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Earth Power Technology

New Solar Reactor Prototype Unveiled 50

chrb writes "Scientists from the California Institute of Technology and the Swiss Federal Institute of Technology have unveiled a new solar reactor prototype that directly converts carbon dioxide or water into carbon monoxide or hydrogen, respectively. The abstract is available in Science. Quoting the BBC writeup: 'The prototype ... uses a quartz window and cavity to concentrate sunlight into a cylinder lined with cerium oxide, also known as ceria. Ceria has a natural propensity to exhale oxygen as it heats up and inhale it as it cools down. If, as in the prototype, carbon dioxide and/or water are pumped into the vessel, the ceria will rapidly strip the oxygen from them as it cools, creating hydrogen and/or carbon monoxide. ...The prototype is grossly inefficient, the fuel created harnessing only between 0.7% and 0.8% of the solar energy taken into the vessel. Most of the energy is lost through heat loss through the reactor's wall or through the re-radiation of sunlight back through the device's aperture. But the researchers are confident that efficiency rates of up to 19% can be achieved through better insulation and smaller apertures. Such efficiency rates, they say, could make for a viable commercial device."
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New Solar Reactor Prototype Unveiled

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  • by otis wildflower ( 4889 ) on Friday December 24, 2010 @06:38PM (#34662380) Homepage

    Looks like they focus light to heat the catalyst, but don't do anything that's specific to photons?

    Why wouldn't this work with, say, thorium reactors or wind power or any other means to generate adequate heat for the reactions?

    • It is purely a thermochemical cycle. It doesn't interact directly with visible light but instead uses the heat produced from the absorbsion of visible light to crack water and carbon dioxide.

      • by karnal ( 22275 )

        Right - but why can't you use other sources of "waste heat" to do this work? Sunlight might not be the most readily available source of heat in certain situations.

        • Sunlight naturally allows this thermochemical cycle to occur, assuming that the device is allowed to cool at night. With other heat sources(geothermal, etc), you would need to remove the device to cut off the heat source for the "off" period of the duty cycle. Also, that makes this device less appealing than it might seem, as this "19%" efficiency cited doesn't mean you only get even 19% of the heat power of your source put in as power out, but thats only during the "on" period of the duty cycle. This may a
    • Like my CPU?
    • I imagine it involves somewhat high temperatures. But both of your examples should work fine.

  • by rossdee ( 243626 ) on Friday December 24, 2010 @06:41PM (#34662390)

    It could be a useful way to produce hydrogen, but whats the point of making Carbon Monoxide? Is there a market for that? (Not many concentration camps around these days)

    • Re: (Score:2, Interesting)

      by Anonymous Coward

      Carbon monoxide can be combined with hydrogen to create methane.

    • Re:Hmmm (Score:4, Informative)

      by otis wildflower ( 4889 ) on Friday December 24, 2010 @06:46PM (#34662422) Homepage

      If it can be used to manufacture methane (or, ideally, longer hydrocarbons such as butanol) it can be used to generate carbon-neutral vehicle fuel from water and atmospheric CO2.

      • I think you are missing a step. If you just put atmospheric air through such a reactor, you might split the CO2 to CO but it will be in a gas stream with 99.96% other gasses (N2 and O2).. then you must separate the CO. Might as well separate the CO2 up front and avoid wasting all that energy heating up so much excess gasses. One can capture CO2 from the air [] and supply it in a concentrated form to the solar reactor.
    • Re:Hmmm (Score:5, Informative)

      by wizardforce ( 1005805 ) on Friday December 24, 2010 @06:53PM (#34662464) Journal

      If only you knew just how useful Carbon Monoxide is in industrial synthesis. Methanol, Acetic acid, Oxalic acid, various synthetic hydrocarbons, catalytic metal complexes like Co2(CO)8, ethylene glycol and a ton of others.
      CO+3HS => CH4 + H2O
      CO+2H2 => CH3OH
      CO+CH3OH => CH3COOH
      CO+2H2+CH2O => ethylene glycol via hydroformylation
      2CO+5H2 => ethanol + H2O via anaerobic fermentation
      etc. etc. etc.

    • by GigsVT ( 208848 )

      Carbon monoxide is flammable. Most people don't know this. You can directly burn carbon monoxide as a fuel.

