In my blog on the future of energy I made a very bold statement about he future of flight being cut by 50% by 2030. A lot of comments on the article informed me I was probably wrong – and this got me thinking. With my other predictions there is a reasonably clear de-carbonisation pathway i.e. heat moving to heat pumps and automotive to electric batteries (with some hydrogen for freight). Air travel just doesn’t seem so clear – right now there is no readily available and technically proven option for air travel.
Every minute 84 flights take off somewhere in the world with over 4 Billion journeys being made by plane. Burning nearly 300 million tonnes of Jet Fuel annually making up 2.7 percent of global CO2 emissions and global air travel is expected to double over the next two decades! (so quite a big gap from my prediction of a reduction of 50%!) This isn't a problem that is just going to go away!
Recently I’ve been really excited to see small electric planes taking off such as Alice. Using battery technology taken from automotive these planes have been able to travel reasonable distances on one charge – carrying a couple of a passengers. There have also been some pretty bold statements about having electrically powered large aircraft by the end of the decade from the likes of easyjet. These innovation steps however are nowhere near to decarbonising a long (or even a short) haul flight.
The fundamental challenge of decarbonising flight is the energy density of the storage… The physics of batteries seem to work for smaller applications… but not necessarily for bigger aircraft. Currently Lithium Iron batteries can store around 250Whr per Kg which is 30 times less dense than Jet Fuel. So the weight of the batteries ends up limiting the ability of larger planes even to get themselves off the ground – never mind carry a payload. Research has suggested that for battery powered aircraft to work the energy density would need to be nearer to 800WHr/Kg so nearly triple that of best available technology today. At the current rate of technology improvement this kind of energy density isn’t going to be available till well after 2050.
Even if the improved energy density could be achieved a huge challenge still remains – that of charging large airliners on the ground. To put it into context a 747 needs around 40 to 50 MW of power on take-off. A 747 currently has a turnaround time of 150 minutes and a 737 for the likes of Ryanair 27 minutes! The infrastructure required to be able to charge such a large battery so quickly would be quite incredible (never mind charging 1300 flights a day at Heathrow!). Even if the energy density challenge can be resolved there is still a long way to go to be able to charge the aircraft once its on the ground!
Looking to next decade what does the above mean for air travel?
1. The development of smaller emissions electric air-planes may mean we see an explosion of smaller regional airports with pilot less air taxis. The shorter available distances will mean that short hop aviation may become a real thing. Also smaller planes will be able to fly at lower altitudes avoiding congestion and with weight becoming critical in range removing the pilot starts to make sense – accelerating autonomous flying to enhance the economic case.
2. Electricity demand at transport hubs will become an increasing problem. With an increase in electric vehicles the demand on local electricity infrastructure will increase – Heathrow airport for example has 51,000 car parking spaces! Just charging that many vehicles will take a huge re-enforcement of electricity provision. Assuming slow chargers (3KW) and about 10% of vehicles on charge you'd need a 15MW connection just for the vehicles! – never mind if you wanted to start charging giant airliners (in quick turn around times!) as well. With smaller electric planes there will be no need to use giant hub infrastructure like now – operators will be able to move to cheaper smaller airports where charging provision is more easily provided (from local solar for example).
3. For larger aircraft alternative fuels such as Hydrogen with higher energy densities may make more sense than electrification. The energy density of these fuels will make a switch over more logical.the development of regional Hydrogen centres presents opportunities globally however as of today no one is commercially flying on Hydrogen so there is still a long way to go.
In conclusion with current technology the only way to reduce carbon emissions is to fly less. There just isn’t a clear enough pathway to lower or zero) carbon flight. Smaller electric planes may supplement existing routes – but without significant regulatory intervention they won’t replace our existing hydrocarbon hungry fleet any time soon!
About John Armstrong
John Armstrong is an engineer whose career has spanned the extremes of the energy industry. He began his career constructing oil refineries before moving to work across fossil and renewable electricity generation. John has lead the growth of decentralised energy and district heating in the UK and is a seasoned energy infrastructure executive. John is a Fellow of the Institute of Mechanical Engineers, a member of the Energy Institute and has an MBA n Global Energy from Warwick Business School.