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Instead of rocket fuel, they’re burning biomass.
Arbor Energy might have the flashiest origin story in cleantech.
After the company’s CEO, Brad Hartwig, left SpaceX in 2018, he attempted to craft the ideal resume for a future astronaut, his dream career. He joined the California Air National Guard, worked as a test pilot at the now-defunct electric aviation startup Kitty Hawk, and participated in volunteer search and rescue missions in the Bay Area, which gave him a front row seat to the devastating effects of wildfires in Northern California.
That experience changed everything. “I decided I actually really like planet Earth,” Hartwig told me, “and I wanted to focus my career instead on preserving it, rather than trying to leave it.” So he rallied a bunch of his former rocket engineer colleagues to repurpose technology they pioneered at SpaceX to build a biomass-fueled, carbon negative power source that’s supposedly about ten times smaller, twice as efficient, and eventually, one-third the cost of the industry standard for this type of plant.
Take that, all you founders humble-bragging about starting in a dingy garage.
“It’s not new science, per se,” Hartwig told me. The goal of this type of tech, called bioenergy with carbon capture and storage, is to combine biomass-based energy generation with carbon dioxide removal to achieve net negative emissions. Sounds like a dream, but actually producing power or heat from this process has so far proven too expensive to really make sense. There are only a few so-called BECCS facilities operating in the U.S. today, and they’re all just ethanol fuel refineries with carbon capture and storage technology tacked on.
But the advances in 3D printing and computer modeling that allowed the SpaceX team to build an increasingly simple and cheap rocket engine have allowed Arbor to move quickly into this new market, Hartwig explained. “A lot of the technology that we had really pioneered over the last decade — in reactor design, combustion devices, turbo machinery, all for rocket propulsion — all that technology has really quite immediate application in this space of biomass conversion and power generation.”
Arbor’s method is poised to be a whole lot sleeker and cheaper than the BECCS plants of today, enabling both more carbon sequestration and actual electricity production, all by utilizing what Hartwig fondly refers to as a “vegetarian rocket engine.” Because there’s no air in space, astronauts have to bring pure oxygen onboard, which the rocket engines use to burn fuel and propel themselves into the stratosphere and beyond. Arbor simply subs out the rocket fuel for biomass. When that biomass is combusted with pure oxygen, the resulting exhaust consists of just CO2 and water. As the exhaust cools, the water condenses out, and what’s left is a stream of pure carbon dioxide that’s ready to be injected deep underground for permanent storage. All of the energy required to operate Arbor’s system is generated by the biomass combustion itself.
“Arbor is the first to bring forward a technology that can provide clean baseload energy in a very compact form,” Clea Kolster, a partner and Head of Science at Lowercarbon Capital told me. Lowercarbon is an investor in Arbor, alongside other climate tech-focused venture capital firms including Gigascale Capital and Voyager Ventures, but the company has not yet disclosed how much it’s raised.
Last month, Arbor signed a deal with Microsoft to deliver 25,000 tons of permanent carbon dioxide removal to the tech giant starting in 2027, when the startup’s first commercial project is expected to come online. As a part of the deal, Arbor will also generate 5 megawatts of clean electricity per year, enough to power about 4,000 U.S. homes. And just a few days ago, the Department of Energy announced that Arbor is one of 11 projects to receive a combined total of $58.5 million to help develop the domestic carbon removal industry.
Arbor’s current plan is to source biomass from forestry waste, much of which is generated by forest thinning operations intended to prevent destructive wildfires. Hartwig told me that for every ton of organic waste, Arbor can produce about one megawatt hour of electricity, which is in line with current efficiency standards, plus about 1.8 tons of carbon removal. “We look at being as efficient, if not a little more efficient than a traditional bioenergy power plant that does not have carbon capture on it,” he explained.
The company’s carbon removal price targets are also extremely competitive — in the $50 to $100 per ton range, Hartwig said. Compare that to something like direct air capture, which today exceeds $600 per ton, or enhanced rock weathering, which is usually upwards of $300 per ton. “The power and carbon removal they can offer comes at prices that meet nearly unlimited demand,” Mike Schroepfer, the founder of Gigascale Capital and former CTO of Meta, told me via email. Arbor benefits from the fact that the electricity it produces and sells can help offset the cost of the carbon removal, and vice versa. So if the company succeeds in hitting its cost and efficiency targets, Hartwig said, this “quickly becomes a case for, why wouldn’t you just deploy these everywhere?”
