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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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When I reached out to climate tech investors on Tuesday to gauge their reaction to the Senate’s proposed overhaul of the clean energy tax credits, I thought I might get a standard dose of can-do investor optimism. Though the proposal from the Senate Finance committee would cut tax credits for wind and solar, it would preserve them for other sources of clean energy, such as geothermal, nuclear, and batteries — areas of significant focus and investment for many climate-focused venture firms.
But the vibe ended up being fairly divided. While many investors expressed cautious optimism about what this latest text could mean for their particular portfolio companies, others worried that by slashing incentives for solar and wind, the bill’s implications for the energy transition at large would be categorically terrible.
“We have investments in nuclear, we have investments in geothermal, we have investments in carbon capture. All of that stuff is probably going to get a boost from this, because so much money is going to be flowing out of quote, unquote, ‘slightly more established’ zero emissions technologies,” Susan Su, a climate tech investor at Toba Capital, told me. “So we’re diversified. But for me, as a human being, and as somebody that cares about climate change and cares about having an abundant energy future, this is very short-sighted.”
Bigger picture aside, the idea that the Senate proposal could lead to more capital for non-solar, non-wind clean energy technologies was shared by other investors, many of whom responded with tentative hope when I asked for their thoughts on the bill.
“The extension of the nuclear and geothermal tax credits compared to the House bill is really important,” Rachel Slaybaugh, a climate tech investor at DCVC, told me. The venture firm has invested in the nuclear fission company Radiant Nuclear, the fusion company Zap Energy, and the geothermal startup Fervo Energy. As for how Slaybaugh has been feeling since the bill’s passage as well as the general sentiment among DCVC’s portfolio companies, she told me that “it's mostly been the relief of like, thank you for at least supporting clean, firm and bringing transferability back.”
Indeed, the proposed bill not only fully preserves tax credits for most forms of zero-emissions power until 2034, but also keeps tax credit transferability on the books. This financing mechanism is essential for renewable energy developers who cannot fully utilize the tax credits themselves, as it allows them to sell credits to other companies for cash. All of this puts nascent clean, firm technologies on far more stable footing than after the House’s version of the bill was released last month.
Carmichael Roberts of Breakthrough Energy Ventures echoed these sentiments via email when he told me, “the Senate proposal is a meaningful improvement over the House version for clean energy companies. It creates more predictability and a clearer runway for emerging technologies that are not yet fully commercial.” Breakthrough invests in multiple fusion, geothermal, and long-duration energy storage startups.
Amy Duffuor, co-founder of Azolla Ventures and managing director at the Prime Impact Fund also acknowledged in an email that it’s “encouraging” that the Senate has “seen the way forward on clean firm baseload power.” However, she issued a warning that the unsettled policy environment is leading to “material risks and uncertainties for start-ups reliant on current tax incentives.”
Solar and wind are by far the most widely deployed and cost-competitive forms of renewable energy. So while they now mainly exist outside the remit of venture firms, there are numerous climate-focused startups that operate downstream of this tech. Think about all the software companies working to optimize load forecasting, implement demand response programs, facilitate power purchase agreements, monitor grid assets, and so much more. By proxy, these startups are now threatened by the Senate’s proposal to phase out the investment and production tax credits for solar and wind projects beginning next year, with a full termination after 2027.
“I think solar and wind will survive. But it's going to be like 80% of the deals don't pencil for a long time,” Ryan Guay, co-founder and president of the software startup Euclid Power, told me. Euclid makes data management and workflow tools for renewable project developers, so if the tax credits for solar and wind go kaput, that will mean less business for them. In the meantime though, Guay expects to be especially busy as developers rush to build projects before their tax credit eligibility expires.
