The Future of Aviation: Sustainable Fuel vs Energy-Dense Batteries

January 7, 2023
The future of aviation is through SAFs and energy dense batteries - futuristic plane flying over modern Shanhai in this image.

There are two key ways the aviation industry can move toward reduced emissions. Sustainable aviation fuels (SAFs) are one such option. They are presently in use, albeit expensive, and adoption is not widespread. Energy-dense batteries are another intriguing option, where companies such as Amprius are pushing today’s battery technology into the future.

While certain improvements can make today’s batteries even better, there are also much-needed improvements to make SAFs realistic for widespread use. Both have a part in decarbonizing aviation.

What is the aviation industry’s goal for CO2 emission reduction?

In October 2021 (PDF), the aviation industry released a commitment called Fly Net Zero 2050. The signatories agreed to push toward what they call the third era of air transport — net-zero carbon global connectivity.

The air transport sector set a long-term climate commitment that “global civil aviation operations will achieve net-zero carbon emissions by 2050, supported by accelerated efficiency measures, energy transition and innovation across the aviation sector and in partnership with governments around the world.”

The industry knows that the goal is ambitious and challenging, and requires coordinated efforts among multiple stakeholders. One of the key elements of reaching this goal is the decarbonization of air transport. That includes increasing the use of sustainable aviation fuels as part of a wider aviation energy shift.

The goals also include research, development and deployment of electric and/or hydrogen-powered aircraft. The aviation industry sees value and potential in sustainable aviation fuels and electric aircraft, powered by energy-dense batteries.

Why is aviation a difficult sector to decarbonize?

Aviation is difficult to decarbonize for a variety of reasons (PDF). Air traffic continues to grow even during recessions, downturns, and other challenges that might seem like they would reduce growth. So, even as technology improves to reduce emissions, emissions grow with more traffic. The post-pandemic outlook continues this trend.

Technology is slow to be replaced. So, again, even as airplanes improve, companies are reluctant to switch entire fleets.

The industry (and perhaps the world at large) sees aviation as a small part of global emissions, even though there is a need to act now. Passengers are reluctant to accept the cost of low-emission solutions, given that sustainable aviation fuels are still quite expensive.

Where are we with battery technology for electric planes?

As this Time article states, the future of battery technology is in airplanes. And at the same time, fuel is one of the industry’s biggest expenses. Aviation companies may be likely to jump on any improvements, even incremental, that keep costs down and provide a path to the future.

Battery technology for electric planes is an ongoing area of interest, especially as sustainable aviation fuels remain challenging to deploy at scale. While electric planes are also a challenge in this regard, they may offer more longevity and cost savings than sustainable aviation fuels in the long-term.

Are electric planes already a reality?

Electric planes are flying, albeit in small-scale scenarios. We have seen test flights, short trips, and training operations. In August 2022, the world’s first commercial electric plane completed a point-to-point flight. That flight joins many others designed to push electric flight to its limits in hopes of true commercial service available in the future.

What must be addressed before electric planes are widespread?

The key issue with batteries is that they are heavy. To match the density of aviation fuel, today’s batteries need to be large. With size comes weight, meaning that planes will struggle to take off and stay in flight with the batteries required.

The more energy a plane needs, the more batteries required. The heavier the plane is, the more energy and batteries needed for power. It is a cyclical problem that aviation experts are trying to solve. Ultimately, for electric planes to be widespread, we need ever smaller, lighter, more energy-dense batteries.

Why is the progress of battery tech so important?

As batteries are developed that are increasingly small, light, and powerful, viability of electric planes becomes more feasible. There may be smaller planes — many are in the works — and hybrid planes deployed in years to come, but something like a jumbo jet requires far more battery weight than currently feasible.

Modern jet engines have incredibly high power density, so battery technology will have to keep up. Until then, hybrid-electric planes are certainly an option, as are smaller planes powered with cutting-edge batteries.

How does battery technology compare with gas planes?

Jet A fuel, the standard fuel for aviation, has an energy density of about 12,000 watt-hours per kilogram. By comparison, Amprius’ batteries currently deliver 450 watt-hours per kilogram for each cell. While it is important to note that about two-thirds of jet fuel is lost as heat, it is clear that battery technology still needs to improve to fully compete with jet fuel.

What is sustainable aviation fuel (SAF)?

How is SAF made?

Sustainable aviation fuel is produced from sustainable feedstocks like cooking oil, animal waste oil, solid waste from homes like food scraps, and forestry waste. In other words, sustainable aviation fuel is made from non-fossil fuels feedstocks or renewable hydrocarbon sources. That means that the feedstocks can be resourced over and over again.
The feedstock is collected from one or many sources, then refined to produce fuel. It is blended with traditional fuel to be used in jet engines.

What are the different types of SAFs?

FOGs are the first generation of biofuels, made of fats, oils and greases. Biomass and municipal solid waste (MSW) represent the next generation. They use algae, crop residues, animal waste, sludge waste, and forestry residue. Power-to-liquid is the newest type. This converts renewable energy into fuels with electrolysis.