Initial customers will likely be (no surprise here) the Microsofts, Googles and Metas of the world — hyperscalers with growing data center needs and ambitious emissions targets. “What Arbor unlocks is basically the ability for hyperscalers to stop needing to sacrifice their net zero goals for AI,” Kolster told me. And instead of languishing in the interminable grid interconnection queue, Hartwig said that providing power directly to customers could ensure rapid, early deployment. “We see it as being quicker to power behind-the-meter applications, because you don’t have to go through the process of connecting to the grid,” he told me. Long-term though, he said grid connection will be vital, since Arbor can provide baseload power whereas intermittent renewables cannot.
All of this could serve as a much cheaper alternative, to say, re-opening shuttered nuclear facilities, as Microsoft also recently committed to doing at Three Mile Island. “It’s great, we should be doing that,” Kolster said of this nuclear deal, “but there’s actually a limited pool of options to do that, and unfortunately, there is still community pushback.”
Currently, Arbor is working to build out its pilot plant in San Bernardino, California, which Hartwig told me will turn on this December. And by 2030, the company plans to have its first commercial plant operating at scale, generating 100 megawatts of electricity while removing nearly 2 megatons of CO2 every year. “To put it in perspective: In 2023, the U.S. added roughly 9 gigawatts of gas power to the grid, which generates 18 to 23 megatons of CO2 a year,” Schroepfer wrote to me. So having just one Arbor facility removing 2 megatons would make a real dent. The first plant will be located in Louisiana, where Arbor will also be working with an as-yet-unnamed partner to do the carbon storage.
The company’s carbon credits will be verified with the credit certification platform Isometric, which is also backed by Lowercarbon and thought to have the most stringent standards in the industry. Hartwig told me that Arbor worked hand-in-hand with Isometric to develop the protocol for “biogenic carbon capture and storage,” as the company is the first Isometric-approved supplier to use this standard.
But Hartwig also said that government support hasn’t yet caught up to the tech’s potential. While the Inflation Reduction Act provides direct air capture companies with $180 per ton of carbon dioxide removed, technology such as Arbor’s only qualifies for $85 per ton. It’s not nothing — more than the zero dollars enhanced rock weathering companies such as Lithos or bio-oil sequestration companies such as Charm are getting. “But at the same time, we’re treated the same as if we’re sequestering CO2 emissions from a natural gas plant or a coal plant,” Hartwig told me, as opposed to getting paid for actual CO2 removal.
“I think we are definitely going to need government procurement or involvement to actually hit one, five, 10 gigatons per year of carbon removal,” Hartwig said. Globally, scientists estimate that we’ll need up to 10 gigatons of annual CO2 removal by 2050 in order to limit global warming to 1.5 degrees Celsius. “Even at $100 per ton, 10 gigatons of carbon removal is still a pretty hefty price tag,” Hartwig told me. A $1 trillion price tag, to be exact. “We definitely need more players than just Microsoft.”
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Some of the Loan Programs Office’s signature programs are hollowed-out shells.
With a stroke of President Trump’s Sharpie, the One Big Beautiful Bill Act is now law, stripping the Department of Energy’s Loan Programs Office of much of its lending power. The law rescinds unobligated credit subsidies for a number of the office’s key programs, including portions of the $3.6 billion allocated to the Loan Guarantee Program, $5 billion for the Energy Infrastructure Reinvestment Program, $3 billion for the Advanced Technology Vehicle Manufacturing Program, and $75 million for the Tribal Energy Loan Guarantee Program.
Just three years ago, the Inflation Reduction Act supercharged LPO, originally established in 2005 to help stand up innovative new clean energy technologies that weren’t yet considered bankable for the private sector, expanding its lending authority to roughly $400 billion. While OBBBA leaves much of the office’s theoretical lending authority intact, eliminating credit subsidies means that it no longer really has the tools to make use of those dollars.
Credit subsidies represent the expected cost to the government of providing a loan or a loan guarantee — including the possibility of a default — and thus how much money Congress must set aside to cover these potential losses. So by axing these subsidies, Congress is effectively limiting the amount of lending that the LPO can undertake, given that many third-party lenders would be reluctant to finance riskier, more novel, or larger projects in the absence of federal credit support.
