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A new report demonstrates how to power the computing boom with (mostly) clean energy.
After a year of concerted hand-wringing about the growing energy needs of data centers, a report that dropped just before the holidays proposed a solution that had been strangely absent from the discussion.
AI companies have seemingly grasped for every imaginable source of clean energy to quench their thirst for power, including pricey, left-field ideas like restarting shuttered nuclear plants. Some are foregoing climate concerns altogether and ordering up off-grid natural gas turbines. In a pithily named new analysis — “Fast, scalable, clean, and cheap enough” — the report’s authors make a compelling case for an alternative: off-grid solar microgrids.
An off-grid solar microgrid is a system with solar panels, batteries, and small gas generators that can work together to power a data center directly without connecting to the wider electricity system. It can have infinite possible configurations, such as greater or smaller numbers of solar panels, and more or less gas-generated capacity. The report models the full range of possibilities to illustrate the trade-offs in terms of emission reductions and cost.
An eclectic group of experts got together to do the research, including staffers from the payment company Stripe, a developer called Scale Microgrids, and Paces, which builds software to help renewable energy developers identify viable sites for projects. They found that an off-grid microgrid that supplied 44% of a data center’s demand from solar panels and used a natural gas generator the rest of the time would cost roughly $93 per megawatt-hour compared to about $86 for large, off-grid natural gas turbines — and it would emit nearly one million tons of CO2 less than the gas turbines. A cleaner system that produced 90% of its power from solar and batteries would cost closer to $109 per megawatt-hour, the authors found. While that’s more expensive than gas turbines, it’s significantly cheaper than repowering Three Mile Island, the fabled nuclear plant that Microsoft is bringing back online for an estimated $130 per megawatt-hour.
One challenge with solar microgrids is that they require a lot of land for solar panels. But a geospatial analysis showed that there’s more than enough available land in the U.S. southwest — primarily in West Texas — to cover estimated energy demand growth from data centers through 2030. This shouldn’t be taken as a recommendation, per se. The paper doesn’t interrogate the need for data centers or the trade-offs of building renewable power for AI training facilities versus to serve manufacturing or households. The report is just an exercise in asking whether, if these data centers are going to be developed, could they at least add as few emissions as possible? Not all hyperscalers care about climate, and those that do might still prioritize speed and scale over their net-zero commitments. But the authors argue that it’s possible to build these systems more quickly than it would be to install big gas turbines, which currently have at least three-year lead times to procure and fall under more complicated permitting regimes.
Before the New Year, I spoke with two of the authors — Zeke Hausfather from Stripe and Duncan Campbell from Scale Microgrids — about the report. Stripe doesn’t build data centers and has no plans to, but Hausfather works for a unit within the company called Stripe Climate, which has a “remit to work on impactful things,” he told me. He and his colleagues got interested in the climate dilemma of data centers, and enlisted Scale Microgrids and Paces to help investigate. Our conversation has been lightly edited for clarity.
Why weren’t off-grid solar microgrids really being considered before?
Zeke Hausfather: As AI has grown dramatically, there’s been much more demand for data centers specifically focused on training. Those data centers have a lot more relaxed requirements. Instead of serving millions of customer requests in real time, they’re running these incredibly energy intensive training models. Those don’t need to necessarily be located near where people live, and that unlocks a lot more potential for solar, because you need about 50 times more land to build a data center with off-grid solar and storage than you would to build a data center that had a grid connection.
The other change is that we’re simply running out of good grid connections. And so a lot of the conversation among data center developers has been focused on, is there a way to do this with off-grid natural gas? We think that it makes a lot more sense, particularly given the relaxed constraints of where you can build these, to go with solar and storage, gas back-up, and substantially reduce the emissions impact.
Duncan Campbell: It was funny, when Nan [Ransohoff, head of climate at Stripe] and Zeke first reached out to me, I feel like they convinced me that microgrids were a good idea, which was the first time this ever happened in my life. They were like, what do you think about off-grid solar and storage? Oh, the energy density is way off, you need a ton of land. They’re like, yeah, but you know, for training, you could put it out in the desert, it’s fine, and hyperscalers are doing crazy things right now to access this power. We just went through all these things, and by the end of the call, I was like, yeah, we should do this study. I wasn’t thinking about it this way until me, the microgrids guy, spoke to the payments company.
So it’s just kind of against conventional logic?
Campbell: Going off-grid at all is wild for a data center operator to consider, given the historical impulse was, let’s have 3x more backup generators than we need. Even the off-grid gas turbine proposals out there feel a little nuts. Then, to say solar, 1,000 acres of land, a million batteries — it’s just so unconventional, it’s almost heretical. But when you soberly assess the performance criteria and how the landscape has shifted, particularly access to the grid being problematic right now, but also different requirements for AI training and a very high willingness to pay — as we demonstrate in our reference case with the Three Mile Island restart — it makes sense.
