---
title: "Startup’s undersea volcano power plant made net electricity for 8.7 seconds"
description: "Endurance Energy’s seafloor test at Axial Seamount was brief and ended in a short circuit. Next up is a plant of up to 12 megawatts for Tonga"
author: "Nate Ledger"
published: 2026-10-19T19:27:24Z
modified: 2026-10-20T03:00:00Z
url: https://rews.cc/a/startup-s-undersea-volcano-power-plant-made-net-electricity--40121c
language: en
tags: ["energy", "renewables", "ocean", "geothermal", "startup", "tech"]
publisher: "Rews (https://rews.cc)"
---

# Startup’s undersea volcano power plant made net electricity for 8.7 seconds

*Endurance Energy’s seafloor test at Axial Seamount was brief and ended in a short circuit. Next up is a plant of up to 12 megawatts for Tonga*

By Nate Ledger · October 19, 2026 · https://rews.cc/a/startup-s-undersea-volcano-power-plant-made-net-electricity--40121c

## In brief

- Seattle startup Endurance Energy tested a 100-kilowatt subsea geothermal plant at Axial Seamount in the Pacific in September
- The drilled well, 52 feet deep and 2 inches wide, did not deliver enough hydrothermal fluid to run the plant
- On a natural vent, the plant made 60 watt-hours and was net-positive for about 8.7 seconds, peaking at 16.5 kW net
- The run ended after a software shutdown and then a seawater short circuit in a pump cable
- The company plans up to six 2 MW generators off diesel-dependent Tonga in 2027; a Stanford expert expects high costs

Here is a business plan. You find an underwater volcano. You drill a hole in the seafloor next to it, about a mile down, and very hot fluid comes out. You put a small power plant on top of the hole, run the hot fluid through a turbine, and send the electricity somewhere useful. Then you sell that electricity to an island nation that currently burns imported diesel. Every step of this is hard. Last month a Seattle startup called Endurance Energy did a little of every step, all at once, for a few seconds.

As [Jeremy Hsu reported for Ars Technica](https://arstechnica.com/science/2026/10/startup-taps-underwater-volcano-as-energy-source-in-proof-point-test/), Endurance carried out what it calls the world’s first demonstration of a subsea geothermal power plant. The test ran over three weeks in September at Axial Seamount in the northeast Pacific, which the National Science Foundation’s ocean observatory program describes as [the largest and most active volcano on the Juan de Fuca Ridge](https://oceanobservatories.org/array/cabled-axial-seamount-array/). The 3-ton prototype, a 100-kilowatt plant called Adélie, made more electricity than it used for about 8.7 seconds. Then its software shut it down. Then a cable shorted. That was the end of the test.

“It’s the proof point,” Andrew Redd, Endurance’s founder and CEO, told Ars. “Net-positive is the threshold that matters: the plant made more power than it took to run itself on the seafloor, which no one had done before.”

Why put a power plant underwater at all? A geothermal plant turns a temperature difference into electricity, so it needs a hot side and a cold side. On land you have to build the cold side. On the seafloor it surrounds you. “The deep ocean gives us unlimited cold seawater for cooling, and its weight keeps the system and the well pressurized, so our plants can be compact,” Redd said in an email to Ars. That is the pitch: the ocean supplies the cooling and the pressure for free. The catch is that the ocean also makes installing and fixing everything much harder.

![A cylindrical industrial machine glows orange amid flowing lava and dark volcanic rocks, releasing a fiery plume beneath swirling teal clouds.](https://rews.cc/img/2162b7849e9cadfec08b16e0a2916652b73bb959.webp)

## The plumbing

The well came first. A subsea lander drill went down from the ship Ocean Guardian, run by Stabbert Maritime, and drilled two holes at about 5,000 feet (1,524 meters). The site is roughly 300 miles off the coast of Oregon, [according to ThinkGeoEnergy](https://www.thinkgeoenergy.com/endurance-energy-demonstrates-subsea-geothermal-power-in-pacific-ocean/). Both holes started venting hydrothermal fluid at about 500°F (260°C). The team cased and cemented the second one and capped it with a valve, which made it a well. Canada’s remotely operated submersible ROPOS helped hook Adélie up to it. Adélie was also plugged into the [Regional Cabled Array](https://interactiveoceans.washington.edu/about/regional-cabled-array/), a 559-mile (900-kilometer) network of seafloor fiber-optic and power cables that is funded by the NSF, run by the University of Washington, and normally used to keep watch on the volcano. So the plant was controlled from a command center in Seattle, over a science network built to monitor the thing it was drawing heat from.