”The LPO is statutorily allowed to take loans on its books to finance these projects in these categories, but it has no credit subsidy by which to take the risk required to do so,” Advait Arun, senior associate of energy finance at the Center for Public Enterprise and a Heatmap contributor, told me.
The particular programs that have been eliminated support new and improved energy technologies, clean energy infrastructure, fuel efficient vehicles, and help native communities access energy project financing. The long-running Loan Guarantee Program and the advanced vehicles program in particular are behind some of the best known LPO efforts, supporting companies such as Tesla, Ford, and NextEra Energy, and projects such as Georgia’s Vogtle nuclear reactors, the Thacker Pass lithium mine, and Shepherd’s Flat, one of the world’s largest wind farms.
The Loan Guarantees Program is “the big Kahuna,” Arun told me. “This is the longest-standing program of the LPO. So to see this defunded is like, you’re decapitating the LPO’s crown jewel.”
The program only has about $11 million left over in credit subsidies, consisting of funding that it received prior to the IRA’s appropriations. That won’t be enough to make any meaningful loans, Arun said, and is more likely to be used to “keep a skeleton crew online” for any remaining administrative tasks.
Then there’s the Energy Infrastructure Reinvestment Program, which the IRA stood up with a whopping $250 billion in lending authority to transition and transform existing fossil fuel infrastructure for clean energy purposes. Now, OBBBA has axed the program’s remaining $5 billion in credit subsidies and replaced it with $1 billion in new subsidies for projects that “retool, repower, repurpose, or replace” existing energy infrastructure, with a focus on expanding capacity and output as opposed to decarbonizing the economy. It also refashioned the program as the predictably-named “Energy Dominance Financing” initiative.
The new-old program — which the law extended through 2028 — no longer requires LPO-funded infrastructure to reduce or sequester emissions, broadening the office’s lending authority to include support for fossil fuel and critical minerals projects. It also adds language encouraging the LPO to “support or enable the provision of known or forecastable electric supply,” which Arun fears is a “backend way of penalizing the addition of renewable energy” on previously developed land.
“Under the Trump administration’s direction, [the LPO] can use that term, ‘known and forecastable,’ to actually just say, well, guess what? Renewables are not known or forecastable because they are intermittent due to the weather,” Arun told me. So while government and private industry were once excited about, say, turning sites originally developed for coal mining or coal ash disposal into solar and battery facilities, those days are probably over.
Carbon capture in particular stands to suffer from this reprogramming, Arun said, explaining that while the Biden LPO saw potential in adding carbon capture to natural gas and coal plants, its current incarnation will no longer allocate funding in any meaningful amount “because reducing emissions is no longer part of the LPO’s mandate.” Some policymakers and clean energy developers had also hoped that excess renewable energy would make it economically feasible to power the production of hydrogen fuel with renewable energy. But with this law — and really each passing day under Trump — a mass buildout of solar and wind seems less and less likely, making it doubtful that green hydrogen will move down the cost curve.
As bleak as this looks, it’s better than it could have been. There was no guarantee that Trump would keep the LPO around at all. Even in this denuded state, the office can still fund the expansion of existing nuclear projects, and perhaps even the buildout of transmission lines or battery projects on brownfield sites, Arun said, depending on how LPO’s leadership ends up interpreting what it means to “increase the capacity output of operating infrastructure.”
But in many ways, what happened with the LPO looks like another instance of the Trump administration picking winners and losers: Yes to clean, firm energy and fossil fuels, no to solar, wind, and electric vehicles.
Take the Advanced Technology Vehicle Manufacturing Program, for example. OBBBA nixed both its credit subsidies and its tens of billions of dollars in lending authority. That’s hardly a surprise, given that the Bush administration created the program in 2007 explicitly to support the domestic development and manufacture of fuel-efficient vehicles and components. But it means that unlike the LPO programs for which lending authority still stands, even if Congress wanted to, it could not redesign the advanced vehicles program to serve a more Trump-aligned purpose. Safer, I supposed, to remove any opening for funding EVs and hybrids altogether..
The latest LPO rescissions add to the growing list of reasons the private sector has to be wary of the consistently inconsistent landscape for federal funding, Arun told me. He worries that slashing the LPO’s authority at the same time as there’s so much uncertainty around tax credit eligibility will lead some companies to forgo federal funding opportunities altogether.
“We’ll see if private developers even want to play around with the LPO,” Arun told me, “given the uncertainty around the rest of the federal landscape here.”
