Endurance Energy Generates Subsea Geothermal Power in Oregon Test

Endurance Energy has completed a field test of Adélie, its subsea geothermal power unit, according to the company. The demonstration took place in September off the Oregon coast, marking a practical application of the technology in a marine environment.

The unit operated at Axial Seamount, a submarine volcano located in the Pacific Ocean. By harnessing heat from this underwater geological feature, the test aimed to validate the system's ability to generate power directly from subsea geothermal resources.

This trial represents a specific step in developing alternative energy sources that utilize oceanic heat. The results of the September test provide data on the unit's performance under real-world conditions at the seamount.

The Demonstration Results

The Adélie unit generated electricity for approximately 29 seconds on Sept. 27, according to the company. During this brief window, the system produced about 60 watt-hours of power. While these figures indicate a successful initial validation of the hardware, they highlight the current limitations of the prototype. Generating power at such a low scale is standard for early-stage field tests, where the primary goal is confirming that the machinery functions correctly in a hostile environment rather than delivering commercial-grade energy output. For investors and engineers, these preliminary results serve as a baseline. They confirm that the core components can survive the pressure and temperature of the deep ocean, but they do not yet demonstrate sustained, high-volume generation. The short duration and modest energy yield suggest that significant engineering challenges remain before the technology can contribute meaningfully to a local grid. The data collected during those 29 seconds provides critical insights into how the system handles real-world variables, such as fluid flow rates and thermal differentials, which are difficult to replicate in laboratory settings. This initial step verifies the feasibility of extracting heat from the seamount, but it leaves open the question of scalability and long-term reliability.

The 3-ton unit relies on an organic Rankine cycle system to convert thermal energy into electricity. This technology uses a working fluid with a lower boiling point than water, allowing it to vaporize at the moderate temperatures found in many geothermal resources. By expanding this vapor through a turbine, the system generates power without requiring the extreme heat associated with traditional steam cycles. This approach is particularly relevant for subsea applications where temperature gradients may not be sufficient for conventional methods. The successful operation of this cycle in a marine setting demonstrates that the unit can manage the complex thermodynamics required for subsea power generation. However, the small size of the unit limits its immediate impact. It acts as a proof of concept, showing that the mechanical and thermal processes work as designed in the field. Future iterations will likely need to scale up this cycle to produce useful amounts of electricity, but the current test confirms the fundamental viability of the organic Rankine cycle in this specific subsea geothermal context.

Engineering and Operations

• A submarine robot connected the unit to a natural vent.
• The test used a fiber-optic cable network for remote operation.

The physical integration of the power unit with the geothermal source required precise robotic intervention. A submarine robot performed the connection between the Adélie unit and a natural vent at Axial Seamount. This automated approach highlights the logistical difficulties of deploying hardware in the deep ocean, where human divers cannot operate. Using robotics for such critical mechanical tasks allows engineers to maintain safety protocols while ensuring the device is correctly positioned to capture thermal fluids. The reliability of this robotic connection is essential for any future commercial deployment, as manual intervention at such depths is impractical and hazardous.

Remote management of the system was facilitated through a fiber-optic cable network. This infrastructure enabled operators to control the unit from a distance, transmitting data and commands without requiring physical presence at the seafloor. Fiber-optic connections offer high bandwidth and low latency, which are vital for monitoring real-time performance parameters during the test. For subsea energy projects, establishing robust telecommunications links is a foundational engineering challenge. It ensures that operators can respond to mechanical issues or adjust operational settings immediately, minimizing downtime and protecting the integrity of expensive equipment in a harsh environment.

Company Background and Funding

Endurance Energy operates out of Seattle and was established in January 2025. The startup has secured $63 million in venture capital funding to support its development efforts. This level of early-stage financing is substantial for a company just months old, suggesting strong investor confidence in the commercial potential of subsea geothermal energy. Venture capital typically provides the liquidity needed to bridge the gap between prototype validation and larger-scale field trials, allowing teams to refine hardware and secure intellectual property rights before seeking debt financing or strategic partnerships. The speed at which the company was founded and funded reflects a broader trend in the clean energy sector, where investors are increasingly looking beyond mature technologies like wind and solar to explore next-generation baseload power sources that can operate independently of weather conditions.

The leadership team includes founder Andrew Redd, a former SpaceX engineer. His background in aerospace and high-stakes engineering suggests a company culture focused on rigorous testing, iterative design, and solving complex technical problems under extreme conditions. This expertise is particularly relevant for subsea applications, where equipment must withstand immense pressure and corrosive environments without easy access for repair. Investors often view technical leadership with deep experience in challenging physical environments as a key risk mitigator. By leveraging talent from sectors known for high-reliability systems, Endurance Energy aims to address the durability and precision requirements inherent in deploying power units on the ocean floor. This profile aligns with the needs of early-stage hardware startups, where engineering credibility often drives both technical progress and further capital attraction.

What to watch

The immediate next milestone is a planned deployment of a refurbished unit this winter. This repeat test will scrutinize whether the system’s performance holds up over extended operational periods, moving beyond the initial proof-of-concept window. For hardware developers, durability under continuous subsea conditions is often the primary barrier to commercial viability, so the results from this upcoming deployment will be critical in assessing long-term reliability.

Looking further ahead, a commercial-scale system is targeted for 2027. Bridging the gap between a small demonstration unit and a larger, grid-connected installation involves significant engineering hurdles, particularly regarding power transmission and maintenance logistics. Progress on this timeline will indicate whether the technology can scale efficiently without prohibitive cost increases, a key concern for potential investors and utility partners.

International expansion is also on the horizon, with a partnership established with the Kingdom of Tonga for a 2-megawatt project. This collaboration suggests an early focus on island nations, where energy security and independent power generation are often high priorities. Such projects typically serve as valuable real-world testbeds for new technologies before broader market adoption.

Founder Andrew Redd summarized the current achievement by stating, "Adélie made it exist, and now we know it’s possible." This sentiment underscores the shift from theoretical feasibility to practical execution. Readers should monitor the winter deployment results and the progress of the Tonga project as the clearest indicators of the technology's readiness for wider commercial application.