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Comment by leoedin | Hacker News Reader

The article kind of glosses over the fact that one of the inputs to the process is hydrogen.

That really makes this whole process a way of converting energy stored in hydrogen to energy stored in hydrocarbons. This is pretty desirable - hydrocarbon fuels are much easier to work with, fit in with our existing transport - but not really a new source of energy.

The problem with sequestering CO2 as hydrocarbons is that you need to put a whole load of energy (embodied in the hydrogen you're combining it with) into the ground and leave it there. Fortunately renewables (especially solar) are heading in the right direction. On a sunny day in an area with lots of solar panels, electricity is essentially free. We're still some way from having enough free energy available to be able to put large amounts of it back into the ground though.

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It's kind of funny, really: through human history, we "gained" a lot of "free" energy by burning fossil fuels; now, to fully recover our atmosphere from the externalities of that energy generation, we would have to expend just as much, if not more, than that total amount of energy we ever "gained", to essentially un-burn those same fossil fuels.

> we would have to expend just as much, if not more, than that total amount of energy we ever "gained", to essentially un-burn those same fossil fuels.

Ironically enough, our renewable electrification process is like a turbo coming up to speed. There is simply so much energy hitting the Earth from the Sun (if I recall off hand, about an hour of sunlight can power humanity for a year, or thereabouts) that if we continue to rapidly deploy solar and wind, we'll have orders of magnitude more energy than humanity currently requires for a first world lifestyle while also having enough energy to sequestor all of the original carbon burned through fossil fuel based industrialization.

"A long way around the block" if you will.

https://www.iea.org/publications/renewables2017/

https://www.energy.gov/eere/articles/4-charts-show-renewable...

"[The sun] blasts unimaginable quantities of energy into space each instant, and virtually every joule of it is wasted entirely. Incomprehensible riches can be ours if we can but stretch our arms wide enough to dip from this eternal river of wealth."

- Nwabudike Morgan

Giant mirrors in space, redirecting energy to the surface of the earth...

Be more ambitious: the solar wind is already electricity. Engineer vast magnetic funnels to direct it into storage batteries (or just position your storage at the north/south magnetic poles and let Earth's natural field do (part of) the job).

I pray this is the case. I dream of a world where energy is so cheap we could bury our roads in tunnels underground, freeing the surface from their blight.

Don’t dream, find opportunities to contribute.

I myself am working on transitioning out of security engineering into renewable energy/utility storage deployment.

This is something I’m interested as well. How are you making the transition?

Reading as much as possible on construction and project management, electrical transmission design & regulations, and plain ol’ cold calling everyone in the industry who will return my voicemails (“will work for experience”). Also volunteering whenever possible to lend a hand for solar and wind generation installs.

It goes without saying, if you’re in the industry and hiring, I’m interested! (Wink wink nudge nudge Tesla Puerto Rico)

Meanwhile the US is announcing billions of dollars to prop up coal plants

Doesn't this feel like we are shifting the problem somewhere else? I'm not sure it is a sustainable option.

Solar panels take huge amounts of energy to produce, which may not be recovered in the life of the panel.

Its only sustainable if it's possible to have a solar panel factory powered by solar panels... Which seems unlikely

The idea that solar panels take more energy to produce than they are able to output would make solar panels economically unviable as the energy cost must be recovered to at least break even. That may have been true several decades ago but the solar panels of today are competing economically just fine.

Is there any data on this? It takes huge furnaces running at thousands of degrees to melt and process the silicon for the panels, not to mention all the electronics needed to be manufactured. I just can't see how a panel can recover that amount of energy, but maybe I should go and crunch the numbers

But deployment is slowing in jurisdictions that have decided they can't afford the subsidies and what it does to power prices.

Solar and wind are cheaper than coal without subsidies.

there are two ROI points, one ecological/energy wise and the other economical. the former has been roundabout 1.5 years of production a decade ago. I assume this has gotten better through more efficient production. the latter depends very much on the price of electricity. but since the kWh production price for photovoltaics recently fell below that of coal shows that solar totally makes sense.

Indeed. It's like we've been accruing technical debt for centuries by taking the "easy way out" until our technology was developed enough, and now need to pay it all back, with interest.

But does the interest rate of this debt exceed the economic gains we've made from fossil fuels? (Also, did you just use technical debt as a metaphor for regular old debt?)

