The global war on emissions has exploded in recent years, with every company, industry, and government on earth now desperately attempting to reduce its carbon footprint. From the introduction of carbon taxes to the adoption of electric vehicles and the rising market share of renewable energy, carbon is under attack. But not all industries are equal, and the aviation industry, in particular, has proven incredibly hard to decarbonize. Today, we will take a look at why jet fuel is so hard to replace and whether it will ever be possible to fly emissions-free.
How Much Carbon Do Planes Emit?
While the transportation sector is responsible for 16% of global emissions, the aviation industry accounts for only 2% of global emissions. That may be surprising for some, as flying is the single most carbon-intensive thing that an individual can do, but it makes sense when you consider the size of other industries in the world.
So while it is important to reduce aviation emissions, it is understandable that a lot of the advances we’ve seen in the fight against carbon so far have come from other sectors. That’s not to say there haven’t been some developments in aviation, with biofuels, electric planes, and hydrogen planes all getting their fair share of attention. So let’s have a look at the strengths and weaknesses of each.
Biofuels are fuels manufactured from organic materials, normally crops, wood, or waste. While they do produce carbon when burned, the theory is that the carbon was absorbed by the organic matter when it was growing, so the net carbon produced by biofuels is zero. Fossil fuels, on the other hand, were trapped deep down in the earth and are now being dug up and burned. Realistically, biofuels are a form of emissions reduction rather than a way to fly “emissions-free”.
There is a chance you have already flown on a plane powered by biofuels, with the first biofuel flight having taken place in 2008. Since then, it has become a relatively accepted part of commercial aviation, with the IATA aiming for a 2% penetration by 2025. In 2018, however, biofuels made up only 0.1% of total aviation fuel.
The major strength of biofuels is that they require minimal modifications to aircraft and infrastructure in order to be used. They can be blended with jet fuel or used independently and have a high energy content. Biofuels also emit less carbon than fossil fuels when burned, with fossil fuels emitting 75.1g of CO2 per megajoule of energy compared to 39g of CO2 from biofuel. When you dig a little deeper into biofuels, however, some serious problems begin to emerge.
In 2017, a group of 177 scientists in the Netherlands signed an open letter urging the government to stop biofuels from food crops from being included in the EU’s sustainable development agenda. The reason for the resistance to crop biofuels is that when you take into account the space required to grow these crops and the processing and transportation of the crops, they emit an average of 1.8 times as much CO2 as fossil fuels. The Dutch scientists also pointed out that crop biofuels were driving up demand for vegetable oil and food crops as well as destroying biodiversity.
Another issue facing biofuels is a more fundamental problem with the assumption that they are carbon neutral. In order for biofuels to be carbon neutral, they cannot come from an area or piece of land that was already a carbon sink. Unfortunately, there is limited suitable land in the world for growing the organic matter necessary for biofuels, and most of that land is already capturing carbon in one way or another. It is possible to make biofuel from waste and crop waste that is already part of the system, but the quantity of such waste puts a limit on just how much biofuel we could realistically produce. There is also the problem that burning these biofuels directly into the atmosphere rather than allowing them to decompose in the soil is reducing the number of nutrients in arable land and impacting farming. While there seems to be a place for some biofuels in the future of the aviation industry, it is far from an emissions-free solution.
From companies racing to build flying electric taxis to claims that commercial electric planes are ‘tantalizingly close’, electric planes are certainly headline-grabbing. Unfortunately, as with many of these things, the reality is slightly less sexy than the headlines might suggest.
Electric planes may seem like a natural evolution from electric cars, but as the size of the vehicle increases, the size of the problem also grows. The major problem facing electric planes is the energy density of lithium batteries (currently the most efficient batteries available). If you consider that the top range of Tesla’s most efficient car is 379 miles, you can begin to understand the problem.