    • by dbIII ( 701233 )
      It's a really good reducing agent that would be a lot easier to ship about than hydrogen and could be useful in chemical production.
  • not new (Score:4, Informative)

    by wizardforce ( 1005805 ) on Friday December 24, 2010 @06:47PM (#34662426) Journal

    This is water thermochemical cracking and it isn't new. Not by a long shot. Most of the attention has been on the Sodium Manganese, Sulfur Iodine and this cycle which really hasn't been terribly efficient comparatively. The Cerium cycle which this thermochemical cracking system uses works at a much higher temperature than the other cycles as well. See here [] for details.

    Water thermochemical cracking is probably the most efficient method of converting solar energy to chemical energy that we have, perhaps that even exists considering the inefficiency of electrolysis.

    • All those cycles you've mentioned involve nasty chemicals, non-trivial separation or both. For example, one step in the sulfur iodine cycle is the conversion of sulfuric acid into its components:
      H2SO4 -> H2O + SO2 + 1/2O2

      The problem is that all these components are gasses, and they have to be separated as perfectly as possible (we don't want SOx in the air). So, as a result, a lot of expensive components are needed. With the sodium manganese, iron, and cerium cycles, you simply have to pump gasses aw
      • Disclaimer: I work on this professionally, so I have a vested interest.

        There are other well known cycles. Ceria is one of them. So is iron oxide, cobalt oxide, and a few others. Those are solids. I think the solids have a lot more potential than the gases. Ceria is actually what I did my PhD thesis on, and it's my favorite contender. We use it for water splitting and chemical reduction (the same thing they did at caltech), but I'm rather surprised their efficiency is so low. We get quite a lot higher, certa

        • Disclaimer: I work on this professionally, so I have a vested interest.

          Cool. I'm a highschool student with a chemistry interest. Thermochemical engines were a subject I dug into a while back. I wrote a program using Gibbs free energy data from NIST to automatically balance and find the equilibrium constant of the reactions. I used this program to try to predict the outcomes of various reactions for cycle construction. I looked through the data and I found the following cycles to be interesting:
          Gaz de France (will explain)
          Heat rechargeable batte

          • I'm not aware of any systems that are robust enough to be used commercially yet, but they aren't terribly far away. I would be surprised if it goes more than 2-3 more years before at least someone is doing it.

            I know that this company is doing something related, although non-catalytic. It's some pretty ninja chemistry though.


            • Sundrop, AFAIK, is doing a solar-assisted biomass to liquids program. What they appear to be doing is gasification with:
              CxHyOz + H2O -> CO2 + CO + H2O + H2

              Instead of:
              CxHyOz + O2 -> CO2 + CO + H2O + H2

              So it's not thermochemical - it's biomass to liquids. But it's a heck of a lot more efficient than say, corn ethanol.
    • Water thermochemical cracking is probably the most efficient method of converting solar energy to chemical energy that we have, perhaps that even exists considering the inefficiency of electrolysis.

      First, with present technology, this is incorrect. Using solar photovoltaic plus electrolysis to produce fuels (hydrogen, carbon monoxide, or a mixture (syngas) appropriate for liquid hydrocarbon fuel synthesis) can be done with >30% sunlight-to-syngas efficiency using expensive concentrated photovoltaics ( ~40% []) combined with high-efficiency high temperature electrolysis (>90%, see here [] and here []). So far no thermochemical cycle has been demonstrated to achieve such a high efficiency.

      Second, it is

  • by Black Gold Alchemist ( 1747136 ) on Friday December 24, 2010 @07:41PM (#34662688)
    Here's just a description of the reactions and why you want CO and gasoline. You want gasoline as the end product because gas is our infrastructure. You don't want methane, alcohol, or some other fuel, because conversion of vehicles to such fuels is virtually impossible with EPA regulations. Instead you want normal (though high octane) gasoline fuel.