As Guay explained to me, it’s not just the rescission of tax credits that he believes will kill such a large percent of solar and wind projects. It’s the combined impact of those cuts, the bill’s foreign entity of concern rules restricting materials from China, and Trump’s tariffs on Chinese-made components. “You’re not giving the industry enough time to actually build that robust domestic supply chain, which I agree needs to happen,” Guay told me. “I’m all for the security of the grid, but our supply chains are already very constrained.”
Many investors also expressed frustration and confusion over why Senate Republicans, and the Trump administration at large, would target incentives for solar and wind — the fastest growing domestic energy sources — while touting an agenda of energy dominance and American leadership. Some even used the president’s own language around energy issues to deride the One Big Beautiful Bill’s treatment of solar and wind as well as its repeal of the electric vehicle tax credits.
“The rollbacks of the IRA weaken the U.S. in key areas like energy dominance and the auto industry, which is rapidly becoming synonymous with the EV industry,” Matt Eggers, a managing director at the climate-tech investment firm Prelude Ventures, wrote to me in an email. “This bill will still ultimately cost us economic growth, jobs, and strategic positioning on the world stage.”
“The only real question is, are we going to double down on the future and on American dynamism?” Andrew Beebe, managing director at Obvious Ventures, asked in an emailed response. “Or are we going to cling to the past by trying to hold back a future of abundant, clean, and affordable energy?”
Su wanted to focus on the bigger picture too. While the Senate’s proposal gives tax credits for solar and wind a much longer phaseout period than the House’s bill — which would have required projects to start construction within 60 days of the bill’s passage and enter service by 2028 — Su still doesn’t think the Senate’s version is much to celebrate.
“The specific changes that came through in the Senate version are really kind of nibbling at the edges and at the end of the day, this is a huge blow for our emissions trajectory,” Su told me. She’s always been a big believer that there’s still a significant amount of cutting edge innovation in the solar and wind sectors, she told me. For example, Toba is an investor in Swift Solar, a startup developing high-efficiency perovskite solar cells. Nixing tax credits that benefit the solar industry will hit these smaller players especially hard, she told me.
With the Senate now working to finalize the bill, investors agreed that the current proposal is certainly not the worst case scenario. But many did say it was worse than they had — perhaps overly optimistically — been holding out for.
“To me, it's really bad because it now has a major Senate stamp of approval,” Su told me. The Senate usually tempers the more extreme, partisan impulses of the House. Thus, the closer a bill gets to clearing the Senate, the closer it usually is to its final form. Now, it seems, the reconciliation bill is suddenly feeling very real for people.
“At least back between May 22 and [Monday], we didn't know what was going to get amended, so there was still this window of hope that things could change more dramatically." Su said. Now that window is slowly closing, and the picture of what incentives will — and won’t — survive is coming into greater focus.
Rob and Jesse talk with John Henry Harris, the cofounder and CEO of Harbinger Motors.
You might not think that often about medium-duty trucks, but they’re all around you: ambulances, UPS and FedEx delivery trucks, school buses. And although they make up a relatively small share of vehicles on the road, they generate an outsized amount of carbon pollution. They’re also a surprisingly ripe target for electrification, because so many medium-duty trucks drive fewer than 150 miles a day.
On this week’s episode of Shift Key, Rob and Jesse talk with John Henry Harris, the cofounder and CEO of Harbinger Motors. Harbinger is a Los Angeles-based startup that sells electric and hybrid chassis for medium-duty vehicles, such as delivery vans, moving trucks, and ambulances.
Rob, John, and Jesse chat about why medium-duty trucking is unlike any other vehicle segment, how to design an electric truck to last 20 years, and how President Trump’s tariffs are already stalling out manufacturing firms. 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.
You can also add the show’s RSS feed to your podcast app to follow us directly.
Here is an excerpt from our conversation:
Robinson Meyer: What is it like building a final assembly plant — a U.S. factory — in this moment?
John Harris: I would say lots of people talk about how excited they are about U.S. manufacturing, but that's very different than putting their money where their mouth is. Building a final assembly line, like we have — our team here is really good, that they made it feel not that hard. The challenge is the whole supply chain.
