This article was written by Michael Marshall and first published in Direct Industry EMag.
Ronald Halim has a plan. His team has built an array of glass tubes, bathed in light, in which they grow billions of single-celled green algae. These algae produce large quantities of an oil, not unlike rapeseed oil. A few chemical reactions later, and the oil is transformed into fuel for a jet aeroplane.
Halim hopes that his green algae will be a new source of sustainable aviation fuel: a fuel that can power aeroplanes without producing greenhouse gas emissions. The aim is to help cut aviation’s enormous carbon footprint.
His project exists thanks to an array of governmental actions. The government of Ireland, where Halim is based, produced a policy roadmap for sustainable aviation fuel in August 2025. At a larger scale, the European Union (EU) has issued a swathe of directives aimed at cutting aviation emissions and boosting the use of sustainable aviation fuel. The challenge now is to turn lab-scale projects like Halim’s into commercially-viable production facilities – and turn sustainable aviation fuel from a niche concern into a global industry.
Clean jet fuel
Most world leaders have committed to limiting global warming to 2°C. This requires drastic cuts in greenhouse gas emissions and ultimately for the world to achieve net-zero emissions.
One of the most challenging emissions sources is aviation. It is responsible for about 2.5% of annual global CO2 emissions. As demand for air travel grows, so will emissions from aviation.
Cars and other road vehicles can be made climate-friendly by electrifying them. However, batteries are not currently a practical option for aeroplanes, because they are too heavy.
“Unlike some other transport modes, there is no immediate option in aviation to switch to electric or hydrogen at scale,” says a spokesperson at Ireland’s Department of Transport.
Instead the aviation industry is pinning its hopes on sustainable aviation fuel (SAF). Instead of powering its planes using fossil fuels, it plans to create replacement fuels from renewable sources.
There are international standards for aeroplane fuel, covering things like thermal stability and combustion, set by ASTM International. “SAF is a fuel that is certified to the exact same standards,” says Agnes Thornton, co-founder of Sustainable Flight Solutions in Dublin, Ireland. The idea is to create a “drop-in fuel” that can be transported using existing infrastructure and inserted into the fuel tank of an existing plane.
There are multiple potential pathways to make SAF, according to a September 2025 report by the International Air Transport Association (IATA), the trade association for the world’s airlines.
One possibility is to use renewable energy to synthesise fuels from green hydrogen and CO2 captured from biogenic sources: the so-called power-to-liquid (PtL) pathway. If this was done using green hydrogen, which is itself made using renewable energy, it would have virtually no net greenhouse gas emissions.
However, power-to-liquid faces considerable obstacles. “Hydrogen, especially green hydrogen, is not available at the scale that will be needed, and there is huge competition for it,” says Thornton. “It is a very promising pathway for SAF production, there’s no doubt about it. But the technology is still in development and it’s not running at commercial scale.”
Happily, PtL is just one option. SAF could also be produced from several forms of biomass, such as energy crops, forestry waste and vegetable oils. Of these, only one is currently operating at commercial scale. That is hydroprocessed esters and fatty acids (HEFA), which can be obtained from food-grade oils such as rapeseed oil and palm oil. According to the IATA report, HEFA accounts for 90% of all existing and upcoming SAF production.
The shortfall
Despite this diversity, SAF production is still falling short of what is needed. According to IATA, humanity needs to be able to make 500 million tonnes of SAF annually by 2050, but we are on course to achieve only 400 million tonnes per year – leaving a shortfall of 100 million tonnes.
“One way of reaching that or filling that gap is to increase the feedstock base,” says Thornton – to take another source of SAF and transform it from a theoretical source to something practically and commercially feasible.
That’s what Halim, who is based at University College Dublin in Ireland, is trying to do with his SusAlgaeFuel project, which Thornton is involved in. Some species of single-celled algae store energy in the form of oils, which can be converted into jet fuel.
So far, this has not been practical because of the “high cost”, says Halim. There are three stages, all of which must be made cheaper: growing the algae, obtaining the oil from the algae, and converting the oil into fuel.
Halim’s solution is to grow the algae on the waste from anaerobic digesters, which are used to convert farm waste into methane. The waste is a cheap source of nutrients, and using it is a thrifty option. Next, his team is working on a method of breaking the cells open using a pulsed electric field, rather than expensive chemicals. They are also experimenting with the catalysts used to convert the oils into jet fuel.
The project began in 2024 and will run for four years. At present the work is lab-scale, but in 2027 the team plans to build a full-scale pilot next to an existing anaerobic digester, to demonstrate that the process can work continuously at scale.
Support for SAF
The challenge for governments is to ensure that R&D work, like that done by SusAlgaeFuel, is converted into commercial-scale SAF production.
The Irish government’s policy roadmap identifies four areas where progress is needed, and where the government may need to intervene. For instance, markets need greater certainty and that requires unified policies, so as a first step the roadmap identifies the “competent authorities” responsible for key steps, like ensuring that aviation fuel at Irish airports includes a minimum amount of certified SAF. The roadmap also emphasises the need to support production and uptake of SAF.
At the EU level, there are multiple directives in play. The bloc established overall targets in its Renewable Energy Directive, which was introduced in 2009 and made more ambitious in 2018 and 2023. The latest version set a binding target of 42.5% renewable-sourced energy for transport by 2030. The Directive also established rules about biofuels, including those used for aviation, to ensure they do not encroach on non-cropland areas like forests.
In 2021 the EU passed the Fit for 55 package, which aims to reduce the continent’s net greenhouse gas emissions by 55% by 2030, compared to 1990 levels. To support this, in 2024 the EU established ReFuelEU Aviation, which is specifically focused on SAF. It states that all flights from EU airports must include a minimum amount of SAF: this scales up over time, from 2% in 2025 to 70% in 2050.
The challenge will be making this happen. “Given the nascent nature of SAF production, it is currently facing a number of challenges with regard to financing, cost and investment,” says the Department of Transport spokesperson.
“It’s about scaling the technologies and the approaches that those projects [like SusAlgaeFuel] develop,” says Thornton. “That scaling is crystallising out as one of the big bottlenecks in all this.” While governments are supporting lab-scale R&D, they are not doing enough to support larger pilot projects that can demonstrate the commercial viability of SAF. Companies won’t fund those projects either. “They want a return on investment, which is not going to come from a pilot facility.”
The question is always “is this scaleable?” says Halim. “Those questions have to be addressed, and they have to be addressed at pilot scale rather than at lab scale.”