Transition to electrical propulsion of aircraft required to hold down aviation's share of global CO2 in 2050
Thu 13 Dec 2018 – A transition to electrical propulsion is required if aviation’s current share of global CO2 emissions, around 3%, is to remain the same by 2050, reports consultancy Roland Berger. Presenting its findings at the recent Royal Aeronautical Society’s annual Greener by Design conference, it estimated that if the sector was to continue to evolve at its current technological and fleet growth pace, aviation could account for as much as 24% of global CO2 emissions by mid-century as other industries rapidly decarbonise. At the conference, Airbus said the prospects for all-electric aircraft were very promising for shorter range aircraft but the challenge remained of how to power and reduce the environmental impact of the large aircraft sector. Jeff Engler of US start-up Wright Electric, which is being supported by low-cost airline easyJet in efforts to have an electric passenger aircraft in operation by 2030, said getting to commercialisation would require huge spending in research, as well as industry support and policy intervention.
Robert Thomson, an aerospace and aviation adviser and managing partner at Roland Berger, said there had been a great acceleration over the past two years in new programmes developing all-electric or hybrid-electric propulsion aircraft concepts. There were now around 130 projects worldwide, with the bulk focused on general aviation and urban air taxis, with around 12% of the total developing regional and large commercial aircraft concepts.
A survey Roland Berger carried out 12 months ago of aerospace and defence professionals found that most broadly agreed a hybrid-electric aircraft capable of carrying 50 passengers could be flying between London and Paris (around 200nm) by the early to mid 2030s. Opinions on when an all-electric passenger aircraft would come into commercial operation were more varied but the early 2040s was the more likely.
The consultancy modelled four scenarios to estimate the impact electric propulsion could have on aviation’s share of global CO2 emissions in 2050. Using historical trends and fleet forecasts, under its baseline scenario A, if the industry was to continue to evolve at its current pace – fleet growth of 4% per year, aircraft retirement age of 25 years, fuel burn reduction of 1% per year on new aircraft technology improvements (with a 15% cap) and no production of electric or hybrid regional or large commercial aircraft – it estimated aviation’s share could range from a low of 5% to as high as 24%, with a mean of 8%.
Scenario B assumes the baseline scenario plus an accelerated evolution of today’s technology, with annual fuel burn reduction rising to 2.5% from greater improvements in aircraft technologies, operations and ATC efficiencies (with a 42% cap). Aviation’s share of the total would then be estimated to range between 4% and 19%, with 6% the most likely. Scenario C assumes Scenario B but with production of hybrid-electric aircraft starting in 2035 and all-electric in 2040, predominantly on short-range routes. This would lead to a most likely share of 5%, with a range of 4% to 11%.
Scenario D assumes a regulatory-driven transition to electrical propulsion, akin to what is now happening in the automotive sector, with forced retirement of aircraft at around 10 years and replaced with electric or hybrid-electric aircraft from 2030 onwards. This would bring aviation’s global share in 2050 down to around 3%, in line with the sector’s share today.
This scenario estimates all-electric aircraft flying predominantly short-haul routes and forming around 45% of the global fleet by 2050, with about 25% of the fleet being hybrid-electric. The remaining 30% would consist of conventional gas turbine-powered aircraft, mostly wide-bodies for long-haul routes.
A caveat to the scenarios is that no assumption has been made for the emissions reduction benefits of using sustainable aviation fuels.
Although significant progress is being made to overcome the technological barriers to electrical propulsion, there are many other questions still to be answered, said Thomson, such as on regulatory policy, certification and airport infrastructure requirements. Airlines too would have to consider the cost of ownership and the willingness to take a new technology risk. Aerospace companies such as Airbus and Boeing face major decisions in their aircraft development strategies, and the balance between investment in conventional aircraft and hybrid-electric aircraft.
“If they go down the conventional route, do they spend billions of dollars developing all-new aircraft to replace the A320s and 737s due to enter service in the early 2030s and then run the risk of that aircraft being technically obsolete five or 10 years later?” he questioned.