If we look at what we build here in-house at Harbinger, we have a final assembly line where we bolt parts together to make chassis. We also have two sub-component assembly lines where we take copper and make motors, and where we take cells and make batteries. All three of those lines work pretty well. We're pumping out chassis, and they roll out the door, and we sell them to people, which is great. But it’s all the stuff that goes into those, that's the most challenging. There's a lot of trade policy at certain hours of the day, on certain days of the week — depending on when we check — that is theoretically supposed to encourage us manufacturing.
But it's really not because of the volatility. It costs us an enormous amount to build the supply chain, to feed these lines. And when we have volatile trade policy, our reaction, and everyone else's reaction, is to just pause. It’s not to spend more money on U.S. manufacturing, because we were already doing that. We were spending a lot on U.S. manufacturing as part of our core approach to manufacturing.
The latest trade policy has caused us to spend less money on U.S. manufacturing — not more, because we're unclear on what is the demand environment going to be, what is the policy going to be next week? We were getting ready to make major investments to take certain manufacturing tasks in our supply chain out of China and move them to Mexico, for example. Now we’re not. We were getting ready to invest in certain kinds of automation to do things in house, and now we're waiting. So the volatility is dramatically shrinking investment in US manufacturing, including ours.
Meyer: And can you just explain, why did you make that decision to pause investment and how does trade policy affect that decision?
Harris: When we had 25% tariffs on China, if we take content out of China and move it to Mexico, we break even — if that. We might still end up underwater. That's because there's better automation in China. There's much higher labor productivity. And — this one is always shocking to people — there’s lower logistics costs. When we move stuff from Shenzhen to our factory, in many cases it costs us less than moving shipments from Monterey.
Mentioned:
CalStart’s data on medium-duty electric trucks deployed in the U.S.
Here’s the chart that John showed Rob and Jesse:
Courtesy of Harbinger
It draws on data from Bloomberg in China, the ICCT, and the Calstart ZET Dashboard in the United States.
Jesse’s case for EVs with gas tanks — which are called extended range electric vehicles
On xAI, residential solar, and domestic lithium
Current conditions: Indonesia has issued its highest alert level due to the ongoing eruption of Mount Lewotobi Laki-laki • 10 million people from Missouri to Michigan are at risk of large hail and damaging winds today • Tropical Storm Erick, the earliest “E” storm on record in the eastern Pacific Ocean, could potentially strengthen into a major hurricane before making landfall near Acapulco, Mexico, on Thursday.
The NAACP and the Southern Environmental Law Center said Tuesday that they intend to sue Elon Musk’s artificial intelligence company xAI over alleged Clean Air Act violations at its Memphis facility. Per the lawsuit, xAI failed to obtain the required permits for the use of the 26 gas turbines that power its supercomputer, and in doing so, the company also avoided equipping the turbines with technology that would have reduced emissions. “xAI’s turbines are collectively one of the largest, or potentially the largest, industrial source of nitrogen oxides in Shelby County,” the lawsuit claims.
The SELC has additionally said that residents who live near the xAI facility already face cancer risks four times above the national average, and opponents have argued that xAI’s lack of urgency in responding to community concerns about the pollution is a case of “environmental racism.” In a statement Tuesday, xAI responded to the threat of a lawsuit by claiming the “temporary power generation units are operating in compliance with all applicable laws,” and said it intends to equip the turbines with the necessary technology to reduce emissions going forward.
Shares of several residential solar companies plummeted Tuesday after the Senate Finance Committee declined to preserve related Inflation Reduction Act investment tax credits. As my colleague Matthew Zeitlin reported, Sunrun shares fell 40%, “bringing the company’s market cap down by almost $900 million to $1.3 billion,” after a brief jump at the end of last week “due to optimism that the Senate Finance bill might include friendlier language for its business model.”
