A Seattle-based energy startup, Endurance Energy, announced the world’s first successful attempt to generate electricity from geothermal heat on the ocean floor. They demonstrated the first end-to-end operation of an underwater geothermal power plant, comprising the entire process from drilling to electricity generation.
The startup also showed that operators in Seattle could control the system from an offshore location, remotely starting and stopping the equipment, monitoring temperatures and pressures, and collecting data without being underwater.
The company said the newly installed underwater test plant, named Adelie, generated a net power of 2 kilowatts for nearly 9 seconds. The electricity produced exceeded than the system needed to operate, the startup claimed, founded just over a year ago in January 2025.
In the latest trial, completed on September 27, the company moved beyond testing single components to make geothermal energy from the seabed a reality.
The process included drilling a well, landing and operating a power plant on the seafloor, converting geothermal heat into electricity, and communicating with the system from shore in real time, all in nearly three weeks.
”On Sept. 27, we put a power plant on an active underwater volcano and made power,” said Andrew Redd, founder and CEO of Endurance Energy. “This historic milestone is also our first end-to-end test. We now know, firsthand, what works at depth, what needs to be improved, and how to build the next system for sustained commercial generation.”
From drilling hole to turning turbine
Engineers at the company tapped the heat energy of a nearby active volcano to produce the clean electricity from the ocean floor. They began deploying a power plant at Axial Seamount volcano, located 300 miles off the Oregon coast at a depth of nearly a mile in the Pacific Ocean.
Using a robotic drilling machine resting on the seabed, they first began drilling to locate a geothermal well at the bottom of the ocean. Imagine drilling for oil—but instead of looking for oil, you’re drilling into hot rock and hot water.
Inside the crater (caldera) of an underwater volcano, roughly 5,000 feet (1,500 meters) below the ocean’s surface, the team completed drilling of an offshore geothermal well.
The machine bored two closely spaced holes, and both reached hydrothermal fluid, superheated water that occurs naturally underground. The team then inserted a steel pipe inside the hole, a process called casing, while also filling the gap around the pipe with cement.
Following this, they installed a valve that allows engineers to control the flow of hot fluid. The finished well extended 52 feet (16 meters) below the seabed and produced water at 500°F (260°C), hot enough to generate electricity.
After the drilling operation, the team accurately placed the 3-ton power plant from a ship to the seabed instead of relying only on the drilled well, connecting the system to an existing hydrothermal vent. The vent naturally discharged water at 281°C, spinning the turbine at 26,000 rpm (over 430 revolutions per second). This turbine movement generated 2kW of net-positive electricity for only 8.7 seconds.
”The main question we had is can the system generate more power than it uses,” said Redd. “Adélie did. Goddard’s first liquid-fueled rocket flew for two and a half seconds. Our first net-positive run lasted about nine. Our approach is to make it exist, then make it good.”
Remote operation controls
The startup also showed that operators in Seattle could control the system from an offshore location, remotely starting and stopping the equipment, monitoring temperatures and pressures, and collecting data without being underwater. The commands and data traveled through the Regional Cabled Array, undersea fiber-optic cables owned by the National Science Foundation.
Meanwhile, the latest trial looks promising for operating a geothermal system on the deep-ocean floor; however, the company cautioned that the current system is not a commercial-scale power plant. It said the plant faces challenges, including sudden shutdowns due to battery overload, mineral buildup, and heat-transfer issues, that must be addressed before commercial use.
It added that once commercialized, the deep-sea geothermal systems would offer a continuous, weather-independent clean electricity by converting heat beneath the ocean floors. The energy generated could power coastal grids, industrial sites, and data centers around the Pacific and worldwide.