The seafloor is doing something that engineers in Seattle have been considering for years, approximately 200 miles off the coast of Washington, in waters so deep that no sunlight reaches the bottom. Before exiting at vent areas dispersed over the Juan de Fuca Ridge, hydrothermal fluids traveling through volcanic rock are reaching temperatures of 750 degrees Fahrenheit. For millions of years, there has been heat. It’s not going anywhere. Adélie, a 100-kilowatt generator constructed by a small business named Endurance Energy, is intended to sit on the seafloor adjacent to those vents and convert that heat into power.
Any engineer familiar with organic Rankine cycle power plants on land would recognize the device’s closed-loop system. The hot fluid is accessed through boreholes that are bored around 200 feet into the seafloor close to the vent field. This fluid transfers its heat to a refrigerant that circulates in a closed loop by passing through titanium tubing inside a heat exchanger. Electricity is produced when the refrigerant boils, expands, and turns a turbine. The refrigerant is then condensed back into liquid for the subsequent cycle by the chilly deep-ocean saltwater, which is only a few degrees above freezing at that depth. There is a huge temperature difference between the surrounding water and the volcanic fluid, and heat engines are powered by such differences.
The fact that Endurance Energy‘s founders came from SpaceX, Blue Origin, and fusion energy projects speaks something about the company’s aspirations and technical culture. Similar discipline and tolerance for the kinds of issues that don’t manifest until you’re actually operating in the environment you designed for are needed when building dependable, long-duration mechanical systems in extreme environments, whether that environment is the vacuum of space, the thermal stress of a rocket engine, or the crushing cold pressure of the deep ocean. The Adélie unit is a prototype, and the team is aware that most deep-tech endeavors fail in the gap between a functional prototype and a system that can be deployed commercially.
The baseload argument is the main justification for using subsea geothermal energy for offshore infrastructure. The weather, season, and time of day all affect the intermittent nature of solar and wind generation. A hydrothermal vent field produces dependable power continuously, regardless of the weather, and without the need for energy storage. Baseload power from a subsea geothermal source is far more useful than an equivalent rated capacity from solar or wind for offshore platforms that must operate 24 hours a day regardless of conditions, such as oil and gas infrastructure, underwater data processing systems, remote research stations, or the kind of floating habitation platforms that architects and planners have been envisioning for decades.
Because there is a significant difference between the floating city concept and the existing reality, it is important to handle it cautiously. The UN Human Settlements Programme-backed business Oceanix has created comprehensive plans for modular floating towns, which are platforms that could accommodate thousands of people, produce their own food and energy, and be placed in coastal waters or farther offshore. The engineering elements are actually taken into consideration, and the architectural work is serious.
However, these platforms are only hypothetical concepts, early prototypes, and renderings. No one is residing on a subsea geothermal floating city. The energy component that would make such a platform physically possible is what Endurance Energy is actually constructing: a baseload power source that lies beneath the platform rather than on top of it, drawing heat from volcanic geology instead of relying on weather.
A comparable component of the offshore infrastructure challenge is being developed by Panthalassa: floating AI data centers that naturally cool their server infrastructure using cold deep-ocean seawater. The condenser side of Endurance Energy’s power cycle benefits from the same thermal characteristics that make the deep ocean suitable for cooling computational devices. These projects are connected by a logical engineering logic: hot water near volcanic geology for power generation, cold water at depth for cooling and heat rejection, and electrical transmission cables to link it all. The question that both firms are trying to answer is whether the economics work at the scale required to make these systems profitable investments, as opposed to striking demonstrations.
