US — Ars Technica

Startup taps underwater volcano as energy source in "proof point" test

MobilityOctober 20, 20261 min read

A small startup, Endurance Energy, tested the world's first subsea geothermal power plant near an underwater volcano. It made electricity for less than 10 seconds, which shows the idea can work.

A first test under the sea

Endurance Energy, a startup based in Seattle, tested a small underwater power plant in September. The plant uses heat from deep inside the Earth, near an active underwater volcano in the northeast Pacific Ocean. The test lasted three weeks. The plant made more power than it used, but only for less than 10 seconds.

Key facts

The prototype power plant weighs about 3 tons.
The test site is the Axial Seamount, almost a mile (about 1,524 meters) below the ocean surface.
The test lasted three weeks, and the plant ran for less than 10 seconds of net-positive electricity.
The test went more than 2.5 times the height of One World Trade Center in New York City, the tallest building in the United States.

What is geothermal power?

Geothermal power uses heat from inside the Earth to make electricity. On land, this is already done in many places. Under the sea, the company wants to use the same idea. The company says the deep ocean's cold water helps cool the system, and the water's weight helps keep the system under pressure, so the plant can be small.

Why it matters

The company hopes to sell this power to Pacific island nations. These places often pay a lot to import fossil fuels like oil. If the idea works at a low cost, it could give them another clean energy choice. But experts say that building and running plants under the sea will likely cost more than on land, so the company must show it can run steadily and be affordable.

What to watch next

Whether Endurance Energy can run its plant steadily for longer periods under the sea.
Whether the company can show that the plant costs less than or close to land-based geothermal power.
Whether any island nations or other customers sign up to buy the power.

Glossary

Endurance Energy: A Seattle startup that is building small underwater geothermal power plants.
Geothermal power: Electricity made from heat that comes from deep inside the Earth.
Axial Seamount: An active underwater volcano in the northeast Pacific Ocean where the test took place.

Same story, different eyes

The EngineerAI

Ten seconds of net power, and a whole new set of questions answered

Putting a 3-ton power plant a mile down and getting it to run at all is a big engineering step, because every wire, seal and drill has to work with no one nearby to fix it. I like the idea that the deep sea's cold water and crushing pressure become part of the design, letting the plant stay compact. Whether it can run steadily for months and bring costs down is not yet known.

The SkepticAI

Ten seconds of net power, and a clear next question

A net-positive result lasting under 10 seconds is a lovely first proof point, and what I'd love to see next is how long it can hold steady. If the plant runs for hours or weeks and the cost per kilowatt-hour is shared, it would be easier to judge against land-based geothermal, which Stanford's Roland Horne expects to be cheaper. How the equipment holds up in deep, hot seawater over time is also something I'm curious about, and it hasn't been shared yet.

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