Sustainable aviation fuel (SAF), widely deemed key to decarbonizing the airline industry, is coming under fire.
Environmental group Clean Air Task Force (CATF), in a report released last week, argued that SAF can be a "misleading" and "obfuscating" term that can be applied to biofuels that are little more sustainable than conventional jet fuel. SAF can include biomass-derived fuels, for instance, that have lifecycle greenhouse gas emissions that are comparable to conventional fuels.
Synthetic fuels, hydrogen, and electrification all have the potential to compete with SAF as the technology of choice for aviation in a low-carbon world, the report said. But they are in the early stages of development compared with biofuels.
The aviation sector accounts for about 2pc of global CO2 emissions now, a percentage which could triple by 2050 without policy changes — new investments and policy support for low-carbon alternative fuels will be needed to meet demand and low-carbon goals, CATF said.
SAF producer World Energy sustainability vice president Adam Klauber acknowledges that today's SAF blends will not get the airline sector to net-zero. But tomorrow's products will move the sector closer to that goal.
"Everything we do in the human world right now has a carbon footprint, Klauber said. "There is not a single product that is net-zero on a sector-wide basis."
World Energy uses green hydrogen and wind and solar energy in its SAF production, but some of its upstream suppliers still have carbon associated with the powering of facilities. And even for material that is sustainably produced, there is currently no effective certification system in place to prove that a product was made with no emissions, Klauber said.
World Energy is embracing full transparency regarding its emissions, since exposing those emissions is what will help to decarbonize the industry. "Let's all be honest about carbon," Klauber said.
Finnish biofuels producer Neste projects that SAF will account for about 65pc of emissions reductions by 2050. "SAF is not the only solution we need," Neste said. "The challenge of combating climate change needs multiple solutions working together."
Neste is targeting global SAF production to 1.5mn t/yr by the end of 2023 and plans to explore new production pathways, like power to liquid fuels, and the use of lignocellulosic raw materials and algae as feedstocks.
Not all SAF blends are created equal. US carbon utilization firm Air Company says it has developed a carbon-neutral SAF made from green hydrogen and captured CO2 from industrial processes.
The CATF report warns that biomass supply constraints could arise because of limited amounts of land on which it can be grown, leading to potential shortages of biofuels.
US biofuel production — assuming the repurposing of all production for aviation — would need to more than double to meet domestic demand for commercial aviation fuel consumption of 3.2 quads by 2030, and 4.1 quads in 2050, according to the US Energy Information Administration's 2021 Annual Energy Outlook. To put that in perspective, the IEA projects total global biofuels production will be 11.1 quads/yr, meaning biofuels alone will be hard-pressed to meet the aviation sector's demands.
While synthetic fuels hold promise as an alternative, they will require substantial investment and policy support to achieve "anything close to cost parity" with conventional jet fuels, the report notes.
Electric motors can eliminate contrails and boast savings on operational costs, but battery-electric powertrains today are not feasible for larger aircraft for medium- to long-distance flights, the report says. Today's batteries are about 14 times less energy dense than conventional jet fuel — the largest electric aircraft flown to-date was a nine-seater with a 100-mile range.
But half of all US flights clock in at under 500 miles, and electric flights could connect smaller communities without major airports "in ways previously not possible," senator Maria Cantwell (D-Washington) said last week, after a successful electric airplane test in Washington state. But for longer flights with heavier aircraft, the industry may still need to look to other options.
Hydrogen is lightweight compared with batteries and can be deployed in existing commuter and regional aircraft with limited retrofits. But research projects that using hydrogen in short-range aircraft in 2040 could increase operating costs by 25pc per passenger compared with conventional jet fuel, CATF says.
