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New Solar Reactor Prototype Unveiled

Soulskill posted more than 3 years ago | from the bright-ideas dept.

Earth 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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Photon-specific or driven by temperature? (2)

otis wildflower (4889) | more than 3 years ago | (#34662380)

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?

Re:Photon-specific or driven by temperature? (1)

wizardforce (1005805) | more than 3 years ago | (#34662490)

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.

Re:Photon-specific or driven by temperature? (1)

karnal (22275) | more than 3 years ago | (#34663156)

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.

Re:Photon-specific or driven by temperature? (2)

KibibyteBrain (1455987) | more than 3 years ago | (#34663398)

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 allow more flexible, if even a bit less efficient ways of converting heat to energy in "constant heat source" applications produce higher average power output from the same source.
That is probably why these researchers are pushing it for solar power applications, as its strengths(fair decent efficiency for the cost) stand but its [obvious] negatives(cycling) are a built in limitation of all solar power systems.

Re:Photon-specific or driven by temperature? (0)

Anonymous Coward | more than 3 years ago | (#34673296)

Are you suggesting that the operation of this cycle would be like: heat up the ceria by concentrated sunlight all day, then at night as it cools, expose the reduced ceria to H2O or CO2 to split them? You would need to move ceria through the hot zone all day, and then back through it at lower temperature all night. This would be a very different design than any of the thermochemical reactors being studied where they just cycle the material into the sunlight and back out again (e.g. on a rotary).

Re:Photon-specific or driven by temperature? (1)

benjamindees (441808) | more than 3 years ago | (#34663242)

I imagine it involves somewhat high temperatures. But both of your examples should work fine.

This is great (0)

Anonymous Coward | more than 3 years ago | (#34662384)

I can't wait to get one in my house!

Hmmm (2)

rossdee (243626) | more than 3 years ago | (#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:Hmmm (2, Interesting)

Anonymous Coward | more than 3 years ago | (#34662410)

Carbon monoxide can be combined with hydrogen to create methane.

Re:Hmmm (3, Informative)

otis wildflower (4889) | more than 3 years ago | (#34662422)

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.

Re:Hmmm (1)

cgraves (1213828) | more than 3 years ago | (#34673334)

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 [scientificamerican.com] and supply it in a concentrated form to the solar reactor.

Re:Hmmm (0)

Anonymous Coward | more than 3 years ago | (#34662434)

CO can be reacted with hydrogen to produce "syngas" http://en.wikipedia.org/wiki/Syngas

Re:Hmmm (4, Informative)

wizardforce (1005805) | more than 3 years ago | (#34662464)

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+2H2+CH2O => ethylene glycol via hydroformylation
2CO+5H2 => ethanol + H2O via anaerobic fermentation
etc. etc. etc.

Re:Hmmm (0)

Anonymous Coward | more than 3 years ago | (#34662576)

Not many concentration camps? You don't read much do you.

Re:Hmmm (0)

GigsVT (208848) | more than 3 years ago | (#34662812)

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

Re:Hmmm (1)

dbIII (701233) | more than 3 years ago | (#34664128)

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.

CO2 to CO. What WHAT? (0)

Anonymous Coward | more than 3 years ago | (#34662416)

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.

Re:CO2 to CO. What WHAT? (3, Informative)

wizardforce (1005805) | more than 3 years ago | (#34662474)

1) CO is very useful industrially being used to produce various organic molecules including Methanol, Acetic acid, catalytic metal complexes, hydrocarbons, alcohols etc.

2) this process does produce oxygen:
2Ce2O3 + 2CO2 => 2CO + 4CeO4
4CeO4 + extreme heat => 2Ce2O3 + O2

not new (3, Informative)

wizardforce (1005805) | more than 3 years ago | (#34662426)

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 [wikipedia.org] 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.

