Jolly green jumbos

Imagine flying in near silence, unconcerned about your carbon footprint because your airplane’s being driven by battery power. Fantasy? Maybe not. 

If electric engines manage to supplement, or even take over from the fossil fuelled power plants that currently drive aircraft, clean air travel won’t just be pie in the sky. But as hopeful as industry experts are, they’re also well aware of the challenges. Batteries are still too bulky and relatively power-light to take over from existing engines for anything but short-hop flights. And hydrogen technology like fuel cells is still in its relative infancy.

What is clear is that change is necessary. Air transportation accounts for some 1 billion tonnes of carbon dioxide equivalent emissions annually, which is just under 2 per cent of the total worldwide emissions.¹ With the number of aircraft expected to rise to a million by 2050 from around 600,000 today, it’s clear that the industry needs to do something to clean itself up to meet UN climate change targets.

“There are great opportunities here,” says André Borschberg, co-founder of the Solar Impulse project, the first ever round-the-world solar flight and co-founder of electric propulsion start-up H55. “Combustion engines are inefficient. More than half of fuel not used for propulsion is lost. Engines require a lot of maintenance. By contrast, electric motors are near 100 per cent efficient, require little maintenance and can allow different configurations with multi-engines solutions.” 

One key problem to the transition is weight. The energy contained within jet fuel is 12,000 watt hours per kilogram versus 250 watt hours for lithium batteries. Fortunately, there are some factors favouring electric engines. For instance, conventional combustion engines are only a third as efficient as electric in converting energy to power. So once efficiencies are factored in, the ratio of energy density drops significantly. And once future battery development is factored in, it could be narrowed to 3 to 1, argues Matheu Parr, customer director of Rolls Royce Electrical, the aircraft engine maker’s electrical subsidiary. And they are cheaper:  energy costs for battery powered planes were lower than jet fuel prices per kilowatt hour in 2022, according to BloombergNEF.

Meanwhile, battery energy density isn’t the only challenge facing the electrification of the aircraft industry. Electric airplanes will need fast recharge times. That will put pressure on the electric grid. To manage peak load requires civil engineering or buffer batteries on site. Airplane batteries will also have a high replacement rate in order to meet very strict safety requirements. However, these replaced batteries can be used on the ground for energy storage.

Hybridisation

Fully electric powered flights are only one solution. Another is hybrid electric engines. These have the potential to reduce energy consumption by 30 per cent for aircraft up to 50 seats.

Over the next 20 years, electric aircraft will initially be for short flight times, this will be followed by hybrids and then finally for larger aircraft, Borschberg forecasts. Starting with small electric airplanes will allow critical data to be collected and give engineers the experience that is likely to prove valuable in developing larger electric aircrafts.

Another is hydrogen. It can either be burned for combustion engines or used in fuel cells, which could also supplement existing engines. Work needs to be done on both, but if technical hurdles can be overcome the attractions are great.

Using liquid hydrogen is particularly challenging, not least in getting storage temperatures low enough, says Parr. But if these can be overcome, hydrogen can be used either in combustion, similarly to how jet fuel is used, or consumed in a fuel cell to produce electricity. Combustion is energy dense but complex. Fuel cells are cleaner, but don’t yet have the power density airplanes need, he adds. Rolls Royce is looking at both solutions, with the latter mostly focused on smaller airplanes.

While hydrogen is still just a pipe dream, electric motors have already made inroads into aviation. For instance, Borschberg is working on projects where airplanes used to train pilots are electric-powered. Canadian sea planes, used for commuter flights in Vancouver of up to 30 minutes are also moving to electric. 

Airplanes don’t need to go full electric to have positive outcomes. For instance, hybrid solutions can improve gas turbine efficiency by some 2 per cent to 4 per cent. That may not seem much, but the 15 per cent achieved in gas turbines over the past 30 years have made a huge difference to the industry, says Parr.

The shift to fully clean flying will take a while yet. But it’s clearly heading in the right direction.

Insights for investors

• The IATA estimates that airline will generate net profit of USD4.7bn on revenues of USD779 billion in 2023 – USD522bn in passenger business revenues and USD149 billion in cargo business. 
• The total global fleet size in 2022 was 28,674 aircraft, with 23,513 active and 5161 grounded. 
• 2040 traffic is expected to be 20 trillion revenue passenger kilometers, with growth of 3.9 per cent per year from 2019, according to Airbus.