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Power Earth Transportation

Solar-Powered Tower Produces Carbon-Neutral Jet Fuel from Just CO2, Water, and Sunlight (newatlas.com) 53

Long-time Slashdot reader Bodhammer shared this story of a remarkable solar-powered tower that produces carbon-neutral, sustainable versions of diesel and jet fuel — using only water and carbon dioxide (plus sunlight) as its inputs. One hundred and sixty-nine sun-tracking reflector panels, each presenting three square meters (~32 sq ft) of surface area, redirect sunlight into a 16-cm (6.3-in) hole in the solar reactor at the top of the 15-m-tall (49-ft) central tower. This reactor receives an average of about 2,500 suns' worth of energy — about 50 kW of solar thermal power.

This heat is used to drive a two-step thermochemical redox cycle. Water and pure carbon dioxide are fed in to a ceria-based redox reaction, which converts them simultaneously into hydrogen and carbon monoxide, or syngas. Because this is all being done in a single chamber, it's possible to tweak the rates of water and CO2 to live-manage the exact composition of the syngas. This syngas is fed to a Gas-to-Liquid (GtL) unit at the bottom of the tower, which produced a liquid phase containing 16% kerosene and 40% diesel, as well as a wax phase with 7% kerosene and 40% diesel — proving that the ceria-based ceramic solar reactor definitely produced syngas pure enough for conversion into synthetic fuels....

The team says the system's overall efficiency (measured by the energy content of the syngas as a percentage of the total solar energy input) was only around 4% in this implementation, but it sees pathways to getting that up over 20% by recovering and recycling more heat, and altering the structure of the ceria structure. "We are the first to demonstrate the entire thermochemical process chain from water and CO2 to kerosene in a fully-integrated solar tower system," said ETH Professor Aldo Steinfeld, the corresponding author of the research paper. "This solar tower fuel plant was operated with a setup relevant to industrial implementation, setting a technological milestone towards the production of sustainable aviation fuels."

"The solar tower fuel plant described here represents a viable pathway to global-scale implementation of solar fuel production," reads the study.

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Solar-Powered Tower Produces Carbon-Neutral Jet Fuel from Just CO2, Water, and Sunlight

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  • by PPH ( 736903 ) on Sunday July 24, 2022 @11:43AM (#62729440)

    Looks like we're short about 2499 suns.

    What the hell did they even mean by this? Is that the concentration ratio?

    • by VeryFluffyBunny ( 5037285 ) on Sunday July 24, 2022 @11:47AM (#62729454)
      It means you should wear SPF 2,500 while working around or hear the top of the tower.
      • It means you should wear SPF 2,500 while working around or hear the top of the tower.

        Considering the target temperature (from TFA) is 1,450 C (2,642 F), that still might not help. :-)

    • Yeah, the math seems pretty bad. 169 x 3m^2 panels should give you over 60kW peak electrical power, so about 2-3x that much thermal power. But, if they have calculated their efficiency to only be 4%, that's pretty meh. You are probably better off growing sugar cane or beets and fermenting the sugar.
      • by Anonymous Coward

        Apparently plants are even less efficient than that. Besides, since the inputs are sunlight, CO2, and water, efficiency isn't all that interesting. You can brute-force your way through for a good start, then refine your methods and increase efficiency later. Better 4% efficiency here than 10% efficiency burning coal, or something like that.

        Also, using plants we can eat as feedstock for fuel is generally a bad idea. Using inebile leftovers, different story.

        • by hAckz0r ( 989977 )

          Very true, and you can kind of think of it this way. That small 4% is 100% more than what you get without it.

          If you don't have to pay for the energy used to produce it then this is free fuel. Obviously there are water bills and operating costs that make it not free, so the real criteria is how efficient is the process in terms of manpower for operation and maintenance.

      • The use case scenario is desert lands (not in places where sugar canes can grow).

        • by HiThere ( 15173 )

          Well, they're already talking about recycling the water, but I'd think they'll want to add a separate stage where they feed in brine and extract the water for input to the process. Then process the concentrated brine for the recovery of, O, Iodine or Bromine. Possibly some other things. And, of course, salt.

      • by gtall ( 79522 )

        Yup, it is well-known that the first time a process is invented, it is has reached its maximum potential and all further research should end right there.

      • It's still much more efficient in terms of land usage than photosynthesis, and biological processes are still more tricky then industrial chemistry. However, whether this complicated contraption is a better idea than a flexible, grid-connected electrolyzer seems questionable. For one, in many countries, the latter will work much better since many countries don't have a lot of sunny days and concentrating solutions will have a very low duty cycle for them.
      • by vivian ( 156520 )

        Solar irradiance at the surface is about 1000w/sqm, when the sun is perpendicular to it. These panels track the sun, so they are going to be roughly perpendicular to it at peak. (actually off by half the apparent angle of the sun to the solar tower, for each mirror)

        The small hole into the furnace makes it approximate a black body object, with nearly all the energy going in but very little able to reflect out of the small 15cm window, so it seems to me that most of the energy would be retained in the furnac

        • by MrKaos ( 858439 )

          So 1 day of perfect conditions is going to generate enough fuel to keep a 747 cruising for a bit over 1 minute, which burns the stuff at 240L per minute.

          We are going to need a lot of these, if this is the plan to make jets run on renewable energy.

          For a pilot plant that's quite an achievement. We know with Solar the energetic efficiency of the plant increases as it is scaled up so the same surface area in a larger plant may produce an increased yield of jet fuel relative to the efficiency of the conversion process.