That’s not to say that there haven’t been plenty of breakthroughs. In June 2020, the largest electric plane to ever fly reached 2,500 feet and remained in the air for 28 minutes. In October 2020, the hybrid-electric Eel aircraft broke the record for the longest electric aircraft flight when it flew 341 miles without stopping. Looking forward, there is even an electric plane race scheduled in 2022, in which e-planes will race around a circuit at a height of 32 feet and reach speeds of up to 250mph. But all of these breakthroughs are also demonstrations of how far is still left to go for electric planes. The largest pure electric plane to ever fly has space for only 9 passengers, the Eel aircraft is a hybrid – with an electric motor in the nose and a traditional combustion engine in the rear – and the much-hyped Air Race E is set to take place with very small planes with a battery that has not yet been released. Unfortunately, short of a major breakthrough in battery technology, it seems fully electric planes won’t be going mainstream any time soon.
According to calculations by Duncan Walker, a lecturer of applied Aerodynamics at Loughborough University, an Airbus A380 – which can currently fly 15000 kilometers in a single flight – would only be able to fly 1000 kilometers if powered by batteries. It is more likely that, as demonstrated by the Eel aircraft and the E-Fan X project, the future of electric planes will be hybrid rather than emissions-free. Even then, bringing the costs down to an acceptable level is a daunting task.
When it comes to solving the energy density problem that faces electric vehicles, particularly large ones, hydrogen is often considered the best solution. Broadly speaking, hydrogen comes in three different forms, green hydrogen, blue hydrogen, and grey hydrogen. Put simply, green hydrogen is produced from renewable energy and water, blue hydrogen is produced from natural gas and water with the resultant C02 captured and stored, and grey hydrogen is produced from natural gas and water but emits the C02 into the atmosphere.
In many ways, hydrogen is the ultimate clean fuel. Not only does hydrogen have three times as much energy-density-per-unit mass as jet fuel, but it also produces nothing but clean water when it burns. At first glance, a 100% clean fuel with more energy than jet fuel looks like the perfect solution to our emissions problem. But there is one major problem – producing hydrogen at a competitive price and without a large carbon footprint is proving to be incredibly difficult. In other words, both green and blue hydrogen are expensive compared to grey hydrogen that has a significant carbon footprint. Another smaller problem is that, once you get your hands on it, hydrogen proves difficult and expensive to transport.
Unlike the problems facing electric planes and biofuels, the hydrogen problems appear to be eminently solvable. In fact, Airbus is so confident about the hydrogen future of planes that in September 2020 it revealed three concepts for the world’s first zero-emissions commercial aircraft. These concepts, it hopes, will enter service by 2035. The largest of the three concepts would be able to carry 200 passengers and with a range of over 2000 nautical miles. The good news for Airbus is that Carbon Capture and Storage (used for blue hydrogen) and renewable energy (used for green hydrogen) are likely to see major breakthroughs in the coming decade. As well as that, plenty of nations are now looking to a hydrogen economy as a way to reduce their emissions. With investment and incentives in everything from hydrogen cars and trucks to hydrogen tankers, an infrastructure that would support hydrogen planes is no longer a pipe dream.
One final issue with hydrogen planes that can’t be overlooked is it would realistically call for a redesign of planes as the gas needs to be stored in a specialized pressurized tank. While jet fuel and biofuel are typically stored in the wings of planes, this tank would have to be placed in the fuselage. This is yet another cost to implementing the change that will likely delay its implementation. As you can see from the different Airbus concepts, the new designs may be able to work with a remodeling of current designs or could require an entirely new fleet of planes.
What’s The Best Way To Reduce Aviation Emissions?
Strangely enough, the thing that has done the most to reduce emissions in the aviation industry in the last 40 years has been the gradual efficiency increases achieved by industry engineers. U.S. airlines have increased their fuel efficiency by 130% over the last 40 years, an impressive achievement. The law of diminishing returns would suggest that those efficiency improvements are nearing their limit, however, and a new technological breakthrough will be needed if the airline industry is going to significantly lower emissions further.
Biofuels certainly have a part to play in a low emissions future for airlines, but only very specific biofuels and most likely in relatively small volumes. Electric planes, on the other hand, are unlikely to become commercial any time soon, although this might be the area where you would most expect technological breakthroughs due to the importance of battery technologies in multiple industries of the future. That said, even then you will likely be looking at a hybrid plane that combines fuel and batteries. It seems hydrogen planes are the best long-term solution for an emissions-free aviation industry, but building and developing a global hydrogen infrastructure while keeping costs low is going to take some time.