Endurance Energy

Endurance Energy is a Seattle, Washington-based developer of subsea geothermal power systems that generate electricity from hydrothermal fluids at deep-ocean volcanic and tectonic spreading zones. The company positions subsea geothermal as a baseload renewable resource that operates continuously regardless of weather or fuel supply, with generation and transmission equipment sited on or under the seafloor and therefore no surface footprint. Its stated design approach emphasizes modular, factory-produced units that can be clustered toward gigawatt scale, and it draws on established oil and gas and geothermal engineering practice.

The operating concept described by the company and reporters involves drilling a narrow borehole roughly 200 feet into the seafloor at a distance from active vent fields to access hydrothermal fluid; that fluid heats a closed-loop refrigerant through titanium tubes until it boils and drives a turbine, after which naturally cold seawater condenses the refrigerant and the warmed water is returned to the seafloor. Control electronics are housed in oil-filled, pressure-balanced chambers to withstand deep-ocean pressure. Prototype units are named after sea creatures ascending the food chain (krill, silverfish, and later an "orca pod"). The next system, Adélie, is a 100 kW generator intended to operate for one year inside the Axial Seamount caldera off the Oregon coast on the Juan de Fuca Ridge, connected to the Ocean Observatories Initiative Regional Cabled Array operated by the University of Washington, which will return performance data to shore.

Endurance targets markets where power is scarce or expensive, including island nations, industrial sites, and hyperscale data centers. Its founder estimates roughly 6 terawatts of geothermal potential could be developed around the Pacific Ring of Fire over the next five to ten years, with resources ranging from a few dozen to a few hundred miles offshore; site selection is described as an optimization between submarine cable cost, resource scale, and onshore market size, while avoiding sensitive habitats near hydrothermal vents.

Founding story

Founder and CEO Andrew Redd grew up in the Pacific Northwest and, after working as an engineer on the Dragon and Starship programs at SpaceX, decided to pursue renewable energy with what he described as a first-principles rather than incremental approach. He ruled out nuclear on regulatory and construction timelines, solar and wind on 24/7 availability without batteries, and hydropower on siting limits, concluding that geothermal was the only readily deployable baseload renewable and that offshore volcanic systems were an untapped opportunity.

Business model

Endurance develops and deploys its own subsea geothermal generation hardware, moving from prototypes to full-stack systems and, subsequently, commercial power projects; the first commercial pilot is planned with the Kingdom of Tonga. Permanent installations are described as delivering electricity to shore via undersea cables. The sources do not describe pricing or contracting terms.

Not described in the sources; the company is pre-commercial, with its first commercial pilot planned in Tonga.

Traction

Four completed prototype deployments to depths of about 3,300 meters (roughly two miles) and hydrothermal temperatures up to 386°C (about 726°F), at the Juan de Fuca Ridge, Mariana Trough, East Pacific Rise off Mexico, and in Tonga; a signed agreement with the Government of Tonga; a fifth deployment, the 100 kW Adélie unit, scheduled for September 2026; and a team of roughly three dozen, including 12 SpaceX alumni and veterans of Helion Energy and Blue Origin.

Latest developments

As of August 2026 the company was assembling Adélie for a September 7, 2026 pilot demonstration at an undersea volcano off Oregon, its fifth seafloor deployment. Work on a megawatt-scale device for the first commercial pilot with Tonga was set to begin once Adélie is deployed, with a goal of shipping the following year. GeekWire reported total capital raised of $63 million.