          Even given those inefficiencies the, now fact, that there is a process that can produce quality jet fuel that is also carbon neutral means it is now *possible* to gradually improve it and replace existing jet fuel sources.

          This is really

      • Plants aren't very efficient either, and they require a lot more work (and time) and we'd be a lot better off just continuing to use them for food.

        THIS has been a long time coming. Our methods of solar collection are hugely better than plants, but the problem has always been the biochemical process to convert the energy into hydrocarbon fuel. (since short of nuclear it's by far the densest way to store energy) Our "mastery" of biochem right now is akin to building a fine swiss watch using tools the size o

    • by Junta ( 36770 )

      Duh, it clearly means this tower manages to get a nonillion watts of power from solar. They have solved all our energy problems many many times over.

    • The news article is not clear indeed but from the full paper, the concentration ratio was 2500 in a yearly average, 4000 at peak, where 1 sun = 1 kW/m^2 https://doi.org/10.1016/j.joul... [doi.org]

      However the article says the researchers did not disclose how much litres of actual kerosene their system produced. They disclosed it produced 5191 L of syngas in 9 d at a pressure of 30 bars at the exit. According to http://dx.doi.org/10.2523/iptc... [doi.org] the energy efficiency of GtL is around 60%, so one could calculate how muc

    • by K. S. Kyosuke ( 729550 ) on Sunday July 24, 2022 @12:45PM (#62729588)
      "Suns" is the unit of light concentration (power density relative to unconcentrated direct illumination at a given time and place) but they obviously shouldn't use the concentration factor and "worth of energy" in a single sentence.
    • by Ed_1024 ( 744566 )

      I agree, it is an appallingly bad way of trying to get a point across, and if taken literally would have vaporised the Earth and anything nearby in pretty short order when they turned it on.

      I assume they meant: concentrate the power from the sun so it is 2,500x more intense in this area than from direct sunlight. Why did they not just say that?

    • 30% efficiency is a useful goal to reach. That's typical in the chemical industry.
  • So, will the diesel generated by this be soot-neutral as well as carbon-neutral? If not, I think I'll stick to my electric car, thank-you-very-much.

    • No. It'll be a stop-gap measure for aircraft and other vehicles that for now can't do without the energy density of burning hydrocarbons.
    • by sfcat ( 872532 )
      That's nice you like your EV. I like mine too (I am on my 2nd EV). But there isn't even close to enough Li on Earth to make enough EVs to do any real good. Also, synthetic fuel has far less particulate matter (about 7-15% as much, that's 85-93% less). My next car will be an ICE, I don't want to waste Li on a car. It is one of the more rare elements we use.
      • But there isn't even close to enough Li on Earth to make enough EVs to do any real good.
        Yes there is.
        And Li wont be the main factor for batteries for a long time anyway.

        OTOH, the platinum in your ICE car: that is a rare element.

      • Rare? Lithium is more common than lead or tin [wikipedia.org], there are multiple known reserves with millions of tonnes each and more being registered all the time. It's easily recyclable, and there's also the 230-odd gigatonnes dissolved into seawater, so we're not going to run out anytime soon. Nor would EVs care much if we did run low, since we can make pretty decent batteries out of sodium and lots of other things [wikipedia.org] too.

    • The target is aviation fuel because there won't be transoceanic electric passenger planes any time soon.

  • I've brought up the option for synthesized hydrocarbon fuels before and the usual response is that hydrocarbon synthesis requires electrolysis of water for hydrogen, electrolysis of water for hydrogen is horribly inefficient, so therefore hydrocarbon fuel synthesis will forever be too inefficient to be viable. This demonstration proves we can synthesize hydrocarbon fuels in what is essentially a single step process, and do so without the inefficient process of electrolysis of water for hydrogen.

    This techno

  • Until tech is mature there is little point in non-professional discussion as the general public have nothing to contribute including understanding.

  • Getting cheap pure CO2 or CO without just burning fossil fuel is the hard part, synthesis the easy part.

    • by PPH ( 736903 )

      Getting cheap pure CO2 or CO

      Scrubbing point sources (natural gas fired power plants, cement plants, etc.) isn't that difficult. With an economic incentive, they might make some money selling the stuff.

      Direct atmospheric CO2 scrubbing may not be economical for some time, if ever.

  • I can make coal from just leftover trees and stuff.

    Takes a while, I grant you.

  • by joe_frisch ( 1366229 ) on Sunday July 24, 2022 @09:59PM (#62730786)
    How does this technology compare with building an equal area of solar cells, and using the electricity for electrolysis of water into H2, then react with CO2.

    It might be much more efficient, but the article doesn't provide a good comparison.
    • by AmiMoJo ( 196126 )

      The mirrors must be motorized so they can track the sun, so it depends if you are comparing it to fixed solar panels or motorized ones. Aside from the amount of energy involved, there's the mechanical reliability.

  • The article says (emphasis added):

    Carbon-neutral fuels are drop-in replacements for today's kerosene Jet-A fuel; they mix in with regular fuel and get burned in jet engines as per normal, producing the normal amount of carbon emissions. The difference is that rather than pulling that carbon straight out of the ground, carbon-neutral fuels grab CO2 from elsewhere; it'll still end up in the atmosphere, but at least it does some useful work before it gets there, and every gallon burned is a gallon of conventio

  • Hurray! Global warming has now been solved. Now that that's taken care of, can we please move on to other subjects, like how many aliens are in one of those UFOs?

Truly simple systems... require infinite testing. -- Norman Augustine

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