The aviation industry is looking for ways to cut emissions without waiting for a completely new generation of aircraft. One of the technologies attracting growing attention is electro-sustainable aviation fuel, or eSAF, a synthetic jet fuel made using renewable electricity, water and captured carbon dioxide. Unlike conventional jet fuel, which begins with crude oil, eSAF begins with electricity. The process essentially turns renewable power into a liquid hydrocarbon that can be used in aviation.
It starts with renewable electricity
The first input is electricity generated from renewable sources such as solar, wind or hydropower. That electricity is used to produce one of the key building blocks of eSAF: green hydrogen. Inside an electrolyser, electricity is passed through water, splitting it into hydrogen and oxygen. The hydrogen is then separated and purified for use in the fuel-production process. This is important because hydrogen provides the chemical energy needed to build the hydrocarbon molecules that eventually become jet fuel. But hydrogen alone is not enough. The process also needs carbon.
The carbon comes from CO₂
Instead of extracting carbon from crude oil, eSAF producers use carbon dioxide. The CO₂ can come from different sources, including industrial processes, biogenic sources such as biogas facilities, or Direct Air Capture, which removes carbon dioxide directly from the atmosphere. The source of the CO₂ matters. For eSAF to deliver substantial lifecycle emissions reductions, the carbon needs to come from a source that does not simply add new fossil carbon to the atmosphere. Once captured, the CO₂ is purified and prepared for synthesis. This creates the two central ingredients of the process: green hydrogen and carbon dioxide.
Hydrogen and CO₂ become the building blocks for fuel
The hydrogen and CO₂ are then brought together in a chemical process. One important step is the Reverse Water-Gas Shift reaction, which converts CO₂ and hydrogen into carbon monoxide and additional hydrogen. The result is a mixture known as synthesis gas, or syngas. This is where the process starts to resemble conventional fuel production. Syngas can be converted into hydrocarbons through several routes, with two important pathways being Fischer-Tropsch synthesis and methanol-to-jet. In the Fischer-Tropsch route, catalysts convert the syngas into longer-chain hydrocarbons. These products can then be hydrocracked and treated to create hydrocarbons suitable for aviation. In the methanol-to-jet route, the syngas is first converted into methanol. The methanol is then chemically upgraded into hydrocarbons in the jet-fuel range. In both cases, the objective is the same: build hydrocarbon molecules that have the characteristics required of aviation fuel.
The final product is synthetic kerosene
The resulting hydrocarbons are refined and upgraded to meet the specifications required for aviation fuel. The finished product is synthetic kerosene that can be blended with conventional jet fuel. That is one of eSAF’s biggest advantages. Airlines do not need to replace their aircraft fleets or build an entirely new fuelling infrastructure simply to use the fuel. Instead, certified synthetic aviation fuels can be incorporated into existing aviation systems within the blending limits established by their relevant fuel standards. For airlines, this makes eSAF potentially more practical than technologies that would require completely new aircraft or airport infrastructure.
The carbon cycle is what makes eSAF different
The central environmental argument for eSAF is not simply that it uses hydrogen. It is the combination of renewable electricity and non-fossil carbon. When synthetic fuel made from captured CO₂ is burned in an aircraft, carbon dioxide is released back into the atmosphere. But if that carbon was originally captured from the atmosphere or a biogenic source, the process can approach a closed carbon cycle. The carbon is effectively captured, converted into fuel and eventually released again. That does not mean eSAF is completely emissions-free. The aircraft still produces CO₂ when the fuel burns, and the overall climate impact depends on how the electricity, hydrogen and CO₂ are produced, as well as the energy consumed throughout the production chain. But when renewable power and appropriate carbon sources are used, lifecycle greenhouse-gas emissions can be dramatically lower than those associated with fossil jet fuel.
Electricity is the real feedstock
This also changes the economics of sustainable aviation fuel. Traditional bio-based SAF depends on physical feedstocks such as used cooking oil, agricultural residues, waste fats or other forms of biomass. eSAF does not depend on those resources. Its fundamental inputs are renewable electricity, water and carbon dioxide. That potentially gives the technology a much larger long-term resource base. But it creates another challenge.
Producing fuel this way requires large amounts of renewable electricity. The electricity first has to produce hydrogen. More energy is then consumed in converting hydrogen and CO₂ into hydrocarbons and refining those hydrocarbons into fuel. As a result, producing large quantities of eSAF will require enormous amounts of additional renewable generation. The challenge is therefore not simply building an eSAF plant. It is building enough cheap, reliable renewable power around it.
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Why eSAF matters for aviation
Aviation is one of the harder sectors of the economy to electrify directly. Electric cars can use batteries. Trains can increasingly use overhead electricity. Commercial aircraft, however, require extremely high energy density because carrying heavy batteries reduces the amount of payload an aircraft can carry and the distance it can travel. Liquid hydrocarbons remain exceptionally energy-dense. That is why synthetic aviation fuel is attractive: it attempts to decarbonise the fuel while keeping the aircraft architecture largely unchanged. Rather than asking airlines to abandon jet engines, eSAF attempts to change what goes into them.
The biggest constraint is scale
The chemistry is increasingly understood. The harder question is whether the industry can produce eSAF at the scale aviation requires and at a price airlines can afford. That means solving several problems simultaneously. Renewable electricity needs to become cheaper and more abundant. Electrolysers need to be deployed at large scale. Reliable supplies of low-carbon CO₂ need to be secured. Fuel-synthesis plants need to become larger and more efficient. And all of this infrastructure has to operate economically. This is why eSAF is increasingly being viewed not simply as a new type of aviation fuel, but as an emerging industrial system connecting renewable power, hydrogen, carbon capture and aviation.
