Solar kerosene – how Swiss pilot project could revolutionize aviation

Can we fly to Bali in the future without remorse? Plans by the airline Swiss, which belongs to the Lufthansa Group, indicate this.

Since last year, Swiss has been working with the cleantech company Synhelion to bring climate-friendly solar fuel onto the market.

The first Swiss aircraft fueled with sustainable kerosene, the so-called SAF (Sustainable Aviation Fuel), is now scheduled to take off next year.

Solar kerosene: dismantling based on the Lego brick principle

But what is behind the “sustainable” kerosene that ends up on the plane?

“When fuel is burned, CO2, water vapor and heat are created,” explains Synhelion spokeswoman Carmen Murer to FOCUS online. “We reverse the combustion process by converting CO2 and water vapor back into what it was originally using solar heat Although kerosene.”

Murer compares the process to dismantling assembled Lego bricks: the bricks are taken apart during combustion. Synhelion collects them and uses solar energy to arrange them so that they end up making kerosene again.

The process begins with the extraction of CO2 and water from the atmosphere. This can be done using machines (“direct air capture”) or plants that extract CO2 from the air through photosynthesis. In the end, when the kerosene is burned, only as much CO2 is emitted as was previously extracted from the atmosphere to produce the fuel. This closes the cycle.

Solar kerosene and fossil kerosene are chemically almost the same

Syngas is produced from the components obtained using solar energy. A so-called mirror field is used for this. Here, a multitude of mirrors direct the sunlight onto the top of a tower, which also houses the reactor that converts the components CO2 and water into synthesis gas.

The synthesis gas is then liquefied to produce synthetic crude oil. This is processed in a refinery into kerosene, which has the same chemical properties as fossil, petroleum-based kerosene.

For this reason, according to Murer, solar kerosene can simply be added to fossil kerosene. This means that no separate distribution channels and tank farms are required.

Flights with pure SAF are currently not permitted

Synhelion is currently building its first solar fuel system in Jülich. The construction is scheduled to be completed at the end of the year with the aim of starting fuel production in 2024 and thus also refueling the first Swiss machine.

However, 100 percent solar kerosene will not end up in the tank. That wouldn’t be legally possible: “In aviation, people are very careful about certification. It is currently permitted to mix up to 50 percent SAF with conventional kerosene – no more,” explains Carmen Murer.

However, this has not yet been a problem because the quantities available on the market are currently still small. The company spokeswoman explains that availability has been very low so far, with demand that is only just developing.

EU quotas for sustainable kerosene will apply from 2025

This will now be reinforced by the fact that quotas for SAF in aviation will be introduced in the EU from 2025. Accordingly, from 2025, two percent of the kerosene used in the EU must be sustainable. This value should be steadily increased over the years. By 2050, the quota should be 70 percent, so that only 30 percent of kerosene can come from petroleum.

In addition, the flights require large quantities of kerosene, which cannot yet be produced due to a lack of capacity. Germany alone wastes almost ten million tons of kerosene every year.

The facility in Jülich, which will supply the fuel for the Swiss flight next year, is not designed for this. It is primarily used to demonstrate that the system works and that the fuels can be used.

Sustainable fuel is already on the market

However, solar kerosene is not the first sustainable fuel on the market. As Swiss announced upon request, SAF has been available to customers since 2019.

Last year, the Lufthansa Group used around 13,000 tonnes of biogenic fuel, which is mainly made from residues such as used cooking oils or fats.

However, this corresponded to just under 0.2 percent of the Lufthansa Group’s total fuel requirements and around five percent of the SAF available worldwide.

No regular flights planned yet

Synhelion’s first commercial plant is scheduled to be built by 2025 in Spain, where weather conditions are also more favorable for solar energy. This is expected to produce around 1,000 tons of fuel per year. According to Synhelion, this is still a comparatively “very small amount”, but with which you can regularly fly short distances.

The company wants to continuously increase this amount and be able to cover around half of Switzerland’s kerosene requirements within ten years. This corresponds to seven percent of German requirements.

The first flight with solar kerosene is a milestone for Swiss and Synhelion, but it is not yet the starting signal for the everyday use of the SAF: “It will take some time before solar fuel is used regularly in flight operations. This will only be possible when Synhelion starts operating a commercial plant with larger production quantities,” explains Melanie Heiniger, Head of Sustainability at Swiss, when asked by FOCUS online.

Details about the flight have not yet been announced

Synhelion has not yet published more detailed information, such as the date, how much solar fuel will actually be refueled or the distance the aircraft should travel. According to the company spokeswoman, details like these also depend on how quickly the corresponding amount of kerosene can be produced and what the weather conditions will be like in the coming year.

The flight will not yet make a gigantic difference in the CO2 balance. Like the production of solar kerosene, the flight is primarily intended to demonstrate the direction in which aviation is developing in the future.

Other airlines are already making efforts to use sustainable aviation fuel in their aircraft. The Dutch airline KLM adds one percent SAF made from biogenic raw materials to every flight that flies from Amsterdam. Nevertheless, Swiss sees itself as a pioneer when it comes to SAF. Melanie Heiniger: “By working together to promote and market solar fuel, Swiss and Synhelion are taking a pioneering role in the production and use of sustainable fuels.”