Startup taps undersea volcanoes as energy source in Proofpoint test. Future Developments in Geothermal Energy Production Endurance Energy, a leading company in geothermal energy, recently completed a groundbreaking test installing a geothermal power plant over a natural hydrothermal vent. This test, conducted for research and demonstration purposes, showcased the potential for future expansion using drilled wells instead. To minimize environmental impacts on the seabed and marine life, Endurance Energy carefully selected the test location to be the "least destructive" and continuously monitored the process. Their research team meticulously sampled the water, recorded seafloor arrays of tubeworms, snails, crabs, and bacterial mats. Additionally, independent researchers operated scientific sensors, and samples were sent to independent labs for analysis. Looking ahead, the company has exciting plans for its next commissioning in winter 2026-2027, which will involve a refurbished and upgraded Adélie (now named Gentoo) to sustain higher power production. Endurance Energy is also developing a larger 2-megawatt commercial generator, with the initial deployment planned in collaboration with the Kingdom of Tonga in 2027. This move is crucial for Tonga, a Polynesian island nation heavily reliant on imported diesel fuel for its power grid, particularly as global oil prices continue to rise. "A 2 MW commercial generator is about the size of a shipping container, and we deploy up to six of these generators off the coast of Tonga," shared Redd, a key figure at Endurance Energy. "The physical footprint of this project will be relatively small." Experts, like those at Stanford University, acknowledge the cost-effectiveness of geothermal energy projects on land. However, they caution that any factors leading to an increase in the price of geothermal power could jeopardize its competitiveness. Nevertheless, Endurance Energy's successful operations in Tonga could pave the way for broader adoption, especially as governments worldwide seek renewable energy alternatives amidst escalating fossil fuel prices. "Vast markets with abundant marine geothermal resources, such as the United States, the Pacific Northwest, Alaska, Taiwan, and Japan, present promising opportunities for our technology," Redd emphasized. "As we continue to refine our approach, we aim to offer cost-competitive, uninterrupted power to utilities and large energy consumers, independent of weather conditions."

Endurance Energy demonstrates subsea geothermal power in Pacific Ocean. 19 October 2026 Endurance Energy has announced the successful demonstration of net-positive power generation from a subsea geothermal system deployed in the Pacific Ocean. Seattle-based geothermal technology developer Endurance Energy (Endurance) has announced the successful testing of its Adélie subsea geothermal power system at Axial Seamount, approximately 300 miles off the coast of Oregon, USA. During a three-week expedition, the company drilled and completed a geothermal well at the seafloor, deployed a compact power generation unit at a depth of approximately 1,500 meters, and demonstrated net-positive electricity generation. The pilot achieved a peak net output of 16.5 kW, although electricity generation was sustained for only 8.7 seconds. Although operational issues were encountered, the demonstration still represents an important proof of concept for subsea geothermal power generation. Endurance has indicated that it is now working toward longer-duration operations and the development of commercial-scale systems. Endurance has raised USD 63 million in funding to date, including a USD 54 million Series A round led by Founders Fund. In a short interview with ThinkGeoEnergy, Endurance Energy founder and CEO Andrew Redd provided additional insights into the technology, the lessons learned from the pilot, and the company's plans for commercial development. Demonstrating geothermal power generation at the seafloor. The Adélie demonstration took place at Axial Seamount, an active submarine volcano along the Juan de Fuca Ridge. The location provides access to high-temperature hydrothermal resources associated with volcanic activity beneath the ocean floor. During the expedition, Endurance drilled two closely spaced boreholes at a water depth of approximately 1,500 meters. Both encountered hydrothermal fluids, with the second hole completed as a 16-meter-deep geothermal well. Following cementing, the well produced fluids at a temperature of approximately 260°C. The company also deployed its three-ton Adélie power generation system, which was operated remotely from Seattle through the National Science Foundation's Regional Cabled Array, a subsea fiber-optic network operated by the University of Washington. For the power generation test, Adélie was connected to a nearby natural hydrothermal vent with a fluid temperature of approximately 281°C. The turbine reached approximately 26,000 rpm, generating a median net output of about 2 kW and a peak of 16.5 kW during an 8.7-second period. The newly drilled geothermal well was not used for the net-positive power generation test, as its flow capacity was insufficient. The generation run was also cut short by a battery protection system, followed by a power cable failure during a subsequent restart attempt. Despite these limitations, Redd considers the demonstration an important validation of the company's technological approach. "The biggest lesson is that every step of subsea geothermal power can be done at depth," Redd told ThinkGeoEnergy. "In a single three-week expedition, we drilled and completed the world's first offshore geothermal well, landed a 3-ton power plant on target nearly a mile down, operated it from Seattle and produced net-positive electricity." Redd also highlighted the precision achieved during the expedition, with the drilling system and generator repeatedly landing within a few feet of their intended targets. Another achievement was the ability to rapidly modify the equipment between deployments. According to Redd, the team recovered, modified, recharged, and redeployed Adélie in less than 16 hours. The expedition also provided data on seafloor drilling, geothermal well flow, heat transfer, mineral deposition, and remote operation of subsea equipment. Engineering a geothermal power plant for deep-ocean conditions. Endurance has designed Adélie specifically for these operating conditions. The power generation unit has a footprint comparable to that of a passenger car. As Redd explains, Adélie can be designed to be compact because exactly because it is designed to operate underwater. Unlimited cold seawater keeps the system coo, while the weight of the ocean keeps it well pressurized. To address corrosion issues, Adélie has been constructed using titanium, while a significant portion of the company's internal research focuses on materials and engineering solutions that will allow the equipment to operate reliably for extended periods in deep-ocean conditions. Endurance is already