Another big question he foresaw was who is going to control the development and certification of electrical propulsion systems – will it be the airframer, engine company or electrical systems company?
A further issue is that electrical propulsion will only be greener if the source of power generation was green as well. Taking Scenario D and assuming 24-hour constant charging for replacement batteries, Roland Berger’s modelling shows that the power demand for electric aircraft in the UK would be in the region of 3.5 gigawatts, with around a third needed at Heathrow. This is about 0.5% of the forecasted UK 2050 total generation capacity. If to be supplied by renewable energy, the estimated 1.3 gigawatts required by Heathrow is currently equivalent to solar arrays covering around 30 times the ground area of Heathrow or 2,000 90-metre tall wind turbines.
Colin Hodges, E-Fan X Systems Architect at Airbus, said the reality was that aviation fuel is “an incredible substance” with a very high energy density. “If we are able to concentrate the same level of energy density into a battery as we have in aviation fuel then it would be fantastic but we’re not there yet and it will take time,” he told delegates. “In terms of larger aircraft, we need to look at concepts such as hybrid-electric, which is what we have started doing with the E-Fan X demonstrator. This is an exponential leap that gives us a platform for learning and coming up with future concepts for new aircraft.”
Dr Rod Self, professor of aeroacoustics at Southampton University’s Institute of Sound and Vibration Research, pointed out electric aircraft may not necessarily be quieter than the equivalent conventional aircraft. “This will come as a surprise to many people. Although electric cars may be quieter than a conventional car, with aircraft it’s not the case,” he said.
“You have to power an aircraft with a fan of some description and there is the airflow over the airframe, which are principal sources of noise. You get rid of the turbine noise but you introduce the electric motor noise, with energy density basically driving the noise. Novel designs introduce new noise sources. The aircraft would take off slower and take longer to climb, so staying over the population below for longer.
“How people respond to noise levels depends on a lot of factors – it’s not simply a case of how loud it is, which is what we tend to think. For example, distributed electrical propulsion with many rotors across the wing produces a multi-tonal noise signature. The smaller the airframe, the more the problem with tones.”
Dr Self said the most annoying noise for populations is a new noise and predicts there will future problems with drones potentially being used extensively for delivering packages and urban aircraft. “If you introduce them over people who haven’t experienced aircraft flying overhead before, this is going to have a major effect,” he said. “It’s not just the noise, it’s the level of intrusion as they will fly at lower altitudes so people will see them more. Getting public trust and understanding on urban aviation is going to be a major issue, which could have implications for electric passenger aircraft.
“I think hybrid-electric and electric aircraft are likely to show substantial noise benefits but the variations in the noise signature is going to require us to look at how we measure such noise around airports.”
Jeff Engler’s Wright Electric has teamed with UK low-cost carrier easyJet to develop an electric-propelled, 186-seat passenger aircraft by 2030 – a daunting prospect, he admitted. “It will require new advances in batteries as you can’t use today’s chemistries,” he said. “We are encouraged by progress in higher density batteries but we’re not relying on it, so for that reason we are looking at both all-electric and hybrid-electric systems.”
He said 20% of flights within Europe had a range of less than 350 miles. “Even if we can do the one-hour flights, say between London and Paris and London and Amsterdam, that’s still a start,” he said.
Engler reported that the company hope to have a 9-seater electric plane flying in 2019. He hadn’t previously seen the aircraft in commercial terms but said there had been outside interest in it. He cited a recent report that UK regional carrier Loganair plans to use an electric aircraft by 2021 for its island-hopping service off the north coast of Scotland, where one of its flights is just 1.7 miles.
He said the UK should follow the example of Norway’s ambition of having all short flights 100% electric by 2040.
“If the UK were to set stringent requirements, maybe the rest of the world would follow,” he suggested. “Getting to commercialisation is going to require enormous spending and research. It’s a question of taking the first small step today to push towards zero emissions aviation in the future and establishing momentum.”