Hausfather: We should be clear, when we talk about reliability, a data center with what we model, which is solar, batteries, and 125% capacity backup gas generators, is still probably going to achieve upwards of 99% reliability. It’s just not gonna be the 99.999% that’s traditionally been needed for serving customers with data centers. You can relax some of the requirements around that.
Can you explain how you went about investigating what it would mean for data centers to use off-grid solar microgrids?
Campbell: First we just built a pretty simple power flow model that says, if you’re in a given location, the solar panel is going to make this much power every hour of the year. And if you have a certain amount of demand and a certain amount of battery, the battery is going to charge and discharge these times to make the demand and supply match. And then when it can’t, your generators will kick on. So that model is just for a given solar-battery-generator combo in a given location. Then what we did is made a huge scenario suite in 50-megawatt increments. Now you can see, for any level of renewable-ness you want, here’s what the [levelized cost of energy] is.
Hausfather: As you approach 100%, the costs start increasing exponentially, which isn’t a new finding, but you’re essentially having to overbuild more and more solar and batteries in order to deal with those few hours of the year where you have extended periods of cloudiness. Which is why it makes a lot more sense, financially, to have a system with some gas generator use — unless you happen to be in a situation where you can actually only run your data center 90% of the time. I think that’s probably a little too heretical for anyone today, but we did include that as one of the cases.
Did you consider water use? Because when you zoom in on the Southwest, that seems like it could be a constraint.
Hausfather: We talked about water use a little bit, but it wasn’t a primary consideration. One of the reasons is that how data centers are designed has a big effect on net water use. There are a lot of designs now that are pretty low — close to zero — water use, because you’re cycling water through the system rather than using evaporative cooling as the primary approach.
What do you want the takeaway from this report to be? Should all data centers be doing this? To what extent do you think this can replace other options out there?
Hausfather: There is a land rush right now for building data centers quickly. While there’s a lot of exciting investment happening in clean, firm generation like the enhanced geothermal that Fervo is doing, none of those are going to be available at very large scales until after 2030. So if you’re building data centers right now and you don’t want to cause a ton of emissions and threaten your company’s net-zero targets or the social license for AI more broadly, this makes a lot of sense as an option. The cost premium above building a gas system is not that big.
Campbell: For me, it’s two things. I see one purpose of this white paper being to reset rules of thumb. There’s this vestigial knowledge we have that this is impossible, and no, this is totally possible. And it seems actually pretty reasonable.
The second part that I think is really radical is the gigantic scale implied by this solution. Every other solution being proposed is kind of like finding a needle in a haystack — if we find this old steel mill, we could use that interconnection to build a data center, or, you know, maybe we can get Exxon to make carbon capture work finally. If a hyperscaler just wanted to build 10 gigawatts of data centers, and wanted one plan to do it, I think this is the most compelling option. The scalability implied by this solution is a huge factor that should be considered.
Money is pouring in — and deadlines are approaching fast.
There’s no quick fix for decarbonizing medium- and long-distance flights. Batteries are typically too heavy, and hydrogen fuel takes up too much space to offer a practical solution, leaving sustainable aviation fuels made from plants and other biomass, recycled carbon, or captured carbon as the primary options. Traditionally, this fuel is much more expensive — and the feedstocks for it much more scarce — than conventional petroleum-based jet fuel. But companies are now racing to overcome these barriers, as recent months have seen backers throw hundreds of millions behind a series of emergent, but promising solutions.
Today, most SAF is made of feedstocks such as used cooking oil and animal fats, from companies such as Neste and Montana Renewables. But this supply is limited by, well, the amount of cooking oil or fats restaurants and food processing facilities generate, and is thus projected to meet only about 10% of total SAF demand by 2050, according to a 2022 report by the Mission Possible Partnership. Beyond that, companies would have to start growing new crops just to make into fuel.
That creates an opportunity for developers of second-generation SAF technologies, which involve making jet fuel out of captured carbon or alternate biomass sources, such as forest waste. These methods are not yet mature enough to make a significant dent in 2030 targets, such as the EU's mandate to use 6% SAF and the U.S. government’s goal of producing 3 billion gallons of SAF per year domestically. But this tech will need to be a big part of the equation in order to meet the aviation sector’s overall goal of net zero emissions by 2050, as well as the EU’s sustainable fuels mandate, which increases to 20% by 2035 and 70% by 2050 for all flights originating in the bloc.
