Christopher Hailstone has extensive experience with energy management, renewable energy, and electricity delivery. He is also our Utilities expert and provides valuable insights on grid reliability and security.
When did you first become interested in the field of solar fuels? Was there a specific event or experience that directed your focus towards solar energy?
Thank you for this question. Since the early days of my career, the production of solar fuels has been a significant aspect of my research. The driving motivation was the understanding that with just 0.1 percent of the Earth’s land area, one could collect enough solar energy to meet the global energy demand. Furthermore, solar energy reserves are vast and environmentally friendly. A notable challenge, however, is that solar radiation is dilute, intermittent, and unequally distributed. This realization motivated me to research methods of capturing and storing solar energy so it could be used to power various modes of transportation and industries efficiently.
What were the main challenges you faced when starting your research on solar fuels? How did you address the issue of solar energy being dilute, intermittent, and unequally distributed?
The primary challenges included the dilution, intermittency, and uneven distribution of solar energy. Initially, my focus was on producing hydrogen from water using solar energy, but the difficulties in storing, distributing, and utilizing hydrogen as a transportation fuel led me to pivot towards the production of drop-in fuels. These are synthetic fuels that can be seamlessly integrated into existing fuel infrastructure, allowing for the straightforward replacement of fossil fuels without the need for new technologies, which helps overcome some of the challenges associated with solar energy.
Can you explain the concept of “drop-in fuels”? What advantages do drop-in fuels offer over traditional fossil fuels? How do solar kerosene and other synthetic fuels help make aviation more sustainable?
Drop-in fuels are synthetic liquid hydrocarbons such as kerosene, gasoline, or diesel, which can directly replace fossil fuels. These fuels can be stored, distributed, and used within the existing infrastructure designed for conventional fuels. Drop-in fuels offer the significant advantage of being produced from renewable sources like sunlight and air, which makes them environmentally friendly. Specifically, solar kerosene allows the aviation industry to reduce its carbon footprint since these synthetic fuels can power aircraft in a manner similar to traditional jet fuels but with a significant reduction in greenhouse gas emissions.
What led you to join the Paul Scherrer Institute (PSI) in 1991? How did your transition to ETH Zurich come about?
After completing my doctoral studies and a postdoctoral research stay, I joined the Paul Scherrer Institute (PSI) in 1991 to head the Solar Technology Laboratory. This role provided a unique opportunity to build a research group specializing in solar chemistry, an emerging and promising field at the time. In 1999, I was appointed as a Professor at ETH Zurich. Over the next years, I gradually transferred my research from PSI to ETH, where I developed a robust research program focused on advancing chemical engineering sciences applied to solar energy technologies.
What was the focus of your research at ETH Zurich? How did your work at ETH Zurich contribute to the field of solar energy technologies?
My research at ETH Zurich emphasized the development of solar energy conversion technologies. We concentrated on creating technological solutions for capturing and converting solar energy into usable fuels. These innovations have been pivotal in advancing the field of solar fuels. Notably, we successfully demonstrated the production of drop-in fuels from sunlight and air, which contributed significantly to the development of sustainable and climate-neutral energy sources.
How did Climeworks and Synhelion emerge from your research group? What are the main achievements of Synhelion so far?
Climeworks and Synhelion are spin-offs from our research group at ETH Zurich, stemming from our work on carbon capture and solar fuel production technologies. Climeworks specializes in direct CO2 capture from air, while Synhelion focuses on producing solar fuels. The most significant achievement of Synhelion has been commissioning the first industrial solar refinery in 2024, known as “Dawn.” Synhelion is also set to operate a larger refinery in Spain by 2027, with the goal of ramping up commercial solar fuel production to meet a significant portion of Europe’s sustainable aviation fuel demand.
Can you describe the key steps involved in producing drop-in fuels from sunlight and air? How does the solar redox unit work in this process?
The production of drop-in fuels involves several crucial steps integrated within a solar refinery. First, the direct air capture (DAC) unit extracts CO2 and H2O from ambient air. Then, the solar redox unit (SR) uses concentrated solar energy to convert these into a mixture of CO and H2 (synthesis gas). Finally, this synthesis gas is converted into liquid hydrocarbons (such as kerosene, gasoline, diesel, or methanol) using the gas-to-liquid (GTL) unit. The solar redox unit is central to this process, leveraging high temperatures generated by concentrated sunlight to drive the necessary chemical reactions.
How do synthetic fuels produced by your methods achieve carbon neutrality? What are the environmental benefits of using solar kerosene over fossil kerosene?
Synthetic fuels produced through our methods achieve carbon neutrality by ensuring that the amount of CO2 released during fuel combustion is equivalent to the amount captured from the air during production. This balance minimizes overall carbon emissions. Using solar kerosene over fossil kerosene offers significant environmental benefits, including an 80% reduction in greenhouse gas emissions. When the production materials are sourced from renewable energy, it brings us close to zero emissions, thereby offering a substantial climate advantage.
Which synthetic fuels are suitable for cars, trucks, ships, and airplanes? How do these fuels integrate into existing transportation infrastructures?
Synthetic fuels like solar gasoline and diesel are suitable for cars, trucks, and ships, while solar kerosene is ideal for aviation. These fuels can be used within the current transportation infrastructure, including storage, distribution, and combustion systems, without requiring new technologies. This compatibility ensures a seamless transition from fossil fuels to synthetic alternatives.
What factors currently make solar fuels more expensive than fossil fuels? How can the cost of solar fuels be reduced over time? Do you think policy measures could help bring solar fuels to market more quickly?
Currently, solar fuels are more expensive than fossil fuels due to high energy production costs, technology efficiencies, and initial investment in infrastructure. However, costs can be reduced over time through scaling effects, process optimizations, mass production of key components, and learning-by-doing practices. Policy measures, such as mandating a minimum share of sustainable aviation fuels (SAF) for airlines, can accelerate market adoption. These measures would help scale production, reduce costs, and make solar fuels a competitive alternative in the near future.
What is your forecast for the future of solar fuels?
I am optimistic about the future of solar fuels. The technologies we have developed can be scaled to competitive costs globally. As production scales and costs decrease, solar fuels will play a crucial role in decarbonizing sectors like aviation and transportation, leading us towards a more sustainable energy future.