That never materialized. Instead, the Finance Committee’s draft proposed terminating the residential clean energy tax credit for any systems, including residential solar, six months after the bill is signed, as well as the investment and production tax credits for residential solar. SolarEdge and Enphase also suffered from the news, with shares down 33% and 24%, respectively. You can read Matthew’s full analysis here.
Chevron announced Tuesday that it has acquired 125,000 net acres of the Smackover Formation in southwest Arkansas and northeast Texas to get into domestic lithium extraction. Chevron’s acquisition follows an earlier move by Exxon Mobil to do the same, with lithium representing a key resource for the transition from fossil fuels to renewable energy sources “that would allow the company to pivot if oil and gas demands wane in the coming decades,” Bloomberg writes.
“Establishing domestic and resilient lithium supply chains is essential not only to maintaining U.S. energy leadership but also to meeting the growing demand from customers,” Jeff Gustavson, the president of Chevron New Energies, said in a Tuesday press release. The Liberty Owl project, which was part of Chevron’s acquisition from TerraVolta Resources, is “expected to have an initial production capacity of at least 25,000 tonnes of lithium carbonate per year, which is enough lithium to power about 500,000 electric vehicles annually,” Houston Business Journal reports.
The Federal Emergency Management Agency prepared a memo titled “Abolishing FEMA” at the direction of Homeland Security Secretary Kristi Noem, describing how its functions can be “drastically reformed, transferred to another agency, or abolished in their entirety” as soon as the end of 2025. While only Congress can technically eliminate the agency, the March memo, obtained and reviewed by Bloomberg, describes potential changes like “eliminating long-term housing assistance for disaster survivors, halting enrollments in the National Flood Insurance Program, and providing smaller amounts of aid for fewer incidents — moves that by design would dramatically limit the federal government’s role in disaster response.”
In May, FEMA’s acting administrator, Cameron Hamilton, was fired one day after defending the existence of the department he’d been appointed to oversee when testifying before the House Appropriations subcommittee. An internal FEMA memo from the same month described the agency’s “critical functions” as being at “high risk” of failure due to “significant personnel losses in advance of the 2025 Hurricane Season.” President Trump has, on several occasions, expressed a desire to eliminate FEMA, as recommended by the Project 2025 playbook from the Heritage Foundation. The March “Abolishing FEMA” memo “just means you should not expect to see FEMA on the ground unless it’s 9/11, Katrina, Superstorm Sandy,” Carrie Speranza, the president of the U.S. council of the International Association of Emergency Managers, told Bloomberg.
The Spanish government on Tuesday released its report on the causes of the April 28 blackout that left much of the nation, as well as parts of Portugal, without power for more than 12 hours. Ecological Transition Minister Sara Aagesen, who heads Spain’s energy policy, told reporters that a voltage surge in the south of Spain had triggered a “chain reaction of disconnections” that led to the widespread power loss, and blamed the nation’s state-owned grid operator Red Eléctrica for “poor planning” and failing to have enough thermal power stations online to control the dynamic voltage, the Associated Press reports. Additionally, Aagesen said that utilities had preventively shut off some power plants when the disruptions started, which could have helped the system stay online. “We have a solid narrative of events and a verified explanation that allows us to reflect and to act as we surely will,” Aagesen went on, responding to criticisms that Spain’s renewable-heavy energy mix was to blame for the blackout. “We believe in the energy transition and we know it’s not an ideological question but one of this country’s principal vectors of growth when it comes to re-industrialisation opportunities.”
Metrograph
“It seems that with the current political climate, with the removal of any reference to climate change on U.S. government websites, with the gutting of environmental laws, and the recent devastating fires in Los Angeles, this trilogy of films is still urgently relevant.” —Filmmaker Jennifer Baichwal on the upcoming screenings of the Anthropocene trilogy, co-created with Nicholas de Pencier and photographer Edward Burtynsky between 2006 and 2018, at the Metrograph in New York City.