Endurance Energy is building subsea geothermal power plants that aim to turn seafloor heat into always-on electricity. The Seattle startup has raised a $54 million Series A led by Founders Fund, betting that clean power demand is rising faster than conventional projects can be built. The problem is simple: heavy industry, EV charging, and AI infrastructure all want round-the-clock electricity, but a lot of low-carbon options are either intermittent or painfully slow to deploy. Founder and CEO Andrew Redd, a former SpaceX engineer who worked on Dragon and Starship, started Endurance in 2025 after deciding renewable power needed a more radical hardware approach.
What is Endurance Energy's subsea geothermal system?
Endurance’s subsea geothermal plan is to place power hardware on or near hot seafloor hydrothermal systems along tectonic spreading zones, then send that electricity back to shore through submarine cables. Its seafloor hydrothermal generators could deliver gigawatts of baseload power from Ring of Fire regions where volcanic heat sits much closer to the surface than it does at most land-based sites.
Here’s the practical workflow. Endurance identifies offshore geothermal resources and deploys drilling and prototype hardware from vessels. It then mates a wellhead system to a vent or drilled well and pumps hydrothermal fluid through equipment that measures temperature and flow. In one field update, the company said its first wellhead prototype was already operating on a submarine volcano in Tonga’s Lau Basin, where vent fluids exceed 300°C. All pumping, sensing, and communications were powered onboard by solid-state thermoelectric generators.
That matters because it shifts a lot of ugly manual work away from the land-based geothermal playbook. Instead of chasing scarce surface leases in the best-known geothermal corridors and drilling deeper inland, Endurance is trying to use hotter offshore resources and standard offshore engineering habits. That includes vessels and subsea handling. Also robotic operations, corrosion-resistant hardware, and cable economics. Redd has said site choice comes down to an optimization algorithm balancing cable cost, resource size, and demand onshore, while avoiding sensitive habitats near hydrothermal vents.
Who founded the subsea geothermal startup Endurance Energy?
The founding story
Redd’s pitch starts with a hard filter. He wanted an energy source that’s renewable or at least non-polluting, available 24/7, and scalable into the tens or hundreds of gigawatts. In his words, that clean-power requirement was “my non-negotiable,” and it pushed him past nuclear, wind, solar, and hydropower toward geothermal, which he called “the only real deployable, baseload renewable.”
The origin story is unusually direct for climate tech. Redd grew up in the Pacific Northwest and has linked that experience, especially the region’s heat waves and fires, to his decision to work on energy. More important, he left SpaceX convinced that an incremental fix wouldn’t cut it, and that the next company had to be built from first principles.
Why Andrew Redd looks like a believable builder
Redd isn’t a classic geothermal founder. That’s both the appeal and the risk. His background is in brutal hardware execution, not years of utility permitting or conventional reservoir engineering. His public profile shows Princeton University as his alma mater before stints at SpaceX sites in Hawthorne, California, and Starbase, Texas.
Still, the fit isn’t random. Endurance is trying to fuse space-style iteration with subsea industrial systems. That favors teams comfortable with hard environments, rapid prototyping, and custom machinery. The company has leaned into that identity: its Seattle waterfront base lets it load seafloor drills and prototype generators directly onto vessels. Very different from a software-heavy climate startup.
Traction, team, and early signals
For a company founded in 2025, Endurance has moved fast. TechCrunch reported that the startup had grown to 25 employees by June 11, 2026, including 12 alumni from SpaceX, and that its vice president of engineering came from fusion startup Helion Energy. Company posts show it had already completed multiple deep-sea missions, entered a pilot collaboration with Tonga, and tested hardware in both shallow water near Puget Sound and at mile-plus ocean depths in the South Pacific.
The Tonga work is one of the clearest signs this isn’t just slideware. On February 27, 2026, Tonga’s prime minister signed an MOU with Endurance to explore subsea geothermal development, and by late spring the company said it had completed its first deep-sea deployment in Tongan waters. That doesn’t mean commercial power is close. It does mean Endurance has crossed from concept art into field operations. That's a big line in any deeptech company.
The $54M round and who joined it
The new financing is a $54 million Series A led by Founders Fund, with Ascend, Construct Capital, Felicis Ventures, First Round Capital, Point72 Ventures, Riot Ventures, and Voyager Ventures also participating. Redd has said the money will go toward developing Endurance’s power-plant plans as electricity demand climbs from AI data centers, EVs, and heavy industry.
