Sustainable Aviation Fuels (SAF) are crucial if aviation is to achieve its target of net-zero carbon emissions by 2050.

Even if electric, hybrid and hydrogen aircraft projects materialize as planned, a fleet rollover will extend well beyond 2050 and, in any case, will only be a solution for short and medium-haul flights for the foreseeable future.

SAF, on the other hand, can be blended with fossil fuel and so serve as a drop-in fuel to be used with existing aircraft and engine technologies. Furthermore, they can be transported via the established supply infrastructure. Most SAF reduce CO2 emissions by up to 80% compared with fossil fuels and power-to-liquid (PtL) or sun-to-liquid (StL) processes almost completely eliminate CO2.

To date:

  • Over 450,000 flights have used SAF
  • Approximately 100 million liters of SAF was produced in 2021 and some 14 billion litres of SAF are in forward purchase agreements
  • Close to 50 airlines have experience with SAF


Industry first

Seven technical pathways exist for SAF production, all centered on using biomass. But renewable electricity and solar heat are on the cards as new production methods. Both need synthesis gas as an intermediate, a mixture of hydrogen and carbon monoxide. Industrial gas-to-liquid processes then turn this into liquid fuel.

“Presently, there are only biofuels available on the market and their production volume is limited” says Jan Pechstein, Head of Corporate Emissions Management and SAF Lufthansa Group. “But PtL and StL technologies are on the brink of market introduction, and we will see the first commercial plants within the next five years. Their production capacities need to rise quickly to enable the aviation sector to reach its CO2 emission reduction targets.”

SWISS and the Lufthansa Group are working with Synhelion to develop StL fuel in what will be an industry first. Synhelion has developed a unique technology that will ultimately use solar heat to drive thermochemical processes for the production of SAF. Solar heat is the cheapest renewable energy source available and solar-fuel plants don’t need to be connected to a power grid as they are built in an independent, stand-alone configuration. It means that production capacities are quickly and independently scalable.

Most importantly, StL closes the fuel carbon cycle. When combusted, it will only emit as much CO2 as went into its manufacture.

Essentially, when the sun is shining, solar radiation is reflected by a mirror field, concentrated onto a receiver, and converted into high-temperature process heat. The generated heat is fed to a thermochemical reactor that produces synthesis gas. This is then processed into fuels by standard gas-to-liquids technology such as the Fischer-Tropsch process. The set-up also includes thermal energy storage, which enables fuel production around the clock.

To progress as quickly as possible, Synhelion is building an industrial-scale solar fuel plant at Brainergy Park Jülich in Germany. The commissioning of the plant and the start of fuel production is planned for 2023.

By 2025, Synhelion aims to produce 500,000 liters of fuel per year, rising to 875 million liters just five years later, enough to cover about half of Switzerland’s jet fuel demand. The company’s goal is to raise production capacities to cover half of Europe’s jet fuel demand by 2040.

“The beauty of solar fuels is that they are a drop-in fuel,” says Gianluca Ambrosetti, CEO and co-founder of Synhelion. “So, we can use the existing fuel distribution infrastructure. And we expect that production costs will be below €1 per liter by 2030. To generate global impact, solar fuels must be competitive with fossil fuels.”


Sustainability strategy

Synhelion is already looking further ahead and developing a range of reactor technologies to produce synthesis gas. This will help the company meet changing customer demands and legislative requirements.

In the first plants, Synhelion will use water as well as biogenic CO2 and methane as feedstocks for a solar-driven reforming reaction to produce solar fuels. In parallel, Synhelion is also developing reactor technologies that perform pure thermochemical splitting of CO2 and water. Whatever the solution though, high-temperature solar heat will be the core of production.

“The sun is the most abundant and most evenly distributed renewable energy source there is,” informs Ambrosetti. “Our Sun-to-Liquid technology minimizes the number of energy conversion steps by using the solar heat directly instead of making a detour via renewable electricity, thus maximizing fuel production efficiency.”

Another advantage is that thermal energy storage is much cheaper and environmentally friendlier than battery storage.

“We are proud that SWISS will be the first airline in the world to fly with solar fuel,” says SWISS Chief Executive Officer Dieter Vranckx. “In partnering with Synhelion, we are supporting Swiss innovation and are actively pursuing and promoting the development, the market introduction and the scaling-up of this highly promising technology for producing sustainable fuels.”

SWISS will be substantially increasing its use of sustainable aviation fuels in the next few years to help achieve its climate objectives. And the limited availability of biofuels means alternative SAF production methods will be required.

“This is why we are actively supporting the development of solar fuels,” stresses Vranckx. “We want to be a pioneer in their use. So, our involvement with Synhelion is a key element in our long-term sustainability strategy.”


Credit | Synhelion