Endurance Energy raises $54M to harness a massive untapped energy source on the ocean floor

Endurance Energy raises $54M to harness a massive untapped energy source on the ocean floor

Subsea geothermal startup, founded by SpaceX alumni, deploys first 100kW generator this fall

By: Robert Buluma

After you've worked on rockets that find their way to outer space, it can be hard to come up with a second act. For SpaceX alumni Andrew Redd, it meant looking not to the stars, but to the deepest, darkest reaches of the ocean floor.

Redd, who grew up in the Pacific Northwest—a region scarred by uncharacteristic heat waves and catastrophic wildfires in recent years—knew he wanted to tackle climate change. But after a decade at SpaceX working on the Dragon capsule and Starship, incrementalism wasn't in his blood.

That philosophy has led to Endurance Energy, a stealthy startup that is today announcing a $54 million Series A round to build the world's first subsea geothermal power plants. Founders Fund led the round, with participation from Felicis, Voyager Ventures, Riot Ventures, Construct Capital, Point72 Ventures, First Round Capital, and Ascend. The new funding will allow the company to scale from prototype to full-stack systems at a time when energy demand is surging from AI data centers, electric vehicle manufacturing, and re-industrialization.

From SpaceX to the seafloor

The origins of Endurance Energy read less like a traditional cleantech founding story and more like the plot of a hard science fiction novel. Redd spent years helping build spacecraft designed to operate in the vacuum of space, subject to extreme temperature swings and punishing radiation. When he left to start his own company, he began looking for a similarly hostile environment where the physics were challenging but the potential payoff was planetary in scale.

He found it 3,300 meters below the surface of the Pacific Ocean.

The Earth's crust is thinnest not in Iceland or California's Geysers, but along the mid-ocean ridges—the sprawling, volcanic mountain ranges where tectonic plates are pulling apart. Along the so-called Ring of Fire, which encircles the Pacific from New Zealand to Chile to the Pacific Northwest, superheated water circulates through cracks in the crust, reaching temperatures above 386°C before venting back into the deep ocean.

That heat represents a staggering amount of energy. Redd estimates there is roughly 6 terawatts of geothermal potential that could be developed in the next five to ten years along the Ring of Fire alone. To put that in perspective, the world uses an average of about 20 terawatts across all energy sources—coal, gas, nuclear, solar, wind, and hydro—at any given moment.

But no one had ever tried to build a geothermal power plant on the seafloor. The reasons are obvious: crushing pressure, corrosive saltwater, biological fouling, and the simple fact that almost everything we know about power generation was designed for dry land.

For Redd, a veteran of an industry that routinely lands rockets on drone ships in the middle of the ocean, those challenges looked less like showstoppers and more like engineering problems waiting for a SpaceX-style solution.

Before founding Endurance, Redd went through an exhaustive first-principles analysis of every major energy source. He had three non-negotiable criteria. First, the energy had to be renewable or effectively non-polluting—as Redd told TechCrunch, "That's my non-negotiable." Second, it had to be available 24/7—what the industry calls baseload power. And third, it had to be capable of scaling to tens or hundreds of gigawatts quickly.

Nuclear power was quickly ruled out. Even the most advanced small modular reactors face a decade-long path to commercialization. Solar and wind, while cheap and fast to deploy, aren't available around the clock without massive battery installations. Hydropower is geographically limited; the best sites are already dammed.

Conventional geothermal has always been constrained by location. The best resources—where the crust is thin and hot magma flows close to the surface—are mostly already tapped. Newer startups like Fervo Energy and Sage Geosystems have pioneered enhanced geothermal systems that drill thousands of feet deeper to reach hot rocks, but those sites are often far from population centers. The Western U.S. has plenty of heat, but transmitting that power to coastal cities like Los Angeles, Seattle, or Tokyo requires hundreds of miles of new transmission lines.

Redd saw an entirely different map. The Pacific Ring of Fire runs directly offshore of those same coastal cities. The heat is there, often within 50 miles of shore. The problem was that it was underwater.

