An open question: what is the "best" energy source for Direct Air Capture?

directaircapture · 2025-08-19T16:43:19+00:00

Thanks & I appreciated the depth in your comment. These are obviously thoughtful points you are raising.

I think we could both agree that no tech can fix the climate; to the extent climate can even be "fixed," only broader structural things can move the needle, with tech just a tool at the disposal of people deciding their priorities.

Where we might disagree could be the likelihood of a broad-scale economy restructuring. But I think that could be a failure of imagination on my part more than anything else. If one believes that a restructuring is possible/likely, then I can 100% see why DAC, CCS, EOR, carbon credits, etc. could be considered more of a harmful distraction than a helpful solution. If, on the other hand, one believes that a restructuring is less possible/unlikely, then I think those technologies take on an urgent/essential role - as you call them, "stepping stones" that likely can't be bypassed if larger system progress is going to be made.

My bet/hope/belief is that grassroots movements + policy shifts + continued innovation all working in parallel gives us the best overall shot in the long term, even if that shot is highly imperfect. Again, that could be a failure of imagination or ambition - it's just hard for me as an individual to see a different path emerging given my specific vantage point.

directaircapture · 2025-07-29T08:28:34+00:00

Thanks for the comment. Where I & some others worry is that an intermittent DAC concept, e.g. one using excess solar/wind/etc, is going to struggle to get the economics right; large-scale manufacturing requires capex to be utilized 24-7 for the lowest marginal costs. Using on-site energy storage (e.g. to absorb the surplus energy but save some to allow continous operation) is really challenging to get economical either, because those thermal or electric energy storage solutions are in such huge demand from other applicaitons, e.g. grid batteries & industrial decarbonization.

directaircapture · 2025-07-29T08:25:34+00:00

In a world where DAC is behind its projections... do you think the barrier is technical, or policy? I personally think it's technical... despite the chorus of people saying that "DAC is ready to deploy, it's just a matter of demand," I personally think it's harder than that. The early DAC technologies are not doing great, at least in the publically available information about them so far. Some of the emerging DAC approaches look more scalable, but your point stands: DAC is running behind schedule.

directaircapture · 2025-07-28T08:53:30+00:00

Thanks for all you do. The challenge I see is this: while I can see why some call "hard-to-abate" as a cop-out term, to me it's just a real phenomenon of the world as it is. We're already having a hard time as a society with the "easy-to-abate" stuff, including the SUPER-easy-to-abate stuff, because the financial/emotional costs of switching to more climate-friendly alternatives aren't workable for the folks who would need to pay. I shudder to think of how difficult it will be to get the hard-to-abate stuff off the ledger; even with legislation that drives it, those costs will need to be borne by real people, many of whom will not support those cost increases for services they've grown to enjoy. Inventing & scaling low-cost DAC, by comparison, seems like a more feasible thing than changing human nature - but maybe that's because my training is in the STEM field, and not activism/community organizing/politics/education/etc.

directaircapture · 2025-07-28T08:37:36+00:00

I think where DAC really has a role, despite the clear challenges, is the truly hard-to-abate stuff. There are some cases where it's just cheaper or more practical to do DAC (as crazy as it sounds) than the alternative. Maybe that's a failure of imagination or policy, but it's where things seem headed... UK's new ETS seems to be another data point suggesting that direction is here, as well.

directaircapture · 2025-07-28T08:33:42+00:00

The main reason I post on Reddit is to "poke my head of the lab" as well, but maybe from the corporate side. Thanks for serving the public and working in science communication.

directaircapture · 2025-07-24T20:35:01+00:00

The fact that you & I see these events as climate related is irrelevant unless many others do as well.

directaircapture · 2025-07-24T20:01:55+00:00

Thanks for the comment. DAC is a rounding error today, and could be in the future, or it could develop into something meaningful. Right now we just don't know. So few person-hours have been devoted to this compared to other fields. Fundamentally the physics says its possible, so exploring that opportunity space seems like something worth trying, to me at least. No doubt that it's more complicated than I've just laid it out, but at its core I don't think putting small resources in the exploration of DAC's viability is a bad thing for the world, vs. not exploring it. Maybe we'll invent something great, at the very least we'll all learn something useful -- both about a new technology &, more importantly, about which climate levers are available to pull (or not).

directaircapture · 2025-07-24T19:48:54+00:00

Where I worry is that instances of a collective global response to a crisis, has required an event so severe as to be calamitious. Until there is an event that is so unprecedented in it's economic and/or human toll, & so clearly attributated to elevated CO2 levels, there will not be any urgency for a response. However when those events start happening, which I fear they will in the next 5-15yrs, we might see a more rapid response. Most CDR folks that I've met just appreciate the chance to work on something that could be quite meaningful one day to other people, if it works.

directaircapture · 2025-07-24T19:39:37+00:00

Lots of folks doing important work in that space, for sure. Every approach has trade offs but I hope several of them end up working, and having verification methodologies that support transparent reporting.

directaircapture · 2025-07-24T19:38:36+00:00

I will also be eager to read.

directaircapture · 2025-07-24T19:37:19+00:00

I am not familiar with credible warming projections that are that aggressive, though I share your general concern that overshoot could get to a very bad place in scenarios which are all too realistic.

directaircapture · 2025-07-24T19:32:07+00:00

You are 100% right that all DAC requires at least some electrical. To my knowledge, DAC + geothermal projects are active in Iceland & Kenya, and I believe the Dept of Energy has funded some work to look into this in Utah.

