable power. One persistent challenge for geothermal energy has been the lack of precise, continuous monitoring of subsurface activity. Fiber-optic sensing offers a potential solution, improving both operational efficiency and investor confidence.

Regulators are also monitoring the technology’s potential. Agencies have begun evaluating whether fiber-based monitoring could be included in national geothermal guidelines to reduce permitting times and strengthen safety requirements.

Although cost and scalability remain concerns, developers are moving quickly to adopt the approach. Fiber sensing is now being tested in more varied settings, including sedimentary basins and retired oil fields.

As geothermal expands beyond traditional regions, such monitoring tools may become essential. While still in early deployment, fiber-optic sensing could help turn geothermal from a niche resource into a mainstream pillar of clean energy supply.