A collaborative research team from ETH Zurich, the Paul Scherrer Institute (PSI), and Caltech has built a solar reactor to make syngas – a precursor for hydrocarbon fuels (You may need to click the ‘translating’ link for completion.) uses only CO2, water and sunlight.

The device is a solar cavity-receiver reactor that can thermochemically split both water and CO2 using concentrated solar radiation.   The reactor uses a solar-driven thermochemical cycle for splitting the CO2 and H2O using metal oxide redox reactions. In a two-step cycle the process starts with a thermally reducing non-stoichiometric cerium oxide at above 1,500°C and then re-oxidizing it with the H2O and CO2 at below 900°C to produce H2 and carbon monoxide for making the syngas product.

Operating the ETH PSI CalTech Solar Reactor. Click Image for more info.

Aldo Steinfeld, a professor of mechanical and process engineering at ETH Zurich and head of the solar technology laboratory at PSI, who leads the team said, “The operation at high temperatures and the use of the entire solar spectrum provides a thermodynamically attractive path to solar fuel production.”

Experimental tests with the reactor have been carried out at the 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 8 tenths of one per cent.

Philipp Furler, a doctoral student in Steinfeld’s group said, “This efficiency value is about two orders of magnitude greater than the one observed with state-of-the-art photocatalytic approaches for CO2 dissociation.”  Furler is currently working on the reactor optimization with help of fluid mechanics and heat-transfer simulation models. Thermodynamic analyses show that efficiencies above 15 per cent are attainable. Eight tenths of one to a full fifteen percent will be a huge jump towards practicality.

The solar reactor is a light funnel above 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 a lower positioned axially centered outlet port.

Solar Reactor for Making Fuel by ETH PSA and Caltech. Click image for more info.

The team is now focusing on optimizing the solar reactor technology with the aim of building megawatt-sized systems.  No estimations are offered as to the application of home, small business or farm sized units or the costs.

Steinfeld is offering this though, “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.”   Well said.

Worldwide scientists and business people are discussing the question: How can you store solar energy from the sunniest spots on earth with wide-open areas and transport it to the industrialized centers where most of the energy is needed?  The question motivates researchers across the range from biology, such as sunlight converted to a biological chemical stored energy leading to the forms of liquid fuels that can be saved and transported over unlimited distances on to the physics and chemistry of sunlight harvests to make heat, on to electrical generation or simply generate electricity that are limited to the transmission investment.

Vast areas could be used to collect solar energy.  The question after existing fuel and energy supply prices exceed the costs to profitably produce alternatives is the type of harvest needed, electrical power or portable fuels.

The team’s efforts should they get to an economical 15% efficiency, look to answer a worldwide market demand.  Syngas is great material for making fuels.  Solar driven, with cheap enough water for the H2O input, an economical means to source or concentrate the CO2 feeding a low cost means to rapidly choose and make the fuel products suggests both the problems to be solved and the huge opportunity.

This technology path looks really good.  Fifteen percent efficiency to fuel should be competitive if the water and CO2 can be supplied cheaply enough.  With no moving parts, no extremely costly materials and what can be supposed to be a very long useful life makes for an interesting calculation.   A major question is going to be if the combined process from sourcing CO2 and the H2O through to the fuel delivered is at or below the cost of the biological path.

It’s worthwhile to keep going, Congratulations for great innovation and ingenuity so far.

Click here for the Science published paper.


3 Comments so far

  1. World Spinner on January 20, 2011 11:43 AM

    Making Fuel With CO2 and Sunlight | New Energy and Fuel…

    Here at World Spinner we are debating the same thing……

  2. Mohamma on March 24, 2011 11:24 AM

    I need a solar concentrating system with liquid/gas flow or batch facility for conversion of liquid/gas using photo reaction.

  3. Mohammad on March 24, 2011 11:25 AM

    need more details of this system I am intrested to get more information and benefits.

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