Then came the problem. The well went only 52 feet (16 meters) into the seafloor and was 2 inches (5 centimeters) across. Oil, gas and onshore geothermal wells usually have casings 20 to 36 inches wide, so this one was 10 to 18 times narrower. It did not deliver enough fluid to run the plant. “For our first well, the goal was to show we could drill, case, cement, and cap a well on the seafloor, so we kept it small and shallow,” Redd said. “That limited how much fluid it could deliver, and deeper wells should change that.” The company’s current drill can reach about 260 feet (80 meters), five times the depth of the test well.

![A pipe with a valve rises from layered dark rock, drawing glowing red liquid from underground pools and releasing a single drop against a teal sky.](https://rews.cc/img/24277d01a1768f9b23509cb4082750ac332629f4.webp)

So the team moved Adélie onto a nearby natural vent that was already pushing out fluid at about 538°F (281°C), and on September 27 they turned it on. Over nearly half a minute, the turbine reached about 26,000 rpm and the generator produced 60 watt-hours of electricity. That is enough to run a 100-watt bulb for 36 minutes. The net-positive stretch lasted about 8.7 seconds, with a median of about 2 kilowatts of net power and a peak of 16.5 kilowatts. The peak was about a sixth of the plant’s rated capacity. If you multiply the median by the duration, you get a rough net total of about 5 watt-hours. It is a small number, but it is above zero, and that was the point of the test.

Then two things went wrong. Before the generator takes over, Adélie runs its pumps, thrusters and controls off a battery, which also gets the turbine spinning. During spin-up, a battery module recorded a short spike in current and then stopped reporting. The plant’s software kept relying on the module’s last reading and shut everything down as a safety precaution. While the team was restarting it, seawater got through a flaw in the casing of the cable feeding the refrigerant pump and shorted two of its conductors. Endurance says it will use the experience to improve how it builds and tests subsea cables. Seawater getting into a cable is about as basic an ocean problem as there is.

Endurance says sitting the plant on a natural vent was a one-off for research and demonstration, and future deployments will use drilled wells. It also says it chose the “least disruptive” site and monitored the work continuously: it sampled the water, recorded the tubeworms, snails, crabs and bacterial mats on the seafloor, compared its findings with sensors run by independent researchers, and sent water, rock and mineral samples to outside labs. In its [own announcement](https://finance.yahoo.com/energy/articles/endurance-energy-drills-worlds-first-160000565.html), the company called this its fifth deep-sea deployment in just over a year and the first to test every step together.

![A crab, spiral shells, and tube worms rest among seabed rocks beside a damaged underwater cable with exposed orange strands.](https://rews.cc/img/cee069ce635a465cb271d84891d766adbcd9e072.webp)

## The customer

Next comes Gentoo, a refurbished and upgraded Adélie (the naming theme is penguins), due for a trial in the winter of 2026–2027 that aims to sustain higher power. After that comes the commercial business: a 2-megawatt generator for a first deployment with the Kingdom of Tonga in 2027. Tonga’s grid runs mainly on imported diesel, which has become much more expensive since the United States and Israel launched their war with Iran. “The 2 MW commercial generators will be about the size of a shipping container, and we are deploying up to six of these generators \[to\] offshore Tonga,” Redd said. Six times 2 megawatts is up to 12 megawatts, which is 120 times Adélie’s rating and several hundred times what Adélie actually produced at its peak. [GeekWire reports](https://www.geekwire.com/2026/go-inside-endurance-energy-the-seattle-startup-tapping-underwater-volcanoes-for-geothermal-power/) that Endurance has raised $63 million from investors.

Roland Horne, a professor of energy science and engineering at Stanford, is skeptical about the cost. “It’s probably technically feasible, but it would undoubtedly be more expensive than to do it on land,” he told Ars. Land geothermal is already “on the edge of competitive pricewise,” he said, and anything that adds cost would “push it to the noncompetitive side.”

I think the interesting question is what you compare it with. Horne is comparing seafloor geothermal with geothermal on land, and on that comparison the ocean adds cost. Tonga is comparing it with diesel shipped across the Pacific at wartime prices, and that comparison changes whenever oil prices do. Endurance doesn’t need to beat land geothermal in general. It needs to beat one particular fuel bill, and keep doing it reliably for long enough that other customers notice. Redd’s list of those other customers is ambitious: “Large markets with ample offshore geothermal resources include the United States—Pacific Northwest and Alaska—Taiwan, and Japan,” he said. “As the technology matures, we expect to compete on cost and deliver continuous, weather-independent power to utilities and large energy users.”

For now, the record for continuous power stands at 8.7 seconds. Weather wasn’t what ended the run. A cable was.