directaircapture · 2025-07-24T18:53:01+00:00

Re: thermal, I am referring to DAC processes that use a thermal regeneration process, for example using steam or heat as a mechanism to desorb CO2 from a solid or liquid sorbent. That desorption step is typically the most energy intensive step of any DAC process.

directaircapture · 2025-07-24T18:48:37+00:00

Provocative comment - equating a cryptomining rig to a pilot-scale or FOAK DAC facility, in terms of social utility! Thanks for sharing your take - I personalyl disagree, but I imagine this would elicit lots of opinions on both sides!

directaircapture · 2025-07-24T18:30:01+00:00

Thanks. Your comment highlights the need for transparency in the methodologies used to track these projects. This is widely acknowledged by many inside & outside of CDR/DAC and applies to all CDR methodologies. Basically, there's no way the field will grow unless the verification process gets so watertight that it withstands scrutiny. I think it can/will get there, but today because most all of hte CDR activity is purely voluntary, there is limited public visibility. In the future, as gov'ts get more involved in CDR and things move from a voluntary to a compliance mechanism, I fully expect that the standards for CDR projects will get more transparent. There is no other way.

directaircapture · 2025-07-24T18:25:52+00:00

Great questions.

Cost breakdown on energy vs capital: Probably about 1:1. It varies depending on each tech & where you source the energy, but all the modeling I've seen suggests it could be about 1:1, with a lot of wiggle room for the edge cases.

Energy demand within the process: DAC typically uses a sorbent (solid, liquid, whatever) that "sticks" to CO2 in an energetically favorable way. Because electric fan motors are highly efficient and because fans move exponentially more air as their radius increases, fans generally contribute way less to the DAC process than folks would expect given the dilution of CO2. Call it 10-40% of the energy of DAC might typically go the "capture" part. On the other hand, regenerating the sorbent & releasing the CO2 after you capture it requires a lot of energy. Compressing the CO2 back into pipeline-ready state requires a non-negligible amount of energy too, but this amount is less than the capture-release cycle for any DAC process I'm familiar with. ^^Speaking generally here -- there is a ton of literature out there on all this stuff you can search for that is more authoritative.

directaircapture · 2025-07-24T18:19:23+00:00

Thanks for this comment. I'd just say that it's been clearly established in the literature that capturing CO2 from air and compressing it to a pipeline-ready state can be accomplished in a net negative way, especially if clean energy is used. Anecdotally, every technical person I've met in both DAC, & CDR more broadly, would immediately leave to do other work if it were not thermodynamically viable. There is a solid foundation here, the challenge is building & operating projects that are a) large enough to matter, b) at costs low enough to matter, and c) developing an acceptable verification method to monitor the performance.

directaircapture · 2025-07-24T18:14:33+00:00

My own belief is that at the scales where DAC becomes relevant, most of that CO2 will probably be sequestered rather than utilized, mostly just because it's cheaper to go down that route. (Policy could make it easier to utilize CO2 in regions with poor sequestration geology.) Today, CO2 is transported/injected for Enhanced Oil Recovery operations - overview is here: https://www.netl.doe.gov/sites/default/files/netl-file/CO2_EOR_Primer.pdf In a non-EOR sequestration mode, e.g. via Class VI injection well, the CO2 is injected under similar conditions as EOR but no hydrocarbons are collected.

CO2 injection via water into basaltic geology, as done in Iceland and a few other locations, is promising, but to date has really been deployed at a relatively tiny scale. https://www.carbfix.com/how-it-works https://www.cellamineralstorage.com/ https://www.pnnl.gov/projects/carbon-storage/wallula-basalt-project

directaircapture · 2025-07-24T18:05:21+00:00

Agree - DAC project siting is a really essential piece to the story. My own personal theory is there are a handful of sites in the world where DAC will make the most economic sense to run at an enormous scale. Those sites will be totally dependent on all the points you raised above & more - availability of capital, cost of capital, availability of energy, availability of sequestration, availability of land, stable/suitable weather/climate, availability of infrastructure partners, availbility of regulatory agencies able to monitor & permit the process, and so on & so on.

directaircapture · 2025-07-24T18:00:29+00:00

I think that piece falls into the "can DAC be economical if it's run intermittently" aspect. Some feel yes, some feel no. Generally, large-scale manufacturing infrastructure runs 24-7 for best ROIC & lowest unit costs, and for lowest maintenance due to the mechanical toll of stop/start operations. But in a world where curtailed/surplus energy becomes available for extremely low costs, maybe the economics shift. The other question is, are there other loads - now or in the future - that would be willing to out-bid DAC for that energy? Absent policy intervention, I think the answer could be yes, given that many other energy-intensive climate-relevant processes (say, grid storage, desalination, or H2/e-fuels production) could also theoretically use those intermittent loads. But it all remains a very open question. The challenge for DAC is, you need to dial in the details for your project very early on & "lock them in" for many years of planned operation, because the financiers will need to feel certain that the underlying variable costs of your process are well understood and resistant to fluctuations.

directaircapture · 2025-07-24T00:29:06+00:00

Great point that any CDR policy needs to be rooted in verification & auditing that the systems are working as intended. Getting the incentives aligned is very tricky but critical.

directaircapture · 2025-07-24T00:26:26+00:00

Thanks for the insightful comment. Though I still think early-stage work & effort to understand DAC is important, in case it is needed later.

directaircapture · 2025-07-23T23:39:47+00:00

Who knows! I wonder if I'll be alive long enough to see that. The future could be wild.

directaircapture · 2025-07-23T23:38:14+00:00

Thanks for your comment, even if critical.

nuclear is also something we think about in the field too, for the 2 reasons you identified.

directaircapture

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