“That’s going to be a massive jump because currently, SAF uptake is about 0.2% of fuel,” Nicole Cerulli, a research associate for transportation and logistics at the market research firm Cleantech Group, told me. The head of the airline industry’s trade association, Willie Walsh, said in December at a media day event, "We’re not making as much progress as we’d hoped for, and we’re certainly not making as much progress as we need.” While global SAF production doubled to 1 million metric tons in 2024, that fell far below the trade group’s projection of 1.5 million metric tons, made at the end of 2023.
Producing SAF requires making hydrocarbons that mirror those used in traditional jet fuel. We know how to do that, but the processes required — electrolysis, gasification, and the series of chemical reactions known as Fischer-Tropsch synthesis — are energy intensive. So finding a way to power all of this sustainably while simultaneously scaling to meet demand is a challenging and expensive task.
Aamir Shams, a senior associate at the energy think tank RMI whose work focuses on driving demand for SAF, told me that while sustainable fuel is undeniably more expensive than traditional fuel, airlines and corporations have so far been willing to pay the premium. “We feel that the lag is happening because we just don’t have the fuel today,” Shams said. “Whatever fuel shows up, it just flies off the shelves.”
Twelve, a Washington-based SAF producer, thinks its e-fuels can help make a dent. The company is looking to produce jet fuel initially by recycling the CO2 emitted from the ethanol, pulp, and paper industries. In September, the company raised $645 million to complete the buildout of its inaugural SAF facility in Washington state, support the development of future plants, and pursue further R&D. The funding includes $400 million in project equity from the impact fund TPG Rise Climate, $200 million in Series C financing led by TPG, Capricorn Investment Group, and Pulse Fund, and $45 million in loans. The company has also previously partnered with the Air Force to explore producing fuel on demand in hard to reach areas.
Nicholas Flanders, Twelve’s CEO, told me that the company is starting with ethanol, pulp, and paper because the CO2 emissions from these facilities are relatively concentrated and thus cheaper to capture. And unlike, say, coal power plants, these industries aren’t going anywhere fast, making them a steady source of carbon. To turn the captured CO2 into sustainable fuel, the company needs just one more input — water. Renewable-powered electrolyzers then break apart the CO2 and H2O into their constituent parts, and the resulting carbon monoxide and hydrogen are combined to create a syngas. That then gets put through a chemical reaction known as “Fischer-Tropsch synthesis,” where the syngas reacts with catalysts to form hydrocarbons, which are then processed into sustainable jet fuel and ultimately blended with conventional fuel.
Twelve says its proprietary CO2 electrolyzer can break apart CO2 at much lower temperatures than would typically be required for this molecule, which simplifies the whole process, making it easier to ramp the electrolyzers up and down to match the output of intermittent renewables. (How does it do this? The company didn’t respond when I asked.) Twelve’s first plant, which sources carbon from a nearby ethanol facility, is set to come online next year, producing 50,000 gallons of SAF annually once it’s fully scaled, with electrolyzers that will run on hydropower.
While Europe may have stricter, actually enforceable SAF requirements than the U.S., Flanders told me there’s a lot of promise in domestic production. “I think the U.S. has an exciting combination of relatively low-cost green electricity, lots of biogenic CO2 sources, a lot of demand for the product we’re making, and then the inflation Reduction Act and state level incentives can further enhance the economics.” Currently, the IRA provides SAF producers with a baseline $1.25 tax credit per gallon produced, which gradually increases the greener the fuel gets. Of course, whether or not the next Congress will rescind this is anybody’s guess.
Down the line, incentives and mandates will end up mattering a whole lot. Making SAF simply costs a whole lot more than producing jet fuel the standard way, by refining crude oil. But in the meantime, Twelve is setting up cost-sharing partnerships between airlines that want to reduce their direct emissions (scope 1) and large corporations that want to reduce their indirect emissions (scope 3), which include employee business travel.
For example, Twelve has offtake agreements with Seattle-based Alaska Airlines and Microsoft for the fuel produced at its initial Washington plant. Microsoft, which aims to reduce emissions from its employees’ flights, will essentially cover the cost premium associated with Twelve’s more expensive SAF fuel, making it cost-effective for Alaska to use in its fleet. Twelve has a similar agreement with Boston Consulting Group and an unnamed airline
Eventually, Flanders told me, the company expects to source carbon via direct air capture, but doing so today would be prohibitively expensive. “If there were a customer who wanted to pay the additional amount to use DAC today, we'd be very happy to do that,” Flanders said. “But our perspective is it will maybe be another decade before that cost starts to converge.”
