Endurance Energy tested its novel underwater geothermal tech off the coast of Oregon. The firm has raised $63 million for its “eyebrow-raising” approach.
A tiny power plant notched a big win last month off the coast of Oregon: For nearly 30 seconds, it generated electricity using the heat of an underwater volcano.
The startup Endurance Energy deployed its test unit, called Adélie, about a mile below the surface of the Pacific Ocean during a three-week demonstration in September. On Monday, the Seattle-based company announced the results, which it says mark a milestone for the world’s emerging and highly uncertain efforts to develop offshore geothermal power.
“We follow the adage ‘make it exist, then make it good,’” said Andrew Redd, founder and CEO of Endurance Energy. “Adélie made it exist, and now we know it’s possible.”
Redd, who is a former SpaceX engineer, launched the startup in January 2025 with the goal of scaling a clean, always-on energy source. The company has since raised $63 million from an array of venture capital firms and is partnering with the Kingdom of Tonga on a plan to deploy a 2-megawatt project that would help reduce the island nation’s reliance on imported diesel.
First, though, the Endurance team needs to ensure its technology can run for more than half a minute.
The Adélie test is perhaps the most far-flung example of the growing push to expand America’s geothermal power capacity using next-generation technologies and in less-conventional locations. While most everyone else is focused on harnessing heat terrestrially, Redd said he sees the most promise in the volcanically active regions where tectonic plates are spreading apart.
“It’s an eyebrow-raising approach,” said Emily Pope, a geologist and senior fellow at the Center for Climate and Energy Solutions.
She said that while offshore geothermal is intriguing from a scientific perspective, it’s hard to see how projects could pencil out economically, given the cost and complexity of operating in harsh, salty ocean conditions and the long distances the power would have to travel to reach customers. Remote island nations, seemingly ideal candidates for the technology, could far more easily adopt lower-cost solar power and batteries to meet their energy needs.
“It is adding so much technological challenge to an energy production technology, without there being a really significant demand for it,” Pope said of the subsea pursuit.
Existing offshore geothermal initiatives have primarily focused on conducting research, not chasing commercial power. In 2016, a team of Chinese scientists produced a few watts of sustained power from a hydrothermal vent where the southwest Indian Ocean meets the southeast Atlantic Ocean. In southwest Iceland, a government-backed project drilled a geothermal well near the Mid-Atlantic Ridge, but corrosive seawater caused major engineering hurdles.
Redd said Endurance differs from earlier initiatives. The company aims to operate at a far greater scale and is designing technology “from scratch” to survive the intense pressure and corrosiveness of the deep sea, including by using a lot of titanium.
The Adélie expedition began last month aboard the Ocean Guardian vessel, which sailed about 300 miles west of Oregon to the Axial Seamount, an active submarine volcano along the Juan de Fuca Ridge. The area is a focus of oceanographic research for the University of Washington and the National Science Foundation’s Ocean Observatories Initiative, making it an ideal place to operate the project and monitor environmental conditions, Redd said.
From the vessel, Endurance guided down a modified geotechnical drill that offshore oil and gas developers typically use to extract core samples of subsea rocks. The team remotely drilled a relatively shallow well into a vent field at the base of the volcano, from which flowed hot, mineral-rich seawater.
Endurance then lowered Adélie onto the seafloor, where a submarine robot connected it to the well. The 3-ton power system contains an organic Rankine cycle system — the kind used on many land-based geothermal projects — that transfers heat from the hydrothermal fluid to spin a turbine and generate electricity.
Ultimately, Adélie wasn’t able to produce power from the well. So Endurance moved the unit to a nearby natural vent. On Sept. 27, the turbine produced about 60 watt-hours over about 29 seconds. For nearly 9 of those seconds, it generated more power than it used to operate, with the extra electricity charging the battery backup system. But the run ended after the battery’s overcurrent protection kicked in; when a power cable failed soon after, the dive was over.
“This was our first end-to-end demonstration of subsea geothermal as a concept, and we learned just an incredible amount from every stop along the way,” Redd said. A crew in Seattle received real-time temperature and flow-rate data from the site and operated the plant remotely using an existing fiber-optic cable network.
Endurance now is “rearchitecting” some of the core components of Adélie, he said. The startup plans to deploy the refurbished unit this winter with the aim of generating higher power output and for a longer stretch of time. At the same time, the company is developing what could become a far heftier commercial-scale system, which Redd posited might start generating electricity in 2027.
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Maria Gallucci is a senior reporter at Canary Media. She covers emerging clean energy technologies and efforts to electrify transportation and decarbonize heavy industry.