Solar Fuels & The Concentrating Solar Power Connection

Solar fuels are synthetic fuels that come under the same general umbrella as electrofuels, or e-fuels as they are sometimes called. The common denominator is the use of renewable energy to produce hydrogen gas, which can then be combined with captured carbon to formulate liquid fuels.

The difference is that e-fuels can deploy electricity from any renewable resource, including wind, marine, and geothermal energy, as well as solar. Nuclear power plants have also been cited as a zero-emission source of electricity for hydrogen in the e-fuel supply chain.

Solar fuels refer more specifically to solar-powered electrolysis, “artificial leaf” photoelectrochemical cells, and other systems that deploy solar energy, including concentrating solar power systems.

The Energy Department’s National Renewable Energy Laboratory has been zeroing in on concentrating systems as a means of reducing the cost of solar fuels. One pathway involves high-temperature electrolysis, which could provide for improved energy efficiency. High heat can also be deployed for thermochemical hydrogen production.

Cutting The Cost Of Solar Fuels With Concentrating Solar Power

CleanTechnica caught wind of the concentrating solar power connection back in 2018, when we took note of a solar fuels research project at Washington State University, in collaboration with the US Department of Energy’s Argonne National Laboratory and Pacific Northwest National Laboratory.

Solar fuels researchers have been busy since then. One recent example comes from a team of engineers at MIT, who have come up with a more efficient approach to solar thermochemical hydrogen production.

Thermochemical systems are based on a steam-driven, superfast version of the rusting process that occurs when iron encounters water. That process releases hydrogen. After being reheated in a vacuum, the metal is reconstituted and ready to repeat the oxidation process.

If that sounds inefficient, it is. “Only about 7 percent of incoming sunlight is used to make hydrogen,” MIT News reported earlier this month. “The results so far have been low-yield and high-cost.”

Well, that was then. The MIT team tweaked the process to capture up to 40% of energy from the sun. Among the innovations is a new design that sends a train of boxy reactors traveling in circles around the central tower of a concentrating solar power plant.

The Channels & Pores Solution

Another approach to improving thermochemical technology comes from a team of engineers at ETH Zurich, in Switzerland. They tackled the challenge of maximizing the transfer of heat from the concentrating solar power system to the interior of the reactor.

Their solution leverages a parabolic trough-style concentrating solar power system to heat a solar reactor up to 1,500 degrees Celsius. The reactor contains a structure made of cerium oxide, a variation of the metal cerium. Cerium oxide is known for its use in ceramics and glass-making.

The cerium oxide structure designed by the ETH team is described as a porous ceramic structure, designed to ensure that heat from the concentrating solar power system reaches the interior of the reactor with minimal interference.

The team called in an extrusion-based 3D printer to fabricate the structure with channels and pores that are wider at the surface to capture more sunlight. The printer also deployed a unique ink containing a high concentration of ceria particles to help boost the reaction.

“Hierarchically ordered designs with channels and pores that are open at the surface exposed to the sunlight and become narrower towards the rear of the reactor have proven to be particularly efficient,” ETH explains.

The ETH reactor also combines water-splitting with captured carbon dioxide to produce a ready-mixed combination of hydrogen and carbon monoxide, which can then undergo additional steps to produce liquid kerosene jet fuel.

A New Hope For Concentrating Solar Power

The ETH team reports that they have demonstrated a significant improvement in energy efficiency for their 3D-printed structure, with the ability to produce twice the amount of fuel compared to conventional structures when exposed to the same level of heat.

The next steps are up to the company Synhelion, which spun out of the ETH research and has licensed the 3D printing technology. Synhelion has already laid plans for a demonstration scale solar kerosene jet fuel plant in Germany integrated with a concentrating solar power plant, with Swiss International Air Lines lined up to test the fuel in its aircraft. Construction began about 12 months ago, so stay tuned for a startup date.