Small electric planes are already flying, but more research is needed to make the technology available for commercial flight. The challenge for passenger planes is creating electric batteries which are energy dense, yet light enough to be carried onboard. In the meantime, hybrid-electric planes, which use both electric power and liquid fuel, offer a viable solution.
When will commercial electric aircraft become a reality?
While fully electric commercial aircraft are still some way off, hybrid-electric aircraft, which pairs electrification with traditional jet fuel, are currently being prototyped by some of the biggest players in the aerospace industry
- Small battery-powered electric aircraft already exist and are used in training flights and two-person operations
- Hybrid-electric aircraft to be used in commercial flights are currently being prototyped by the aviation industry
- A propulsion system that uses a 50% electrical-power drivetrain and has a battery energy density of 1,000 watt-hours per kilogram would produce almost 50% less lifecycle CO2 emissions than a modern conventional aircraft
How do electric planes work?
Like electric cars, electric planes use electricity to power their engines rather than traditional liquid jet fuel. Currently, there are two main options for supplying electricity to an aircraft:
Battery power: Planes powered by electrically charged batteries are a feasible power option for electric aircraft, but current batteries are heavy and, while cars have roads to help support their weight, planes need to support themselves in the air. The challenge for batteries is to pack in enough energy to replace jet fuel but remain light enough to not increase a plane’s weight too much. To put it in perspective, liquid jet fuel currently yields roughly 43 times more energy than an equivalent mass of battery.
Aerospace manufacturers are doing vast amounts of research and development into aviation battery technology, working alongside battery companies in the automotive and storage space. As next-generation planes become lighter and more aerodynamic, and as battery energy density improves, battery-powered flights could be a not-so-distant reality.
Hydrogen power: An alternative to battery power is hydrogen-powered electric planes. California start-up ZeroAvia is currently developing a hydrogen fuel cell system that can generate the electricity needed to power a six-seater aircraft. The aircraft will be fitted with tanks carrying compressed hydrogen gas, which the fuel cell uses to generate electrical energy by combining with oxygen. This powers the propellers, with only water vapour released from the aircraft. ZeroAvia is hoping to supply the system for zero-emissions flights to small (up to 20-seat) commercial airliners and aircraft manufacturers by 2022. This will allow 10-20-seater aircraft to replace a smaller number of larger aircraft at under-utilised small airports.
Do battery-powered electric aircraft exist?
Electric aircraft are already flying on a small scale, in training flights and two-person operations. It is a rapidly developing area of research, with over 100 projects underway in different parts of the world to explore options for using either electric or hybrid-electric propulsion.
The first demonstration took place in 2011, when engineers from the University of Stuttgart flew 300 miles non-stop over the French Alps on one single battery. The two-seater aircraft, known as the e-Genius, climbed 20,000 feet in under two minutes, and reached speeds of 142 miles per hour. During the flight, the plane consumed just a fifth of the energy of a typical, fuel-powered two-seater airplane.
Other examples include the Pipistrel Alpha Electro, a popular two-seat trainer with an endurance of one hour plus 30 minutes reserve, and Eviation Alice, which is designed to take nine passengers and pilots up to 650 miles at a cruise speed of 240 knots. Alice is powered by three 260kW electric motors developed by the Siemens eAircraft business, which was recently acquired by Rolls-Royce. At 3,700kg, the battery accounts for 60% of the aircraft take-off weight.
When will fully electric commercial aircraft become a reality?
These examples show the potential of battery-operated aircraft, but fuelling commercial aircraft through battery technology alone is still some way off. In the short-term, electric propulsion is likely to be restricted to so-called ‘air taxi’ operations which are expected to start service in a small number of cities from around 2023-2025. These will provide two- to four-person commuter flights to avoid ground traffic congestion.
As the battery technology develops, so will the size of the aircraft able to fly. Harbour Air in Canada has teamed up with MagniX to retrofit a six-seat fully electric seaplane. The aircraft performed its first test flight in December 2019 and has since been undergoing regulatory and safety testing before it enters commercial service. Watch the video:
Other similar sized aircraft are also under development. We can expect to see six- to nine-seat electric options introduced between 2022 and 2025, and up to 19-seat options emerge around 2030. Larger aircraft will follow, and are likely to be led by turboprop style aircraft, which can be used to explore novel power systems more easily than in larger jets. Advanced research is already taking place in this space.