Re:not new (1)

Black Gold Alchemist (1747136) | more than 3 years ago | (#34662596)

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 away from the solids. The problem that occurs in these cycles is that the solids are powdered, and as they cycle through the system, the grains of the powder fuse together, reducing surface area, and thus reaction rate. Interestingly, this same process occurs in rechargeable batteries, and leads to their failure. Maybe robots can grind up the solids and increase their surface area?

In addition, in the sulfur iodine cycle, you've got SOx and I2 gases on the lose at high temperature. This can corrode the containers of the system.

My hope is that these thermochemical engines can crack aluminum and zinc oxides down to the metals. Then we can have engines reduce the metals, and use them in metal-air fuel cells. Metallic fuels are much cheaper and less of a hassle than hydrogen.

Re:not new (2)

Gibbs-Duhem (1058152) | more than 3 years ago | (#34664302)

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, certainly far higher than solar PV + electrolysis, but the catalysts just don't last very long at high temperatures.

That said, I'm excited that if it's getting in the news, new or not, because it improves my odds of getting funding to use that tech. The more people working on it, the safer of a bet it will look like to funding agencies. It's a robust, efficient, and cheap technology that should be used everywhere. Just a question of who will solve the catalyst stability and reactor material problems first.

Re:not new (2)

Black Gold Alchemist (1747136) | more than 3 years ago | (#34664554)

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 batteries (will explain)

The Gaz de France (see slide show [stanford.edu] slide 26) runs as follows:
1. K2O2(l) + H2O(g) -> 2KOH(l) + O2(g) at 100 C
2. 2KOH(l) + 2K(g) -> 2K2O(l) + H2(g) at 725 C
3. 2K2O(l) -> 2K(g) + K2O2(l) at 850 C
Yes. That's potassium. All liquids and gases. No gas-gas separation. If this could really work, I'm sure there's a modification to it to produce elemental potassium. In that case, you can reduce mostly anything.

The idea with heat rechargeable batteries was as follows - using tin and iron as an example:
1. Fe + H2O + SnO -> Fe(OH)2 + Sn (aqueous battery - produces electrical current)
2. Sn + H2O -> SnO + H2 (corrosion of the tin - likely with heat)
3. Fe(OH)2 + H2 -> Fe + 2H2O

So it is an electrochemical heat engine. I know tin would likely make life more difficult by forming SnO2 but I left this out to illustrate the way the cycle works. You need two metals, call them A and B. A has to have as negative an electrode potential as possible but still be reducible by hydrogen. Iron fits the bill. Metal B has got to have as positive an electrode potential as possible but still be able to hydrolyze. Tin fits the bill. Copper would be better, but as far as I know, the reaction of copper with water to form hydrogen just does not proceed.

That said, I'm excited that if it's getting in the news, new or not, because it improves my odds of getting funding to use that tech.

Good. This tech needs a heck of a lot more funding. It's basically ignored - you read the news, you hear about EV's, fuel cells, solar panels, etc. But you almost never hear about thermochemical engines. The way I think about it, a solar panel is like a Ferrari. It's expensive and fun, but not a great way to cross Africa. A thermochemical engine is like a Toyota Landcruiser. It's durable, it's cheap, and it gets the job done. Have you heard of anyone getting VC funding for this thermochemical stuff?

Re:not new (1)

Gibbs-Duhem (1058152) | more than 3 years ago | (#34665408)

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.

http://www.sundropfuels.com/ [sundropfuels.com]

Re:not new (1)

Black Gold Alchemist (1747136) | more than 3 years ago | (#34666442)

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.

Re:not new (1)

cgraves (1213828) | more than 3 years ago | (#34673238)

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% [technologyreview.com]) combined with high-efficiency high temperature electrolysis (>90%, see here [doi.org] and here [wikipedia.org]). So far no thermochemical cycle has been demonstrated to achieve such a high efficiency.

Second, it is not about efficiency. In many cases one can achieve very high efficiency at the expense of using expensive materials. The idea here is to use cheap ceria-based oxide materials in the solar thermochemical reactor instead of expensive high-purity silicon semiconductors and other semiconducting materials in photovoltaics or photoelectrochemical cells.

