Startup’s underwater power plant generated more than it consumed for 8.7 seconds — Ars Technica
Startup Endurance Energy conducted a demonstration of an underwater geothermal power plant near the Axial underwater volcano in the northeastern Pacific Ocean. During the test, the Adélie unit generated more electricity for 8.7 seconds than it consumed for its own operation. This was the first such demonstration on the seafloor, Ars Technica reports.
Wells and hot fluid
The three-ton prototype was deployed in September at a depth of about 1,524 meters. An underwater drilling rig from the Ocean Guardian vessel drilled two wells into the ocean floor. Hydrothermal fluid with a temperature of approximately 260°C emerged from them. One of the wells was cased, cemented and fitted with a valve.
Adélie has a capacity of 100 kilowatts. The unit is designed to convert hydrothermal fluid into steam that spins a turbine and drives a generator. However, the 16-meter well with a diameter of 5 centimeters proved insufficiently productive to operate the power plant.
Test at a natural vent
The unit was then moved to a natural hydrothermal vent, where the fluid temperature reached about 281°C. On September 27, the turbine accelerated to approximately 26,000 revolutions per minute in nearly half a minute, and the generator produced 60 watt-hours of electricity. Median net power was about 2 kilowatts, while peak power was 16.5 kilowatts.
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The test was halted by a software error after a brief current spike in the battery module. During an attempt to restart, the coolant pump cable also failed: seawater entered through a defect in the sheath and caused a short circuit between two conductors.
Next tests
Endurance Energy plans to test an upgraded Gentoo unit during the winter period of 2026–2027, designed for longer-duration generation. The company is also developing a 2-megawatt commercial generator for a project planned for 2027 near Tonga, where up to six such units are expected to be installed.
Stanford University professor Roland Horne said the technology is likely technically feasible but would cost more than land-based geothermal energy. Endurance Energy founder and CEO Andrew Redd said deeper wells should provide a greater flow of hot fluid.
