Sustainable Aviation Fuel From Solar Energy: Not A Dream Any More

The search for sustainable aviation fuel was once dominated by biofuel stakeholders, but the aviation industry could take off in a new direction that skips the plant-based middleperson in favor of a straight line from solar energy to liquid kerosene. In the latest development on that score, the Swiss institution ETH Zurich has just unveiled a new pilot-scale, all-in-one, solar powered process for converting water and carbon dioxide straight into jet fuel.

The Green Hydrogen Angle On Liquid Fuel From Solar Energy

If you guessed green hydrogen is somewhere in the mix, that would be correct. ETH Zurich (the Swiss Federal Institute of Technology in Zurich), describes its pilot project as a thermochemical process that deploys solar energy in a single, integrated chain that goes from hydrogen gas, oxygen and carbon dioxide to liquid kerosene fuel in a “solar tower.”

“We evaluate the performance of the solar reactor − the cornerstone technology − based on five primary metrics (namely: reaction selectivity, syngas quality, fuel purity, energy efficiency, and material stability) and experimentally validate its stable operation and full integration in the solar tower fuel plant,” ETH explains. They list the following highlights of the project:

  1. Entire process chain from H2 O and CO2 to solar kerosene realized in a solar tower
  2. 50-kW solar reactor demonstrated for ceria-based thermochemical redox splitting
  3. Consecutive redox cycling produced syngas suitable for Fischer-Tropsch synthesis
  4. 4.1% solar-to-syngas energy efficiency achieved without implementing heat recovery

CleanTechnica got advance word on the results of the demonstration under embargo, which will be lifted by the time you read this. The details should be available in the journal Joule at DOI 10.1016/j.joule.2022.06.012.

A press release may also be forthcoming from the ETH media office, and in the meantime you can find more info elsewhere on the ETH website regarding their solar energy to fuel research.

Solar Energy To Liquid Fuel, Not A Dream

If all this sounds like it popped up out of nowhere, that’s probably because biofuels have dominated most of the attention in the sustainable aviation fuels area. CleanTechnica has covered many different angles in the biofuel area including bio-waste products, algae, seaweed, and waste paper, among others.

Meanwhile, activity in the electrofuel area has been stirring. Wind power can get the e-fuel job done on the green hydrogen side, but the ETH project demonstrates how solar energy can come into play, too.

There being no such thing as a free lunch, the road to commercial-scale solar fuel has been a long one. The research goes back to at least 2011, under the Solar-Jet project that concluded in 2015.

In 2014, our friends over at Chemistry World took note of the obstacles encountered by the Solar-Jet project, further noting that three years of work had resulted in a single glass of kerosene.

“Unfortunately, the idea has suffered from two problems. One is that the dissociation of carbon dioxide and water only takes place at very high temperatures, typically above 2200°C. But the other, more difficult, problem is that the syngas cannot be tackled by the Fischer–Tropsch process until all the oxygen is removed as it is dangerously explosive,” they wrote, while observing that the concentrating solar pathway would resolve the first problem.

ETH seems to have taken the ball and run with it. The institute went on to participate in the EU/Swiss “Sun-to-Liquid” project, which validated the core solar technology along with the integrated chemical plant in 2019.

For the validation process, the Sun-​to-Liquid project constructed a concentrating solar power plant at the IMDEA Energy Institute in Spain. The power plant was designed to concentrate sunlight by a factor of 2,500. That is triple the level of typical concentrating systems.

“This intense solar flux, verified by the flux measurement system developed by project partner DLR, allows to reach reaction temperatures of more than 1,500°C within the solar reactor positioned at the top of the tower,” the project website explained.

“The solar reactor, developed by project partner ETH Zurich, produces synthesis gas, a mixture of hydrogen and carbon monoxide, from water and CO2 via a thermochemical redox cycle,” they added. “An on-site gas-​to-liquid plant that was developed by the project partner HyGear processes this gas to kerosene.”

Next Steps For Solar Energy To Liquid Fuel

The Sun-to-Liquid project was scheduled to conclude at the end of 2019, and it seems that ETH has not let the grass grow under its feet since then. Last fall, the institute published a paper in the journal Nature that describes the operation of a rooftop mini “solar refinery.”

“Analyses of the entire process show that the fuel would cost 1.20 to 2 euros per litre if it were produced on an industrial scale,” ETH enthused, pointing out that the technology could be in desert areas with plenty of solar energy resources but little arable land for biofuel crops.

So, What Good Is This?

If all goes according to plan, the advantages of solar energy enabled fuels over conventional biofuel are pretty clear. Even though the biofuel industry is moving away from food-sourced inputs, stakeholders in the area of ​​energy crops still have to contend with land use conflicts at a time when climate change and Russian warmongering have placed new burdens on global food systems.

In contrast, the solar-to-fuel model does not have to deal with drought, floods, hail, feral hogs, or other contingencies that can interrupt a crop-based supply chain.

The solar tower model also allows for more localization and decentralization. That can help alleviate disruptions in the global shipping and commodities areas.

As for how the solar energy model helps prevent catastrophic climate change, it doesn’t. That ship has already sailed. The catastrophic impacts of human-induced climate change are already here.

Reducing the risk of further damage is the name of the game, and in that regard every tool in the non-fossil toolkit should be brought to bear on pushing fossil stakeholders out of the energy sector.

Unfortunately, over here in the US, the policy making toolkit has been shrinking by the minute, thanks to an unforced ruling by the six Republican-appointed Justices on the Supreme Court, along with uniform opposition to federal action on climate change by all 50 Republicans legislators who populate the US Senate, and an assist from a lone Democratic Senator who happens to hold a stake in the coal business (looking at you, Joe Manchin).

Democratic President Joe Biden could declare a climate emergency to grease the climate action wheels despite Republican pushback. Apparently that’s not in the works at the present time, but stay tuned for an update.

Follow me on Twitter @TinaMCasey.

Photo: “Solar tower” model for deploying solar energy to make sustainable aviation fuel from water and carbon dioxide, courtesy of ETH Zurich.


 

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