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Scientists Recycle CO2 with Sunlight to Make Fuel
An anonymous reader brings us this article from Wired about a new method to produce fuel with the help of concentrated sunlight and carbon dioxide. The process "reverses" combustion, breaking down the CO2 into carbon monoxide, which is then used as a building block for hydrocarbons. Quoting:
"The Sandia team envisions a day when CR5s are installed in large numbers at coal-fired power plants. Each of them could reclaim 45 pounds of carbon dioxide from the air daily and produce enough carbon monoxide to make 2.5 gallons of fuel. Coupling the CR5 with CO2 reclamation and sequestration technology, which several scientists already are pursuing, could make liquid hydrocarbons a renewable fuel."
My grandfather used to be an employee in a biotechnology venture in the 30's. It was a two stage process. The first was a corn - or sometimes a potato - plant. The second was a still. ( He was a tinsmith. ) The input was CO2 and sunlight, the output was ethanol.
It enables people to not have to change everything overnight. We have a big investment in carbon based fuel processes, so having away to create hydrocarbons which we then burn, and create CO2, then use solar energy to repeat the process means that hydrocarbons are now just an intermediate step, and that we have a dynamic equilibrium, and can forgo the pain of trying to get rid of all our petrol engines and replace them with fuel cell engines. At least, this won't have to be done overnight, and we actually do stop the increase in greenhouse gases, because we recycle them.
If it works, it is a clever solution.
"Wouldn't it make more sense to make electricity directly from the solar energy and not involve the coal at all?"
To some extent, yes. The main problem is that electricity produced needs to be (almost) instantly consumed. Chemical storage of the energy avoids that problem. As such, there are various forms of chemical energy storage, ranging from batteries, through hydrogen, through ammonia to hydrocarbons, all with their own problems and advantages.
With batteries, the main trouble is they store too little and they (comparatively) rapidly break down.
Fuel cells can run on hydrogen or ammonia, with varying success. Hydrogen is a PITA to store, but perhaps ammonia is a simpler compromise.
Or hydrocarbons. Which have the advantage of being easy to store and fairly stable.
The thing about the energy crisis is there is no lack of energy (in fact, global warming is in essense an excess of it, and provides excesses of it in the form of weather). There's just a huge problem of extracting, transporting and, above all, storing that energy so you can use it when and where you need it.
perhaps ammonia is a simpler compromise
And unlike gasoline, you wouldn't have to clean up an ammonia spill. In ammonia-fueled car, fuel spill cleans you!
It's nice that it might scrub pollutants but it seems the solar energy could be more profitably used to directly produce electricity.
Great idea in the equatorial region, but solar really doesn't count as an option in the polar two-thirds of the planet (at least not until we have near-100% efficient PV panels that cost a pittance).
I would also point out that very few companies seem to want to build solar power plants, even in ideal places such as the vast tracts of desert wasteland in the US SouthWest. I presume this results because the long term costs might look great, but the books would take a big hit up front, and most companies (or at least, their current boards) couldn't care less beyond next quarter.
Given those two facts, we can either talk endlessly about why we don't use cool-tech-X, or we can deal with the reality we have now: We use a LOT of cheap and dirty coal power plants. And it costs considerably less to retrofit them with spiffy scrubbers such as TFA mentions than it does to rebuild new clean plants.
Also, who says only power plants can use this? Why couln't I (and everyone else who might care enough to give something like this a try) buy one (probably a scaled-down version to make it affordable) and toss it in my backyard? Five or ten tons a year, times a few hundred thousand people who want a free gallon or two of gasoline per day, could really make a difference.
No one renewable energy source will solve all our problems. Between them all, however, perhaps we can at least keep the planet habitable for a few more generations of humans.
I am working on a similar process that synthesizes hydrocarbon fuels from carbon dioxide, water, and non-fossil energy (could be solar) and should eventually have some publications out about this. There are several ways to go about this. But first, let me comment on some of the comments:
... all this thing does right now is produce carbon monoxide." comment, reducing CO2 to CO is the hardest part of the process. Once you have concentrated CO, you can follow the coal-to-liquids processes and water-gas shift (CO + H2O => CO2 + H2) to get hydrogen and run the syngas (CO + H2 mixture) into Fischer-Tropsch reactors. They've been doing this for 50 years in South Africa to produce synthetic diesel.
Regarding the "They're leaving the production of actual liquid fuel to other people
Regarding the "Renewable not!" comment and using power-plant flue gas CO2 as the input to this process, this would indeed not be sustainable. However, if industrial capture of CO2 from the air is available, one can fully close the loop and have a sustainable hydrocarbon fuel cycle. Flue gas CO2 could be a good option in the short term, however. For instance, if solar and other nearly-carbon-free energy sources begin to rapidly take over, coal plants will not immediately be shut down. Other CO2-emitting industrial plants such as aluminum smelters, etc, will also have CO2 emissions to deal with, and this form of using it to store non-fossil energy by recycling it once as a liquid fuel would be worthwhile. One comment discussed this transition well.
Related, other comments say "why not just use the solar energy to produce electricity". These intermittent resources need storage, and liquid fuel storage is not a bad method (and very versatile). Others responded about storage.
So, processes like this are a way to store non-fossil energy as a convenient energy-dense fuel which can be used in our existing petroleum fuel infrastructure and vehicles (as opposed to hydrogen and batteries). Biofuels can do the same, and there are many comments above ("I saw something like this... it's called a tree") mentioning biofuels and how this process replicates it with much more complexity; indeed you could call this whole process including the Fischer-Tropsch fuel synthesis "artificial photosynthesis". However, this process cuts out the middle-man of the plant in biofuels processes, which has much lower sunlight-to-fuel efficiency than industrial solar collectors (PV or thermal) and requires a lot of fertilizers and pesticides to boost growth rate. Such land- and resource-intensive agriculture is not sustainable in its current form and may not ever be on the scale we will need it.
TFA discusses a solar-heat-driven thermochemical process that has potential. A somewhat similar solar-heat thermolytic process splits CO2 directly at higher temperatures. There are many other methods of accomplishing this that are at different levels of development and being researched, including electrochemical (pdf link1, pdf link2), photoelectrochemical, photo(bio)chemical...