Adam Vaughan is a writer.
There are reasons for hope in science and technology around the world, according to Fix the Planet, the weekly climate change newsletter. Sign up here to get it in your inbox.
Many people plan to fly for the first time after covid-19 arrived. Air travel is still expected to take at least another year or two to return to pre-pandemic levels, but as the aviation industry does recover, you can expect its climate change impact to return to the fore.
The issue with aviation is not so much its size today as it is the rate at which it is growing. A new wave of fuel-hungry journeys is expected this year, as a new supersonic plane is due to have its first flight.
People still want to travel by plane, despite the fact that the only real answer to aviation emissions is to cut demand and fly less. Today's Fix the Planet turns to battery-powered planes as a long-term techno fix.
There is no such thing as a green flight in the short term. More efficient engines are the only real options available today. The first did not stop emissions from rising. The other two are limited.
We are looking at hydrogen, batteries, a combination of the two or something completely new in the long run. I have written before about hydrogen, which is attractive to plane-makers because of the energy it can pack for its mass. It faces a number of issues, including the challenge of making the stuff in a low-carbon way.
Replacing jet fuel with batteries is hard, says Venkat Viswanathan, who works with a team at Carnegie Mellon University. In a paper, Viswanathan and his colleagues lay out the challenges that range from the energy density of batteries, their weight and concerns over mid-flight battery fires to the trade-off of energy density versus how many times you can replenish the battery. The paper is meant to set realism against all the optimism going around. He says that aviation is demanding because it needs safety, economics, and reliability.
We shouldn't rule out the possibility of battery-powered flight because of the progress on battery chemistry and materials. The kind of batteries used in an electric car could be used for small aircraft, according to Paul Shearing at University College London.
Progress is not likely to stop there. A flight from London to another north-western European capital could be possible with the help of new chemistry and materials. The use of a new generation of batteries that are lightweight will be the key to that breakthrough. Shearing thinks that could mean solid-state batteries, where the battery's electrolyte is solid rather than liquid. Solid-state batteries have an energy density of 400 watt-hours per kilogram, which is almost twice as much as most of the other types of batteries.
The US government gave $75 million for a second stage of the programme last year. Viswanathan thinks it is possible to reach 600Wh/kg in the next 10 years, given the investment in batteries for aviation. He thinks that lithium-metal holds promise. He says a good way to find lightweight batteries is to look at single-use batteries and try to develop a version that is rechargeable. There has never been a serious shot by battery scientists looking at aviation as a primary market. The breakthrough that planes need won't be produced by relying on the sort of incremental improvements seen in electric car batteries.
Reducing aviation's climate change footprint is dependent on making batteries work for planes with hundreds of passengers. 95 per cent of aviation's emissions come from large aircraft. Shearing thinks batteries will need to be used in hybrid systems, such as combining them with a hydrogen fuel cell.
A few years ago, Israelientrepreneur Shai Agassi tried to convince the world that electric cars with batteries that could be swapped out were the future. He failed with his start-up. It could be a reasonable strategy for planes because they are centrally managed. No one seems to be pursuing this route yet, but it is being discussed.
The goalposts for energy density for batteries would be changed to aim for 800 watt per kilo rather than 500 watt per kilo. There are several reasons to think that researchers can get there. The first is that the ability to look inside batteries in real time and learn how to fix them is now available thanks to advances in technology. The second is called robotic. The third is using machine learning to find new materials, which he thinks is similar to how pharmaceutical firms are using it to develop new drugs and vaccines.
Shearing is working with groups in the UK to develop better batteries. In the next five to 10 years, he thinks we will see some form of electrification in some parts of the industry, such as flying taxis and larger aircraft. He says he would be optimistic about decarbonising this sector over the next 50 years.
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