Navigating the Turbulent Path to Net-Zero Aviation: The best is yet to fly

The aviation sector is one of the most challenging industries to decarbonise, accounting for 2.5% of global energy-related carbon dioxide (CO₂) emissions (1). As global passenger demand surges, achieving net-zero flight requires a holistic transformation across the entire ecosystem, from aircraft design and airport infrastructure to air traffic management (ATM). This article focuses on one crucial pillar of this transition, evaluating the feasibility, advantages, and engineering limitations of three primary propulsion and fuel technologies: Sustainable Aviation Fuels (SAFs), hydrogen, and electric systems. Ultimately, achieving sustainable aviation relies on cross-sector innovation; therefore, while this piece highlights propulsion, the Solar Impulse Foundation’s Aviation Call for Solutions warmly invites innovators across all aviation sectors, including infrastructure, operations, and efficiency, to submit their solutions.

The Growing Challenge of Aviation Emissions

Lately, global air travel demand has experienced a significant surge. In 2025, passenger demand rose 6% compared to previous years, and data projections show that 2026 is maintaining a similar upward trajectory of roughly 5.8% (2).

While a growing aviation industry drives global economic connectivity, it simultaneously intensifies environmental pressures. Traditional aviation architectures rely almost entirely on petroleum-based kerosene, causing the sector to account for 2.5% of global energy-related CO₂ emissions (1). Although a single-digit percentage may appear minor at first glance, its cumulative environmental impact is non-negligible and expanding. To counteract the ecological footprint of this growth, innovators are deploying new technologies to optimise aircraft efficiency and fundamentally alter propulsion mechanisms.

Evaluating Sustainable Aviation Fuels (SAFs)

Sustainable Aviation Fuels (SAFs) represent the most immediately deployable replacement for conventional kerosene. Derived from non-fossil renewable resources, SAF is already implemented into existing fueling infrastructure, and aircraft engines can reduce lifecycle CO₂ emissions by up to 80% (3). Airlines have already tested and utilised SAF across more than 360,000 commercial flights, proving its immediate operational feasibility (4).

The industry categorises SAF into two primary types based on production methods:

• Bio-SAF (Organic recycling of pre-existing CO₂): This fuel is made by processing organic feedstocks, such as used cooking oils and agricultural waste. It creates a circular carbon loop by recycling organic carbon previously absorbed by plants. However, a recent study by the University of St. Gallen (3) points out that our planet has a limited amount of land and resources to grow these crops, meaning Bio-SAF alone cannot scale up enough to fuel the entire industry. 

• Electro-Fuels (Synthetic E-Fuels): E-Fuels utilise renewable electricity to power electrolysis, splitting water molecules (H₂O) to isolate hydrogen while releasing oxygen into the atmosphere. Industrial fans equipped with chemical filters then capture CO₂ directly from ambient air. Synthesising this green hydrogen and capturing carbon dioxide under high temperatures and pressures creates synthesis gas, which refiners process into synthetic crude oil and e-kerosene. You can read more about how green hydrogen is defined in our following dedicated article on the colors of hydrogen. 

Despite optimism from industry firms targeting 100% SAF consumption by 2050, economic barriers persist (5). SAF remains significantly more expensive than conventional kerosene. Because fuel comprises a major share of airline operating expenses, this price disparity leaves airlines hesitant to adopt the technology.

Hydrogen Propulsion and the Climate Impulse Milestone

A more radical technological shift involves replacing carbon-based fuels entirely with hydrogen. Hydrogen possesses a high gravimetric energy density and produces zero carbon emissions at the point of use.

To demonstrate the viability of this power source, the Solar Impulse Foundation is launching the Climate Impulse project. Led by Swiss explorer and Foundation Chairman Bertrand Piccard alongside co-founder and chief engineer Raphaël Dinelli, this historic mission aims to achieve the first non-stop, nine-day flight around the world using green hydrogen as the sole fuel source.