So far the interest rate has been delightfully low. But the rate is adjustable and the bank has been making noises about massively hiking it. Let’s hope we can pay off the loan before the payments exceed our means.

Well, that depends; like most loans, if you don’t pay it back in a timely fashion, bad things happen... and we don’t really have a bankruptcy procedure.

I think that will largely depend on how we define the ROI.

> Also, did you just use technical debt as a metaphor for regular old debt?

Hahahaha, good catch. I just might have.

It doesn’t really matter, because we’ve already done it and we won’t be doing it again.

It makes all the energy we used basically a loan.

In addition to hydrogen, the Fischer–Tropsch requires carbon monoxide and not carbon dioxide. It can be produced from carbon dioxide, it just requires even more energy (comparable to hydrogen production from water) and potentially rare catalysts.

Energy wise this process might still be favorable to producing biofuels from plants or algae, so I hope they're successful.

I think the important part is that widespread adoption of this would reduce the amount of new CO2 emitted into the atmosphere. Even if it was more expensive to produce than extracting oil from the ground (itself a process which is becoming more and more expensive, see tar sands), states could mandate that an increasing share of all gasoline sold be made from this process.

tar sands is becoming less expensive as time goes on, fracking is vastly less expensive and is the main increase of oil in the last decade.

> The problem with sequestering CO2 as hydrocarbons is that you need to put a whole load of energy (embodied in the hydrogen you're combining it with) into the ground and leave it there.

If sequestering CO2, combining it with CaO to make CaCO3 (calcium carbonate) makes more sense, and is even exothermic. It's also biologically harmless and can be safely dumped, used in building materials, etc.

Isn't CaO largely produced from naturally occuring CaCO3 though? Where do you get a large supply of CaO to react with your sequestered CO2 from?

Apparently when CO2 is injected into hot underground basalt deposits, it is absorbed.

https://en.wikipedia.org/wiki/Carbon_sequestration#Mineral_c... (last paragraph of section)

So I would guess the reason for producing synthetic CaO from CaCO3 is that extracting natural CaO is uneconomical.

CaO generally does not exist in natural stone deposits (no alkaline or alkali earths exist as oxides because they are very reactive). You produce CaO from CaCO3 by calcining and driving off the CO2 (which is emitted to the atmosphere).

My understanding (someone correct me if I'm wrong) is that virgin CaO is released from volcanic activity, and the aforementioned underground basalt is an igneous rock that has not been exposed to surface atmospheric conditions, and thus contains some amount of unreacted CaO.

> The problem with sequestering CO2 as hydrocarbons is that you need to put a whole load of energy (embodied in the hydrogen you're combining it with) into the ground and leave it there.

Why would you be putting energy into the ground? If you're producing hydrocarbons, those will presumably be burned or used for something else (e.g. plastics).

It only removes the carbon from the atmosphere if you don't subsequently burn it.

It burns carbon that was in the air to begin with though. An attempt at a closed loop with gasoline is better than a one way road into the atmosphere

The loop isn't closed — you have to add energy to drive the process.

One of the goals is to close the carbon loop (not the energy loop).

Quoting from the paper:

> An industrial process for large-scale capture of atmospheric CO2 (DAC) serves two roles. First, as a source of CO2 for making carbon-neutral hydrocarbon fuels, enabling carbon-free energy to be converted into high-energy-density fuels. Solar fuels, for example, may be produced at high-insolation low-cost locations from DAC-CO2 and electrolytic hydrogen using gas-to-liquids technology enabling decarbonization of difficult-to-electrify sectors such as aviation. And second, DAC with CO2 sequestration allows carbon removal.

So, to summarize their first role, they would produce hydrogen from water, combine it with CO2 extracted from the atmosphere, and then burn it. Thus no net carbon added to the atmosphere.

Essentially, instead of moving carbon from fossil fuels to the atmosphere, you would borrow carbon from the atmosphere, turn it into fuels, burn it, and return it to where you borrowed it from.

This technology is one answer to an often-heard criticism (often presented with dubious motivation). The criticism is that storing solar or wind energy for when the sun isn't shining or the wind isn't blowing is a problem with renewables. However, if one considers intelligent grid balancing, solar-thermal towers, increasingly better battery technology, and this kind of solar-to-hydrocarbon conversion you have plenty of places to put excess renewable power generation.

