A single long-haul flight can create more carbon emissions in a few hours than the average person in 56 different countries will generate in an entire year. One of the options airlines are able to cut their emissions and lower their carbon footprint is by transitioning away from using petroleum-based fuels to using a low-carbon alternative known as Sustainable Aviation Fuel (SAF). SAFs have the potential to deliver the performance of petroleum-based jet fuel but with a fraction of its carbon footprint, giving airlines solid footing for removing greenhouse gas (GHG) emissions from flight.
What is SAF?
SAF is a fuel that can replace conventional jet fuel without changing the existing engines, infrastructure, or storage facilities. SAFs are chemically identical to conventional jet fuel (or kerosene), which is a mix of hydrocarbons — but instead of fossil fuels, they’re made from a range of renewable starting materials, or feedstocks. Many use biological waste products, including used cooking oils, corn stover (what’s left after the cob is harvested), food scraps, or municipal solid waste. Other SAFs are fully synthetic fuels, or e-fuels, made from carbon dioxide and hydrogen.
However, SAF still has to be blended with traditional aviation fuel, which is made from fossil fuels. Current rules state that SAF can make up a maximum of 50% of the mixture, but there are hopes that airlines will be able to use 100% SAF by 2030.
A key focus for the industry is ensuring that SAF can be used as a “drop-in” replacement for conventional jet fuel. This means that aircraft engines do not have to be modified to use it.
A Menu of Sustainable Feedstocks for Producing SAF
An estimated 1 billion dry tons of biomass can be collected sustainably each year in the United States, enough to produce 50–60 billion gallons of low-carbon biofuels. These resources include:
- Corn grain
- Oil seeds
- Other fats, oils, and greases
- Agricultural residues
- Forestry residues
- Wood mill waste
- Municipal solid waste streams
- Wet wastes (manures, wastewater treatment sludge)
- Dedicated energy crops.
This vast resource contains enough feedstock to meet the projected fuel demand of the U.S. aviation industry, additional volumes of drop-in low carbon fuels for use in other modes of transportation, and produce high-value bioproducts and renewable chemicals.
Feedstocks need to go through a range of steps to turn them into usable jet fuel. One of the most widely-used pathways for producing SAFs so far is taking waste oils, fats, and grease from restaurants and the like, and then putting them through a refining process that’s similar to what’s used for traditional jet fuel. This process, called HEFA (hydrotreated esters and fatty acids), is particularly attractive because it can employ existing oil refineries.
Meanwhile, a fully synthetic fuel that’s produced with renewable energy and CO2 could reduce emissions by 99 percent or more. Using corn stover and waste from sewage treatment plants will likely fall around an 80 percent reduction, while making it from cooking oils will probably be about 50 percent.
Are SAFs currently being used?
The first commercial flight that used a blend of biofuels and regular jet fuel was operated by KLM in 2011, but test flights date back to 2008, with Virgin Atlantic and Air New Zealand among the earliest adopters.
Since then, many major airlines have used SAF in commercial flights, including American, SAS, Lufthansa, Qantas, Alaska, and United, among other. Over 370,000 flights with SAF in the fuel mix have taken off since 2016 alone. Commercially though, supply and infrastructure are limited, so only a few flights today are powered by a limited fraction of SAF.
Most of U.S. SAF production and consumption is in California. In 2020, there was one SAF production facility operating in California and several are under construction or planned. In 2020 4.6 million gallons of SAF were generated, all of which has been consumed in California. The U.S. began importing SAF in late 2020, mostly for use in California. Los Angeles International Airport has used SAF since 2016 and San Francisco International Airport since late 2020.
Why Do We Need SAF, Anyway?
A plane needs to be light enough to fly and carry enough energy with it for its whole journey. That means energy density—the amount of energy stored in a given space and weight—is key. And it’s hard to match jet fuel on energy intensity. A Boeing 737 would require a 600-ton lithium-ion battery to match the energy it carries in jet fuel. That’s multiple times heavier than the total takeoff weight of the plane, which is about 90 tons.
Sustainable Aviation Fuel: Safe, Reliable, Low Carbon
SAF is a biofuel used to power aircraft that has similar properties to conventional jet fuel but with a smaller carbon footprint. Depending on the feedstock and technologies used to produce it, SAF can reduce life cycle GHG emissions dramatically compared to conventional jet fuel. Some emerging SAF pathways even have a net-negative GHG footprint.
SAFs lower carbon intensity makes it an important solution for reducing aviation GHGs, which make up 9%–12% of U.S. transportation GHG emissions, according to the U.S. Environmental Protection Agency.
SAF Benefits Beyond Lowering GHG Emissions
Growing, sourcing, and producing SAF from renewable and waste resources can create new economic opportunities in farming communities, improve the environment, and even boost aircraft performance.
Extra Revenue for Farmers
By growing biomass crops for SAF production, American farmers can earn more money during off seasons by providing feedstocks to this new market, while also securing benefits for their farms like reducing nutrient losses and improving soil quality.
Biomass crops can control erosion and improve water quality and quantity. They can also increase biodiversity and store carbon in the soil, which can deliver on-farm benefits and environmental benefits across the country. Producing SAF from wet wastes, like manure and sewage sludge, reduces pollution pressure on watersheds, while also keeping potent methane gas—a key contributor to climate change—out of the atmosphere.
Improved Aircraft Performance
Many SAFs contain fewer aromatic components, which enables them to burn cleaner in aircraft engines. This means lower local emissions of harmful compounds around airports during take-off and landing. Aromatic components are also precursors to contrails, which can exacerbate the impacts of climate change.
Biofuels Production Supports American Jobs
The United States is the largest producer of biofuels in the world, which contributes to our domestic economy, creates jobs, and reduces GHG emissions.
Expanding domestic SAF production can help sustain the benefits of our biofuel industry and forge new economic benefits, creating and securing employment opportunities across the country. These include jobs in:
- Feedstock production in farming communities
- Construction for building cutting-edge biorefineries
- Manufacturing for operating SAF biorefineries and infrastructure
- Aviation, including countless pilots, crew members, maintenance workers, and other industry professionals.
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