Solar fuels and their role in achieving net zero
Published in 2021, updated in 2023
The transportation sector accounts for roughly a quarter of global CO2 emissions. About 28’0001 aircraft , 105’000 merchant ships2 and 1.4 billion road vehicles worldwide are still mainly powered by fossil fuels emitting CO2 into the atmosphere. If the goal of limiting global warming to 1.5°C is to be achieved, then the transportation sector must 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.3 At the same time, it is one of the most challenging sectors to decarbonize because of the need for high-density energy carriers. There are different levers to decarbonize aviation, whereas the following types of technologies are most commonly considered: electrification, hydrogen, and sustainable aviation fuels (SAF).
Electrification: A potential solution for short-haul flights
Battery-electric propulsion systems can get aircraft 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 the Tesla battery (Model S), for example, 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.4 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.5
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% of aviation CO2 emissions are emitted from flights of over 1’500 kilometers.6
Hydrogen technology: A solution for newly engineered planes of the future
Of all the energy carriers currently available, hydrogen has the highest energy content per kilogram. However, 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 evaluating different 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 2035.7 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 producing it can be carbon intensive. Less than 1% of hydrogen today is produced sustainably, e.g. through water electrolysis, and counts as low-emission hydrogen.8 Nearly all global hydrogen is still made using fossil fuels.9 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 renewable 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, performance, and energy density. 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% blend of SAF and conventional jet fuel. However, leading aircraft and engine manufacturers are pushing to validate and certify 100% SAF use by 2030.
The latest EU Fit for 55 plan sets out a mandatory, successively increasing blending quota of SAF for the aviation industry: The goal of this initiative is to reduce the growing impact of aviation on the environment by boosting the production and uptake of SAF.10
Solar fuels and our roadmap toward net zero
Synhelion’s solar fuels are produced from solar energy. They are a substitute to fossil fuels, enabling sustainable transportation. They are renewable and fully compatible with conventional internal combustion engines, jet engines, and existing global fuel infrastructure.
In 2019, Synhelion produced the first drops of solar fuel under real field conditions. Since then, we have been scaling up our technology. A year later, we successfully tested key components at scale on the solar tower of the German Aerospace Center. In 2022, Synhelion became the first company in the world to succeed in producing syngas on an industrial scale using only solar heat as energy source. With this, the last decisive technical milestone for the industrial production of solar fuels had been reached. Afterwards, we started to build DAWN, the world’s first solar fuel plant at industrial scale. Plant DAWN will be commissioned in 2024 and the fuels produced by DAWN will be used for various showcases across the transportation sector to highlight the importance of sustainable fuels in the transportation sector’s transition to net zero.
Following plant DAWN, Synhelion will build its first commercial plant in Spain and will scale its technology step by step. We aim to produce one million tons of fuel per year by 2033, ramping up to 40 million tons of fuel per year by 2040, which would be enough to cover half of Europe’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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Sources:
[1] statista.com/statistics/282237/aircraft-fleet-size
[2] hbs.unctad.org/merchant-fleet
[3] icao.int/Meetings/FutureOfAviation/Pages/default.aspx
[4] aircraft.airbus.com/en/aircraft/a320/a320neo
[5]
[6] atag.org/facts-figures
[7] airbus.com/en/innovation/low-carbon-aviation/hydrogen/zeroe
[8] iea.org/reports/global-hydrogen-review-2023/executive-summary
[9] iea.org/reports/the-future-of-hydrogen
[10] consilium.europa.eu/en/policies/green-deal/fit-for-55