A SpaceX-style development pace

What makes Endurance different from other geothermal startups isn't just its location—it's its pace of development. The company, which was founded just last year, has already completed four prototype deployments to deep-sea volcanic systems at depths up to 3,300 meters. The team has successfully operated in hydrothermal vent fields with temperatures up to 386°C, conditions that would melt most electronics and destroy conventional equipment.

That heritage is literal. Endurance has grown to 25 employees, 12 of whom previously worked at SpaceX. The company's vice president of engineering came from Helion Energy, the well-funded fusion startup. The leadership team includes Nathan Rodland, who has scaled multi-billion dollar businesses; Nicholas Lima, who has built cutting-edge energy projects; and Jennifer Kenyon, who has implemented national energy policy.

The company is headquartered on Seattle's north Lake Union waterfront—a deliberate choice. The location allows Endurance to load seafloor drills and generators directly onto vessels that carry them to sea, and lets the team build, test, and redeploy hardware quickly between ocean trials.

This fall, the company is on track to deploy its 100-kilowatt "Adelie" generator to the Juan de Fuca ridge, a geologically active spreading center located about 150 miles off the coasts of Washington and British Columbia. Adelie is Endurance's first end-to-end system: drilling, generation, and offtake in a single deployable unit. The system will power a co-located subsea compute module and connect to shore via fiber optic cable.

How it works

The technical challenge Endurance is solving is formidable. A subsea geothermal power plant must drill into the ocean floor, extract superheated water, run it through a turbine, and then reinject the cooled water—all while sitting on the seafloor at depths of up to 3,500 meters, where pressures exceed 5,000 pounds per square inch.

Conventional geothermal plants on land use the heat from deep underground to flash water into steam, which then spins a turbine. But at seafloor pressures, the physics change. Endurance uses a closed-loop binary cycle system, where the hot geothermal fluid passes through a heat exchanger, transferring its energy to a secondary working fluid with a lower boiling point. That working fluid vaporizes and spins a turbine before being condensed and recirculated.

The key insight is that none of the core technologies are new. The drilling technology exists in offshore oil and gas. The turbines are adapted from industrial geothermal and waste-heat recovery systems. The subsea connectors, cables, and pressure vessels have been used for decades by the offshore energy industry. As Redd told TechCrunch, "Geothermal is the only real deployable, baseload renewable. But why is it only 0.4% of U.S. energy?"

That last part—recovery—is crucial. One of Endurance's innovations is the ability to retrieve its generators for servicing, much like SpaceX recovers and refurbishes its rocket boosters. The Adelie unit is designed to be landed on the seafloor, plugged into a pre-drilled well, and operated for years at a time. When maintenance is required, a surface vessel can retrieve the unit, bring it back to Seattle, and redeploy it within weeks.

Environmental risks and rewards

Any energy project that involves drilling into the ocean floor is bound to attract scrutiny from environmental groups. Redd is acutely aware of the concerns. The deep sea is one of the least understood ecosystems on Earth, and hydrothermal vent fields host unique communities of tube worms, giant clams, and other extremophiles that have evolved to thrive in superheated, sulfurous water.

Endurance says it plans to avoid sensitive habitats like active hydrothermal vent fields. The company is targeting areas with high geothermal gradients—where the crust is hot close to the surface—but without the biological richness of active vents.

Redd has said the company plans to avoid sensitive habitats like those near hydrothermal vents, targeting areas that are geothermally hot but biologically barren instead.

There are also environmental advantages to subsea geothermal compared to other forms of energy production. Unlike offshore oil and gas, a geothermal blowout would release superheated water, not hydrocarbons, into the ocean.

"If we have a blowout — quote unquote — you're leaking hot water into the ocean, which is already leaking out in terawatts all over the Earth," Redd said.

Compared to onshore geothermal, subsea systems also avoid land-use conflicts, groundwater contamination risks, and the seismic concerns that have sometimes accompanied enhanced geothermal projects. And because the plants are located offshore, they don't require clearing forests or displacing communities.