    What you get with this system is overall:
    CO2 + H2O + heat -> gasoline + O2

    The first step is to reduce CO2 and H2O:
    Ce2O3 + CO2 -> 2CeO2 + CO (at low temperature)
    Ce2O3 + H2O -> 2CeO2 + H2 (at low temperature)
    4CeO2 + heat -> 2Ce2O3 + O2 (high temperature)

    Next, it you don't have the right mixture of CO2 to H2O, you can do the following:
    CO2 + H2 + heat <-> CO + H2O

    Next, you create methanol:
    CO + 2H2 -> H3COH

    Finally, you create gasoline via the methanol to gasoline process:
    H3COH -> gasoline + H2O

    Now, where do you get the CO2? From CO2 traps, like soda lime:
    CO2 + Mg(OH)2 -> MgCO3 + H2O (in alkaline solution)
    MgCO3 + heat -> MgO + CO2 (heat)

    You could power this CO2 trapper off of waste heat from the engine. This system could be up to 50-60 percent efficient at converting solar energy into gasoline. This is a vast improvement of biofuels, which are often less than 1% efficient. Gasoline engines are only 10% efficient, so the scheme is less efficient than electric cars + solar panels. However, the hydrogen and CO (especially) could be used as reducing agents to reduce metals such as iron and zinc. These metals would then be burned in metal-air fuel cells to provide power on demand. You also need hydrogen to produce ammonia and other industrial chemicals.
    • And with solid-oxide fuel cells, you can use liquid gasoline or diesel instead of H2 gas for a fully electric vehicle.. []

    • What on earth are you talking about? The process of thermochemical reduction is going to be:

      CO2 -> CO + O* (where * represents O absorbed by the supports change in oxidation state).
      O* -> O2 (oxygen released during temperature change and accompanying change in oxidation state).

      Yeah, you can mix it with water as well, but why not just do them separately and produce CO and H2 in two tanks which can be combined to get whatever carbon number you want on average in your fuel after a one-step fischer-tropsch

      • What on earth are you talking about? The process of thermochemical reduction is going to be:...

        I understand you're reactions, but I'm giving the basic chemical equations, so I don't have O* on the surface, I have Ce2O3 + 1/2O <->2CeO2. I have the H2 and CO listed so that I don't repeat the reactions.

        You have this thing going through methanol? Huh? These are all going to decrease your overall yield.

        I have it going through methanol, because methanol synthesis and methanol to gasoline are (at least relatively) proven processes AFAIK. The claimed 50-60 percent is the maximum theoretical efficiency. I believe I've read a paper with 20% practical solar->hydrogen efficiency with zinczinc oxid

        • Okay. I'd buy 50-60 percent as a maximum theoretical, I guess if you assume a carnot cycle since this is done at 1200-1400C most often.

          The fischer-tropsch process was developed in 1926. It is extremely mature, and was used by Germany in WWII to produce nearly all of their gasoline and diesel from syngas. South Africa did similarly. In both cases it was for the same reason; they wanted to take gasified coal and convert it to liquid fuels because trade embargoes prevented importing those liquids.

          The reaction

    • Gasoline engines are only 10% efficient, so the scheme is less efficient than electric cars + solar panels.

      This is a good point! Imagine we build a fleet of GenIV nuclear reactors which could power the world for 500 years just on the nuclear waste we already have sitting around. That's reliable, baseload power despite the weather or season or that other great problem solar advocates don't like to mention, 'the night'. Now imagine most cars are Electric, and just charge at home or work or the shops. There c

  • This sounds eerily similar to the Solex device that Scaramanga stole in the movie "The Man With the Golden Gun".

  • direct application of solar energy would probably be more efficient if concentrated directly on water. [] This method would probably be a great way to purify seawater. If you had a farm of parabolic solar concentrators focused on a highly efficient heat conductive material. Run the material to a sheltered cove of seawater under a tower. Use solar energy (hydrolysis? and fuel cells?) to cool the top of the tower to assist condensation. Runners alo
  • So who is going to work on developing the aperture science tech to improve the efficiencies of this method?

  • Abstract isn't free. The summary doesn't say what size vessel they use. But cerium oxide is about $15 / lb []. At 0.07 percent efficiency, given global average insolation, that gives you about 100 gge / acre / month []. Not bad at all. Not as good as corn ethanol, but corn doesn't grow in the desert.

...there can be no public or private virtue unless the foundation of action is the practice of truth. - George Jacob Holyoake