Solar fuels and their role in achieving net zero

The transportation sector accounts for roughly a quarter of global CO2 emissions. About 1.4 billion road vehicles and 27’000 aircraft1 worldwide are still mainly powered by fossil fuels emitting CO2 into the atmosphere. If the goal of limiting global warming to 1.5 degrees Celsius is to be achieved, then the transportation sector needs to undergo a fundamental transformation. There is no way around new types of propulsion and alternative fuels.

However, achieving net zero is not just about developing new sustainable technologies. It is about choosing the most efficient approach for each application, conserving resources, and using what is already out there in the most sustainable way possible.

This blog post provides an overview of the latest developments in the decarbonization of aviation and long-distance transportation. We also compare promising solutions to enable sustainable change in transportation.

Current solutions for decarbonizing aviation

The aviation sector is forecasted to grow massively over the following decades. Yet, at the same time, it is one of the most challenging sectors to decarbonize because of the need for high-density energy carriers. Three types of technologies have taken on the challenge of decarbonizing aviation: electrification, hydrogen technology, and sustainable aviation fuels (SAF).

Electrification: A potential solution for short-haul flights

Battery-electric propulsion systems can get aircrafts flying without producing any tailpipe emissions. They are highly efficient and offer hardly any power losses, even at high altitudes. However, compared to conventional fuels, batteries have a very low energy and power density. Jet A fuel has a specific energy density of 43.1 MJ/kg, while today’s best battery – the Tesla Model S – has a specific energy density of 0.4 MJ/kg. Let’s see what this would mean for an Airbus A320 neo, one of the most widespread short-to-medium-haul aircraft that can carry 194 passengers up to 6’300 kilometers.2 To power the aircraft, a battery weighing 1’185 tons would be necessary, but maximum take-off mass is 79 tons. Even with tomorrow’s projected best batteries with a specific energy density of 1.8 MJ/kg, the aircraft battery would weigh 263 tons – still way too heavy for take-off.3 This example illustrates why battery-electric propulsion systems can only be used for small aircraft and cover short distances. Long-haul flights are not likely to be electrified in the near future, despite being the ones with the biggest climate impact by far. In fact, around 80 percent of aviation CO2 emissions are emitted from flights of over 1’500 kilometers.4

Hydrogen technology: Building new planes

Of all the energy carriers currently available, hydrogen has the highest energy content per kilogram. But, its liquid form has a much lower volumetric energy density than kerosene. To address this issue, hydrogen can be stored in cylindric pressurized tanks at very low temperatures. In aviation, the certification path for pressurized hydrogen is largely unexplored. Airbus is currently evaluating three concepts for hydrogen-powered aircraft to assess whether they could be matured into viable future products, hoping that their first zero-emission commercial aircraft could enter service by 2035.5 Because of the bulky hydrogen tanks needed, engineers will have to design the aircraft differently than conventional planes from the ground up. To roll out hydrogen technology, a global hydrogen distribution infrastructure would need to be built and the existing planes would need to be replaced. Given the fact that airliners have a typical lifespan of 30 years and that it will still take years of development for hydrogen planes, the impact on greenhouse gas emissions reduction will be slow.

Hydrogen emits only water when burned. But creating it can be carbon intensive. Less than 0.1 percent of hydrogen today is produced through water electrolysis. Nearly all global hydrogen is still made using fossil fuels.6 The production of hydrogen has yet to switch to renewable energy sources.

Sustainable aviation fuels: Using existing infrastructure to achieve net zero

SAF is the generic term for regenerative fuels that are not based on raw fossil materials. These can be biofuels or synthetic fuels. Read about the different types of SAF in our blog post explaining how they are produced. SAF are comparable to fossil fuels in terms of quality and performance. They are compatible with conventional jet engines and can use the existing infrastructure for storage and refueling. Aircraft are currently only allowed to operate on a 50 percent blend of SAF and conventional jet fuel. However, leading aircraft and engine manufacturers are pushing to validate and certify 100 percent SAF use by 2030.7

The latest EU Fit for 55 plan sets out a mandatory, successively increasing blending quota of SAF for the aviation industry: two percent in 2025, five percent in 2030, 20 percent in 2035, 32 percent in 2040, and 63 percent in 2050.8 The goal of this initiative is to reduce the growing impact of aviation on the environment by boosting the production and uptake of SAF.

Solar fuels and our roadmap toward net zero

Synthetic fuels that are produced from solar energy are called solar fuels. They are a climate-friendly substitute to fossil fuels, enabling sustainable transportation without changing current equipment. Additionally, they are renewable and fully compatible with conventional internal combustion engines, jet engines, and existing fuel infrastructure.
In 2019, we produced the first drops of solar fuel under real field conditions. Since then, we have been scaling up our technology. In 2020, we successfully tested key components at scale. In 2021 and 2022, we are testing the integrated system on the solar tower of the German Aerospace Center. This marks the last milestone before building the world’s first solar fuel plant at industrial scale in 2022. From 2023 onwards, we will produce next-generation synthetic fuels, which are produced more efficiently than competing technologies due to the direct use of solar heat in the production processes. For 2030, we are aiming for a production capacity of 875 million liters a year, which would be enough to cover half of Switzerland’s jet fuel demand.

Join us on our path to net zero

The technologies to decarbonize transportation do exist – they just need to be implemented. There is no looking past alternative fuels if aviation wants to comply with and achieve its net zero agreements and targets. Solar fuels are the most affordable, efficient, scalable, and environmentally friendly solution for clean, long-distance transportation.

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