preparing its next demonstration system, Gentoo, a refurbished and upgraded version of Adélie designed to achieve higher power output and longer periods of sustained generation. Deployment is planned for the coming winter. The company is also developing Leopard, a 2-MW commercial generator intended to form the basis of its future subsea geothermal installations. Future deployments will also seek to improve geothermal well productivity. Although the Adélie pilot well reached only 16 meters, Endurance's existing subsea drilling system is capable of drilling to approximately 80 meters. The company expects deeper wells to provide the higher fluid flow rates necessary for sustained power generation. Targeting geothermal resources around the Pacific Ring of Fire. Endurance's approach to geothermal exploration combines geological and geophysical information with techniques developed through decades of oceanographic research. Although hydrothermal vents provide evidence of accessible high-temperature resources, the company does not intend to locate its commercial systems directly within sensitive vent ecosystems. "While hydrothermal vents signal that a suitable heat source is nearby, we aim to stay clear of these sensitive ecosystems," said Redd. "To find promising sites, we combine publicly available and proprietary data, including known vent fields, heat flow measurements, and young crust at ocean spreading centers, where hot hydrothermal resources are typically found." Once a prospective area has been identified, Endurance uses geological and geophysical surveying methods to map the seafloor, identify hydrothermal activity, and locate potential heat sources beneath the seabed. The environmental implications of subsea geothermal development are also considered as part of the company's technology development. During the Axial Seamount expedition, Endurance conducted environmental monitoring that included water sampling, seafloor video surveys, and observations of local marine communities. According to the company, preliminary monitoring found no significant changes to local hydrothermal activity, seafloor ecosystems, or seismic and volcanic conditions. More than 40 samples were also collected for independent laboratory analysis. Endurance is initially focusing its commercial exploration efforts on the Pacific Ring of Fire, where volcanic activity and tectonic processes provide favorable conditions for geothermal resources. "We are primarily targeting areas around the Pacific Ring of Fire. Our first commercial project will be in the Kingdom of Tonga," Redd said. "Large commercial markets with ample offshore geothermal resource include the U.S. (in the Pacific Northwest and Alaska), Taiwan, and Japan." Moving toward commercial subsea geothermal in Tonga. The next major step for Endurance is the development of its first commercial subsea geothermal project in the Kingdom of Tonga, where the company is targeting initial electricity generation in 2027. To this end, Endurance and the Government of Tonga have signed a memorandum of understanding to explore supplying geothermal electricity to Tongatapu, the country's most populous island. The project is particularly relevant to Tonga's efforts to reduce its dependence on imported diesel fuel for electricity generation. Redd described the Tongan government as a collaborative partner in developing the project, particularly in ensuring that electricity can be delivered to the island's grid responsibly and equitably. "Like many island nations, the Kingdom of Tonga relies on imported diesel for most of its electricity, which leaves it exposed to a volatile global fuel market," Redd explained. "Recent global events have pushed diesel prices sharply higher, and Tonga is looking for reliable, domestically produced energy instead." Beyond Tonga, Endurance envisions operating as an independent power producer, developing subsea geothermal projects at gigawatt scale. The company's longer-term strategy is to serve coastal electricity markets and industrial customers, particularly in regions with abundant offshore geothermal resources and high dependence on imported fuels. "Our power will replace those imports with reliable, around-the-clock baseload electricity that strengthens local energy security," said Redd. "As the technology matures, we expect to compete on cost in open electricity markets." While the Adélie demonstration establishes that net-positive electricity generation is technically possible at the seafloor, the short duration of the test and the limited flow capacity of the pilot well underscore the engineering challenges that remain. The upcoming Gentoo deployment and the development of the 2-MW Leopard system will therefore be important steps in determining whether Endurance can translate its initial technical achievements into sustained, commercially viable subsea geothermal power generation.

Endurance Energy completes $54 million funding round to develop subsea geothermal technology. Subsea geothermal systems by Endurance Energy (source: Endurance Energy) US-based Endurance Energy has raised $54 million in Series A funding to advance the development of their technologies for subsea geothermal systems. U.S.-based startup Endurance Energy has announced the successful completion of a USD 54 million Series A funding round to develop its technology to harness energy from subsea geothermal systems. According to the company, the funding will allow them to transition from prototype to full-stack systems and scale their offshore operational capability. The funding round was led by Founders Fund, with participation from Ascend, Construct Capital, Felicis, First Round Capital, Point72 Ventures, Riot Ventures, and Voyager Ventures. Founded by former SpaceX engineer Andrew Redd, Endurance Energy is developing technology to harness geothermal energy from subsea volcanic systems. According to the company, it has so far already completed four prototype deployments to deep sea volcanic systems at depths up to 3300 meters and hydrothermal temperatures up to 386°C. They are now also on-track to deploy a 100 kW generator at the Juan de Fuca ridge off the coast of the Pacific Northwest region of North America in the coming Fall. Earlier this year, Endurance Energy signed an agreement with the Government of Tonga to explore opportunities for developing subsea geothermal resources within the Kingdom's territorial waters. The partnership aims to assess the potential of offshore volcanic systems as a source of reliable renewable energy for the island nation. Evaluation of geothermal prospects in offshore settings had already been undertaken in previous years, with work being mainly focused in the North Sea region. However, this may be the first time that a funded startup is developing and deploying such technologies. While the geologic potential is certainly present, it remains to be seen how the economics of subsea geothermal will be optimizing considering the costs of subsea power distribution and the proximity to sizable onshore markets. Carlo Cariaga