// eSAF vs the alternatives
Weaning aviation off fossil kerosene is difficult but necessary. There are essentially four feasible options. Each one has a real shot at part of the problem, and a real reason it cannot solve all of it. Here is where they stand.
Weaning aviation off fossil kerosene is difficult but necessary. There are essentially four feasible options. Each one has a real shot at part of the problem, and a real reason it cannot solve all of it. Here is where they stand.
A lithium battery stores about 0.25 megajoules per kilogram. Jet fuel stores 43. To carry the same energy as a full tank of kerosene, you would need a battery pack roughly 40 times heavier. That is not a problem anyone is close to solving, and as the IEA notes, "the energy density of batteries would need to increase by a factor of around 30" to match liquid fuels for long-range flight.
Short-haul electric aircraft under 500 km are in development. Heart Aerospace, Eviation, and others are flight-testing prototypes for regional routes. For commuter hops between nearby cities, batteries may well work. But for the transatlantic, transcontinental, and long-haul flights that account for the majority of aviation emissions, batteries are not a solution. Not because the industry lacks ambition, but because the physics of energy density is not expected to change within the timeframe that matters for climate targets.
Verdict. Real for short hops. Not an option for the flights that produce most emissions.
// Energy density · same energy on board
A lithium battery stores 0.25 MJ/kg against 43 for jet fuel. Same energy on board, about 40 times the weight.
Source Energy density: approximately 0.25 MJ/kg (Li-ion) versus 43 MJ/kg (jet fuel). IEA aviation assessment.
Hydrogen carries three times the energy of jet fuel per kilogram, and as a zero-carbon fuel it is a genuinely promising prospect for flight. The challenge is storing it: hydrogen has to be compressed to 700 bar or chilled to minus 253 degrees Celsius, which needs large, heavy tanks quite unlike the wing tanks aircraft use today.
That makes it a longer road than first hoped. In early 2025 Airbus moved its ZEROe aircraft from 2035 into the 2040s, and the industry's Destination 2050 roadmap revised hydrogen's expected share of aviation's net-zero plan from 20 percent to 6 percent. When it arrives it will suit short and medium routes well; long-haul would need new airframes and new fuelling infrastructure worldwide.
Verdict. A promising fuel for short and medium routes from the 2040s. Not yet ready for long-haul, or for the fleet flying today.
// Storage · same energy
Liquid hydrogen must be kept at -253 C, in a tank far larger than the wing tanks used today. Airbus ZEROe entry into service slipped from 2035 to the 2040s.
Source CompositesWorld 2025; GreenAir News. Storage conditions for liquid hydrogen widely reported.
Bio-SAF is the most established sustainable aviation fuel today. The HEFA pathway turns used cooking oils and animal fats into jet fuel that already flies, and airlines are buying it now. It has earned its place in the transition.
Its limit is supply. Genuine waste oils and fats are finite and already sought by other industries, so scaling further means turning to crops, which raises real questions about food, land and biodiversity. A 2024 study for the SASHA Coalition found large-scale crop biofuels carry a serious biodiversity risk. This is exactly why the EU set a separate sub-mandate for synthetic fuels, rather than leaning on biofuels alone.
Verdict. Valuable today from genuine waste streams. Harder to scale to mandate volumes without pressure on food and nature.
// The issue is scale, not the concept
Used cooking oils and animal fats already make jet fuel that flies today. The supply is finite and already competed for.
Scaling beyond waste means crops: food competition, deforestation risk, and biodiversity loss.
Source SASHA Coalition / Cerulogy 2024.
eSAF is synthetic kerosene made from renewable electricity, water and captured CO₂. It is chemically equivalent to fossil jet fuel, flies on every aircraft in service today, and moves through existing airport fuelling unchanged. Its carbon is captured rather than taken from the ground, so burning it returns only the CO₂ that went into making it.
Its constraints are real: it needs a great deal of renewable electricity, several industrial steps (see our Technology page), and it is still the most expensive SAF pathway today.1
What sets it apart is scale. Its inputs are not limited by land or biology, so it grows with renewable power, and it needs no new aircraft or airports. It works now, on the planes we have, for the long-haul routes that matter most. As ICAO puts it, SAF has the greatest potential to reduce CO₂ emissions from international aviation.2
Published lifecycle figures place eSAF at roughly 70 to 95 percent below fossil kerosene,3 depending on the electricity and CO₂ sources, against the 70 percent minimum that EU RED III requires.4 The cleanest results come from fully renewable grids with biogenic CO₂.
Verdict. Expensive today, and the strongest fit for the hardest part of the job: long-haul flights, on today's aircraft, powered by renewables.
// The ingredients are abundant
It scales with renewable energy, not with land.
Sources 1 ICCT 2025 · 2 ICAO SAF · 3 DR (EU) 2023/1185 · 4 Dir (EU) 2023/2413
// The full picture
There is no single technology that decarbonises aviation. The question is which one covers which flights, and when.
eSAF is the only option covering every range from the late 2020s. Lane heights are scaled to each range’s share of aviation CO₂
Lane heights are proportional to each range band’s share of CO₂ from European departures, 2019: flights over 4000 km were 6% of flights and 48% of CO₂; flights under 500 km were 24% of flights and 3.8% of CO₂; the 500–4000 km middle is the remainder. Bio-SAF appears as a thin band across all ranges, limited by feedstock supply. Battery aircraft (aqua), eSAF and hydrogen from the 2040s all serve the short-haul sliver.
SourceEurocontrol Data Snapshot #4 (2021); Regulation (EU) 2023/2405 ReFuelEU; Airbus ZEROe announcements.
The one SAF that covers every route, every aircraft, and every compliance framework. That is what we will produce at Keflavík from 2029.