Are SAFs currently approved?

Currently in the United States, SAFs are approved when blended with conventional fuel up to a 50 percent mix. SAFs are available at airports like Los Angeles International Airport, which has been using SAFs since 2016 as a small portion of its fuel supply.

What are the benefits of sustainable aviation fuel?

Sustainable aviation fuel reduces greenhouse gas emissions compared to fossil jet fuel. And it can be used as a direct replacement for traditional fuel. It does not require any modifications to engines or fueling infrastructure. There is no need for further infrastructure investment. Sustainable aviation fuels can also provide stability compared to volatile fuel costs with conventional sources.

What are the current challenges of using SAFs?

Currently, sustainable feedstock does not come from enough sources at a high enough level to meet all fuel demands. If SAFs are to fill the gaps in aviation sustainability, production needs to be scaled up. The industry would need production facilities in the thousands versus the handful that currently exists.

Cost is also a barrier. SAFs can be two to four times as expensive compared to jet fuel. As production scales up, the cost may decrease. As of now, SAFs are pricey. Using these alternatives offer little reward for cost-conscious airlines.

In 2021, the White House offered a tax credit for airlines using SAFs. This was one step toward incentivizing production and use of these fuels.

Main difference between electric planes and SAFs

Environmental impact and emissions

Sustainable aviation fuels reduce CO2 emissions by up to 80 percent. Electric airplanes, of course, are fully emission-free. A hybrid electric plane can reduce emissions by up to 50 percent, which holds a lot of potential in conjunction with SAFs.

SAFs are certainly environmentally friendly, as they use feedstocks representing a lot of waste, from inedible fats to municipal waste. They are perhaps best considered as a long-term, interim solution to decarbonizing aviation, while truly emission-free battery technology improves enough for widespread use.

Performance

Sustainable aviation fuels may provide somewhat better performance (PDF) than conventional jet fuels as the volume of use increases. That is because sustainable aviation fuels, with fewer emissions, run cleaner than conventional fuels. This puts less stress on engines, improving overall performance.

Electric aircraft are also poised to be high-performance. We can expect from 2.1 to 3.2 times more entry-efficiency during cruise compared with their conventional counterparts.

Both SAFs and electric airplanes offer performance improvements over conventional jet engines. Ultimately, as battery technology improves enough to be the sole source of airplane power, it is possible that aviation companies will spend less time servicing and maintaining systems like engines. In a starry-eyed future, there may be no need for fuel at all.

Which is more expensive to operate?

In 2022, the cost of jet fuel was $0.50 per liter. The cost of sustainable aviation fuel was $1.10 per liter. This means that SAFs cost more than twice as much as conventional jet fuel. According to Statista, fuel cost for jet fuel is about 19 percent of total expenditure for the aviation industry. Thus, the fuel cost for SAF-based planes as a share of total expenditure is even higher.

Some estimates say electric planes can reduce aviation industry fuel costs by up to 90 percent. Ultimately, an electric plane may be more of an investment upfront, but has the potential pay off in the long term. Not having to continually fuel a plane — especially with decarbonized, but still very expensive SAFs — will add up.

It’s wise to consider SAFs while battery technology improves. Cost, however, remains a major downfall of using sustainable aviation fuels.

Are SAFs better for long-range flights?

Presently, battery-powered planes do not have extensive flight range, due to the relationship between energy density and weight. To travel long-range, an electric plane would need to carry many heavy batteries to maintain power, which complicates the calculations required to produce such long-range flights.

It is a challenging problem with today’s technology. Companies are working hard to solve the issue while making significant technology improvements along the way.

Realistically, with today’s technology, consumers and aviation companies will be looking at shorter-range, regional flights versus long-range travel using electric planes. For that reason, companies operating long-range flights and wanting to cut down on emissions would be more likely to consider SAFs at present.

As battery technology improves, it is possible that long-range flights will become feasible. Until then, with a goal of decarbonization, SAFs will certainly have a role to play for the aviation industry.

Will electric planes become more popular when battery technology improves?

There are many benefits to electric planes that SAFs cannot quite reach. Being fully emission-free, with no fuel cost at all, and much less upkeep and maintenance on systems is very appealing.

While battery technology is not presently enough to power commercial flights as we know them today, we know that battery companies such as Amprius are focused on making steady improvements. Will electric planes become more popular and viable as battery technology improves? We think so!

Looking at electric cars as an example can be telling. While many thought that electric cars were a wild idea, never likely to reach commercial success or buy-in, in today’s world consumers are eager to invest in these vehicles. They are better for the environment and better for people’s wallets.

The interest in electric cars has helped drive more technological improvements. In turn, these improvements have reduced the cost of electric cars and made the technology more accessible to all. If electric planes follow a similar trajectory, we may see an era of greatly improved, well-utilized electric plane batteries and a new chapter in aviation.