The Seattle-based startup Endurance Energy has successfully executed the world's first demonstration of a subsea geothermal power plant near the active Axial Seamount submarine volcano in the Northeast Pacific Ocean, at a depth of nearly one mile below the water's surface. During a three-week test of a 3-ton prototype, the plant managed to generate positive net electricity for less than 10 seconds, which developers considered a practical proof of the technical feasibility of exploiting this type of renewable energy in deep-sea environments.
Test details and operational challenges
The project required the use of a marine drill launched by the support vessel Ocean Guardian to drill two holes in the ocean floor at a depth of about 5,000 feet. The two holes produced hot hydrothermal fluids reaching temperatures of about 500 degrees Fahrenheit. After preparing one of the wells, a 100-kilowatt power generation plant named Adélie was deployed, designed to vaporize the thermal fluids and rotate a turbine that drives an electric generator, connected to the company's control center via a network of fiber optic cables and subsea electrical cables managed by the University of Washington with funding from the U.S. National Science Foundation.
The test faced several technical obstacles, most notably that the first experimental well was thin and narrow, measuring two inches in width, and did not pump a sufficient amount of fluid, which prompted the team to temporarily redeploy the plant over a natural thermal vent. In that experiment, the turbine reached 26,000 RPM and produced about 60 watt-hours, achieving positive net energy for 8.7 seconds and an average net power of about 2 kilowatts. However, a software glitch related to the starter battery and a minor seawater leak into the cooling pump supply cable led to an early termination of the test.
Future commercial plans
The company seeks to overcome these obstacles by drilling deeper and wider wells in its upcoming tests during the winter of 2026-2027 using an upgraded version called Gentoo. The company also plans to develop a larger 2-megawatt commercial generator the size of a shipping container, and to deploy up to six generators for the Kingdom of Tonga, a Polynesian island nation in the Pacific Ocean, in 2027 to provide a sustainable alternative to its current reliance on imported diesel fuel.
Why does this news matter?
This test represents a potential technical turning point for providing clean energy independent of weather fluctuations for island nations and coastal communities that rely on importing expensive fossil fuels. Although energy experts such as Professor Roland Horne of Stanford University point out that the operational cost of deep-sea activities will be higher compared to land-based projects, the success of the proof-of-concept opens the door to exploring vast marine geothermal energy resources in regions such as the U.S. Pacific Northwest, Alaska, Taiwan, and Japan.