Future fuels for everyone powered by the sun

Apr 07, 2011 By Holly Bigelow Martin
Sossina Haile and William Chueh next to the benchtop thermochemical reactor used to screen materials for implementation on the solar reactor. Credit: California Institute of Technology

(PhysOrg.com) -- New scheme would use only sunlight, air and water to supply energy for cars, laptops, GPS systems.

"At the California Institute of Technology, they're developing a way to turn sunlight and water into fuel for our cars."--President , Jan. 25, 2011

The Sun is Earth's primary energy source and harnessing its abundant light is the Holy Grail of renewable energy

Now, a group of scientists has demonstrated a new way to use sunlight, water (H2O) and (CO2)--some of the cheapest and most commonplace stuff on Earth--to make unlimited amounts of fuel to power almost anything, anywhere.

The method uses concentrated heat from the sun to convert water and carbon dioxide into hydrogen (H2) or carbon monoxide (CO). Large amounts of these two gases could be combined to make that fits into America's existing energy economy.

"Alternatively, you could use the H2 and CO to make methane (natural gas) for a gas-fired electricity generator," said Sossina Haile, professor of and of Chemical Engineering at California Institute of Technology in Pasadena. "Or, because the fuels we produce are so pure, they could be easily used to run fuel cells, which generate power very efficiently."

Future fuels for everyone powered by the sun
The ETH-Caltech solar reactor for producing hydrogen and carbon monoxide from water and carbon dioxide via the two-step thermochemical cycle with ceria. Credit: California Institute of Technology

The researchers say one of the most exciting things about the discovery is its versatility. "We are not dictating to the user what the should be," Haile said. "We are making solar energy easy to use by putting it into a form that our industry is used to seeing and making it available on demand."

Doing the two-step

Scientists have long known how to convert water and carbon dioxide into hydrogen and carbon monoxide. But to do it cheaply and efficiently enough to make the process affordable on a wide scale has been the issue. Part of the problem was the need for expensive and rare elements, such as platinum or , to act as catalysts that encourage the conversion to happen.

So Haile and her team took a novel approach; they tried ceria, a material used in the walls of self-cleaning ovens. Ceria is the oxidized or "rust" form of the element cerium, which is more abundant, and therefore cheaper, than other metals that could do the same job.

The new method requires two steps, the first at high temperature using concentrated heat from the sun (about 3,000 degrees Fahrenheit), and the second at a much lower temperature.

Haile describes the process this way, "If we heat ceria up, the material 'naturally' releases some oxygen from its structure. If we then cool it back down, those oxygen vacancies want to be refilled. In other words, the ceria 'exhales' oxygen at high temperature and then 'inhales' it back when the temperature is lowered."

To make fuel, the second step requires the presence of water and carbon dioxide gases. "At lower temperatures, the cerium, the hydrogen and the carbon all want the oxygen, but the cerium wants it most," Haile said. "So the oxygen vacancies in the ceria are filled by stripping oxygen from H2O and CO2, leaving H2 and CO."

An international collaboration

Haile and her Caltech team, supported by an award from the National Science Foundation, recently published a paper describing the breakthrough in the journal Science. For this project, they collaborated with researchers led by Aldo Steinfeld, a renewable energy technology professor at the Swiss Federal Institute of Technology, also called ETH Zürich, in Switzerland. Steinfeld also leads the Solar Technology Laboratory at the Paul Scherrer Institute in Switzerland.

The ETH-Caltech solar fuel reactor uses concentrated heat from the sun to create fuel from water and carbon dioxide. Credit: California Institute of Technology (Caltech) Jointly owned by California Institute of Technology and ETH Zurich

Two pieces of equipment were needed for the experiment. The first piece, built at Caltech, is a reactor "just a bit smaller than a gallon-jug," Haile said. The reactor is basically a cylindrical container lined with ceria that has input and output lines for the gases.

The second piece is a solar concentrator, which is the most difficult part to build. The concentrator is basically a set of giant curved mirrors that gather sunlight from a wide area. For this experiment, the researchers were able to use an existing solar concentrator located at the Paul Scherrer Institute.

The Caltech scientists took their reactor to Switzerland and attached it to the bottom of the concentrator, allowing the sunlight to heat up the ceria inside. Then they piped steam and carbon dioxide into the reactor and measured the hydrogen and gases flowing out.

Cheaper and more efficient

How far reaching could this new technology be and how much oil, gas or coal could it replace?

"The abundance of cerium means that this approach could have a significant impact on our national energy budget," Haile said. Because cerium is 100,000 times more abundant than the precious metal platinum, she said, the cost would be many orders of magnitude smaller.

For this experiment, the efficiency of the reactor at converting sunlight to usable energy measured just under one percent, which Haile said is comparable to other methods. However, this was a first cut, aimed at simply proving that the process is practical and could be done economically.

Before bringing the technology to market, Haile said, the reactor design needs to be much tighter to get better efficiency.

"As a second step, it will be important to develop materials with even better characteristics than ceria," she added.

"Ideally, one wants a material with a smaller temperature swing required as this will also increase efficiency," Haile said. "In addition, if both the high and low temperatures can be lowered, the overall system lifetime will be improved. Better materials could result in a better process."

