"When we published our initial work on capturing CO2 from the air 20 years ago, no one was interested. Today it’s a priority research topic at the world’s leading universities. The situation regarding research on solar fuels is similar," says Aldo Steinfeld, who since the beginning of his scientific career has been investigating the production of fuels and energy-intensive materials such as metals and cement using concentrated solar energy. As a young assistant professor, he wrote perspective articles on these subjects, recognising their key importance and potential for the future even then. "Research projects such as these were extremely daring as they weren’t in keeping with the direction of mainstream research. I’m happy now that I took this risk."
Steinfeld has persistently pursued his goals, focusing on what was impactful and far-reaching. His research and development work has spawned two of ETH’s most highly regarded spin-offs in recent years: Climeworks and Synhelion. Climeworks markets the technology for capturing CO2 from the air, while Synhelion has brought the technology for producing solar fuels to market. But this passionate motorcyclist is thrilled that he made the world’s first ride powered by solar gasoline on his own Harley-Davidson just before retirement. And, of course, he is pleased that his vision is becoming a reality - that all forms of transport, from aeroplanes and ships to trucks and cars, can run on carbon-neutral solar fuel.
Fuel from sunlight and air
For Steinfeld, it all began with the synthesis of hydrogen. If it is made from water with the aid of solar energy, it can be regarded as a sustainable fuel. Storing it, however, is troublesome. There is also a lack of any mass-market infrastructure for using hydrogen in the global transportation sector. It was clear to Steinfeld that synthetic liquid fuels such as kerosene, diesel and gasoline - known as drop-in fuels - were needed. They are fully compatible with the existing infrastructure for storage, delivery and end use. The major challenge consists in ensuring that these synthetic fuels are carbon neutral. "The production of drop-in fuels using solar energy has been the main focus of my research. Although the solar radiation reserve is essentially unlimited and its use is ecologically harmless, it only occurs intermittently, in diluted intensity and is unevenly distributed across the globe. Determining how best to store and use it was critical. The vision of aeroplanes flying on solar kerosene motivated me to search for ways to convert solar energy into drop-in fuels."How is solar fuel made?
A solar refinery consists of three successive thermochemical conversion processes. The first step occurs in the Direct Air Capture unit (DAC), where CO2 and H2O are extracted from the ambient air. In the second step, which occurs in the Solar Redox unit (SR), concentrated solar energy is used to split CO2 and H2O into a blend of CO and H2 (synthesis gas). The third step occurs in the Gas-to-Liquid unit (GTL), where synthesis gas is processed into liquid hydrocarbon products such as kerosene, gasoline, diesel or methanol. These synthetic fuels are compatible with existing internal combustion engines and jet propulsion engines.video clip explaining the solar refinery
It goes without saying that things don’t always go according to plan when you are conducting pioneering work. "Good engineering and perseverance helped us to overcome the many failures we experienced along the way. Our joy in succeeding was even greater because we knew that we could truly make a difference," Steinfeld states, recalling one of the happiest moments of his career when he and his team commissioned the world’s first solar mini-refinery on the roof of the Machine Laboratory (ML building) in 2019 and witnessed the production of the first drops of methanol made exclusively from sunlight and air. "This unique demonstration system was the result of decades of research into several fundamental topics. Numerous doctoral and master’s theses have been written in the field of chemical engineering sciences. They dealt with thermodynamics and kinetics, heat and mass transfer at high temperatures, concentrated radiation optics as well as functional materials and ceramic structures. Basic research has enabled us to develop efficient solar reactors and the associated process technology," Steinfeld explains, who is satisfied with all these achievements.
The path to a life’s work
Over the years, Steinfeld’s research topics have evolved to address some of the most important challenges in the fields of energy and the environment. That’s why he also won the Lifetime Achievement Award from the SolarPACES International Energy Agency in 2024. "Naturally, I feel deeply honoured to be the recipient of such awards. Although it’s my name on them, the credit is due to every member of my group. I was privileged to work with an incredible team of doctoral students, master’s students and postdocs. They were all’extremely talented and hard-working and wanted to contribute to a future with renewable energy. I am deeply grateful to all’of them."Steinfeld was born in 1960 in Montevideo, Uruguay. His German-sounding name stems from his Eastern European forefathers who, being Jewish, fled to South America before the Second World War. He earned his BSc in Aeronautical Engineering from the Technion, his MSc from Tel Aviv University and his PhD from the University of Minnesota. In 1991, he joined the Paul Scherrer Institute in Switzerland. For him, this was "a unique opportunity to help set up a research group in the then emerging field of solar chemistry." In 1999, Steinfeld was appointed a professor at ETH Zurich. Over the last 25 years, he has supervised 60 doctoral theses, published over 360 academic articles and registered 27 patents. He has set particular store by the training of future engineers in the field of energy conversion. In the course of his teaching work, for example, he has taught the subject of thermodynamics to over 6,000 Bachelor’s students. In response to the question of why going into industry was not an option, he states: "On the one hand, I really enjoy teaching. On the other hand, it’s the freedom to research and explore terra incognita." While industry focuses on developing and marketing products, he says, in academia you can research novel processes from the ground up. "It requires innovation, revolutionary thinking and courage. ETH is the place where a professor has to be a visionary."
Don’t lose sight of reality
For all’his visionary thoughts, however, Steinfeld has always kept his feet firmly on the ground, and nothing could be further from his mind than utopian ideas. "Although our technologies are contributing to a sustainable future, I regard the term sustainability as a misused and frequently misunderstood buzzword. For engineers, sustainability is very simple: you have to make sure that the materials cycle is closed." The solar drop-in fuels he has developed precisely fulfil this requirement. Their combustion releases exactly the same amount of CO2 as is removed from the air for their production. The carbon cycle is closed.Anyone wanting to bear witness to his trailblazing developments and experience this passionate speaker in action can do so at his farewell lecture. It will be entitled Fuels from Sunlight and Air. In this lecture, he will show that solar fuels are already a reality. In addition to discussing breakthroughs, he will also address failures as a crucial part of innovative research. After that, Steinfeld and his wife will embark on an extended trip through Europe on their Harleys. However, he doesn’t intend to withdraw from his work entirely. Besides his teaching assignments, he wishes to take a more active role in the projects of Synhelion and Climeworks - driven by his passion for science and technology.
Farewell lecture
Professor Aldo Steinfeld will give his farewell lecture entitled Fuels from Sunlight and Air in the Audi Max on Wednesday, 21 May at 5.15 p.m.The event will be streamed live at http://bit.ly/audimax-stream.
