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New Solar Reactor Prototype Unveiled
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."
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?
I can't wait to get one in my house!
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)
Thats what we were all hoping for...
Using the inert molecule CO2 and creating a highly toxic gas is NOT what I would consider a viable commercial device...
If it produced O2, that would make it considerly more interesting.
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.
Sigs are too short to say anything truly profound so read the above post instead.
Easy to print these numbers when you get some of the most amount of sun in the country.
Initial thought: The top half looks almost not at all like it would concentrate light rays into the conversion chamber. But whatever, maybe I'm wrong.
The neat part is generating hydrogen and good old carbon monoxide.
Carbon monoxide is the starting point for Fischer-Tropsch synthesis.
Dog is my co-pilot.
Oh wait..people already answered this question.
Teach me to reply first and read the thread second...
Admit nothing. Deny Everything. Make Counter-accusations.
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.
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Your signature is ominously relevant here.
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. http://en.wikipedia.org/wiki/High-temperature_electrolysis 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 along the side of the tower could be used to channel the salt free water inland. Enough of these could irrigate desert areas such as baja california, namibia, northern africa, or the arabian peninsula. Direct application of solar energy through parabolic concnetrators to water is the way to go. Any comments on why this cannot be used to create large amounts of oxygent, hydrogen, and desalinized water?
So who is going to work on developing the aperture science tech to improve the efficiencies of this method?
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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.
"I assumed blithely that there were no elves out there in the darkness"
Ahh ... Cough ... Cough ... Mmmmm .
No!
-308
100 gge / mo is 1200 gge / yr. And that's actually much better than corn ethanol, which only yields about 270 gge per season.
This should be unsurprising, really. Photosynthesis is extremely inefficient. Take sugar cane for example:
Ethanol fuel in Brazil has a calculation that results in: "Per hectare per year, the biomass produced corresponds to 0.27 TJ. This is equivalent to 0.86 W per square meter. Assuming an average insolation of 225 W per square meter, the photosynthetic efficiency of sugar cane is 0.38%." Sucrose accounts for little more than 30% of the chemical energy stored in the mature plant; 35% is in the leaves and stem tips, which are left in the fields during harvest, and 35% are in the fibrous material (bagasse) left over from pressing.
The plant has only 0.38% total efficiency, and the sucrose is only 30% of that. You can knock off at least another 20% to account for distillation (which is generous). And optimistically you're looking at total efficiency of around 0.01%. So do we really need to improve on 0.07% ?
"I assumed blithely that there were no elves out there in the darkness"
The other solar reactors I've seen similar to this produce useful things, mainly hydrocarbon fuels.
I must admit I'm stumbling over the point of this; Using photovoltaics to electrolyse hydrogen from water/water vapour is easier and doesn't produce CO!!
And the process uses cerium, which is currently only manufactured in China! Another glorious advance of Mao Zedong Thought...
There are a number of ways to produce hydrocarbon fuels from solar energy. This thermochemical cycle is one technology and it is a promising one. Others include solar to electricity followed by electricity to fuel. There is an excellent review article published recently that discusses the relative merits in detail including discussion of the economics.