Subsea geothermal proved feasible; not yet ready as a diesel substitute

For a small team planning energy supply or off-grid projects: this shows a technical option that could cut fuel-import risk long term, but it will not alter budgets or schedules today.

What actually changed

The world's first demonstration of a subsea geothermal power plant took place in September at Axial Seamount in the northeast Pacific Ocean, almost a mile below the surface. Endurance Energy, a Seattle-based startup, deployed a roughly 3-ton prototype for three weeks and achieved net-positive electricity generation for less than 10 seconds during the trial. The company reported the test as a demonstration of technical feasibility for extracting geothermal energy from an underwater volcanic site.

Endurance’s founder, Andrew Redd, framed the approach around using the deep ocean as a cooling medium and pressure source; he described the deep ocean as offering "unlimited cold seawater" for cooling and keeping the system and well pressurised so plants can be compact. The prototype’s brief net-positive run is the core proof point: it confirms the concept works at depth in field conditions, not merely in laboratory models.

Who it affects

• Pacific island governments and utilities that currently import fossil fuels for electricity, because the company explicitly targets those customers seeking alternatives to imported fuel.
• Project teams and funders tracking alternative baseload options for remote or maritime sites; the test signals a path forward for subsea geothermal developers and researchers.
• Regulators and environmental review bodies will need to consider a new class of offshore energy infrastructure if commercial projects proceed.

What it costs or what it replaces

The announcement does not state pricing for equipment, deployment or power. Endurance Energy positions subsea geothermal as an alternative to importing expensive fossil fuels for island customers, which in practice typically means diesel and other fuel-oil generation. The prototype replaces none of a customer’s existing assets today: the three-week field test demonstrated feasibility but did not deliver sustained commercial output.

What we don't know

• How much a full-scale subsea geothermal plant will cost to build, install and operate.
• The levelised cost of electricity (LCOE) for this approach compared with diesel or other renewables.
• Long-term reliability and maintenance requirements for equipment operating nearly a mile deep.
• Environmental impacts on the seafloor ecosystem and the permitting pathway for large-scale deployments.
• Timelines to commercial availability or market-ready units.
• Whether Endurance plans partnerships, financing models, or standardised modules for island-scale projects.

What to do next

1. If your organisation relies on imported fuel, update your supply-risk register to note subsea geothermal as a potential mid-to-long-term disruption and track Endurance Energy’s public updates and test results.
2. Commission a brief feasibility note (one to two pages) that compares current diesel costs and logistics with a scenario where subsea geothermal becomes commercially available, leaving placeholders for capital cost and LCOE until Endurance publishes numbers.
3. For teams with project time and budget: reach out to Endurance Energy to request technical data sheets or to express interest in pilot partnerships; do not assume immediate availability or cost parity until the company provides commercial figures.