Endurance Energy conducted a three-week test of its 3-ton prototype power plant, Adélie, at the Axial Seamount in the Pacific Ocean during September. The system was deployed at a depth of 1,524 meters using a subsea lander drill to access hydrothermal fluids. The initial test well, measuring 16 meters deep and 5 centimeters wide, failed to provide sufficient fluid flow to operate the plant.
The team subsequently connected the 100-kilowatt plant to a natural hydrothermal vent with temperatures reaching 281° C. On September 27, the turbine reached 26,000 rpm, generating 60 watt-hours of electricity. The system achieved net-positive power for 8.7 seconds, reaching a peak of 16.5 kilowatts of net power before a software error and a short circuit in a power cable halted the trial.
The company plans to use deeper wells, up to 80 meters, in future deployments to increase fluid delivery. A refurbished version of the plant, renamed Gentoo, is scheduled for testing in the winter of 2026–2027. Endurance Energy aims to deploy up to six 2-megawatt commercial generators in the Kingdom of Tonga by 2027 to provide an alternative to imported diesel fuel.
Experts note that while geothermal energy is established on land, subsea operations face significant cost and technical challenges. Endurance Energy intends to target markets in the US, Taiwan, and Japan as the technology matures, aiming to provide continuous, weather-independent power to utilities.