On federal layoffs, copper tariffs, and Texas flood costs
Current conditions: Three people were killed in southern New Mexico after heavy rains on Tuesday caused flooding • Parts of the western Mediterranean Sea are 12.6 degrees Fahrenheit warmer than average • Search operations are underway for 30 people missing in India’s Himachal Pradesh state following flash floods and landslides.
The Supreme Court on Tuesday lifted a lower court ruling that had blocked mass layoffs of federal workers, clearing the way for a significant reduction in the civil service. Justice Ketanji Brown Jackson was the only dissenting vote, writing that the court had a “demonstrated enthusiasm for greenlighting this President’s legally dubious actions in an emergency posture.” Technically, SCOTUS’ ruling is only temporary, and the case could eventually return for the court to consider at a later date, with Justice Sonia Sotomayor noting, “The plans themselves are not before this Court, at this stage, and we thus have no occasion to consider whether they can and will be carried out consistent with the constraints of law.” But “in practice,” the court’s move allows President Trump to “pursue his restructuring plans, even if judges later determine that they exceed presidential power,” The New York Times writes.
The Trump administration has signaled its intention to reduce the workforce by 107,000 employees in the next fiscal year. It plans the steepest cuts for the Department of Education, the Office of Personnel Management, and the General Services Administration, but roles at the National Aeronautics and Space Administration, National Science Foundation, and Department of Energy are also up for reductions. As I’ve previously written, such cuts to the civil service will long outlast President Trump. “It will be very difficult, if not impossible, to restore the kind of institutional knowledge that’s being lost,” Jacqueline Simon, policy director of the American Federation of Government Employees, the largest union of federal government workers, told me.
President Trump announced on Tuesday that he intends to impose a 50% tariff on copper, a move that follows earlier tariffs on steel and aluminum. The process for imposing those tariffs, my colleague Matthew Zeitlin notes, involves recognizing that the product being tariffed is “essential to national security, and thus that the United States should be able to supply it on its own.” But while a steep new tariff could incentivize increased copper mining in the United States, such mines can take years to open, and copper must be smelted and refined before it can be used — an industry that is currently at capacity in the U.S. and dominated by China. Nevertheless, copper is crucial for “a broad array of electrical technologies, including transmission lines, batteries, and electric motors,” Matthew writes. “Electric vehicles contain around 180 pounds of copper on average.”
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AccuWeather
The death toll in the Texas floods rose to over 100 on Tuesday, with Governor Greg Abbott telling reporters that another 161 people remain unaccounted for in Kerr County. Already one of the deadliest floods in modern U.S. history, the disaster is also set to be one of the costliest, with AccuWeather estimating total damage and economic loss between $18 billion and $22 billion. “The damage, impacts on future tourism, cost of search and recovery efforts, extensive cleanup that will be needed, as well as insurance claims after this catastrophic flash flood, will have long-lasting economic impacts in the Hill Country region of Texas,” AccuWeather Chief Meteorologist Jonathan Porter said in a statement.
As I wrote on Tuesday, the Texas floods were a disaster despite the forecasting, not because of it. While some global weather models underestimated the storm, NOAA’s cutting-edge specialized models “got this right,” UCLA and UC Agriculture and Natural Resources climate scientist Daniel Swain told me. Funding for those models — as well as research into severe thunderstorms and rainstorms like the one in Texas — is set to be zeroed out in the Trump administration’s 2026 budget.
The Department of Energy has hired three scientists who are among the minority of experts to doubt or downplay the impacts of human activity on global warming, The New York Times has learned. The scientists include physicist Steven E. Koonin, the author of the bestselling book Unsettled: What Climate Science Tells Us, What it Doesn’t and Why it Matters, which has been criticized for “not [comporting] with the evidence”; meteorologist Roy Spencer, the author of The Great Global Warming Blunder: How Mother Nature Fooled the World’s Top Climate Scientists, which alleges IPCC researchers made a “mix-up between cause and effect when analyzing cloud and temperature variations”; and atmospheric scientist John Christy, who’s been accused of using misleading graphs to downplay the extent of human activity on climate change. The New York Times was unable to immediately learn “what the three scientists were working on or whether they were being paid,” but the hires come at a time when the federal government is also laying off long-tenured climate and atmospheric scientists as well as removing mentions of climate change from government websites.