Yeah, I’d like to know the cycle efficiency.

True, but the new energy could be renewable/clean.

In that case, it's like you're using hydrocarbons as a storage and transport mechanism for renewables. Also lets you have nearly net-zero carbon emissions from the billions of hydrocarbon-burning engines in the world.

Efficiency still matters -- Renewable doesn't mean unlimited or cheap -- if it takes 10X more energy to create hydrocarbons than you get back from burning them, maybe it's better to use that energy for more efficient transportation storage systems. Then you can use some of the energy saved for direct carbon sequestration.

Something is going to burn it no matter what. The microbiome considers hydrocarbons food.

No? Coal for example, when buried underground, does not spontaneously re-enter the atmosphere as CO2.

Carbon sequestration is a real thing, we just lack either economic or political will to prioritize it.

https://en.wikipedia.org/wiki/Carbon_sequestration

But then it has a chance to become biomass for bacteria, plants, and fungi instead of atmospheric CO2.

Sealed containers?

A new purpose for Yucca Mountain?

Ideally we'd sequester enough to bring us back down to the 280 ppm we had before we started

Any realistic plan for that is over a century away. By now, it will take luck and hard work to achieve even the 2 degree scenario (2DS), where we have cut net emissions by 60% in 2050 and we reach zero net emissions some time in the 2060s-2070s. Forget about reaching 280 ppm, if we can stabilize at 450 ppm by 2100 it'd be a huge achievement.

Sure, but they asked why we would put energy in the ground. To get back to 280 eventually, is why.

> The problem with sequestering CO2 as hydrocarbons is that you need to put a whole load of energy (embodied in the hydrogen you're combining it with) into the ground and leave it there.

That sounds like a problem into you translate it into "leave rice straw on the fields".

The real thing this article glosses over is how the hydrogen is produced!

95% of hydrogen is produced by splitting hydrocarbons, not by splitting water. Clearly, the assumption is the hydrogen comes from some miracle carbon-neutral source...but it doesn’t.

Isn’t the hydrogen included in the $94 Per ton? And it’s still viable.

No. The prices they quote are JUST getting the CO2 out of the air. Other technologies for getting CO2 from Flue Gas using amines or ammonia have been commercially demonstrated at scale for similar prices.

The hydrogen production, FT reactors, post-treating refinery will cost a lot more.

If you want hydrogen from water, you need electricity. A lot of it. Nuclear reactors will be the most viable way to do that.

Yeah I skimmed through the linked article[1] very quickly, and the word "hydrogen" appears only twice. It does seem like they're glossing over the cost of hydrogen, which wouldn't be cheap if they want to produce fuel. (All the energy stored in the fuel basically comes from hydrogen.)

[1] https://www.cell.com/joule/fulltext/S2542-4351(18)30225-3

The cheap way to obtain hydrogen is to produce it from natural gas, which is of course missing the whole point of CO_2 sequestration.

Well, kinda. You can do methane to hydrogen with CO2 capture and storage.

But my big question is why would you want to convert it into hydrocarbons for transport then? Direct air capture (DAC) is a maybe-way-out-in-the-2050s technology, but even assuming it were readily and cheaply available in large scale today, doing DAC straight to storage and then just using oil and gas like we've always done would be a much cheaper and more efficient method than going what you propose. Basically:

air->CO2->storage AND (CH3)n->burn

versus

air->CO2[a] AND (CH3)n->CO2[b] + H2[b] AND CO2[a] + H2[b] -> (CH3)n->burn AND CO2[b]->storage

(Obviously not taken to be real well-defined balanced chemical reactions).

Why anyone would try to capture CO2 from AIR (at 410 ppm) when you could get it from flue gas (from a power plant), where it exists at tens of thousand of ppm (i.e. %) is beyond me. The technology has been commercially demonstrated to capture CO2 and compress it for about $100/tonne.

The hydrogen is needed for making fuel, but why would it be needed for sequestering?

The carbon is sequestered by turning it into fuel.

No, the carbon is sequestered buy pumping it deep underground. There's no reason to make fuel if you don't plan on burning it.

That's what you do when you sequester it with calcium oxide.

This article is about using carbon dioxide to produce usable fuel, that you would burn. Scaled up it would provide a carbon-neutral solution to long-term energy storage.

The article also mentions sequestering underground, there's just no way to make a profit doing so at the moment.

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