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Endurance Energy says its Adélie test unit generated about 60 watt-hours of electricity for roughly 29 seconds at a natural hydrothermal vent near Oregon’s Axial Seamount in September 2026. The test showed the system could produce power briefly, but it did not achieve sustained operation: a battery protection system stopped the run, and a cable later failed. The company plans another test this winter.
Endurance Energy says its Adélie test unit generated about 60 watt-hours of electricity over roughly 29 seconds at a hydrothermal vent near Oregon’s Axial Seamount in September. The short run marks an early technical demonstration of the Seattle startup’s seafloor geothermal system, but it did not establish that the technology can operate reliably or produce commercial-scale electricity.
The three-week demonstration took place about 300 miles west of Oregon, at a site roughly a mile beneath the Pacific’s surface. Endurance deployed Adélie from the research vessel Ocean Guardian. The company first drilled a relatively shallow well into a vent field, but the unit did not generate power from that well. The team then moved it to a nearby natural vent.
Adélie weighs about three tons and uses an organic Rankine cycle, a system also used in some land-based geothermal plants. Heat from mineral-rich hydrothermal fluid drives a turbine. A remotely operated submarine connected the unit to the well, while staff in Seattle monitored temperature and flow data and controlled the plant through an existing fiber-optic cable network.
Endurance reported that the turbine produced more power than the unit needed to run for about nine seconds, sending surplus electricity to its backup battery. The test ended after the battery’s overcurrent protection activated. A power cable failed soon afterward, ending the dive. The company said it is redesigning parts of Adélie and intends to send a refurbished unit back to the seafloor this winter.
A Brief Test, a Difficult Scale-Up
The test offers evidence that a geothermal power system can be deployed and operated remotely on the deep seafloor, and that it can briefly convert heat from a vent into electricity. That is a useful engineering milestone for a concept that has mostly been explored through research rather than commercial power projects. It is not, however, evidence that the system can provide dependable electricity over extended periods.
The distinction matters because the proposed value of geothermal power is its potential to supply continuous, low-carbon electricity, unlike sources whose output varies with weather. To deliver that benefit offshore, Endurance would need to extend operation far beyond seconds, increase output, and make equipment dependable in extreme pressure and corrosive seawater. It would also have to show that the costs of installation, maintenance and transmitting power can compete with alternatives.
Endurance has raised $63 million and is working with Tonga on a proposed 2-megawatt project intended to reduce reliance on imported diesel. That plan signals a possible application, not a proven outcome: the test described in the report was a brief demonstration, not a deployment supplying electricity to customers.
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Why Endurance Went Offshore
Founder and CEO Andrew Redd, a former SpaceX engineer, started Endurance in January 2025. The company is pursuing geothermal heat in volcanically active areas where tectonic plates spread apart, rather than limiting its search to land-based resources. The September test took place at Axial Seamount, an active submarine volcano along the Juan de Fuca Ridge. Redd said the area’s established ocean research and monitoring made it a suitable place to conduct the demonstration.
Other efforts have shown small-scale potential but faced limits. The report says Chinese scientists generated a few watts of sustained power at a hydrothermal vent in 2016. A government-backed Icelandic project drilled near the Mid-Atlantic Ridge, where corrosive seawater created engineering difficulties. Endurance says it is designing equipment from scratch for deep-sea conditions, including using substantial amounts of titanium.
Geologist Emily Pope, a senior fellow at the Center for Climate and Energy Solutions, described the approach as “eyebrow-raising.” She questioned whether the added technical challenges could make projects economically viable, especially when remote islands may be able to use lower-cost solar power and batteries. Her comments reflect an assessment of commercial prospects, not a finding about the outcome of Endurance’s test.
“We follow the adage ‘make it exist, then make it good.’ Adélie made it exist, and now we know it’s possible.”
— Andrew Redd, Endurance Energy founder and CEO
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Reliability and Costs Remain Open
The demonstration does not establish how much electricity a future system could produce continuously, how long its components could last, or how often equipment would need repair. Endurance has not reported a commercial operating cost, a power price, or evidence that its system can compete with solar and batteries in Tonga. The company’s proposed 2-megawatt project remains a plan, and the report does not specify its construction schedule or financing.
The immediate causes that ended the test are clearer than the wider performance picture: the battery’s overcurrent protection activated, and a power cable failed soon afterward. It is not clear from the report whether the cable failure caused the protection event or what changes will address each issue. Nor does the short output measurement show what Adélie could sustain after a longer run. The company’s projections for a commercial-scale system producing power in 2027 are its own expectations, not confirmed operating results.
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A Winter Return to the Seafloor
Endurance says it is reworking core components of Adélie and plans to redeploy the refurbished unit this winter. The company’s stated goals are to generate more power and maintain production for longer than the September run. Results from that trial should help show whether the battery and cable problems can be addressed, though a longer demonstration would still leave questions about long-term reliability and economics.
In parallel, Endurance is developing a larger system that Redd said could begin generating electricity in 2027. No further technical specifications or confirmed deployment details are provided in the report. The next milestones are therefore practical ones: whether the redesigned test unit operates for longer, what output it achieves, and whether the company can turn those results into a viable project with Tonga or another customer.
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Key Questions
How much electricity did the test unit generate?
Endurance reported that Adélie produced about 60 watt-hours over roughly 29 seconds at a natural hydrothermal vent. For about nine seconds, it generated more power than it used to operate.
Where did the test take place?
The demonstration was at Axial Seamount, an active submarine volcano about 300 miles west of Oregon and roughly a mile below the Pacific surface.
Why did the test stop?
The company said the battery’s overcurrent protection activated, ending the run. A power cable failed soon afterward, and the dive ended. The report does not specify whether the two issues were related.
Can the system supply power commercially now?
No. The reported test lasted about 29 seconds and generated a small amount of electricity. The company still needs to demonstrate longer operation, higher output and a workable commercial model.
What does Endurance plan to do next?
Endurance says it is redesigning parts of Adélie and plans to redeploy it this winter, aiming for higher output and a longer run. The company is also developing a larger system that its CEO said might generate electricity in 2027.
Source: rss
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