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User comments : 19

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marksthomas
4.2 / 5 (5) Apr 07, 2011
This seems a step in the right direction - good news indeed.
kaasinees
4 / 5 (4) Apr 07, 2011
This news is actually months old(Beginning of 2011).
Altough it seems to be more developed now.
I was wondering when to hear from this again and im glad i did.

I don't think methane will be a good fuel for our cars though... I would rather put it in a dirigible.
Quantum_Conundrum
1 / 5 (6) Apr 07, 2011
AT one percent efficiency, you need something like 1100 m^2 (33m by 33m) of collectors to make about one liter of fuel in one hour.
DoubleD
not rated yet Apr 07, 2011
AT one percent efficiency, you need something like 1100 m^2 (33m by 33m) of collectors to make about one liter of fuel in one hour.


Is that 1L of H2? I would imagine that the energy density of this fuel is somewhat higher than, say 1L of gasoline, ethanol, methane....
harryhill
3 / 5 (2) Apr 07, 2011
Water...it seems that it is very abundant. I wonder why articles note that we are running out of potable water?
Using water to produce 'wonders' might be rethought.
rgwalther
4.2 / 5 (5) Apr 07, 2011
We all know that the oil companies will buy up the patents, have the researchers murdered by Cheney's Black ops and the research will be hidden in the huge underground bunker beneath Bush's Texas farm.
Eikka
5 / 5 (1) Apr 07, 2011
AT one percent efficiency, you need something like 1100 m^2 (33m by 33m) of collectors to make about one liter of fuel in one hour.


Is that 1L of H2? I would imagine that the energy density of this fuel is somewhat higher than, say 1L of gasoline, ethanol, methane....


Based on the figure of 1 kW/m^2 the calculations would make fuel that has the energy density of diesel oil.

Still. Quite a lot if you think about it. If you had one of those dishes on your back yard, you'd make at least a gallon during a sunny afternoon. Maybe even two.
TheGhostofOtto1923
1 / 5 (1) Apr 07, 2011
Water...it seems that it is very abundant. I wonder why articles note that we are running out of potable water?
Using water to produce 'wonders' might be rethought.
I was thinking this. You might need more steps for desalination and filtering.
Roland
not rated yet Apr 07, 2011
What's missing? Where's the part about liquid fuel? There's work on NatGas-to-liquids going on elsewhere, but it's early-stage. This reactor needs to compete with NatGas, which is *real* cheap right now. This guy has a lot of work ahead of him to make this process work in a cost-effective manner.
rgwalther
not rated yet Apr 07, 2011
I don't think methane will be a good fuel for our cars though... I would rather put it in a dirigible.


BOOM!!!!!
djr
not rated yet Apr 07, 2011
"I don't think methane will be a good fuel for our cars though... I would rather put it in a dirigible."

Oooops - better tell Chesapeake Energy company here in Oklahoma - they are in the process of converting their entire fleet to natural gas. Here is a link - http://www.busine...ural-Gas
holoman
1 / 5 (1) Apr 07, 2011
Using a valuable resource like fresh water not too smart.

Now if they can do this with seawater they have something.
Sanescience
not rated yet Apr 08, 2011
http://www.physor...765.html

Seems like 90% conversion of the energy produced by a solar panel of today in the 25% range beats the pants off this approach.
PPihkala
1 / 5 (1) Apr 08, 2011
How about using that solar collector traditionally to heat water up to steam and use that steam to run turbine driven generator. I bet that has better efficiency than 1%, even if the resulting electricity is used to charge a battery. Battery that then drives that EL-car.
antialias_physorg
5 / 5 (1) Apr 08, 2011
Using a valuable resource like fresh water not too smart.

Why? If you burn the H2 (for heating) or use it in a fuel cell (for cars or generating electricity) then you get the water back.
t_m
not rated yet Apr 08, 2011
I am doing some basic research and potentially putting a theory to practice,I am looking into the area of 'Renewable Energy for Developing Countries'..if anyone would like to join a global discussion on this let me know!
Quantum_Conundrum
1 / 5 (1) Apr 08, 2011
How about using that solar collector traditionally to heat water up to steam and use that steam to run turbine driven generator. I bet that has better efficiency than 1%, even if the resulting electricity is used to charge a battery. Battery that then drives that EL-car.


They are already doing that. Parabolic trough solar power plants are extremely efficient: somewhere aroung 60% or so.

The concept was first invented by the Jews, although the components are ironically made by their arch-enemy germany.

The plants use mirrors and black vaccuum tubes to concentrate huge amounts of sunlight on the vaccuum insulated water, which is heated to over 700f.

If you search youtube, you can find some demonstration videos. I think that one plant was 40-something megawatts and does nearly 10,000 gallons per minute at around 725F.

The only real drawback to the technology is that some of the space is wasted due to the fact you need access roads among the troughs...
antialias_physorg
not rated yet Apr 08, 2011
The concept was first invented by the Jews, although the components are ironically made by their arch-enemy germany.

Huh? Live much in the last millennium, do you?
Moebius
not rated yet Apr 11, 2011
The Sun is Earth's primary energy source and harnessing its abundant light is the Holy Grail of renewable energy


Who says it's the holy grail? You have to cover lots of ground to use it, it's only available during some daylight hours when the sun is high and only on clear days.

Geo-thermal is the holy grail. It's unlimited, doesn't require area proportional to the amount of power and available 24/7. Maybe if we started sucking the power out of Yellowstone we could prevent an eruption which would probably destroy this country.

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