No sustainable fuel is even close to cost parity yet — Cerulli told me that it generally comes with a “roughly 250% to over 800%” cost premium over conventional jet fuel. So while voluntary uptake by companies such as Microsoft and BCG are helping drive the emergent market today, that won’t be near enough to decarbonize the industry. “At the simplest level, the cost of not using SAF has to be higher than using it,” Cerulli told me.
Pathway Energy thinks that by incorporating carbon sequestration into its process, it can help the world get there. The sustainable fuels company, which emerged from stealth just last month, is pursuing what CEO Steve Roberts told me is “probably the most cost-efficient long-term pathway from a decarbonization perspective.” The company is building a $2 billion SAF plant in Port Arthur, Texas designed to produce about 30 million gallons of jet fuel annually — enough to power about 5,000 carbon-neutral 10-hour flights — while also permanently sequestering more than 1.9 million tons of CO2.
Pathway, a subsidiary of the investment and advisory firm Nexus Holdings, has partnered with the UK-based renewable energy company Drax, which will supply the company with 1 million metric tons of wood pellets, to be turned into fuel using a series of well-established technologies. The first step is to gasify the biomass by heating the pellets to high temperatures in the absence of oxygen to produce a syngas. Then, just as Twelve does, it puts the syngas through the Fischer-Tropsch process to form the hydrocarbons that become SAF.
The competitive advantage here is capturing the emissions from the fuel production process itself and storing them permanently underground. Since Pathway is burying CO2 that’s already been captured by the trees from which the wood pellets come, that would make Pathway’s SAF carbon-negative, in theory, while the best Twelve and similar companies can hope for is carbon neutrality, assuming all of their captured carbon is used to produce fuel.
The choice of Drax as a feedstock partner is not without controversy, however, as the BBC revealed that the company sources much of its wood from rare old-growth forests. Though this is technically legal, it’s also ecologically disruptive. Roberts told me Drax’s sourcing methodologies have been verified by third parties, and Pathway isn’t concerned. “I don't think any of that controversy has yielded any actually significant changes to their sourcing program at all, because we believe that they're compliant,” Roberts told me. “We are 100% certain that they’re meeting all the standards and expectations.”
Pathway has big growth plans, which depend on the legitimacy of its sustainability cred. Beyond the Port Arthur facility, which Roberts told me will begin production by the end of 2029 or early 2030, the company has a pipeline of additional facilities along the Gulf Coast in the works. It also has global ambitions. “When you have a fuel that is this negative, it really opens up a global market, because you can transport fuel out of Texas, whether that be into the EU, Africa, Asia, wherever it may be,” Roberts said, explaining that even substantial transportation-related emissions would be offset by the carbon-negativity of the fuel.
But alternative feedstocks such as forestry biomass are finite resources, too. That’s why many experts think that within the SAF sector, e-fuels such as Twelve’s that could one day source carbon via direct air capture and then electrolyze it have the greatest potential for growth. “It’s extremely dependent on getting sustainable CO2 and cheap electricity prices so that you can make cheap green hydrogen,” Shams told me. “But theoretically, it is unlimited in terms of what your total cap on production would be.”
In the meantime, airlines are focused on making their planes and engines more aerodynamic and efficient so that they don’t consume as much fuel in the first place. They’re also exploring other technical pathways to decarbonization — because after all, SAF will only be a portion of the solution, as many short and medium-length flights could likely be powered by batteries or hydrogen fuel. RMI forecasts that by 2050, 45% of global emissions reduction in the aviation sector will come from improvements in fuel efficiency, 37% will be due to SAF deployment, 7% will come from hydrogen, and 3.5% will come from electrification.
If you did the mental math, you’ll notice these numbers add up to 92.5% — not 100%. “What we have done is, let's look at what we are actually doing today and for the past three, four, five years, and let's see if we get to net zero or not. And the answer is, no. We don't get to net zero by 2050,” Shams told me. And while getting to 92.5% is nothing to scoff at, that means that the aviation sector would still be emitting about 700 million metric tons of CO2 equivalent by that time.
So what’s to be done? “The financing sector needs to step up its game and take a little bit more of a risk than they are used to,” Shams told me, noting that one of RMI’s partners, the Mission Possible Partnership, estimates that getting the aviation sector to net zero will require an investment of around $170 billion per year, a total of about $4.5 trillion by 2050. These numbers take a variety of factors into account beyond strictly SAF production, such as airport infrastructure for new fuels, building out direct air capture plants, etc.
But any way you cut it, it’s a boatload of money that certainly puts Pathway’s $2 billion SAF facility and Twelve’s $645 million funding round in perspective. And it’s far from certain that we can get there. “Increasingly, that goal of the 2050 net-zero target looks really difficult to achieve,” Shams put it simply. “Commitments are always going up, but more can be done.”