Caltech on pluto ? (0)

Anonymous Coward | more than 3 years ago | (#34662430)

Easy to print these numbers when you get some of the most amount of sun in the country.

Solar Funnel? (0)

Anonymous Coward | more than 3 years ago | (#34662446)

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.

Carbonmonoxide? (-1, Flamebait)

f3rret (1776822) | more than 3 years ago | (#34662616)


This thing turns a relatively nontoxic gas into a highly toxic one? How exactly is this useful?

Ideal Process Description (4, Informative)

Black Gold Alchemist (1747136) | more than 3 years ago | (#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.

Re:Ideal Process Description (2)

Gibbs-Duhem (1058152) | more than 3 years ago | (#34664324)

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 synthesis?

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

Next, you claim a 50-60% efficiency in converting to gasoline? Are you just making stuff up as you go along? The thermochemical cycle has a pretty decent amount of loss simply in the requirement that you cool down and heat up the precursors. Hard to move heat around without losses and all. Not to mention the chemical inefficiencies, plus regular thermal losses, plus mirror losses. 20% is an excellent estimate of the maximum photon to chemical conversion efficiency. Now, cost efficiency on the other hand... mirrors are way cheaper than PV panels, so in that regard you're talking about a 20-fold improvement to energy cost efficiency.

Disclaimer: I work on this professionally, so I'm biased.

Re:Ideal Process Description (1)

Black Gold Alchemist (1747136) | more than 3 years ago | (#34664484)

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 oxide. Maybe 20% is more reasonable.

Re:Ideal Process Description (1)

Gibbs-Duhem (1058152) | more than 3 years ago | (#34665440)

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 is very mature, more mature in fact than alcohol synthesis from syngas. It is costly, but it's very well understood.

Re:Ideal Process Description (1)

Eclipse-now (987359) | more than 3 years ago | (#34668376)

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 could even be fast-charge stations on highways.

Now imagine that we save the precious gasoline for heavy vehicles, trains, and jets. This is doable! I wish the developers in this field the best of luck.

Life imitating art again (1)

JustNiz (692889) | more than 3 years ago | (#34662798)

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

better use for solar concentrator (1)

fadethepolice (689344) | more than 3 years ago | (#34662844)

direct application of solar energy would probably be more efficient if concentrated directly on water. http://en.wikipedia.org/wiki/High-temperature_electrolysis [wikipedia.org] 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?

Aperture Science (1)

SeanTobin (138474) | more than 3 years ago | (#34662962)

So who is going to work on developing the aperture science tech to improve the efficiencies of this method?

Not bad (1)

benjamindees (441808) | more than 3 years ago | (#34663228)

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

Oops (1)

benjamindees (441808) | more than 3 years ago | (#34663980)

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. [wikipedia.org]

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% ?

Re:Oops (1)

dgatwood (11270) | more than 3 years ago | (#34664158)

It's still almost two orders of magnitude lower than state-of-the-art photovoltaics (currently just over 42%). Even their ideal theoretical goal is less than half what PVs can do, though it is somewhat interesting in that it provides one possible solution to the "power at night" problem. So yeah, we really need to improve on 0.07%. A lot.

I realize that storage for PV systems is hard, but that doesn't mean we should necessarily abandon the concept in favor of a completely different means of power production. Maybe, maybe not. Time and the market will decide. :-)

RE: New Solar Reactor Prototype Unveiled (0)

Anonymous Coward | more than 3 years ago | (#34663372)

Ahh ... Cough ... Cough ... Mmmmm .



This is useful because...? (0)

Anonymous Coward | more than 3 years ago | (#34664860)

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!!

China Wins Again (0)

Anonymous Coward | more than 3 years ago | (#34665836)

And the process uses cerium, which is currently only manufactured in China! Another glorious advance of Mao Zedong Thought...

Technologies for solar-driven CO2-to-fuel (0)

Anonymous Coward | more than 3 years ago | (#34673054)

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 [doi.org] published recently that discusses the relative merits in detail including discussion of the economics.

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