Competition and positioning
The obvious comparison set is Fervo Energy, XGS Energy, and Sage Geosystems. But those companies are still mostly attacking geothermal from land: deeper drilling, engineered reservoirs, closed-loop heat harvesting, or pressure-based systems. Fervo closed a $462 million Series E in December 2025, XGS announced a 150 MW geothermal project with Meta in New Mexico in June 2025, and Sage disclosed a Series B of more than $97 million in January 2026. Endurance’s angle is that the hottest, shallowest resources near plate boundaries may be offshore and closer to major coastal demand centers than inland geothermal fields.
That differentiation is real. So is the difficulty. Saltwater corrosion, deep-ocean robotics, subsea maintenance, and cable economics could wreck the model if the engineering or costs go sideways. Redd’s own defense is blunt: if something fails, the environmental downside looks a lot more like hot water release than an oil spill. Investors are buying the upside case that offshore oil-and-gas know-how can be repurposed into offshore geothermal.
Why are investors betting on subsea geothermal now?
This round matters because Endurance isn’t raising seed money to tinker in a garage anymore. A $54 million Series A gives the company room to expand field testing, manufacturing, environmental work, and subsea systems development, but it’s still small compared with the capital needed to build utility-scale infrastructure. That tells you what investors think this round is for: de-risking the platform, not proving out a mature power business yet.
There’s a sharper thesis underneath it. If Endurance can show that offshore geothermal can be drilled, controlled, and cabled back economically, it opens a route to clean firm power near coastal load centers instead of far inland. That's why this is interesting. Not because it’s safe, but because the prize is huge if the hardware works.
How big is the geothermal power market?
Geothermal is still tiny in the U.S. mix. EIA says U.S. geothermal plants in 7 states produced about 16 billion kilowatt-hours in 2025 — roughly 0.4% of utility-scale electricity generation. DOE says the U.S. currently has just over 4 GW of geothermal generating capacity, but advances in next-generation geothermal could lift that to at least 90 GW by 2050.
The demand backdrop is getting tighter, not easier. IEA forecasts global electricity demand growing 3.6% a year from 2026 through 2030, with data centers among the drivers, and it has said that in the U.S. data centers are on course to account for almost half of electricity-demand growth by 2030. That’s the sort of setup that makes investors care a lot more about clean firm power than they did a few years ago.
There’s also a broader geothermal tailwind here. IEA’s 2024 geothermal analysis said geothermal has the second-largest technical potential for electricity generation after solar PV, ahead of onshore and offshore wind on that measure. Endurance’s own pitch pushes the argument even further offshore: Redd estimates about 6 TW could be developed around the Ring of Fire within 5 to 10 years, versus roughly 20 TW of average global energy use today. That estimate is aggressive. But it shows why venture firms are willing to take a swing.
What to watch next for Endurance Energy
Endurance hasn’t proven commercial subsea geothermal yet. Nobody has. But it has already done something a lot of climate hardware startups never manage: it turned a wild idea into repeated field operations in a very nasty environment.
The next test is simple to state and hard to clear. Endurance needs to move from prototypes and pilot deployments to a reliable multi-megawatt system that utilities or islands will actually buy power from. If that answer starts turning into yes, Endurance won’t look like a weird ex-SpaceX side quest anymore. It’ll look early.
Read how Manam Chocolate raised a $9M Series A led by Omnivore to expand its farm-to-retail craft chocolate business and bring its experience-led premium cacao brand to Delhi NCR.
FAQ
- What funding did Endurance Energy raise? Endurance Energy raised a $54 million Series A announced on June 11, 2026. Founders Fund led the round, and the syndicate included Ascend, Construct Capital, Felicis Ventures, First Round Capital, Point72 Ventures, Riot Ventures, and Voyager Ventures.
- How does Endurance Energy’s subsea geothermal technology work? Endurance is developing seafloor systems that capture hydrothermal heat near tectonic plate boundaries and convert it into 24/7 electricity sent ashore by submarine cable. In Tonga, the company said a prototype wellhead had already attached to a vent, pumped hydrothermal fluid, and powered onboard sensing and communications with solid-state thermoelectric generators.
- Who is Andrew Redd? Andrew Redd is Endurance Energy’s founder and CEO, and he previously worked as an engineer on SpaceX’s Dragon and Starship programs. His public background also shows Princeton University and work across SpaceX locations in Hawthorne and Starbase before he launched Endurance in 2025.
- Is Endurance Energy a geothermal or offshore energy company? It’s both, really — Endurance sits in next-generation geothermal but applies offshore industrial methods to reach heat sources under the ocean. That’s what separates it from rivals like Fervo, XGS, and Sage, which have focused on land-based geothermal systems even as the whole category gains momentum.