While the Climate Impulse aircraft modifies propulsion systems to release harmless water vapor instead of greenhouse gases, hydrogen introduces severe engineering and logistical constraints. Liquid hydrogen requires cryogenic storage at temperatures near absolute zero (-253°C), demanding heavily insulated, bulky storage tanks that alter aircraft aerodynamics. Meeting the strict safety protocols and timelines for a non-stop global journey requires rigorous test schedules to validate system reliability under extreme flight conditions.

© Climate Impulse

Electric and Hybrid Propulsion Realities

The third core strategy centers on transitioning to electric and hybrid-propulsion architectures. Fully electric aircraft offer remarkable operational advantages: they eliminate direct flight emissions, operate with highly efficient electric motors that require less maintenance than gas turbines, and drastically reduce acoustic signatures. This noise reduction could allow airports near residential zones to extend their operating hours.

However, severe physics constraints limit fully electric commercial flight. Current battery technologies suffer from poor specific energy compared to jet fuel, meaning an aircraft must carry immense battery deadweight for a relatively low energy return. This weight penalty severely limits the aircraft’s range and complicates landing configurations. Additionally, commercial operations face bottlenecking from long battery charging cycles, which cannot compete with the rapid turnaround times of liquid refueling.

To bridge this gap, engineers are developing hybrid-electric systems (7). Similar to hybrid automobiles, these aircraft utilise electric power to optimise performance during high-emission flight phases, such as takeoff and landing, while relying on conventional gas turbines for efficient cruising.

Unfortunately, hybrid systems compound structural complexity. Carrying dual powertrains (combustion engines and heavy battery packs) adds substantial weight, creates more mechanical failure points, and doubles manufacturing costs. The aviation industry must determine if the environmental offset of a hybrid system justifies the increased financial investment and strict safety margins required.

Our Call For Solutions

Decarbonising global aviation is an environmental necessity that requires a multi-tiered approach. While transforming propulsion through SAFs, hydrogen, and electric architectures represents a massive piece of the puzzle, true sustainability depends on optimising the entire ecosystem, including aircraft design, airport infrastructure, and ATM. To overcome existing barriers, the aerospace sector requires urgent cross-disciplinary collaboration across all of these fields. Recognising that every piece of efficiency matters, the Solar Impulse Foundation has launched its Aviation Call for Solutions. By submitting and scaling innovations from every corner of the industry, engineers, startups, and researchers can actively transform the future of flight into a clean, sustainable reality for generations to come.

References

1. International Energy Agency, 2026. Aviation. Paris: International Energy Agency. Available at: https://www.iea.org/energy-system/transport/aviation [Accessed 26 June 2026].
2. Boston Consulting Group, 2026. Air Travel Outlook: Revenues and Costs Are Rising. Boston: Boston Consulting Group. Available at: https://www.bcg.com/publications/2026/air-travel-outlook-revenues-and-costs-are-rising [Accessed 26 June 2026].
3. University of St. Gallen, 2026. Is the use of more Sustainable Aviation Fuel (SAF) for business travel possible? St. Gallen: University of St. Gallen. Available at: https://www.unisg.ch/en/newsdetail/news/is-the-use-of-more-sustainable-aviation-fuel-saf-for-business-travel-possible/ [Accessed 26 June 2026].
4. Alternative Fuels Data Center, 2026. Sustainable Aviation Fuel. Washington, D.C.: U.S. Department of Energy. Available at: https://afdc.energy.gov/fuels/sustainable-aviation-fuel [Accessed 26 June 2026]
5. International Air Transport Association, 2026. Sustainable Aviation Fuel (SAF). Montreal: International Air Transport Association. Available at: https://www.iata.org/en/programs/sustainability/sustainable-aviation-fuel-saf/ [Accessed 26 June 2026].
6. Engie, 2026. E-fuels, what are they? Available at: https://www.engie.com/en/explore/explainer/e-fuels-what-are-they/ [Accessed 26 June 2026].
7. Airbus, 2026. Hybrid and electric flight. Airbus SE. Available at: https://www.airbus.com/en/innovation/energy-transition/hybrid-and-electric-flight [Accessed 26 June 2026].