This a neat idea. If it can be properly miniaturized to allow the design of an efficient insulationand heat transfer system it may well be useful. What is useful is the production of carbon monoxide and hydrogen in exchangefor the solar input.
Even splitting out the two components may be the answerin terms of economics. At least it givesus an independent source of hydrogen that is not costing us good fuel. So this protocol may really have a future insome application or the other.
Ultimately this is a heat engine system doing the samething as the mirror systems, but possibly a lot cleverer.
New solar fuel machine 'mimics plant life'
By Neil BowdlerSciencereporter, BBC News
In the prototype, sunlight heats a ceriacylinder which breaks down water or carbon dioxide
A prototype solar device has been unveiled which mimicsplant life, turning the Sun's energy into fuel.
The machine uses the Sun'srays and a metal oxide called ceria to break down carbon dioxide or water intofuels which can be stored and transported.
Conventional photovoltaicpanels must use the electricity they generate in situ, and cannot deliver power at night.
Details are published in thejournal Science.
The prototype, which wasdevised by researchers in the US and Switzerland
Ceria has a naturalpropensity 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 rapidlystrip the oxygen from them as it cools, creating hydrogen and/or carbonmonoxide.
Hydrogen produced could beused to fuel hydrogen fuel cells in cars, for example, while a combination ofhydrogen and carbon monoxide can be used to create "syngas" for fuel.
It is this harnessing ofceria's properties in the solar reactor which represents the majorbreakthrough, say the inventors of the device. They also say the metal isreadily available, being the most abundant of the "rare-earth"metals.
Methane can be produced usingthe same machine, they say.
Refinements needed
The prototype is grosslyinefficient, the fuel created harnessing only between 0.7% and 0.8% of thesolar energy taken into the vessel.
Most of the energy is lostthrough heat loss through the reactor's wall or through the re-radiation ofsunlight back through the device's aperture.
But the researchers areconfident that efficiency rates of up to 19% can be achieved through betterinsulation and smaller apertures. Such efficiency rates, they say, could makefor a viable commercial device.
"The chemistry of thematerial is really well suited to this process," says Professor SossinaHaile of the California Institute of Technology (Caltech). "This is thefirst demonstration of doing the full shebang, running it under (light) photonsin a reactor."
She says the reactor could beused to create transportation fuels or be adopted in large-scale energy plants,where solar-sourced power could be available throughout the day and night.
However, she admits the fateof this and other devices in development is tied to whether states adopt alow-carbon policy.
"It's very much tied topolicy. If we had a carbon policy, something like this would move forward a lotmore quickly," she told the BBC.
It has been suggested thatthe device mimics plants, which also use carbon dioxide, water and sunlight tocreate energy as part of the process of photosynthesis. But Professor Hailethinks the analogy is over-simplistic.
"Yes, the reactor takesin sunlight, we take in carbon dioxide and water and we produce a chemicalcompound, so in the most generic sense there are these similarities, but Ithink that's pretty much where the analogy ends."
Daniel Davies, chieftechnology officer at the British photovoltaic company Solar Century, said theresearch was "very exciting".
"I guess the question iswhere you locate it - would you put your solar collector on a roof or would itbe better off as a big industrial concern in the Sahara and then shipping theliquid fuel?" he said.
Solar technology is movingforward apace but the overriding challenges remain ones of efficiency, economyand storage.
New-generation "solar tower"plants have been built in Spain and the United States
A new Spanish project will use moltensalts to store heat from the Sun for up to 15 hours, so that the plant couldpotentially operate through the night.
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