Reactor could produce fuel from sunlight
Share
A research team from ETH Zurich, the Paul Scherrer Institute (PSI), and Caltech has developed a solar cavity-receiver reactor that can thermochemically split water and CO2 using concentrated solar radiation.
Aldo Steinfeld, a professor of mechanical and process engineering at ETH Zurich and head of the solar technology laboratory at PSI, led the team that developed the reactor with researchers at the California Institute of Technology in Pasadena, California.
The reactor makes use of a solar-driven thermochemical cycle for splitting CO2 and H2O using metal oxide redox reactions. The two-step cycle consists in thermally reducing non-stoichiometric cerium oxide at above 1,500°C and re-oxidising it with H2O and CO2 at below 900°C to produce H2 and CO — known as syngas, the precursor of liquid hydrocarbon fuels.
’The operation at high temperatures and the use of the entire solar spectrum provides a thermodynamically attractive path to solar fuel production,’ said Steinfeld.
The solar reactor consists of a cavity with a small windowed aperture into which concentrated solar radiation enters. The dimensions of the cavity ensure multiple internal reflections and efficient capture of the incoming solar energy. A porous, monolithic ceria cylinder inside the cavity is subjected to multiple heating and cooling cycles to induce fuel production. Reacting gases flow radially across the porous ceria cylinder, while products from the reaction exit the cavity through an axial outlet port.
Experiments on the reactor have been carried out at PSI with a 2,000W solar reactor prototype subjected to a solar concentration greater than 1,500 suns. The measured solar-to-fuel energy conversion efficiency — defined as the heating value of the fuel produced divided by the solar radiative power input — reached 0.8 per cent.
’This efficiency value is about two orders of magnitude greater than the one observed with state-of-the-art photocatalytic approaches for CO2 dissociation,’ said Philipp Furler, a doctoral student in Steinfeld’s group, who is currently working on the reactor optimisation with help of fluid mechanics and heat-transfer simulation models. Thermodynamic analyses show that efficiencies above 15 per cent are attainable.
Steinfeld and his team are now focusing on optimising the solar reactor technology with the aim of building megawatt-sized systems.
’The potential of solar fuels has been repeatedly overestimated in the short term and underestimated in the long term. We still have plenty of research and development work to do, but by 2020 we should witness the first industrial solar fuel plants coming into operation,’ said Steinfeld.
Readers' comments (7)
dave bennett | 10 Jan 2011 1:04 pm
It would be nice to know the 0.8% efficiency figure compares with that of green plant photosynthesis?
Unsuitable or offensive? Report this comment
Bhatia Vijay M. | 10 Jan 2011 1:57 pm
It is very interesting phenomena. This can
solve world energy requirements.
I wish the entire team a very good luck in
developing economical reactor so that a
common family can afford to install.
Unsuitable or offensive? Report this comment
Jon Fuge | 10 Jan 2011 2:02 pm
Sugarcane has nearly 8% efficiency, Brazil uses it as a source of fuel for its road transport.
Unsuitable or offensive? Report this comment
B Practical | 10 Jan 2011 4:22 pm
Hmmmm. Sugar cane is the answer then.
I shall now grow this as sole crop in my garden and on the allotment.
Unsuitable or offensive? Report this comment
Zuheir Al-Khaldi | 11 Jan 2011 6:17 am
Dear everyone:
Imagine the situation after may be 100 years, it will be as follows:
- No more fossil fuels or enough quantities
of organic fuels.
- There will be a great energy demand
for either nuclear and/or regenerative
energies or any other kinds of new
energies.
- In such cases, the above idea will
represent a hope to produce an organic
fuels.
Unsuitable or offensive? Report this comment
James Stewart | 17 Jan 2011 2:36 pm
If thermodynamic efficiency is reached, it would be feasible to produce fuel on a reasonably large scale, but economics will play a factor, and mass cultures of algae will far outstrip the net production at a much lower cost. The products of algae will include oil, and ethanol (by fermentation of the residue after oil recovery. These are the building blocks of biodiesel. Enough said.
It would be interesting to make a continuous process of the above with the catalyst made into a wheel, interleaved with aluminum oxide with exhaust ports for the products. The by spinning the wheel, one could easily cycle the temperatures.
Unsuitable or offensive? Report this comment
Phil Henshaw | 23 Jan 2011 1:27 pm
The contest between new energy sources for liquid fuels is important, but overshadows the greater need to reduce, rather to continually add to our liquid fuel use. There are two very clear reasons.
Most people think of fuel use as the traceable amount, and that's a grave error. What is traceable is generally less than 1/5 the true total, even when tracing by the most careful analytical efforts. Most energy uses that businesses rely on are untraceable, nominally 80% higher when estimating whole system energy use rather than just traceable energy use. http://www.synapse9.com/pub/SEA_EROIwind.pdf
The same then applies to the physical impacts of the environmental pressures of energy use! Our problem is not just needing clean energy. CO2 *pollution* is only beginning to have noticeable effects. The destabilizing effects on the environment we already see are from our current energy *uses* that growing the economy and its largely hidden "dark energy" uses would only continually escalate by ever larger steps. http://www.synapse9.com/design/dollarshadow.htm
Unsuitable or offensive? Report this comment