China is constructing nearly three-quarters of all solar and wind power projects being built globally, according to a new report by the Global Energy Monitor. Of about 689 gigawatts currently under construction worldwide, 510 gigawatts of utility-scale solar and wind were within China’s borders, the report found. Additionally, China accounts for 29% of all planned wind and solar projects worldwide, followed closest by Brazil, at just over 9%.
China’s wind and solar capacity surpassed its coal and gas capacity for the first time during the first quarter of 2025, supplying 23% of the country’s electricity consumption, the report adds. Even offshore wind, a “small portion of China’s overall renewable capacity,” now contributes over 50% of the overall offshore wind capacity in construction worldwide. You can read the full report here.
Image: Studio Pizza/Unsplash
Cemeteries are “a mosaic of different habitats. This means that species from forests, hedgerows, grasslands, and even fields can find substitute habitats there.” —Ingo Kowarik, an urban ecologist and retired professor at the Technische Universität Berlin, on the burgeoning field of cemetery biodiversity.
Jesse and Rob go back to basics on the steam engine.
Just two types of machines have produced the overwhelming majority of electricity generated since 1890. This week, we look at the history of those devices, how they work — and how they have contributed to global warming.
This is our second episode of Shift Key Summer School, a series of “lecture conversations” about the basics of energy, electricity, and the power grid for listeners of all backgrounds. This week, we dive into the invention and engineering of the world’s most common types of fossil- and nuclear-fueled power plants. What’s a Rankine cycle power station, and how does it use steam to produce electricity? How did the invention of the jet engine enable the rise of natural gas-generated electricity? And why can natural gas power plants achieve much higher efficiency gains than coal plants?
Shift Key is hosted by Jesse Jenkins, a professor of energy systems engineering at Princeton University, and Robinson Meyer, Heatmap’s executive editor.
Subscribe to “Shift Key” and find this episode on Apple Podcasts, Spotify, Amazon, YouTube, or wherever you get your podcasts.
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Here is an excerpt from our conversation:
Robinson Meyer: It’s interesting thinking about the deployment of steam and these Rankine cycle generators in the late 19th century for us as people who care about the power grid. These are interesting techniques as they’re deploying electricity for the first time. But the use of coal to convert water into steam and the use of steam power actually comes way earlier than any of this, right? Like, it’s steam. That is actually the 19th century — the core 19th century and late 19th century, especially — energy medium. And actually, the history of the 19th century energy is switching from wood and hydropower to coal-powered steam.
And already by the time that the Pearl Street station is built in New York, the United States is crisscrossed with steam engines. Our economy already runs on steam. It’s actually the application of steam and coal — which at that point are kind of old and fundamental technologies to economic function — to power generation. They didn’t have to make any huge discoveries around steam and coal. They were already using steam and coal in factories, they just weren’t intermediating it through the electricity grid.
Jesse Jenkins: That’s right. And in all these cases, you’re just trying to convert that steam, the expansion of that steam, into motion, whether that’s the pistons of a steam engine or the pistons of a reciprocating generator attached to a dynamo in Pearl Street, or, in a lot of factories, just a bunch of belts, right? That would then move equipment throughout the facility. It’s just a lot easier to move energy around, and more precise to do that as electricity. And so over time, the devices in industrial facilities all converted over to using electricity directly, and then you could generate your energy somewhere far away.
And this is the other, second advantage of steam turbines. What made Westinghouse so successful is that they have large economies of scale, so it’s a lot cheaper to generate power from a big steam turbine than the equivalent amount of power from a lot of little steam engines. And that wasn’t … I mean, that’s true for reciprocating engines, but they kind of top out, given their complexity.
The Pearl Strait station generators were in the 100-kilowatt scale. I think there were six of them, originally, so 600 kilowatts, and they only powered a few hundred lights, which is remarkable. These lights, the original lights, were incredibly inefficient, so it took something like 1,000 watts or more per light bulb. Whereas again, now we’re down to like, 10 to 15 watts in an efficient LED bulb. But anyway, they were in that kind of hundreds of watts scale, and that kind of maxed out the scale of the reciprocating engines. Steam turbines you could increase and increase and increase into the megawatt scale, and by doing that utilities or generators were able to lower the cost of energy while expanding customer bases.
Mentioned:
Powering the Dream: The History and Promise of Green Technology, by Alexis Madrigal
This episode of Shift Key is sponsored by …
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Music for Shift Key is by Adam Kromelow.