At 1,500 metres beneath the Pacific Ocean, a small power plant managed to produce more electricity than it consumed. But only for a few seconds.
The experiment took place on Axial, an active volcano located about 480 kilometres off the coast of Oregon, United States. The seafloor there is crossed by water heated deep underground by volcanic activity. The American company Endurance Energy wanted to find out whether this heat could be used to produce electricity, as in geothermal power plants on land.
The active El Gordo hydrothermal vent, at the summit of the underwater Axial volcano, illuminated by observation equipment. This image predates the 2026 Adélie experiment.
Photo: Ocean Observatories Initiative / NSF, public domain.
Wikimedia image
The idea is simple: use a very hot liquid to turn a turbine connected to a generator. But at this depth, everything becomes more difficult. The equipment must withstand considerable pressure, operate without direct human intervention and be controllable from the surface.
The team first drilled a small 16-metre well beneath the ocean floor. The water coming out of it reached 260 °C. This was a successful first step, but its flow rate was insufficient to turn the power plant. The engineers therefore used another nearby heat source, with a hydrothermal water outlet at around 281 °C.
The prototype, named Adélie, weighed three tonnes. Installed on the seafloor, it was controlled from Seattle using an underwater communications cable. During the test on 27 September 2026, its turbine reached approximately 26,000 revolutions per minute.
For exactly 8.7 seconds, the device supplied more electricity than it used to operate. The surplus reached a peak of 16.5 kilowatts, with a median net power of about 2 kilowatts over this short period. The test therefore proves that it is possible to produce a power surplus directly on the seafloor.
But difficulties quickly emerged. An electrical protection system interrupted operation. During an attempted restart a few minutes later, a cable powering a pump was damaged. The experiment had to be stopped.
Endurance Energy now wants to improve its system and drill deeper to obtain a sufficient flow rate. A new test with a modified prototype is planned for the winter of 2026–2027.
In the longer term, the company is considering underwater power plants that would continuously harness the Earth's heat. Their advantage would be to produce electricity without depending on the sun or wind. It remains to be shown that this can operate sustainably, on a large scale, without disturbing marine environments.