World's first subsea geothermal plant generates more power than it uses — for 8.7 seconds
A power plant on the Pacific seafloor generated more electricity than it consumed for 8.7 seconds.
The brief demonstration was an important step for Seattle-based startup Endurance Energy, which is working to make electricity from underwater volcanic heat dependable.
Here's what to know
Endurance tested its Adélie system at Axial Seamount, an active underwater volcano roughly 300 miles from Oregon, Gizmodo reported . Described as the world's first subsea geothermal power plant, the system delivered a median net power of about 2 kilowatts, with a peak of 16.5 kilowatts.
The 100-kilowatt plant initially couldn't draw enough hydrothermal fluid from a drilled, 52-foot-deep well. Engineers moved it to a nearby natural vent, where the flowing fluid measured approximately 538 degrees Fahrenheit.
Adélie then generated more electricity than it needed to operate before a software problem halted operations. A subsequent failure in the power cable supplying its refrigerant pump ended the demonstration.
The test wasn't meant to achieve sustained commercial output. It was successful because it showed Adélie could generate more electricity than it used.
More background
According to Gizmodo, SpaceX alumnus Andrew Redd founded Endurance in January 2025. The organization wants coastal grids and industrial sites to have a continuous electricity supply that doesn't depend on the weather.
"Many of the places with the strongest offshore resources also depend heavily on imported fuel," Redd told Gizmodo. "For them, this is a chance to replace diesel with clean, local baseload power and real energy security. As the technology matures, we expect to compete on cost in open electricity markets."
Offshore placement offers a way around some land-use restrictions onshore projects face. The surrounding seawater supplies cooling and pressurization, and at mid-ocean ridges, drilling requirements could also be reduced because heat lies relatively close to the seafloor.
Operating on the ocean floor presents its own challenges, including corrosive fluids. Dani Merino-Garcia, vice president of research at geothermal nonprofit Project Innerspace, warned Gizmodo that acidic fluids could damage the system's components, particularly its heat exchanger.
What's being done?
Endurance plans to test Gentoo, an overhauled Adélie system with redesigned subsea cables, tougher electronics, and deeper wells, according to Gizmodo. The changes are meant to address the fluid-flow and equipment problems Endurance encountered during the demonstration.
Within 16 hours of its first failed generation attempt, Endurance retrieved Adélie, serviced it, and redeployed it to operate at a seafloor hydrothermal vent.
After such a brief initial run, Endurance faces an ambitious timetable. The company is working on its first commercial installation in the Kingdom of Tonga, aiming to deliver its first power in 2027.
Roland Horne, who leads Stanford University's Geothermal Program, told Gizmodo that the technology appears technically feasible, though deploying it underwater would likely be costly. Affordable electricity is still a goal, not a demonstrated result.
Merino-Garcia noted that the engineering could prove useful even outside of the harshest deep-ocean environments. "The fact that they're able to install power generation units in the subsea is a technical achievement that can be applied to shallower resources or more benign conditions," he told Gizmodo.
Where can I learn more?
Endurance's seafloor test is one of several efforts to tap geothermal heat and generate power underwater.
• In Texas, Sage Geosystems' next-generation geothermal plant stayed connected to the grid for 120 days.
• Utah recently switched on its first utility-scale next-generation geothermal plant .
• Texas is looking to launch geothermal, nuclear, and gas projects on state land to improve grid reliability.
• In the U.K., 750 affordable homes now receive low-carbon heat from mine water .
• Chinese solar cells generated power 33 feet underwater , setting a new record.
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