The path to gigawatts

The $54 million Series A will allow Endurance to transition from prototype to full-stack systems. That means scaling up from the 100-kilowatt Adelie unit to megawatt-class generators, and eventually to multi-megawatt arrays that can be clustered together to form gigawatt-scale power plants.

The economics are compelling. Unlike offshore wind, which has a capacity factor of around 40-50% and fluctuates with the wind, subsea geothermal can run at 90% capacity or higher, 24 hours a day, 365 days a year. And because the resource is so concentrated—superheated water contains vastly more energy per unit volume than wind or sunlight—the power density is extraordinarily high.

"The idea is that you could support any major coastal city on the Ring of Fire," Redd said.

Founders Fund, the venture capital firm led by Peter Thiel that backed SpaceX, Palantir, and Anduril, clearly sees the same potential. The firm has been increasingly active in climate and energy technology, and Endurance fits squarely within its thesis of backing ambitious, hard-tech companies that take on large, incumbent industries.

The market opportunity

The timing for Endurance's technology could hardly be better. Global electricity demand is projected to increase by 30% by 2030, driven by the rapid expansion of AI data centers, electric vehicle manufacturing, industrial electrification, and air conditioning in developing economies.

In the United States alone, grid operators are forecasting demand growth not seen since the 1990s. Data center developers are scouring the country for sites with access to reliable, 24/7 power. Utilities in Virginia, Georgia, and Texas are scrambling to connect new megawatts. And in many cases, they're turning to natural gas plants because wind and solar can't provide the round-the-clock power that AI training clusters require.

Subsea geothermal offers an alternative. A single Endurance plant located 50 miles off the coast of Los Angeles could deliver 500 megawatts of firm, clean power directly into the city's grid without requiring new transmission lines through mountain passes or suburban backyards. The same could be done for Seattle, San Francisco, Vancouver, Tokyo, Shanghai, Manila, Santiago, and a dozen other coastal megacities sitting on the Ring of Fire.

The team and culture

One of the most striking things about Endurance is the team Redd has assembled. In addition to the SpaceX alumni, the company has hired engineers from Tesla, Anduril, and the submarine telecommunications industry. The culture, by all accounts, is intense, mission-driven, and relentlessly focused on execution.

The company is hiring across mechanical, electrical, subsea, controls, operations, and business development roles. Redd said he's looking for people who are comfortable operating in ambiguity, who can design hardware that will survive the deep ocean, and who share the company's obsession with deploying real, working systems as fast as possible.

That ethos is visible in the company's trajectory. In just over a year, Endurance has gone from a founding team with little more than a whiteboard sketch to four deep-sea prototype deployments, a 100-kilowatt generator ready to launch, and $54 million in Series A funding. The pace is SpaceX-like because the people are from SpaceX.

What's next

The immediate future is clear: deploy Adelie to the Juan de Fuca ridge this fall, prove that the system works, and then scale. Endurance is already designing its next-generation generator, which will be ten times more powerful than Adelie. The company is also scouting additional sites along the Ring of Fire, from the Kuril Islands off Japan to the East Pacific Rise off Mexico.

But Redd is already thinking further ahead. The same technology that works on the seafloor could, in theory, work anywhere there's a high-temperature gradient and a body of water to sink the plant into. The Great Rift Valley in Africa, with its volcanic lakes. The Mediterranean, with its subsea volcanoes. The Arctic, where thinning ice is opening new frontiers.

For now, though, the focus is on the Juan de Fuca ridge and the small, rocky patch of seafloor where Endurance will attempt to do something no one has ever done before: generate commercial electricity from the deep ocean.

It won't be easy. The ocean is unforgiving. Things will break. Seals will leak. Electronics will fail. But Redd, who watched SpaceX land its first rocket on a drone ship after four dramatic failures, is not easily discouraged.

See also: The Heat Beneath Our Feet: How Canada’s First National Geothermal Roadmap Could Redefine Clean Energy

Source : Endurance Energy , TechCrunch 

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