While these fully electric commercial aircraft are still some way off from widespread commercial use, hybrid-electric aircraft, which pairs electrification with traditional jet fuel, are currently being prototyped by some of the biggest players in the aerospace industry.
What are hybrid-electric aircraft and how do they work?
In simple terms, hybrid-electric aeroplanes are powered by liquid jet fuel combined with an electric battery. Jet engines work when air is sucked through the front, compressed by fast-spinning blades, and then mixed with fuel. The air and fuel mixture is sparked and blasts out of the engine through the turbine, giving the plane power. Electric batteries use their charge to power an electric motor to spin when magnetic forces pull on a rotor. On a four-engine jet, one or more of the engines could be replaced by an electric motor creating a hybrid aircraft.
This technology is currently being trialled by Airbus with E-Fan X, a hybrid-electric aircraft demonstrator. It is based on a BAe146 regional jet and is powered by three conventional turbofan engines and one 2MW electric motor supplied by Rolls-Royce. A Rolls-Royce AE2100 gas turbine will also be installed in the rear fuselage to power a two megawatt electric generator. The E-Fan X is due to embark on its first flight in 2021.
Hybrid-electric planes will be able to optimise power generation and usage in all phases of flight – particularly when extra thrust is needed in take-off and climb – with both gas turbine and batteries working together. In cruise mode, the gas turbines driving electric motors will significantly cut back on the amount of fuel used during the flight.
When liquid fuel used is based on sustainable aviation fuels – already supplied in a small percentage blend at several airports around the world – you have a low-carbon form of flight.
What difference will hybrid and fully electric aircraft make to emissions?
Like an electric car, a plane fuelled in part or wholly by electricity will be much cleaner because there are fewer or no CO2 emissions from conventional fuel combustion. However, one needs to take into account how the power that’s being used to charge the electric batteries is being produced. To be potentially carbon-zero, it would need to be derived from renewable sources.
A recent study from the Department of Aerospace Engineering at the University of Illinois’ College of Engineering found that a propulsion system that uses a 50% electrical-power drivetrain and has a battery energy density of 1,000 watt-hours per kilogram would produce almost 50% less lifecycle CO2 emissions than a modern conventional aircraft with a maximum range equivalent to that of the average of all global flights. This makes it a viable option for low carbon aviation. By using sustainable aviation fuels in place of conventional liquid fuel, further emissions reductions can be achieved.
Hybrid aircraft can also help to reduce CO2 emissions by using electric motors as a supplementary thrust source during take-off and climb. This allows the use of smaller jet engines when the flight is in cruise mode. The lighter weight of these engines results in further fuel savings and CO2 reductions.
What is the aviation industry doing to reduce CO2 emissions in the interim?
The aviation industry’s global climate action framework is underpinned by three goals, one of which is to reduce net CO2 emissions by 2050 by 50%. While electric and hybrid-electric aviation on a commercial scale may still be a few years away, the aviation industry continues to take other measures to reduce its CO2 output.
This includes technological innovations to render new aircraft more fuel efficient and the development of sustainable aviation fuels (SAFs) made from waste and non-food feedstocks. These can be mixed with conventional aviation fuels and used in existing aircraft and airport fuel systems, without any technical modifications. It’s predicted that SAFs could reduce aviation CO2 emissions by as much as 80%. Find out more about SAFs here. [links to new AB SAF article]
The aviation industry is also working hard to make the next generation of aircraft leaner, lighter and more aerodynamic so they burn less fuel and emit less CO2. Advances in air traffic control and new satellite technology mean shorter journey times and more efficient take-offs and landings, again cutting fuel consumption and CO2 emissions. On the ground, airports are introducing electric vehicles and terminals are being powered by renewable energy, making them much more energy efficient. Find out more about these operational improvements here [Links to ABBB Operational Improvements article]
With the global agreement of CORSIA – the Carbon Offsetting and Reduction Scheme for International Aviation – air transport will be able to achieve its goal of carbon-neutral growth from 2020. Under CORSIA, airlines and other aircraft operators will offset any growth in CO2 emissions above 2020 levels. It is anticipated that CORSIA will mitigate around 2.5 billion tonnes of CO2 between 2021 and 2035, which is an annual average of 164 million tonnes of CO2. Find out more about CORSIA here.